Comment on each of the following observations: (a) When an aqueous solution of potassium cyanide is added to aluminium sulphate Al(OH)_(2) is precipitated. (b) The carbide MgaCs liberated propyne (CH_(3)C=CH) on treatment with water. (c) Magnesium silicate reacts with ammonium bromide in liquid ammonia to form silane,(d)is hydrolysed by aqueous alkali at the same rate as the corresponding Si-D compound.

Comment on each of the following observations: (a) When an aqueous sol

1.	Comment on each of the following observations: (a) When an aqueous solution of potassium cyanide is added to aluminium sulphate Al(OH)_(2) is precipitated. (b) The carbide MgaCs liberated propyne (CH_(3)C=CH) on treatment with water. (c) Magnesium silicate reacts with ammonium bromide in liquid ammonia to form silane,(d)is hydrolysed by aqueous alkali at the same rate as the corresponding Si-D compound.
Answer» The carbide MgaCs liberated propyne `(CH_(3)C=CH)` on treatment with water. Magnesium silicate reacts with ammonium bromide in LIQUID ammonia to form SILANE, Solution :(a) Aqueous solution of KCN is alkaline due to hydrolysis of `CN^(-) lonCN^(-)+H_(2)OtoHCN+OH^(-)` `OH^(-)` formed causes precipitation of `Al_(2)(SO_(4))_(3)` as `Al(OH)_(3)` `AI^(3+)+3OH^(-)to Al(OH)_(3)downarrow` (b) `Mg_(2)C_(3)to2Mg^(2+)+C_(3)^(4-)` `C_(3)^(4)`onis decomposed by. `H_(2)O`giving `CH_(3)C=CH` `C^(3-)-C=C+4H_(2)OtoCH_(2)-C=CH+4OH` `Mg^(2+)+4OHto2Mg(OH)_(2)` Net:`Mg_(2)C_(3)+4H_(2)Oto2Mg(OH)_(2)+CH_(3)-C=CH` (c) Solutions of `NH_(4)Br` (in general ammonium halide) in `NH_(3)` may be used as acids and `SiH_(4)` (Silane) is formed when `NH_(4)Br` in `NH_(3)` reacts with `Mg_(2)Si` (magnesium silicide) `Mg_(2)Si+ 4NH_(4)Brto SiH_(4)+2MgBr_(2)+4NH_(3)` (d) Si-Hor Si-D bond is not broken in rate determining step, it is probable that there is attack of OH on Si.