(a) A zinc salt, E when heated strongly, produced a brown gas with pungent smell, a colourless gas that rekindled a glowing splint, and a residue that was allowed to cool.
(i) identify the salt E.
(ii) Write an equation for the decomposition of E.
(iii) State what would be observed when the residue was allowed to cool.
(b) Describe how 250cm\(^3\) of 0.2 mol dm\(^3\) H\(_2\)SO\(_4\) could be prepared from 150 cm\(^3\) of a 1.0 mol dm\(^{3}\) stock solution of the acid.
(c) State the effect of aqueous solution of Al\(_2(SO_4)_3\) on litmus paper.
Explanation
(a)(i) Zn(NO\(_3\))\(_2\)
ii) 2Zn(NO\(_3\))2\(_{(s)}\) \(\to\) 2ZnO\(_{(s)}\) + 4NO\(_{2(g)}\) + \(O_2\)
iii) The residue was yellow when lost and turns white when cold.
(b) Using the law of dilution
C\(_1\)V\(_1\) = C\(_2\)V\(_2\)
V\(_1\) = \(\frac{C_2V_2}{C_1} = \frac{0.2 \times 250}{1.0}\)
= 50cm\(^3\)
Procedure: 50cm\(^3\) of the stock solution is pipetted from a burette into a 250cm\(^3\) volumetric flask. The flask is topped up to the mark with distilled water. Flask is stoppered and shaken to obtain a uniform solution.
(c) Turns blue litmus paper red.