Class 11 Chemistry NCERT Solutions

Chapter 1: Basic Concepts of Chemistry

Question 1.9

Calculate the atomic mass (average) of chlorine using the following data:

	% Natural Abundance	Molar Mass
³⁵Cl	75.77	34.9689
³⁷Cl	24.23	36.9659

Answer:

The average atomic mass of chlorine

= 26.4959 + 8.9568

= 35.4527 u

∴ The average atomic mass of chlorine = 35.4527 u

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Question 1.8 Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are 69.9 and 30.1 respectively. Given that the molar mass of the oxide is 159.69 g mol–1.

Question 1.10 In three moles of ethane (C2H6), calculate the following (i) Number of moles of carbon atoms (ii) Number of moles of hydrogen atoms (iii) Number of molecules of ethane