HYDROGEN PEROXIDE H2O2

Hydrogen peroxide is another hydride of oxygen. Unlike water it is highly unstable, and therefore, does not exist in nature as such. Its, importance, in recent years has increased due to its use as rocket fuel.

Preparation of Hydrogen Peroxide

1. From sodium peroxide (Merck’s method)

Calculated amount of sodium peroxide  is gradually added to an ice-cold solution of 20%  in small lots with constant stiring.

      

Upon cooling, crystals of  separate out and the resulting solution contains about 30%. The solution also contains some dissolved, but it does not interfere with the reactions of. A pure sample of  may, however, be prepared by vacuum distillation.

2. From barium peroxide-Laboratory method of preparation.

Hydrogen peroxide is prepared from barium peroxide by the following methods:

(a) By the action of dilute sulphuric acid. Apaste of hydrated barium peroxide  is prepared in ice – cold water and then added slowly to an ice-cold solution of 20%.

      

      The white precipitate of is removed by filtration leaving behind a dilute solution (5%) of. In this method, anhydrous barium peroxide can not used since the precipitated  forms a protective layer around unreacted barium peroxide thereby preventing the further reaction

Illustration 12.  A certain sample of hydrogen peroxide is 1.5 M solution. It is to be labelled as X volumes. Calculate the value of X.

Solution:          

                        Or mass of  per litre = 

                        

                        Now 68 g of give  at STP = 22.4 L

                        

                        Thus 1 L of  which contains 51 g of  produces at STP = 16.8 L

                        Hence value of X is = 16.8 L

                        Or The given sample is 16.8 volume.

Limitation

Hydrogen peroxide prepared by this method contains appreciable quantities of  ions (in the form of dissolved barium persulphate) which catalyse the decomposition of.Therefore, prepared by this method cannot be stored for a long time.

Further, also acts as a catalyst for decomposition of.

(b) By the action of carbon dioxide or carbonic acid. When a rapid stream of  is bubbled through a thin paste of  in ice-cold water, and are produced:

      

      The insoluble barium carbonate is removed by filtration leaving behind a dilute solution of 

(c) By the action of phosphoric acid. Hydrogen peroxide can also be prepared by the action of phosphoric acid on barium peroxide:

      

      This method has the advantage over  method since almost all the heavy metal (e.g. Pb etc) impurities present in  and which catalyse the decomposition of  are removed as insoluble phosphates. As a result, the resulting solution of  has good keeping properties.

Manufacture of Hydrogen Peroxide

1. By electrolysis of 50% H2SO4

Hydrogen peroxide is manufactured by the electrolysis of a cold 50% solutions of in an electrolytic cell using platinum as anode and graphite as cathode. The reactions taking place are:

      

      At cathode:          

      At anode : 

Peroxydisulphuric acid formed around anode is withdrawn and then distilled with water under reduced pressure. The low boiling  distils over along with water leaving behind high boiling  which is recovered and recycled.

      

       or, 

 

Modification

Recently, it has been observed that if instead of 50%  an equimolar mixture of H2SO4­ and ammonium sulphate is electrolysed, a more concentrated solution of  is obtained.  

      

      

      At cathode: 

      At Anode: 

Ammonium persulphate formed around anode is withdrawn and distilled with water to give 

      

This process is now used only for the laboratory preparation of, i.e.;

      

                                                           Deutroperoxide

2. By autoxidation of 2-ethylanthraquinol

This is a new method and is widely used in U.S.A. In this process, air is bubbled through a 10% solution of 2-ethylanthraquinol in benzene and cyclohexane when 2-ethylanthraquinol is oxidized to 2-ethylanthraquinone and  is formed according to the following equations.

The  thus formed (about 1%) is extracted with water and the aqueous solution is concentrated by distillation under reduced pressure to give 30% (by weight) solution.

2 – Ethylanthraquinone so produced can be reduced back to the starting to the material i.e.,2-ethylanthraquinol by hydrogen using palladium catalyst.

Thus, we find that the raw material are  and  only.

Concentration of hydrogen Peroxide Solution

Hydrogen peroxide produced by any of the above method is in the form of dilute solution. The solution can not be concentrated by simple heating because it readily decomposes below its boiling point as

      

The dilute solution of hydrogen peroxide is concentrated carefully by the following steps:

(i) Slow evaporation on water bath

The dilute solution of hydrogen peroxide is taken in evaporating dish which is heated carefully on water bath. Slow evaporation continues causing the escaping of water molecules till approximately 50% solution of  is obtained.

(ii) Evaporation in vacuum desicator

The 50% solution is placed in vacuum desicator over concentrated sulphuric acid. The water vapours are absorbed by sulphuric acid leaving approximately 90% solution of.

(iii) Distillation under reduced pressure

The 90% solution of hydrogen peroxide is then subjected to distillation under reduced pressure (10 – 15mm). During this process, water distils over at 303 – 313 K and about 99% pure hydrogen peroxide is left behind.

(iv) Removal of last traces of water

The 99% solution of hydrogen peroxide is cooled in a freezing mixture of solid carbon dioxide and ether. As a result of this, crystals of hydrogen peroxide separate out which are removed, dried and remelted. This gives completely pure hydrogen peroxide.

Storage of Hydrogen Peroxide

Decomposition of hydrogen peroxide into water oxygen is catalysed by traces of metal impurities, strong bases and exposure to light. Because of this property of, the concentrated solution of  can be dangerous as uncontrolled rapid decomposition can result in an explosion. Thus,

(i)   It is stored in wax lined coloured bottles as rough glass surface also causes its decomposition.

(ii)   A small amount of stabilizer like phosphoric acid, or glycerol or acetanilide must to added to retard its decomposition.

