# Chemistry Class 11 NCERT Solutions: Chapter 1 Some Basic Concepts of Chemistry Part 6

Q: 17. A sample of drinking water was found to be severely contaminated with chloroform, , supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).

(i) Express this in percent by mass.

(ii) Determine the molality of chloroform in the water sample.

Answer:

(i) 1 ppm is equivalent to 1 part out of 1 million parts.

∴Mass percent of 15 ppm chloroform in water

(ii) of the sample contains

Molar mass of

∴ Molality of chloroform in water

Q: 18 Express the following in the scientific notation:

(i)

(ii)

(iii) 8008

(iv)

(V)

Answer:

(i)

(ii)

(iii)

(iv)

(v)

Q: 19 How many significant figures are present in the following?

(i)

(ii) 208

(iii) 5005

(iv)

(v) 500.0

(vi)

Answer:

(i)

There are 2 significant figures.

(ii)

There are 3 significant figures.

(iii)

There are 4 significant figures.

(iv)

There are 3 significant figures.

(v)

There are 4 significant figures.

(vi)

There are 5 significant figures.