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##### Q.6 Silver has atomic number 47 and has 16 known isotopes but two occur naturally i.e. Ag-107 and \mathrm{Ag}-109 . Given the following mass spectrometric data calculate the average atomic mass of silver.\begin{tabular}{|l|c|c|}\hline Isotopes & Mass (\mathrm{amu}) & Percentage abundance \\\hline { }^{107} \mathrm{Ag} & 106.90509 & 51.84 \\ { }^{100} \mathrm{Ag} & 108.90476 & 48.16 \\\hline\end{tabular}

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