# Chemistry Class 11 NCERT Solutions: Chapter 1 Some Basic Concepts of Chemistry Part 10

Q: 29. Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is .040 (assume the density of water to be one).

Number of moles present in 1 L water:

Substituting the value of in equation (1),

Molarity of solution

Q: 30. What will be the mass of one?

mole of carbon atoms atom of carbon

of carbon.

Q: 31. How many significant figures should be present in the answer of the following calculation?

(ii)

(iii)

(1)

Least precise number of calculation

Number of significant figures in the answer

Number of significant figures in the least precise number

(ii)

Least precise number of calculation

Number of significant figures in the answer = Number of significant figures in

(iii)

Since the least number of decimal places in each term is four, the number of significant figures in the answer is also 4.

Q: 32 Use the data given in the following table to calculate the molar mass of naturally occurring argon isotopes:

 Isotope Isotopic molar mass Abundance Equation Equation Equation Equation Equation Equation Equation Equation Equation