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

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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).

Chloroform, or trichloromethane, is an organic compound with formula CHCl3.

Structure of Chloroform CHCl3

Chloroform, or trichloromethane, is an organic compound with formula CHCl3.

(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:

Scientific notation is a way of expressing numbers that are too big or too small to be conveniently written in decimal form.

Structure of Scientific Notation

Scientific notation is a way of expressing numbers that are too big or too small to be conveniently written in decimal form.

(i)

(ii)

(iii) 8008

(iv)

(V)

Answer:

(i)

(ii)

(iii)

(iv)

(v)

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

The significant figures in any number are all certain digits plus one doubtful digit

Structure of Significant Figures

The significant figures in any number are all certain digits plus one doubtful digit

(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.