Chapter 7

A volume of \(10 \mathrm{ml}\) of \(0.1 \mathrm{M}\) tribasic acid, \(\mathrm{H}_{3} \mathrm{~A}\) is titrated with \(0.1 \mathrm{M}-\mathrm{NaOH}\) solution. What is the ratio (approximate value) of \(\frac{\left[\mathrm{H}_{3} \mathrm{~A}\right]}{\left[\mathrm{A}^{3-}\right]}\) at the second equivalent point? Given: \(K_{1}=7.5 \times 10^{-4} ; K_{2}=10^{-8}\); \(K_{3}=10^{-12}\) (a) \(10^{-4}\) (b) \(10^{-3}\) (c) \(10^{-7}\) (d) \(10^{-6}\)

\(\begin{array}{ll}\text { The } \text { equilibrium } & \text { carbonate } \text { ion }\end{array}\) concentration after equal volumes of \(0.7 \mathrm{M}-\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(0.7 \mathrm{M}-\mathrm{HCl}\) solutions are mixed, is \(\left(K_{\mathrm{al}}\right.\) and \(K_{\mathrm{a} 2}\) for \(\mathrm{H}_{2} \mathrm{CO}_{3}\) are \(4.9 \times 10^{-6}\) and \(4.0 \times 10^{-11}\), respectively) (a) \(0.7 \mathrm{M}\) (b) \(0.35 \mathrm{M}\) (c) \(0.002 \mathrm{M}\) (d) \(0.001 \mathrm{M}\)

Calcium Lactate is a salt of weak acid and represented as \(\mathrm{Ca}(\mathrm{Lac})_{2} .\) A saturated solution of \(\mathrm{Ca}(\mathrm{Lac})_{2}\) contains \(0.125 \mathrm{~mole}\) of salt in \(0.50 \mathrm{~L}\) solution. The \(\mathrm{pOH}\) of this is 5.60. Assuming complete dissociation of salt, calculate \(K_{\mathrm{a}}\) of lactate acid. \((\log 2.5=0.4)\) (a) \(1.25 \times 10^{-11}\) (b) \(8.0 \times 10^{-4}\) (c) \(3.2 \times 10^{-17}\) (d) \(4 \times 10^{-5}\)

The addition of sodium acetate to acetic acid solution will cause (a) increase in its \(\mathrm{pH}\) value (b) decrease in its \(\mathrm{pH}\) value (c) no change in \(\mathrm{pH}\) value (d) change in \(\mathrm{pH}\) which cannot be predicted

A \(0.1 \mathrm{M}\) acetic acid solution is titrated against \(0.1 \mathrm{M}-\mathrm{NaOH}\) solution. What would be the difference in \(\mathrm{pH}\) between \(1 / 4\) and \(3 / 4\) stages of neutralization of the acid? (a) \(2 \log (0.75)\) (b) \(2 \log (0.25)\) (c) \(\log 3\) (d) \(2 \log 3\)

An amount of \(0.1\) mole of \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) \(\left(K_{\mathrm{b}}=5 \times 10^{-4}\right)\) is mixed with \(0.08\) mole of \(\mathrm{HCl}\) and diluted to one litre. What will be the \(\mathrm{H}^{+}\) concentration in the solution? (a) \(1.25 \times 10^{-4} \mathrm{M}\) (b) \(8 \times 10^{-11} \mathrm{M}\) (c) \(1.6 \times 10^{-11} \mathrm{M}\) (d) \(2 \times 10^{-3} \mathrm{M}\)

When glycinium hydrochloride \(\left(\mathrm{NH}_{2} \mathrm{CH}_{2}\right.\) COOH.HCl) is titrated against \(\mathrm{NaOH}\), \(\mathrm{pH}\) at the first half equivalence point is \(2.40\) and the \(\mathrm{pH}\) at second half equivalence point is \(9.60\). The \(\mathrm{pH}\) at first equivalence point is (a) \(2.40\) (b) \(9.60\) (c) \(6.00\) (d) \(7.20\)

An acid base indicator which is a weak acid has a \(\mathrm{p} K_{\mathrm{a}}\) value \(=5.5\). At what concentration ratio of sodium acetate to acetic acid would the indicator show a colour half way between those of its acid and conjugate base forms? \(\mathrm{p} K_{\mathrm{a}}\) of acetic acid \(=4.75 .[\) Antilog \((0.75)=5.62\), Antilog \((0.79)=6.3\), Antilog \((0.69)=4.93]\) (a) \(4.93: 1\) (b) \(6.3: 1\) (c) \(5.62: 1\) (d) \(2.37: 1\)

An amount of \(0.15\) mole of pyridinium chloride has been added into \(500 \mathrm{ml}\) of 0.2 M pyridine solution. Calculate pH and hydroxyl ion concentration in the resulting solution assuming no change in volume. \(K_{\mathrm{b}}\) for pyridine \(=1.5 \times 10^{-9}\). \((\log 2=0.3, \log 0.3=0.48)\) (a) \(9.0\) (b) \(5.0\) (c) \(8.64\) (d) \(5.36\)

The correct increasing order of solubility of the following substances in \(\mathrm{g} / 100 \mathrm{ml}\) is \(\mathrm{PbSO}_{4}\left(K_{\mathrm{sp}}=2 \times 10^{-9}\right), \mathrm{ZnS}\left(K_{\mathrm{sp}}=1\right.\) \(\left.\times 10^{-22}\right)\), AgBr \(\left(K_{\text {sp }}=4 \times 10^{-13}\right), \mathrm{CuCO}_{3}\) \(\left(K_{\mathrm{sp}}=1 \times 10^{-8}\right) .\) (Atomic masses: \(\mathrm{Pb}=208\), \(\mathrm{Zn}=65, \mathrm{Ag}=108, \mathrm{Br}=80, \mathrm{Cu}=63)\) (a) \(\mathrm{PbSO}_{4}<\mathrm{ZnS}<\mathrm{AgBr}<\mathrm{CuCO}_{3}\) (b) \(\mathrm{PbSO}_{4}<\mathrm{CuCO}_{3}<\mathrm{AgBr}<\mathrm{ZnS}\) (c) \(\mathrm{ZnS}<\mathrm{AgBr}<\mathrm{CuCO}_{3}<\mathrm{PbSO}_{4}\) (d) \(\mathrm{ZnS}<\mathrm{AgBr}<\mathrm{PbSO}_{4}<\mathrm{CuCO}_{3}\)