Chapter 2

Naturally occurring chlorine is \(75.53 \% \mathrm{Cl}^{35}\) which has an atomie mass of \(34.969 \mathrm{amu}\) and \(24.47 \% \mathrm{Cl}^{37}\), which has a mass of \(36.966\) amu. Calculate the average atomic mass of chlorine.

The vapour density of a metal chloride is \(85 .\) If equivalent weight of metal is \(7.01\), calculate the at.wt. of metal.

Potassium chromate is isomorphous to potassium sulphate \(\left(\mathrm{K}_{2} \mathrm{SO}_{4}\right)\) and it is found to have \(26.78 \%\) Cr. Calculate the at.wt. of \(\mathrm{Cr}\) if at.wt. of potassium is \(39.10\).

Use the data given in the following table to calculate the molar mass of naturally occuring argon : \(\begin{array}{lcc}\text { Isotope } & \text { Isotopic molar mass } & \text { Abundance } \\ { }^{36} \mathrm{Ar} & 35.96755 \mathrm{~g} \mathrm{~mol}^{-1} & 0.337 \% \\ { }^{38} \mathrm{Ar} & 37.96272 \mathrm{~g} \mathrm{~mol}^{-1} & 0.063 \% \\ { }^{40} \mathrm{Ar} & 39.9624 \mathrm{~g} \mathrm{~mol}^{-1} & 99.600 \%\end{array}\)

Calculate the mass of \(\mathrm{BaCO}_{3}\) produced when excess \(\mathrm{CO}_{2}\) is bubbled through a solution containing \(0.205\) moles of \(\mathrm{Ba}(\mathrm{OH})_{2}\).

\(P\) and \(Q\) are two elements which form \(P_{2} Q_{3}, P Q_{2}\) molecules. If \(0.15\) mole of \(P_{2} Q_{3}\) and \(P Q_{2}\) weighs \(15.9 \mathrm{~g}\) and \(9.3 \mathrm{~g}\), respectively, what are atomic weighs of \(P\) and \(Q ?\)

(i) Butyric acid contains only \(\mathrm{C}, \mathrm{H}\) and \(\mathrm{O}\). A \(4.24 \mathrm{mg}\) sample of butyric acid is completely burned. It gives \(8.45 \mathrm{mg}\) of carbon dioxide \(\left(\mathrm{CO}_{2}\right)\) and \(3: 46 \mathrm{mg}\) of water. What is the mass percentage of each element in butyric acid? (ii) If the elemental composition of butyric acid is found to be \(54.2 \%\) C, \(9.2 \% \mathrm{H}\) and \(36.6 \%\) O, determine the empirical formula. (iii) The molecular mass of butyric acid was determined by experiment to be \(88 .\) What is the molecular formula?

\(\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) is emprical formula of a crystalline compound of iron. It is used in water and sewage treatment to aid in the removal of suspended impurities. Calculate the mass percentage of iron, sulphur and oxygen in this compound.

A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives \(3.38 \mathrm{~g}\) carbon dioxide, \(0.690 \mathrm{~g}\) of water and no other products. A volume of \(10.0\) litre (Measured at STP) of this welding gas is found to weigh \(11.6 \mathrm{~g}\). Calculate : (i) empirical formula, (ii) molar mass of the gas, and (iii) moleculat formula.

\(5.325 \mathrm{~g}\) sample of methyl benzoate, a compound used in the manufacture of perfumes is found to contain \(3.758 \mathrm{~g}\) of carbon, \(0.316\) \(\mathrm{g}\) hydrogen and \(1.251 \mathrm{~g}\) of oxygen. What is empirical formulia of compound. If mol. weight of methyl benzoate is \(136.0\), calculate its molecular formula.