A sample of drinking water was found to be severely contaminated with chloroform, CHCl3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).- Express this in per cent by mass.
- Determine the molality of chloroform in the water sample.
- Express this in per cent by mass.
- Determine the molality of chloroform in the water sample.
Solution and Explanation
(i) 1 ppm is equivalent to 1 part out of 1 million (106) parts.
Mass percent of 15 ppm chloroform in water
= \(\frac {15}{10^6}×100\)
≈ \(1.5×10^{-3} %\)%
(ii) 100 g of the sample contains 1.5 × 10-3 g of CHCl3.
⇒ 1000 g of the sample contains 1.5 × 10-2 g of CHCl3.
∴ Molality of chloroform in water
= \(\frac {1.5×10^{-2}g}{\text {Molar\ mass \ of} \ CHCl_3}\)
Molar mass of CHCl3 = 12.00 + 1.00 + 3(35.5)
= 119.5 g mol-1
Molality of chloroform in water = 0.0125 × 10-2 m
= 1.25 × 10-4 m
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Concepts Used:
Scientific Notation
Scientific Notation can be defined as a method through which we express numbers that are either too large or too little to be expressed in decimal form. It is also known as 'Scientific Form,' and it is often used by scientists, mathematicians, and engineers for difficult computations involving large numbers. It's generally referred to as "SCI" display mode on scientific calculators.
All numbers in scientific notation are written in the generic form as N x 10m
Read More: Scientific Notation Formula
Scientific Notation Rules:
While writing the numbers in the scientific notation we have to follow certain rules they are as follows:
- The scientific notations are written in two parts one is the just the digits, with the decimal point placed after the first digit, followed by multiplication with 10 to a power number of decimal point that puts the decimal point where it should be.
- If the given number is greater than 1 and multiples of 10 then the decimal point has to move to the left, and the power of 10 will be positive
- Example: Scientific notation for 8000 will be 8 × 103.
- If the given number is smaller than 1 means in the form of decimal numbers, then the decimal point has to move to the right, and the power of 10 will be negative.
- Example: Scientific notation for 0.008 will be 8 × 0.001 or 8 × 10-3.