Question

Which of the following statement (s) is incorrect?
(a) $L{{i}^{+}}$ has a minimum degree of hydration.
(b) The oxidation state of K in $K{{O}_{2}}$is +1.
(c) Na is used to make a Na/Pb alloy.
(d) $MgS{{O}_{4}}$ is readily soluble in water.

Answer 1

Hint: As we can see, all the given statements are related to the elements of alkali metals and alkaline earth metals groups. These both groups are the part of s-block in periodic table. Therefore we must attempt this question by applying the periodic properties of s- block and check each statement whether it true or false.

Complete answer:
Let us check each and every statement as follows:-
(a) $L{{i}^{+}}$ has a minimum degree of hydration: Hydration enthalpy is the heat energy released when new bonds are formed between the ions and the water molecules. Greater the charge density, greater will be the degree of hydration which means smaller the cation (since charge density is inversely proportional to size of ions), more will be the hydration energy. Since $L{{i}^{+}}$ion is smallest among all alkali metals hence it has the maximum hydration energy. Therefore, this statement is false.
(b) The oxidation state of K in $K{{O}_{2}}$is +1: As we know that all alkali metals have 1 electron in its valence shell and can only donate one electron to achieve noble gas configuration. Hence they always have +1 oxidation state. Here K (Potassium) is an alkali metal so its oxidation state will remain +1 no matter what other atom is attached to it. Therefore, it is a true statement.
(c) Na is used to make a Na/Pb alloy: Sodium (Na) is used in the making of Na/Pb alloy which is needed for the formation of $PbE{{t}_{4}}$ . These organometallic compounds of lead were earlier used as anti-knock additives to petrol but nowadays the petrol we get is lead-free. Hence this statement is also true
(d) $MgS{{O}_{4}}$is readily soluble in water: $MgS{{O}_{4}}$and$BeS{{O}_{4}}$ are readily soluble in water because higher hydration energy of $M{{g}^{2+}}$ and $B{{e}^{2+}}$ions overcomes their lattice energy and hence their sulphates are very soluble. Therefore this statement is also true.
-Hence from the above date we conclude that (a) $L{{i}^{+}}$ has a minimum degree of hydration is a wrong statement.

Note:
- Hydration enthalpies are always negative as they are exothermic reactions.
-The oxidation state of O in$K{{O}_{2}}$ is (-1/2) which is calculated by considering K as alkali metal.
-The solubility in water decreases from $CaS{{O}_{4}}$to$BaS{{O}_{4}}$.