Question

The no. of mol. of the independent species present in one mole of potash alum:
(A) 32
(B) 16
(C) 38
(D) 64

Answer 1

Hint: Potash alum contains 24 molecules of water as crystalline water. The molecular formula of the potash alum or alum can be given as ${K_2}S{O_4} \cdot A{l_2}{(S{O_4})_3} \cdot 24{H_2}O$.

Complete step by step solution:
Let me first make it clear what is being asked in this question. Here, we need to give the number of moles of the independent species present in potash alum. So, let us know what potash alum is.
- Potash alum is also known as alum. The molecular formula of potash alum is ${K_2}S{O_4} \cdot A{l_2}{(S{O_4})_3} \cdot 24{H_2}O$.
- Potash alum is used in the purification of water in our daily life. It is also used in dyeing and manufacture of fireproof textiles.
- Now, independent species include ions present in the potash alum as well. Here, crystalline water is not divided into its ionic form and they exist in molecule form.
- We can see in the molecular formula that there are two atoms of potassium (${K^ + }$). So, we count them as two individual species.
- There are two aluminum ions ($A{l^{3 + }}$) as well. So, we can count them as another two individual species.
- There are four sulphate ions. So, they can also be considered as individual species.
- There are 24 molecules of water in potash alum. They are also a kind of species.
- Thus, if we do a total, there are 2+2+4+24=32 individual species present in the potash alum.

Therefore, the correct answer to this question is (A).

Note: Remember that here each positive and negative ions are counted as individual species. So, do not assume that ${K_2}S{O_4}$ and $A{l_2}{(SO)_4}$ as only two species, actually need to count all the ions present in the molecule.