Structure of Hydrogen Peroxide

As established by X – ray studies, hydrogen peroxide molecules has a non – planar structure. The molecules dimensions in gas phase and that in solid phase have given in figure. (a) and (b) respectively. In the crystal, the dihedral angle  reduces to on account of hydrogen bonding. The two oxygen atoms are joined by a single electron – pair bond. The O – O Linkage is also called peroxide linkage.

Properties of Hydrogen Peroxide 

Some of the physical properties of hydrogen peroxide are listed below:

(i) Pure hydrogen peroxide is a colourless, syrupy liquid.

(ii) It has odour like that of nitric acid.

(iii) Its aqueous solution has a bitter taste.

(iv) It is soluble in water, alcohol and ether in all proportions.

(v) Its density is 1.44 g. The high density is due to association of its molecules by intermolecular hydrogen bonds.

(vi) Its boiling points is 423 K at 670 mm pressure and 358 K at 68 mm pressure. Its melting point is 272 K.

Chemical Properties

(a) Decomposition

It is a unstable liquid readily decomposes on heating or on long standing to give water and dioxygen. It is an example of disproportionation decomposition is suppressed by addition of glycerol, acetanilide or phosphoric acid.

(b) Acidic behaviour

Pure hydrogen peroxide is a weak acid (at 298 K). it ionizes in water as:

      

      

Its acidic character can be shown its ability to neutralize bases such as NaOH, etc, to form corresponding peroxides

      

      

Hydrogen peroxide has an interesting chemistry because of its ability to act as oxidizing as well as reducing agent both in acidic and basic solutions.

Oxidising nature of H2O2

can acts as oxidizing agents in acidic as well as basic medium as described below.

 

 

Illustration 13. “Hydrogen peroxide is a strong oxidizing agent both in acid and alkaline medium”. Justify giving suitable reactions.

Solution:          Oxidising agent

                        

                        

                        Reducing agent

                        

 

Illustration 14. What happens when  is treated with

                        (a) acidified potassium permanganate

                        (b) lead sulphide

                        (c) alkaline potassium ferrocyanide

                        (d) acidified ferrous sulphate

                        (e) sulphurous acid.

Solution:          (a) It reduces acidified  solution. The pink colour of  is discharged.

                        (b) 

                        (c) It reduces alkaline potassium ferricyanide to potassium ferricyanide.

                        (d) It oxidizes acidified ferrous sulphates to ferric sulphate.

                        (e) It oxides sulphurous acid to sulphuric acid

 

Illustration 15. What happens when?

                        (i) Chromium hydroxide is treated with hydrogen peroxide in the presence of NaOH.

                        (ii)   Hydrazinc reacts with hydrogen peroxide.

                        (iii) Hydrogen peroxide reacts with.

                        (iv)  Sodium hypochlorite reacts with.

Solution:          (i) is converted into yellow coloured 

                        (ii) Hydrazine is oxidised to  and.

                        (iii) 

                        (iv)  

Bleaching Action

The bleaching action of hydrogen peroxide is due to the nascent oxygen which it liberates on decomposition.

      

The nascent oxygen combines with colouring matter which, in turn, gets oxidised. Thus, the bleaching action of  is due to the oxidation of colouring matter by nascent oxygen. It is used for the bleaching of delicate materials like ivory, feather silk, wool etc.

      

Addition reactions

Hydrogen peroxide reacts with alkenes to form glycols.

Strength of Hydrogen Peroxide

1. As percentage

Some time the actual concentration of hydrogen peroxide in a solution in expressed as percentages of  in solution. Thus, 40% solution of hydrogen peroxide means 40 grams of hydrogen peroxide are present in 100 grams of solution.

2. As volume strength

The most common method of expressing the concentration of hydrogen peroxide solution is, in terms of the volume of oxygen which a solution of hydrogen peroxide gives on decomposition by heat. For example, “10 volume” hydrogen peroxide refers to a solution of hydrogen peroxide whose, 1 litre will give 10 litre of oxygen at STP.

Calculation of Strength of H2O2

It is possible to calculate the strength of hydrogen peroxide from its “volume strength”. Let us calculate the concentration in g/litre of “30 volume” solution of hydrogen peroxide.

A 30 volume solution of hydrogen means that 1 litre of the solution gives 30 litre of oxygen at STP. According to its decomposition reaction.

       

Now 1 litre of hydrogen peroxide gives 30 L of oxygen at STP

From the above equation

22.4 L of oxygen is obtained from  = 

30 L of oxygen at STP is obtained from  = 

Thus, 1L of sample contains  = 91.07g

or Strength of the 30 volume solution of hydrogen peroxide is 91.07 

Illustration 16.  Calculate the strength in, molarity and normality of 40 volume of hydrogen peroxide solution.

Solution:           

                        40 volume  means, 1L of the solution produces 40 L of  at STP

                        Now, 22.4 L of  at STP is produced from  = 68

                        40 L of oxygen at STP is obtained from  = 

                        

                        

                        

                                                            = 

 

Illustration 17. Aqueous solution of an inorganic compound (x) shows the following reactions.

                        (i) It decolourises an acidified  solution accompanied by the solution of oxygen.

                        (ii) It liberates iodine from an acidified KI solution.

                        (iii) It gives a brown precipitate with alkaline  solution with evolution oxygen.

                        (iv) It removes black stains from old oil paintings.

                              Identify (x) and give chemical equations for the reactions at step (i) to (iv).

Solution:          

                        

                        

                        

Exercise 9.       Hydrogen peroxide solution (20 ml) reacts quantitatively with a solution of  (20 ml) with dilute. The same volume of the  solution is just decolorized by 10 ml of  in neutral medium simultaneously forming a dark brown precipitate of hydrated. The brown ppt. is dissolved in 10 ml of 0.2 M sodium oxalate under boiling condition in the presence of dilute. Calculate the molarity of.

 

Exercise 10.

