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Class 9Class 10First YearSecond Year
$Q.18 An unknown metal M reacts with S to form a compound with a formula \mathrm{M}_{2} \mathrm{~S}_{3} . If 3.12 \mathrm{~g} of M reacts with exactly 2.88 \mathrm{~g} of sulphur what are the names of metal M and the compound \mathrm{M}_{2} \mathrm{~S}_{3} ?(Ans: \mathrm{Cr} ; \mathrm{Cr}_{2} \mathrm{~S}_{3} )$

$Q.16 Ethylene glycol is used as automobile antifreeze. It has 38.7 \% carbon 9.7 \% hydrogen and 51.6 \% oxygen. Its molar mass is 62.1 \mathrm{~g} \mathrm{~mol}^{-1} . Determine its empirical formula.?(Ans: \mathrm{CH}_{3} \mathrm{O} )$

$Q.7 Boron with atomic number 5 has two naturally occurring isotopes. Calculate the percentage abundance of { }^{10} \mathrm{~B} and { }^{11} \mathrm{~B} from the following information.Average atomic mass of boron =10.81 \mathrm{amu} Isotopic mass of { }^{10} \mathrm{~B} =10.0129 \mathrm{amu} Isotopic mass of { }^{\prime \prime} \mathrm{B} =11.0093 \mathrm{amu} (Ans: 20.002 \% 79.992 \% )$

$Q.5(a) What are isotopes? How do you deduce the fractional atomic masses of elements from the relative isotopic abundance? Give two examples in support of your answer.$

$Q.25 Explain the following with reasons.i) Law of conservation of mass has to be obeyed during stoichiometric calculations.$

$Calculate the number of grams of \mathrm{K}_{2} \mathrm{SO}_{4} and water produced when 14 \mathrm{~g} of \mathrm{KOH} are reacted with excess of \mathrm{H}_{2} \mathrm{SO}_{4} . Also calculate the number of molecules of water produced.$

$Define the following terms and give three examples of each.(i) Gram atom$