Grade 12Physical Chemistry

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).

sudhanshu

12 Years agoGrade 12

8 Answers

Naveen Kumar

11 Years ago

mole fraction=0.04
So if one molof solution contain 0.04 mol of ethanol and (1-0.04)molof water=0.96
So the mass of water=0.96*18 g=17.28g
So the mass of ethanol=0.04*46 g=1.84g
total mass=18.92g
Assuming the density of solution to be 1g/ml, the vlume of the solution=18.92ml
So if18.92ml of solution contain 0.04 mol of ethanol.
So …....1ml...............................0.04/18.92mol....
so 1000ml...............................(0.04/18.92)*1000=molaritty of the solution=2.11M

Satyam Singh

9 Years ago

Mole fraction of C2H5OH= .................1Let the moles of C2H5OH= XNow density of water = 1 (given)And the weight of 1000ml of water = volume * density (from density = mass/volume)= 1000 x 1=1000gTherefore moles of water = 1000/18= 55.55 mol (18g is molecular mass of water)Also mole fraction of C2H5OH= 0.040 (given)Putting the values in equation 1,we get=0.040=X/X+55.55=0.040X+2.222 = XOR X= 2.3145 molMolarity of solution = 2.314 M

Aniketh

9 Years ago

1 mole of solution contains 0.040 moles of ethanol》1-0.040=0.960 mole of water(as mole fraction sums upto 1)Mass of water=0.960×18=17.280gm=0.040×100÷17.280(divide by 1000 as we convert g intokgg)m=2.31m

Sumit Mukherjee

8 Years ago

Mole fraction of ethanol is given that is 0.040 (X)

As in this case ethanol acted as solute

X= n2(ethanol)/n2(ethanol)+n1(no.of moles of water)

As the solution is diluted tus

1lt of soln=1lt of water

n1(number of moles of water)= 1000g/18=55.5

By putting this in formula

0.040=n2(ethanol)/n2+55.5

By taking reciprocal of this

25=1+55.5/n2

25-1=55.5/n2

24=55.5/n2

n2=2.31

Thus, in 1000g of water contains 2.31 moles of ethanol

Therefore,the molarity of solution is 2.31M.

Marya

7 Years ago

Molarity means moles of solute (ethanol) in one litre of the solution.

1L of ethanol = 1L of water

Number of moles of H₂O in 1L water = 1000g/18

= 55.55moles

For a binary solution,

x₁+x₂ = 1

xH₂O = 1 – xC₂H₃OH

= 1– 0.04

= 0.96

xH₂O = nH₂O/nH₂O + nC₂H₅OH

0.96 = 55.55/55.55+nC₂H₅OH

53.328 + 0.96nC₂H₅OH = 55.55

0.96nC₂H₅OH = 55.55 – 53.328

= 2.222

nC₂H₅OH = 2.222/0.96

2.3145mol

= 0.96

xH₂O = nH₂O

Ajeet Tiwari

6 Years ago

Hello Sudhanshu,
mole fraction=0.04
So if one molof solution contain 0.04 mol of ethanol and (1-0.04)molof water=0.96
So the mass of water=0.96*18 g
=17.28g
So the mass of ethanol=0.04*46 g
=1.84g
total mass=18.92g
Assuming the density of solution to be 1g/ml,
the vlume of the solution=18.92ml
So if18.92ml of solution contain 0.04 mol of ethanol.
So 1ml gives 0.04/18.92mol
so 1000ml gives (0.04/18.92)*1000
=molaritty of the solution=2.11M
Thanks

Yash Chourasiya

6 Years ago

Dear Students

Let consider mole fraction as moles of compounds.

Moles of ethanol = 0.04 mol

Moles of water = 1 - 0.04 = 0.96 mol

Mass of ethanol = 0.04 mol x 46 g/mol = 1.84 g

Mass of water = 0.96 mol x 18 g/mol = 17.3 g

Mass of the solution = 17.3 g + 1.84 g = 19.1g

Assuming density of water to be 1 g/ml,

Volume of solution = mass / density = 19.1 / 1 = 19.1 ml = 0.0191 L

Molarity is the number of moles of solute present in 1 L of solution.
Hence,
Molarity of the solution = 0.040 / 0.0191 = 2.1 M

I hope this answer will help you.
Thanks & Regards
Yash Chourasiya

Anchal Aiswariya Dutta

5 Years ago

Hello friends, getting this answer has many ways but the main thing is to understand its concept. Once u understand then you can make your one formula.

Molarity =mole fraction of solute×1000/mole fraction of solvent×m.m of solvent.

Regards, Anchal A