                        In basic medium, acts as an oxidizing agent in its reactions with

                        (A)                                       (B)  

                        (C)                                 (D) 

 


ANSWERS TO EXERCISES

 

Exercise 1:       (C) 

 

Exercise 2.       (B) 

 

Exercise 3.       (A)

 

Exercise 4.       (C) 

 

Exercise 5:       (C)

 

Exercise 6.       (D)

 

Exercise 7:       (B)


Exercise 8.       
(A)

 

Exercise 9.       m = 0.1                                                

 

Exercise 10:     (A)

 


MISCELLANEOUS EXERCISES

 

Exercise 1:       How is dihydrogen obtained from?

                        (A)  dilute sulphuric acid            

                        (B)  sodium hydroxide

                        (C)  water         

                        Give one equation in each case.

 

Exercise 2:       Although  resembles  chemically yet it is a toxic substance. Explain.

 

Exercise 3:       What is the difference between hydrolysis and hydration?

 

Exercise 4:       What is meant by autoprotolysis of water?

 

Exercise 5:       Why  is not used in the laboratory preparation of dihydrogen?

 

Exercise 6:       What are advantages of using hydrogen as a fuel over gasoline or coal?

 

Exercise 7:       How is a solution of  concentrated? Why it can not be concentrated by distillation at ordinary pressure?

 

Exercise 8:       (a) Name the blue compound formed in the reaction of  with acidified  in ether? Give reaction.

                        (b) What is the principle in the bleaching action of?

 

Exercise 9:       The following statements are true under certain conditions. Mention condition in each case in a few words.

                        (i) Hydrogen reacts with nitrogen to form ammonia.

                        (ii) Hydrogen can be prepared from water at ordinary temperature.

                        (iii) A metal will liberate hydrogen by its reaction with dilute

 

Exercise 10:     Complete the following reactions

                        (i) 

                        (ii) 

                        (iii) 

                        (iv) 

                        (v) 


ANSWERS TO MISCELLANEOUS EXERCISES

 

Exercise 1:       (a) More electropositive elements than hydrogen (eg, Zn, Fe, Mg) react with dilute mineral acids (dil, HCl & H2SO4) to liberate dihydrogen gas.

                              

                        (b) Metals like Be, Zn, Sn, Al etc react with boiling alkali solution liberating dihydrogen.

                              

                              

                        (c) 

                              

                              

 

Exercise 2:       Heavy water is injurious to human being, plants and animals since it slows down the rate of reactions occurring in then. Thus heavy water does not support life so well as does ordinary water.

 

Exercise 3:       Interaction of H+ and OH- ions of H2O with anions and cations of the salt respectively to give the original acid and the original base is called hydrolysis eg.

                        

                        Hydration, on the other hand, means addition of H2O to ions or molecules to form hydrated ions or hydrated salts for eg.

                        

                        

 

Exercise 4:       Auto protolysis of water means that two molecules of water reacts with each other through protons transfer i.e. one acts as the acid while the other acts as the base. The molecule which accepts a proton is converted into H3O+ while that which loses a proton is converted into OH- ion.

                        

 

Exercise 5:       HNO3 is a strong oxidizing agent. It oxidizes the H2 produced.

 

Exercise 6:       Advantages of using as fuel.

                        (i)   Abundantly available.          (ii)         Pollution free as the product is water.

                        (iii)  High calorific fuel.               (iv)        Excellent reducing agent.

                        (v) Time required for regeneration of H2 fuel is short.

Exercise 7:       Concentration of H2O2 is carried out carefully in a number of stages as follows.

                        (i)   Evaporation on water bath – slow evaporation of water continues until the solution contains about 50% H2O2.

                        (ii) Dehydration in a vaccum desiccators

                        50% solution of H2O2 obtained from above is taken in a disk and placed in a vaccum desiccator containing conc. H2SO4. The inside presence is reduce as a result of low, water readily evaporates and the water vapours thus produced are absorbed by conc. H2SO4.The H2O2 obtained is 90% pure.

                  (iii) Distillation under reduced pressure

                        The 90% solution of H2O2 as obtained above is subjected to distillation under reduced pressure (10 – 15 mm). During this process, water distils over between 303 – 313 K leaving behind almost pure 99% H2O2.

                  (iv) Removal of least traces of water

                        The last traces of water in H2O2 are removed by freezing it in a freezing mixture consisting of dry ice (solid CO2) and ether when crystal of H2O2 separate out. These crystals are removed, dried and melted to give pure H2O2.

                        It can not be concentrated by distillation at ordinary pressure because H2O2 decomposes much below its boiling point to give H2O & O2.

Exercise 8:       (a)    

                                                               Chromium pentoxide               

                        

                        (b) The bleaching action of H2O2 is due to the nascent oxygen which it liberate on decomposition

                              

                              The nascent oxygen combines with colouring matter which in turn gets oxidizing. Thus the bleaching of H2O2 is due to the oxidation of colouring matter by nascent oxygen.

 

Exercise 9:       (i) At high pressure (200 atm) and in presence of catalyst Fe, Mo.

                        (ii) Very active metals like Na, K, Ca etc can react with H2O at room temperature.

                        (iii) Metals which are more electropositive than hydrogen.

 

Exercise 10:     (i) CaO (s) + H2 ¾® Ca(OH)2 (aq)

                        (ii) Na2O (s) + H2 ¾® 2NaOH (aq)

                        (iii) 3Fe (s) + 4H2 ¾® Fe3O4 + 4H2

                        (iv) 

                        (v) Co(g) + H2O (g) 


SOLVED PROBLEMS

 

Subjective:

 

Board Type Question

 

Prob 1.    Why is hard water softened before its use in boilers?

 

Sol.         Hard water cannot be used in boilers because on heating it gives precipitates of CaCO3 and MgCO3 alongwith CaSO4 which forms scales in boilers. To avoid the scales formation, hard water is softened before its use in boiler.

