Question

Potassium alum, $KAl{(S{O_4})_2} \cdot 12{H_2}O$ is obtained in the form of octahedral crystals when a solution of ${K_2}S{O_4}$ and $A{l_2}{(S{O_4})_3}$ is concentrated by evaporation. Suggest specific experiments to specify whether it is a complex or double salt.
A) One can determine conductance
B) One can determine freezing points
C) One can detect $A{l^{3 + }}$ , $S{O_4}^{2 - }$ , ${K^ + }$ .
D) All of these

Answer 1

Hint: In order to answer this question, you must recall the properties of double salts. Enlist the properties and observe the properties which you may determine by the given data and then choose the correct options.


Complete solution:
 In this solution, we will enlist the properties and the quantities which we can determine by the given data:
Double Salts: Double salts are salts containing more than one cation or anion, and are obtained by combination of two different salts which were crystallized in the same regular ionic lattice. When dissolved in water, a double salt completely dissociates into simple ions while complexes do not; the complex ion remains unchanged.
The quantities which can be determined are:
1.By measuring conductance we can measure the quantity of ions. If conductance is high that means there are more no. of ions which confirms it is double salt
2.By measuring freezing point we can measure the quantity of ions. Low freezing point means there are more no.of ions which are depressing the freezing point and which confirms it is double salt
3.The detection of different ions can also confirm whether it is a double salt or a complex.

Hence the option D is the correct answer.


Note:Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula $KAl{(S{O_4})_2}$ . It is commonly encountered as the dodecahydrate, $KAl{(S{O_4})_2} \cdot 12{H_2}O$ . It crystallizes in an octahedral structure in neutral solution and cubic structure in an alkali solution. The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.