Important questions based on NCERT syllabus for Chapter 1 - Some Basic Concepts of Chemistry:
Question-1: Calculate the molecular mass of the following:
(i) H2O(ii) C02(iii) CH4
Solution: (i) Molecular mass of H2O = 2(1.008 amu) + 16.00 amu=18.016 amu
(ii) Molecular mass of CO2= 12.01 amu + 2 x 16.00 amu = 44.01 amu
(iii) Molecular mass of CH4= 12.01 amu + 4 (1.008 amu) = 16.042 amu
Question-2: What do you mean by significant figures?
Solution: The digits in a properly recorded measurement are known as significant figures. It is also defined as follows. The total numbers of figures in a number including the last digit whose value is uncertain is called number of significant figures.
Question-3: If ten volumes of dihydrogen gas reacts with five volumes of dioxygen gas, how many volumes of water vapour could be produced?
Solution: H2 and 02 react according to the equation
2H2(g) + 02 (g) ——>2H2O (g)
Thus, 2 volumes of H2 react with 1 volume of 02 to produce 2 volumes of water vapour. Hence, 10 volumes of H2 will react completely with 5 volumes of 02 to produce 10 volumes of water vapour.