 

Prob 2.    What volume of oxygen at NTP will be obtained by the complete decomposition of 100 ml of H2O2 marked 30 volume?

 

Sol.         1 ml H2O2 of 30 volume liberates 30 ml O2 at NTP.

               \  100 ml H2O2 of 30 volumes liberate 30 ´ 100 ml O2 at NTP or 3 litre O at NTP.

 

Prob 3.    Cu does not liberate H2 from dil H2SO4. Explain.

 

Sol.         Cu is placed below H in electrochemical series having oxidation potential -0.34 V hence Cu can not transfer electron to H+ ions of H2SO4 to liberate H2.

 

Prob 4.    A small amount of phosphoric acid or glycerol or acetanilide is added in H2O during its storage. Explain.

 

Sol.         All the three additives act as negative catalyst for the decomposition of H2O2 and thus decomposition of H2O is checked off.

 

Prob 5.    Which isotope of hydrogen is used as a trace in organic reactions?

 

Sol.         Hydrogen has three isotopes, Viz, H, D and T. Due to difference in masses, the rate constants of three isotopes with the same substance are different. In other words, both D and T show isotope effect. But since T is not only radioactive but is also least abundant hydrogen isotope. Therefore D is used as a trace to study the mechanism of organic reactions.

 

IIT Type Question

 

Prob 6.    H2O2 is a very good solvent for ionic compounds. Explain.

 

Sol.         The dielectric constant of pure H2O2 is 93.7 (which also increases on dilution (97 for 90% pure; 120 for 65% pure) which is appreciably high to weaken the electrostatic forces of attraction among ions and to pass them in solution state.

 

Prob 7.    Anhydrous  is not used for preparing  why?

 

Sol.         Anhydrous  is not used because the  formed during the reaction forms a protective layer around the unreacted  and the reaction stops after some time.

 

Prob 8.    Statues coated with white lead on long exposure to atmosphere turns black and the original colour can be restored on treatment with. Why?

 

Sol.         On long exposure to atmosphere, white lead is converted into black PbS due to the action of  present in the atmosphere. As a result, statues turn black

               

               On treatment of these blackened statues with, the black PbS get oxidized to white  and the colour is restored

               

 

Prob 9.    Show with suitable example hydrogen acts as reducing agent as well as oxidizing agent?

Sol.         In the reaction of  with metals to form metal hydrides, it acts as an oxidizing agent.

               

               Here Na has been oxidized to Na+ while  is reduced to hydride  ion.

               In the reaction of heated cupric oxide with dihydrogen to form  and copper metal, dihydrogen acts as a reducing agent

               

               Here, CuO is reduced to Cu while dihydrogen is oxidized to.

 

Prob 10.  Ozone is used for purifying air in crowded place such as cinema halls, tube railways, tunnels etc explain?

Sol.         is easily decomposes to produce  thereby purifying air at crowed places.

Prob 11.  Why is sodium chloride less soluble in heavy water than in ordinary water?

 

Sol.         The dielectric constant of  is less than that of, therefore ionic compounds like NaCl are less soluble in  than in.

 

Prob 12.  Why electrolysis of ordinary water occurs faster than heavy water?

 

Sol.         This is due to lower bond dissociation energy of protium bonds in H – O – H, which is less than deuterium bonds in D – O – D, so electrolysis of  occurs much faster than that of.

 

Prob 13.  Name the class of hydrides to which H2O, B2H6, NaH and LaH3 belong. What is understood by ‘Hydride Gap’?

 

Sol.         H2O - covalent hydride, B2H6 - covalent hydride, NaH - ionic hydride, LaH3 - metallic hydride.

               Hydride Gap: The metals of 7, 8, 9 groups do not form hydride. This is called the hydride gap.

 

Prob 14.  Concentrated sulphuric acid can not be used for drying. Why?

 

Sol.         This is because conc. on absorbing water from moisture generates so much heat that hydrogen catches fire.

 

Prob 15.  A mixture of hydrazine and  with Cu(II)  catalyst is used as rocket propellant. Why?

 

Sol.         The reaction between hydrazine and  is highly exothermic and is accompanied by a large increase in the volumes of the product and hence this mixture is used as a rocket propelled

               


Objective:

 

Probl 1.   HCl is added to the following oxides. Which one would give?

               (A)                                                        (B)  

               (C)                                                         (D)  none of the above

 

Sol.         Since none of the oxides is a peroxide. Hence none of them would give.

               

 

Probl 2.   When the same amount of zinc is treated separately with excess of sulphuric acid and excess of sodium hydroxide, the ratio of volumes of hydrogen evolved is

               (A) 1 : 1                                                         (B)  1 : 2

               (C) 2 : 1                                                         (D)  9 : 4

 

Sol.         

               

               The ratio of volumes of  evolved in both the cases is 1 : 1.

               

 

Probl 3.   Which of the following is the true structure of H2O2?

               (A)

(B)

               (C)

(D)

 

Sol.      Oxygen atom is  hybridized having two large pair of electrons. Therefore the             structure of hydrogen peroxide is  

               

 

Probl 4.   When electric current is passed through an ionic hydride in the molten state

               (A) hydrogen is liberated at the anode              

               (B) hydrogen is liberated at the anode

               (C) no reaction takes place

               (D) hydride ion migrates towards cathode

 

Sol.         Ionic hydride contains  ion which liberates  at the anode.

                

 

Probl 5.   Which of the following can not be oxidized by  ?

               (A) KI + HCl                                                   (B)  

               (C) PbS                                                          (D)  

Sol.         is more powerful oxidizing agent than. So  reduces  to.

               

                                                                       

 

Probl 6.   The reaction                                                  

               Ag2O + H2O2 ¾¾® 2Ag + H2O + O2 takes place in

               (A) basic medium                                            (B)  bleaching agent

               (C) neutral medium                                          (D)  both in acidic and basic medium

 

Sol.         on oxidation gives  only in basic medium

               

 

Probl 7.   Which of the following compounds turns white on treatment with.

