Question

Which of the following decreases gradually from Be to Ba (in the periodic table)?
A. Basic character of hydroxides
B. Solubility of sulphates in water
C. Solubility of hydroxides in water
D. Strength of elements as a reducing agent

Answer 1

Hint: All the metals from Be to Ba are alkaline earth metals. They belong to the second group of the periodic table. This group consists of elements Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium.

Complete Step by Step Answer:
The elements are Beryllium, Magnesium, Calcium, Strontium, and Barium.

We have to find which of the following properties are decreasing from Be to Ba.
A. Basic character of hydroxides
A base is a substance that can release hydroxide ions in its aqueous solution.
Let the hydroxide of these elements be represented by \[{\rm{M - OH}}\].
\[{\rm{M - OH}} \to {{\rm{M}}^{\rm{ + }}}{\rm{ + O}}{{\rm{H}}^{\rm{ - }}}\]
It will act as a base if the ionisation energy of M is low.
If the ionisation energy of M is low, it will help in the breaking of the \[{\rm{M - O}}\] bond in the hydroxide leading to the release of hydroxide ions.
The hydroxides of alkaline earth metals are basic.
The ionisation energies of these metals are low, so their hydroxides are basic.
As the ionisation energy decreases down the group, the basicity of hydroxide increases down the group.
So, A is incorrect.

B. Solubility of sulphates
For a substance to be soluble, there must be a difference between lattice energy and hydration energy. For dissolution hydration energy must be more than lattice energy.
The lattice energy of sulphates is almost equivalent as the sulphate anion has a large size compared to the size of a cation.
So, the solubility relies only on the hydration energy.
Hydration energy rises with a rise in charge and a decrease in size as a small-sized cation can be attached properly by a larger number of water molecules.
We know that down the group size increases.
So, the hydration energy decreases down the group.
So, B is correct.

C. Solubility of hydroxides in water
For a substance to be soluble, there must be a difference between lattice energy and hydration energy. For dissolution hydration energy must be more than lattice energy.
The lattice energy of hydroxides is less due to the small size of the hydroxide ion.
For the lattice energy, a small change in metallic ionic size can make a difference.
The lattice energy decreases with the increase in metallic size from Be to Ba, leading to the rise in the internuclear distance.
So, the solubility of hydroxides increases from Be to Ba.
So, C is incorrect.

D. Strength of elements as a reducing agent
A reducing agent is a chemical species that experiences oxidation while reducing other chemical species.
More the ability to oxidise more will be the strength of the reducing agent.
Down the group, size increases, ability to oxidise also increases.
So, the strength of the reducing agent increases down the group.
So, D is incorrect.

So, option B is correct.

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