concentrated sulphuric acid is added following by heating to each of following test tube .

(i) cane sugar , (ii) sodium bromide (iii) copper turnings ,(iv) sulphur powder (v) potassium chloride

Identify in which of the above test tube the following change will be observed. support your answer with the help of a chemical equation .

a) formation of a black substance

b) evolution of brown gas

c) evolution of colourless gas

d) formation of a brown substance which on dilution become blue

e) disappearance of yellow powder along with evolution of colourless gas.

a) Conc. H₂SO₄ is an excellent dehydrating agent. It therefore removes water from cane sugar to form a black substance called sugar charcoal.
$$\begin{gathered} {\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\stackrel{\mathrm{conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{ \to } 12 \mathrm{C} + 11 {\mathrm{H}}_2\mathrm{O} \\ \mathrm{cane} \mathrm{sugar} \mathrm{sugar} \mathrm{charcoal} \end{gathered}$$

Thus formation of black substance occur in this case.

b) When sodium bromide is heated with conc.H₂SO₄, a brown gas Bromine (Br₂) is obtained.

$$\begin{gathered} 2\mathrm{NaBr} + 2 \mathrm{conc}. {\mathrm{H}}_2{\mathrm{SO}}_4 \stackrel{\mathrm{heat}}{\to }{\mathrm{Na}}_2{\mathrm{SO}}_4 + {\mathrm{Br}}_2 + {\mathrm{SO}}_2 + 2{\mathrm{H}}_2\mathrm{O} \\ \mathrm{sodium} B\mathrm{romine} \\ \mathrm{bromide} \end{gathered}$$
Thus evolution of brown gas occur in this case.

c)​ When potassium chloride is heated with conc.H₂SO₄, a colourless gas hydrogen chloride (HCl) is obtained.
$$\begin{gathered} 2\mathrm{KCl} +\mathrm{conc}. {\mathrm{H}}_2{\mathrm{SO}}_4 \stackrel{\mathrm{heat}}{\to }{\mathrm{K}}_2{\mathrm{SO}}_4 + \mathrm{HCl} \\ \mathrm{potassium} \mathrm{Hydrogen} \\ \mathrm{chloride} \mathrm{chloride} \end{gathered}$$

d) When copper turnings are heated with conc.H₂SO₄ , first a brownish substance (presumably a mixture of unreacted copper turnings and white anhydrous copper sulphate) is formed along with evolution of pungent smelling SO₂ gas.The initially formed brown substance on dilution turns blue due to formation of hydrated copper sulphate .

$$\begin{gathered} \mathrm{Cu} +2 {\mathrm{H}}_2{\mathrm{SO}}_4 \stackrel{\mathrm{heat}}{\to } {\mathrm{CuSO}}_4 +{\mathrm{SO}}_2 + 2{\mathrm{H}}_2\mathrm{O} \\ \mathrm{anhydrous} \\ \mathrm{copper} \mathrm{sulphate} \\ {\mathrm{CuSO}}_{4 }+ 5 {\mathrm{H}}_2\mathrm{O} \to {\mathrm{CuSO}}_{4 }.5 {\mathrm{H}}_2\mathrm{O} \\ \mathrm{Hydrated} \\ \mathrm{copper} \mathrm{sulphate} \end{gathered}$$

e) When yellow sulphur powder is heated with conc. H₂SO₄, sulphur dissolves along with the evolution of ​with evolution of pungent smelling SO₂ gas.82
$S_8 +16 {\mathrm{H}}_2{\mathrm{SO}}_4 \stackrel{heat }{\to }24 {\mathrm{SO}}_2 + 16{\mathrm{H}}_2\mathrm{O}$