               (A) HgS                                                          (B)  PbS

               (C) NiS                                                           (D)  CuS

 

Sol.         

               

 

Probl 8.   The strongest base is

               (A)                                                          (B)  

               (C)                                                        (D)  

Sol.         Basic character decreases as the size of central atom increases in hydrides of group 15 members

               

 

Probl 9.   Semi water gas is a mixture of

               (A)                                                    (B)  

               (C)                                             (D)  none

Sol.         Mixture of CO +  +  is called semi water gas.

               

Probl 10. A hydride of nitrogen which is acidic is

               (A)                                                          (B)  

               (C)                                                         (D)  

 

Sol.         (hydrazoic acid) is the acidic hydride of nitrogen

               

 

True/False

 

Probl 11. Tritium can be obtained from natural sources.

 

Sol.         False

 

Probl 12. H2O2 act as antichlor.

 

Sol.         True

 

Probl 13. Sodium carbonate can remove only temporary hardness of water.

 

Sol.         False

Probl 14. Ortho hydrogen has lower energy and is more stable than para hydrogen.

 

Sol.         True

 

Probl 15. Bleaching action of H2O is due to its reducing nature.

 

Sol.         False

 

Fill in the Blanks

 

Probl 16. When hydrogen peroxide is treated with acidified K2Cr2O7 solution, a ……….. colour        appears.

 

Sol.         Blue green

 

Probl 17. Carbon monoxide combines with hydrogen when heated to 150 - 450oC in presence of ZnO + Cu to form …………..

 

Sol.         CH3OH

 

Probl 18. The mixture of hydrazine hydrate and ………… with a copper (II) catalyst is used as        rocked propellant.

 

Sol.         H2O2

 

Probl 19. Chemical name for permutit is …………….

 

Sol.         Zeolite

 

Probl 20. H2O2 is used as …………….. in toothpaste.

 

Sol.         Antiseptic

 


ASSIGNMENT PROBLEMS

 

Subjective:

 

Level – O

 

1.   Discuss briefly the properties and uses of different types of hydrides.

 

2.   What is the meant by water gas shift reaction?

      Describe it use for the preparation of dihydrogen.

 

3.   Differentiate between

      (a) hard and soft water

      (b) temporary and permanent hardness of water.

      Briefly explain how to remove temporary and permanent hardness of water.

 

4.   Explain the following

      (i) Soft water lathers with soap but not with hard water.

      (ii) Temporary hard water becomes soft on boiling.

      (iii) Water can extinguish most fires but not petrol fire.

      (iv) Hard water is softened before use in boilers. 

 

5.   Explain, why the density of ice is less than water? 

 

6.   Write short notes on

      (i) Ortho and para hydrogen       (ii) Bosch’s process

      (iii) calgon                                   (iv) Ion-exchange method for removal of hardness of water.

 

7.   How is heavy water prepared from normal water? Discuss the importance of heavy water in nuclear reactors. What is the action of heavy water on

      (i) Sodium               (ii) NaOH        (iii)                  (iv) 

 

8.   What is the difference between hydrolysis and hydration? What are the ways in which water molecules are bonded to the anhydrous salt to form hydrate?

 

9.   (a) What are interstitial hydrides? Discuss their important uses. How do they differ from molecular hydrides.

      (b) Distinguish between salt like and covalent hydrides. Discuss briefly the characteristic of salt like hydrides.

      (c) What is understood by hydride gap.

 

10.  Describe permutit process for softening of hard water.

      Calculate the hardness of a water sample which contains 0.001 mole of  dissolved per litre of the solution.

 

11.  A solution of ferric chloride acidified with HCl is unaffected when hydrogen is bubbled through it, but is reduced when zinc is added to some acidified solution. Explain.

 

12.  Why should a bottle of H2O2 be cooled before opening it?

 

13.  What should be the necessary requirements for portable water i.e., water for drinking purposes.

 

14.  Explain why hydrogen is best placed separately in the periodic table of elements?

 

15.  What is understood by hydrogen economy?

 

16.  Metals like platinum & palladium can adsorb large volumes of hydrogen under special conditions. Such adsorbed hydrogen by the metals is called?

 

17. Find out the order of the reaction for the decomposition of hydrogen peroxide .

 

18.  When  is reacted with  & either, the ethereal layer becomes blue, why?

 

19.  Write the correct order of the O – O bond length in and .

 

20.  What would happen when a small quantity of H2O2 is added to a solution of FeSO4?

 

 


Level- I

 

1.   In the preparation of hydrogen in the laboratory from granular zinc. Why the following acids cannot be used.

      (a) Conc.          (b) conc. HCl                        (c) nitric acid

 

2.   Hydrogen peroxide acts both an oxidizing agent and as a reducing agent in alkaline solution towards certain first row transition metal ions. Illustrate three properties of  using chemical equations.

 

3.   20 ml of a solution containing 0.2 g of impure sample of  reacts with 0.316 g of  (acidic). Calculate

      (a) Purity of.

      (b) Volume of dry  evolved at C and 750 mm P.

 

4.   Justify the statement

      “An aqueous solution of hydrogen peroxide is weakly acidic”.

 

5.   Explain. In the preparation of, the use of phosphoric acid has an advantage over dilute sulphuric acid.

 

6.   Given reason

      (a) Marine species cannot survive in distilled water.

      (b) Distilled water in called deionised water.

 

7.   Give ion electron equation for the following reactions

      (a) oxidation of ferrous ions to ferric ions by.

      (b) oxidation of iodide ion to iodine by.

      (c) oxidation of acidified per magnate ion.

      (d) reduction of alkaline ferricyanide ions to ferrocyanide ions.

