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A sample of drinking water was found to be severely contaminated with Chloroform, CHCl3 . The level of contamination was 15 ppm(by mass). (i) Express this in percent by mass. (ii) Determine the molality of chloroform in water.

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6 years ago

Rinkoo Gupta
80 Points
```							1) 15 ppm means 15 parts in 1 millions (10^6) and percentage always for 100 hence 15 ppm = (15/10^6 )*100                 = 15*10^-4                 = 1.5*10^-32) molar mass of chloroform = 118.5g/ mol from percentage by mass  100 gram of sample has 1.5*10^-3 g of chloroformthen 1000 gram of sample has = 1.5*10^-3 g * 1000 gram/ 100 gram                        = 1.5*10^-2 gmolality = moles of solute / mass of solvent in Kg    moles of solute = mass of solute / molar mass            = 1.5*10^-2/ 118.5             =1.266*10^-4 molesmolality =  1.266*10^-4 moles/ 1 Kg =1.266*10^-4 m Thanks & RegardsRinkoo GuptaAskIITians faculty
```
6 years ago
Aarti Gupta
300 Points
```							1).Converting 15ppm in percent by mass-15ppm means 15 parts in 1 million(106)and % means 100so, 15 ppm = 15 * 102/106= 1.5 * 10-32).For Molality-Molality = Moles of solute/Mass of solvent in Kgnow,100gm of sample contains 1.5 * 10-3 of CHCl3therefore, 1000gm will contains = 1.5 * 10-3 * 1000/100= 1.5.* 10-2gMoles of solute is given as = Mass/Molar mass= 1.5 *10-2/118.5  ( 118.5 Molar mass of CHCl3)moles = 1.266 * 10-4 molesThus molality = 1.266 * 10-4/1 Kg= 1.266 * 10-4mThanks & RegardsAarti Guptaaskiitians Faculty

```
6 years ago
Manas Satish Bedmutha
22 Points
```							Here, ppm = parts per million = 15.

Using %w/w = ppm x 10^-4, %w/w = 15/10000 = 0.0015 %

Now take 1 million gm soln.
Wt. solute = 15 g. This means moles of solute = 15/120(approx) = 0.125 mol.
Now wt. of solvent is approx. 10^6 gm.

Molality = moles of solute x 1000 / wt solvent in gm = 0.125/1000
=0.000125 m or 1.25 x 10^-3 m
```
6 years ago
Roma
16 Points
```							15 ppm = 15/ 10^6(As 15 ppm means 15 parts in 1 million)I) percentage means 100Mass % = 15*100/10^6                 =1.5*10^-32) 100g contains 1.5*10^-3Then 1000g will contain 1.5*10^-2Moles = 1.5*10^-2/119.5 = 1.2*10^-4Molality = 1.2*10^-4/ 1kg                 =1.2*10^-4 molar
```
3 years ago
Rishi Sharma
629 Points
```							Hello students,The solution is as follows1).Converting 15 ppm in percent by mass-15 ppm means 15 parts in 1 million(10^6) and % means 100so, 15 ppm = 15 * 10^2/10^6= 1.5 * 10^-32).For Molality-Molality = Moles of solute/Mass of solvent in Kgnow, 100gm of sample contains 1.5 * 10-3 of CHCl3therefore, 1000gm will contains = 1.5 * 10-3 * 1000/100 = 1.5.* 10-2gMoles of solute = Mass / Molar mass= 1.5 * 10^-2 / 118.5 ( 118.5 Molar mass of CHCl3)moles = 1.266 * 10^-4 molesThus molality = 1.266 * 10^-4/1 Kg= 1.266 * 10^-4mIhope the avove solution will solve all your doubts.ThanksAll the best for your exams.
```
7 months ago
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