Rahul set-up an experiment to find resistance of aqueous $$\mathrm{KCl}$$ solution for different concentrations at $$298 \mathrm{~K}$$ using a conductivity cell connected to a Wheatstone bridge. He fed the Wheatstone bridge with a.c. power in the audio frequency range 550 to 5000 cycles per second. Once the resistance was calculated from null point he also calculated the conductivity $$K$$ and molar conductivity $$\wedge_m$$ and recorded his readings in tabular form.
| S.No. | Conc. (M) | $$\mathrm{k~S~cm^{-1}}$$ | $$\mathrm{\wedge_m~S~cm^2~mol^{-1}}$$ |
|---|---|---|---|
| 1. | $$1.00$$ | $$111.3\times10^{-3}$$ | $$111.3$$ |
| 2. | $$0.10$$ | $$12.9\times10^{-3}$$ | $$129.0$$ |
| 3. | $$0.01$$ | $$1.41\times10^{-3}$$ | $$141.0$$ |
Answer the following questions:
(a) Why does conductivity decrease with dilution?
(b) If $$\wedge_{\mathrm{m}}{ }^0$$ of $$\mathrm{KCl}$$ is $$150.0 \mathrm{~S} \mathrm{~cm} \mathrm{~mol}^{-1}$$, calculate the degree of dissociation of $$0.01 \mathrm{M} \mathrm{KCl}$$.
(c) If Rahul had used $$\mathrm{HCl}$$ instead to $$\mathrm{KCl}$$ then would you except the $$\wedge_{\mathrm{m}}$$ values to be more or less than those per $$\mathrm{KCl}$$ for a given concentration. Justify.
OR
(c) Amit, a classmate of Rahul repeated the same experiment with $$\mathrm{CH}_3 \mathrm{COOH}$$ solution instead of $$\mathrm{KCl}$$ solution. Give one point that would be similar and one that would be different in his observations as compared to Rahul.
(a) (i) Why is boiling point of $$1 \mathrm{~M} \mathrm{~NaCl}$$ solution more than that of $$1 \mathrm{M}$$ glucose solution?
(ii) A nonvolatile solute '$$\mathrm{X}$$' (molar mass $$=\mathbf{5 0} \mathrm{~g} \mathrm{~mol}^{-1}$$) when dissolved in $$78 \mathrm{~g}$$ of benzene reduced its vapour pressure to $$90 \%$$.
Calculate the mass of $$\mathrm{X}$$ dissolved in the solution.
(iii) Calculate the boiling point elevation for a solution prepared by adding $$10 \mathrm{~g}$$ of $$\mathrm{MgCl}_2$$ to $$200 \mathrm{~g}$$ of water assuming $$\mathrm{MgCl}_2$$ is completely dissociated.
($$\mathrm{K}_{\mathrm{b}}$$ for Water $$=0.512 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$, Molar mass $$\mathrm{MgCl}_2=95 \mathrm{~g} \mathrm{~mol}^{-1}$$)
OR
(b) (i) Why is the value of Van't Hoff factor for ethanoic acid in benzene close to 0.5 ?
(ii) Determine the osmotic pressure of a solution prepared by dissolving $$2.32 \times 10^{-2} \mathrm{~g}$$ of $$\mathrm{K}_2 \mathrm{SO}_4$$ in $$2 \mathrm{~L}$$ of solution at $$25^{\circ} \mathrm{C}$$, assuming that $$\mathrm{K}_2 \mathrm{SO}_4$$ is completely dissociated.
($$\mathrm{R}=0.082 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$$, Molar mass $$\mathrm{K}_2 \mathrm{SO}_4 =174 \mathrm{~g} \mathrm{~mol}^{-1}$$)
(iii) When $$25.6 \mathrm{~g}$$ of sulphur was dissolved in $$1000 \mathrm{~g}$$ of benzene, the freezing point lowered by $$0.512 \mathrm{~K}$$. Calculate the formula of sulphur ($$\mathrm{S}_{\mathrm{x}}$$). ($$\mathrm{K}_{\mathrm{f}}$$ for benzene $$=5.12 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$, Atomic mass of Sulphur $$=32 \mathrm{~g} \mathrm{~mol}^{-1}$$ )
(a) (i) Write the reaction involved in Cannizaro's reaction.
(ii) Why are the boiling point of aldehydes and ketones lower than that of corresponding carboxylic acids?
(iii) An organic compound '$$\mathrm{A}$$' with molecular formula $$\mathrm{C}_5 \mathrm{H}_8 \mathrm{O}_2$$ is reduced to $$\mathrm{n}$$-pentane with hydrazone followed by heating with $$\mathrm{NaOH}$$ and Glycol. 'A' forms a dioxime with hydroxylamine and gives a positive Iodoform and Tollen's test. Identify '$$A$$' and give its reaction for Iodoform and Tollen's test.
OR
(b) (i) Give a chemical test to distinguish between ethanol acid and ethanoic acid.
(ii) Why is the $$\alpha$$-hydrogens of aldehydes and ketones are acidic in nature?
(iii) An organic compound '$$\mathrm{A}$$' with molecular formula $$\mathrm{C}_4 \mathrm{H}_8 \mathrm{O}_2$$ undergoes acid hydrolysis to form two compounds '$$\mathrm{B}$$' and '$$\mathrm{C}$$'. Oxidation of '$$C$$' with acidified potassium permanganate also produces 'B'. Sodium salt of 'B' on heating with soda lime gives methane.
(1) Identify 'A', 'B' and 'C'.
(2) Out of 'B' and 'C', which will have higher boiling point? Give reason.
(a) Why is chemistry of actinoids complicated as compared to lanthanoids?
(b) Complete the following reaction and justify that it is a disproportionation reaction:
$$3 \mathrm{MnO}_4^{2-}+4 \mathrm{H}^{+} \rightarrow$$________ $$+$$ _________ $$+$$ $$\mathrm{H}_2 \mathrm{O}$$.
(c) The given graph shows the trends in melting points of transition metals:
Explain the reason why $$\mathrm{Cr}$$ has highest melting point and manganese $$(\mathrm{Mn})$$ a lower melting point.