 

8.   What happens when?

      (i) Hydrolith is treated with water.

      (ii) Heavy water reacts with aluminium carbide.

      (iii) Concentrated caustic potash solution is spilled on granulated zinc. 

 

9.   One litre of a sample of hard water contains 1 Mg of CaCl2 and 1 Mg of MgCl2. Find the total hardness of in terms of parts of  per  parts of water of mass.

 

10.  Explain

      (a) act as a bleaching agent.

      (b) Concentration of hydrogen peroxide is difficult.

 

11.  What happens when?

      (a) Barium peroxide is treated with cold dilute sulphric acid

(b) Sodium peroxide is treated with cold dilute sulphuric acid and the resulting mixture is cooled below 273K.

      (c) Barium peroxide is treated with phosphoric acid.

      (d) Hydrogen peroxide is treated with sodium carbonate.

      (e) Hydrogen Iodide is added to hydrogen peroxide.

 

12.  Explain

      (a) Why hydrogen peroxide is stored in coloured plastic bottle?

      (b) H2O2 prepared from hydrated barium peroxide and dilute sulphuric acid can not be stored for a long time.

13.  Two liquids (A) and (B) are made of same elements and are diamagnetic. Liquid (A) on treatment with KI and starch gives blue coloured solution, however. Liquid (B) is neutral to litmus and does not gives response to starch iodine paper. Identify (A) 
and (B).

 

14.  50 ml of an aqueous solution of H2O2 was treated with an excess of KI solution in dil. H2SO4, the liberated iodine required 20 ml of 0.1 N Na2SO3 solution for complete reaction. Calculate concentration of H2O2 in g/litre.

 

15.  Complete the following

      (i)   

      (ii)   

      (iii)  

 

 


Level- II

 

1.   The process  is endometric       .

      Yet salt like sodium hydride are known. How do you account for this?

 

2.   Find the degree of hardness of a sample of water containing 12 mg of  (mol. Mass 120) per kg of water.

 

3.   Explain the following

      (a) A small of amount of acid or alkali is added before electrolysis of water.

      (b) The electrolysis of water for manufacturing hydrogen gas is always carries out in the presence of acid () or alkali (KOH). Yet no  ions are discharged.

 

4.   Explain the following

      (a) A solution of ferric chloride acidified with HCl is unaffected when hydrogen is bubbled through it, but gets reduced when zinc is added to some acidified solution.

      (b) When sodium hydride is fused state is electrolysed, hydrogen is discharged at anode.

 

5.   Explain the following

      (i) Why are the melting and boiling points of are higher than those of ordinary water?

      (ii) Presence of water is avoided in preparation of  from.

      (iii) Hydrogen peroxide gives acidic properties.

 

6.   Explain the following 

      (i) A mixture of hydrazine and  is used as a rocket propellant.

      (ii) Hydrated barium peroxide is used in the preparation of hydrogen peroxide instead of the anhydrous form.

 

7.   What happens when?

      (a) Hydrogen peroxide is added to ferrous ammonium sulphate solution.

      (b) Sodium hydride reacts with diborane.

      (c) Benzene is treated with  in presence of.

 

8.   A 5 ml solution of  liberates 0.508 g of iodine from an acidified KI solution. Calculate the strength of  solution in terms of volume strength at STP.

 

9.   Toa 25 ml solution excess of acidify solution of potassium iodide was added. The iodine liberated required 20 ml of 0.3 sodium thiosulphate solution. Calculate the volume strength of  solution.                        

 

10.  10 ml of a solution of  labeled ’10 volume’ just decolourises 10 ml of potassium per magnate solution acidified with dilute  acid. Calculate the amount of potassium per magnate in the given solution.

 

 


 

Objective:

 

Level– I

 

1.   Volume of same weight of ice is………….than/to the same weight of water

      (A)  More                                                                 (B)  Less

      (C)  Equal                                                                (D)  not related

 

2.   Which of the following hydrides is covalent compound?

      (A)  LiH                                                                   (B)  NaH

      (C)                                                                 (D)  

 

3.   Which of the following hydroxides is amphoteric?

      (A)                                                           (B)  

      (C)                                                            (D)  

 

4.   The O – O – H bond angle in  in gas phase is

      (A)                                                                   (B)  

      (C)                                                                   (D)  

 

5.   Amongst the one with the highest boiling point is

      (A)  because of hydrogen bonding                   

      (B)  because of higher molecular weight

      (C)  because of hydrogen bonding                   

      (D)  because of lower molecular weight

 

6.   Polyphosphates are used as water softening agents because they

      (A) form soluble complexes with anionic species      (B)  precipitate anionic species

      (C)  form soluble complexes with cationic species (D) precipitate cationic species

 

7.   The volume strength of 1.5  solution is

      (A)  4.8                                                                   (B)  5.2

      (C)  8.8                                                                   (D)  8.4

 

8.   The volume of 10 volume  solution that decolourizes 200 ml of 2N  solution in acidic medium is

      (A)  112 ml                                                              (B)  336 ml

      (C)  200 ml                                                              (D)  224 ml

 

9.   An oxide which gives  on treatment with dilute acid is

      (A)                                                                 (B)  

      (C)                                                                 (D)  

 

10.  Acidified solution of chromic acid on treatment with  yield

      (A)                                                 (B)  

      (C)                                                        (D)  

 

11.  The correct increasing order of the acidity of  is

      (A)                                              (B)  

      (C)                                              (D)  

12.  Ammonium per sulphate on heating under reduced pressure gives

      (A)                                                                  (B)  

      (C)                                                                     (D)  

 

13.  The hybridization on the oxygen atom in  is

      (A)                                                                  (B)  sp

      (C)                                                                    (D)  

 

14.  In  proton () exist as

      (A)                                                                  (B)  

      (C)                                                            (D)  all the above

 

15.  The reactions  manifests

      (A)  acidic nature of                                         (B)  alkaline nature of 

      (C)  oxidizing action of                                    (D)  reducing nature of 

 

Assertion/Reason Type Questions

 

Codes:

(a)  Both A and R are true and R is the correct explanation of A.

