A public water supply contains 0.10 ppb (part per billion) of chloroform (CHCl3). How many molecules of CHCl3 would be obtained from 0.478 mL of this water?
A
4×10−13×NA
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B
10−3×NA
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C
4×10−10×NA
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D
None of these
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Solution
The correct option is A4×10−13×NA Density of water = 1 g/mL Weight of 0.478 mL of water = 0.478 g Parts per billion =weight of CHCl3(g)total weight of water (g)×109⇒0.10=weight ofCHCl30.478×109
Weight of CHCl3=0.10×0.478×10−9=4.78×10−11g Molar mass of CHCl3=119.5 g/mol 119.5 g of CHCl3 contains NAmolecules . 4.78×10−11 g will contain = NA119.5×4.78×10−11g=4×10−13×NA No. of molecules = 4×10−13×NA