Chapter 11

Practise calculations involving molar concentrations (see also study exercises \(9.1\) and 9.2). What mass of substance would be required to prepare each of the following aqueous solutions (answer in grams, to four decimal places in each case): (a) \(1000.00 \mathrm{~mL}\) of \(1.0 \mathrm{M}\) sodium chloride solution? (b) \(250.00 \mathrm{~mL}\) of \(0.2004 \mathrm{M} \mathrm{KMnO}_{4}\) solution? (c) \(400 \mathrm{~mL}\) of sodium hydroxide at \(5 \% \mathrm{w} / \mathrm{v} ?\) (d) \(300 \mathrm{~mL}\) of potassium nitrate at \(10 \% \mathrm{w} / \mathrm{w} ?\)

Practise expressing concentrations in different ways. Express all answers to four decimal places. (a) What is \(4.000 \mathrm{~g} \mathrm{~L}^{-1}\) sodium hydroxide expressed in terms of molarity? (b) What is \(0.1\) mol \(\mathrm{L}^{-1} \mathrm{~K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) expressed in \(g L^{-1} ?\) (c) What is \(5 \% \mathrm{v} / \mathrm{v}\) ethanol, expressed in terms of molarity? (Density of ethanol at \(\left.25^{\circ} \mathrm{C}=0.7892 \mathrm{~g} \mathrm{~mL}^{-1}\right)\) (d) What is \(150 \mathrm{mmol} \mathrm{L}^{-1}\) glucose expressed in terms of per cent concentration \((\% \mathrm{w} / \mathrm{v}) ?\)

Using the concepts of 'oxidation numbers' and 'partial ionic equations', balance the following redox reactions which all take place in acid solution. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\mathrm{FeSO}_{4}+\mathrm{H}_{2} \mathrm{SO}_{4}\) $$ \rightarrow \mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}+\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}+\mathrm{K}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O} $$ (b) \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}+\mathrm{I}_{2} \rightarrow \mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}+\mathrm{Nal}\) (c) \(\mathrm{KIO}_{3}+\mathrm{KI}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{K}_{2} \mathrm{SO}_{4}+\mathrm{I}_{2}+\mathrm{H}_{2} \mathrm{O}\) (d) \((\mathrm{COOH})_{2}+\mathrm{KMnO}_{4}+\mathrm{H}_{2} \mathrm{SO}_{4}\) $$ \rightarrow \mathrm{K}_{2} \mathrm{SO}_{4}+\mathrm{MnSO}_{4}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} $$