(b)  Both A and R are true but R is not the correct explanation of A.

(c)  A is true but R is false.

(d)  A is false but R is true.

(e)  A and R both are false.

 

16.  Assertion (A): On passing H2 gas into aqueous Fe3+ solution, resulting solution gives test of Fe3+.

      Reason (R): H2(g) reduces Fe3+ to Fe2+ but Fe2+ IS oxidized to Fe3+ by atmospheric oxygen.

 

17.  Assertion (A): Drinking of heavy water (D2O) mixed water (H2O) could prove fatal.

      Reason (R): There is slower rate of transfer of D+ compared with that of H+ ion in acid-base reaction involved enzyme catalysis.

 

18.  Assertion (A): Hydride (H-) is a conjugate base of hydrogen (H2).

      Reason (R): Every negative ion is an electron-pair donor and is thus, a Lewis base.

 

19.  Assertion (A): Ionic hydrides are the ready-made source of H2.

      Reason (R): LiH is an ionic hydride.

 

20.  Assertion (A): H2O2 decomposes Na2CO3 to give CO2.

      Reason (R): H2O2 has two protons and is thus a strong acid.

 

 

 

 

 

 

 

 

 

 


Level-II

 

1.   Hydrogen will not reduce

      (A)  heated cupric oxide                                           (B)  heated ferric oxide

      (C)  heated stannic oxide                                         (D)  heated aluminium oxide

 

2.   Hydrolysis of one mole of peroxodisulphuric acid produces

      (A)  two moles of sulphuric acid                              

      B)   two mole of peroxomonosulphuric acid  

      (C)  one mole of sulphuric acid and one mole of peroxomonosulphric acid

      (D)  one mole of sulphuric acid, one mole of peroxomonosulphuric acid and one mole of 

 

3.   Which contains both polar and non-polar bonds?

      (A)                                                                (B)  HCN

      (C)                                                                  (D)  

 

4.   The critical temperature of water is higher than that  because the  molecule has

      (A)  fever electrons than oxygen                               (B)  two covalent bonds

      (C)  V – shape                                                         (D)  dipole moment

 

5.   When zeolite which is hydrated sodium aluminium silicate is treated with hard water the sodium ions are exchanged with

      (A)                                                              (B)  

      (C)                                                                  (D)  all of the above

 

6.   Hydrogen gas is liberated by the action of aluminum with a concentrated solution of

      (A)  NaOH                                                               (B)  

      (C)                                                            (D)  none

 

7.   Heavy water is obtained by

      (A)  boiling water                                                     (B)  distillation of 

      (C)  pronged electrolysis of                              (D)  heating 

 

8.   The compound that can work both as an oxidizing agent and a reducing agent is

      (A)                                                              (B)  

      (C)                                                                 (D)  

 

9.   In acidic medium, acts as a reducing agent in its reaction with

      (A)                                                               (B)  

      (C)                                                             (D)  

10.  The decomposition of  can be checked by the addition of

      (A)  alkali metal oxides                                             (B)  benzene

      (C)  acetamilide                                                       (D)  

 

11.  The metal which displaces hydrogen from a boiling caustic soda solution is

      (A)  Mg                                                                   (B)  Fe

      (C)  AS  (D)                                                              Zn

12.  acts as an oxidizing agent in

      (A)  neutral medium                                                  (B)  acidic medium

      (C)  alkaline medium                                                (D)  both acidic & alkaline medium

13.  Decomposition of  is favoured by

      (A)  traces of acids                                                  (B)  alcohol

      (C)  acetanilide                                                        (D)  MnO

 

14.  The maximum possible number of hydrogen bonds a water molecule can form in ice is

      (A)  1                                                                      (B)  2

      (C)  3                                                                      (D)  4

 

15.  and  form  by 

      (A)  electrovalent bond                                             (B)  covalent bond

      (C)  coordinate bond                                                (D) none of these

 

16.  Select correct statements:

      (A)  H2 is more rapidly adsorbed on Mo surfaces than D2

      (B)  H2 reacts over 13 times faster with Cl2 than D2 because H2 has lower energy of activation.

      (C)  both are true

      (D)  none is true

 

17.  H­2 reacts much faster with Cl2 than D2, because

      (A)  rate of diffusion of H2 is greater than D2

      (B)  H2 has lower energy of activation than D2

      (C)  both statements are correct

      (D)  none of the statements is correct

 

18.  Which is true statement about D2O and H2O?

      (A)  D2O has lower dielectric constant than H2O

      (B)  NaCl is more soluble in D2O than in H2O

      (C)  Both of the above are correct

      (D)  none of the above is correct

 

19.  In the following compounds H is covalent bonded in case of

      (A)  BaH2                                                                 (B)  CaH2

      (C)  SiH4                                                                  (D)  NaH

 

20.  Select the correct statement:

      (A)  Ammonia is more soluble in aqueous ammonium chloride than in pure water

      (B)  Solid ammonium fluoride and ice are miscible in all proportions

      (C)  both the statements are correct

      (D)  none of the statements is correct

 

           

 

 

 


ANSWERS TO ASSIGNMENT PROBLEMS

 

Subjective:

 

Level - O

 

4.   (i) The hard water contains bicarbonates cruddy white ppt. chlorides and sulphate of Ca and Mg. When hard water is treated with soap solution, Ca+2 & Mg+2 ions present in water react with anions of fatty acids present in soaps to form curdy white ppt. As a result it does not produce lather with soap.

            

      (ii) When temporary hard water is boiled, bicarbonates of calcium and magnesium respectively.

