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

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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).

This structure is hydrogen bonding for water ethanol

Structure of Ethanol and Water

This structure is hydrogen bonding for water ethanol

Answer:

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 ?

A carbon-12 atom is made up of six protons and six neutrons,

Structure of Carbon Atoms

A carbon-12 atom is made up of six protons and six neutrons,

Answer:

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?

There are three rules on determining how many significant figures

Structure of Significant Figures

There are three rules on determining how many significant figures

(ii)

(iii)

Answer:

(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:

Data on Isotopes
Isotope mass and abundance

Isotope

Isotopic molar mass

Abundance

Answer:

Molar mass of argon