            These insoluble carbonate are removed by filtration and the water is rendered soft.

            

            

      (iii) Petrol being lighter than water, floats over the surface of water. Hence the petrol fire can not be extinguished by water.

      (iv)  The salt of Ca & Mg slowly is long time form a layer on the wall of boilers, making is a bad conductor of heat. So making it unsuitable for use.

 

5.   Ice has open cage like structure with a number of vacant spaces in the crystal lattice. As a result, density of ice is lower than that of water.

 

6.   (i) When the spins of the nuclei are in the same direction (parallel spins), dihydrogen is called ortho hydrogen and when the spins are in the opposite direction (anti parallel spins), dihydrogen is called para hydrogen.

      (iii)  Calgon is the trade name for sodium hexametaphosphate Na2[Na4(PO3)6]. It softens hard water by exchanging its Na+ ions with Ca+2 ions present in hard water.

 

7.   (i) 

      (ii)   

      (iii)  

      (iv)  

 

8.   Water has the ability to combine with some metal salts to form compounds known as hydrates. There are three categories of hydrates.

      (a) Water molecules form complex ions by combining with metal ions through 
co – ordinates bonds.

            e.g.   

      (b)  Water molecules may be hydrogen bonded to certain oxygen containing anions.

            e.g.  CuSO4.5H2O in which four water molecules are coordinated to a central Cu2+ ion while the fifth water molecules is hydrogen bonded to sulphate groups. Thus, it can also be represented as 

            

      (c) 7, 8 & 9th group elements does not form hydride thus it is called as hydride gap

10.  0.1 ppm

 

11.  Reaction of Zn and HCl gives nascent hydrogen which is more powerful reducing agent than ordinary hydrogen and thus ferric chloride solution is reduced.

 

12.  H2O2 being unstable liquid, decomposes into water and oxygen either on standing or on heating. Bottle of H2O is therefore cooled before opening to lower the vapour pressure of contents in it otherwise bumping of liquid may take place.

 

13.  It should be free from suspended impurities, bacterial impurities and also dissolved impurities which are harmful to body.

 

14.  It electronic configuration resembles alkali metals (group I) and halogen group VII and it shows reactions and properties similar as well as dissimilar to the elements of these two groups.

 

15.  The production, storage and transportation of energy in the form of liquid or gaseous hydrogen as a fuel in view of the facts that fossil fuels are limited, electricity can’t be stored and use of nuclear power is restricted.

 

16.  Occlusion

 

17.  First order reaction

 

18.  Cr(OH)2

 

19.  H2O2 > O3 > O2

 

20.  

      or 

 

Level – I

 

1.   (a) Cons. is not used because a part of the acid gets reduced to.

      (b) liberated by conc. HCl on Zn will be impure as it contains fumes of volatile HCl. formed is insoluble in conc. HCl and forms coating on zinc and the reaction stop after some time.

      (c) acts as an acid well as oxidizing agent.

 

2.   Chromium hydroxide is oxidised by  in presence of NaOH into sodium chromate.

      Potassium ferricyanide is reduced to ferricyanide in presence of KOH by.

 

3.   (a) 85%       (b) 124.79 ml                                        

 

5.   When phosphoric acid is used in the preparation of  from, it plays the double role. It liberates  and also acts as preservator by retarding its decomposition.  

 

8.   (i) Hydrolysis of  occurs with evolution of 

            

      (ii) Deuteromethane is evolved

            

      (iii) Zn dissolves in caustic potash solution evolving hydrogen

            

9.   1.95 ppm.

 

13.  A is  and B is.

 

14.  0.68g 

 

15.        (i) 

            (ii) 

            (iii) 

 

Level - II

 

1.   This is due to the reason that high lattice energy released is more that compensates the energy needed for the formation of  ions from  gas.

2.   100 ppm.                                                               

3.   (a) Pure water being a weak  electrolyte and feebly ionized & bad conductor of electricity.

      (b) Sulphate & potassium ions are not discharged as the discharge potential of  is much higher than  ions and the discharge potential of  ions is much higher than ions.

4.   (a) Molecular (ordinary) hydrogen is not so reactive as hydrogen at the moment of formation. Zinc reacts with the acid to produce nascent hydrogen. Which reduces ferric chloride into ferrous chloride.

      (b) Sodium hydride is an electrovalent compound in which hydrogen is present as an anion, H on electrolysis it is discharged at anode.

 

5.   (i) has more molecular mass and greater degree association than  and thus shows higher mid point and boiling point.

      (ii) Water reacts with  to produce NaOH which increases decomposition of.

      (iii) reacts bases to form peroxides (salts) & water

            

            

 

6.   (i) The reaction is highly exothermic. It brings large increase in volume also.

            

      (ii) If anhydrous barium peroxide is used, formed forms an insoluble protective coating on the surface of solid barium peroxide. This prevents further reaction of the acid.

 

7.   (i) 

      (ii) Sodium borohydride is formed

            

      (iii) Benzene in presence of  is converted into phenol.

 

8.   4.48 volume.                                                          

 

9.   1.344

 

10.  0.564 g                                                                  

 

Objective:

 

Level – I

 

            1.         A                                  2.         C                                  3.         C

            4.         D                                  5.         A                                  6.         C

            7.         D                                  8.         D                                  9.         B

            10.        C                                  11.        B                                  12.        A

            13.        D                                  14.        D                                  15.        C

            16.        C                                  17.        A                                  18.        B

            19.        B                                  20.        C                                             

 

Level – II

 

            1.         D                                  2.         C                                  3.         C

            4.         D                                  5.         B                                  6.         A

            7.         C                                  8.         D                                  9.         B

            10.        C                                  11.        D                                  12.        D

            13.        D                                  14.        D                                  15.        A

            16.        C                                  17.        B                                  18.        A

            19.        C                                  20.        C