Question

Assertion: $BaS{O_4}$ is insoluble in water.
Reason: Lattice energy of $BaS{O_4}$ is higher than its hydration energy.
A.Both assertion and reason are correct and reason is correct explanation of assertion
B.Both assertion and reason are correct but reason is not the correct explanation of assertion
C.Assertion is correct but reason is incorrect
D.Both assertion and reason are incorrect.

Answer 1

Hint: The group II elements are basic metals which are known as alkaline earth metals. Hydration energy and solubility are directly proportional to each other whereas they are inversely proportional to lattice energy. As we move down the group the hydration energy decreases and size increases.

Complete answer:
- The basic metals of group II of the periodic table are known as the alkaline earth metals. The word earth was proposed to highlight the fact that the oxides of these metals are insoluble in water and are resistant to heat. These include beryllium, magnesium, calcium, strontium, barium and radium. These metals are reactive at normal temperature and pressure. They have two valence electrons and they readily lose these electrons to gain noble gas configuration and form cation with 2+ charge. They have low densities and low melting and boiling points.
- Barium sulphate is an odourless, white crystalline inorganic compound with chemical formula $BaS{O_4}$. It is a neutral salt as it is formed from a strong base and a strong acid.
- Hydration energy and solubility are directly proportional to each other but solubility is inversely proportional to lattice energy. The $Ba$ and $S{O_4}$ ions are large in size. The lattice energy of barium sulphate is higher than their hydration energy and as discussed solubility and lattice energy is inversely proportional therefore, $BaS{O_4}$ is insoluble in water. The hydration energy decreases down the group as the size of the element increases. Thus, the hydration energy of $BeS{O_4}$ is higher and so it is soluble in water.

So, for the above question we conclude that option (A) is correct that both assertion and reason are correct and reason is the correct explanation of the assertion as with increasing size and lattice energy solubility and hydration energy decreases.

Note:
Barium is a white liquid which is used for examining x-ray reports. Barium is not harmful for the human body as it passes through the digestive system. Whereas barium sulphate may cause high heart rate, stomach problems, weakness and pale skin. It is also used in oil well drilling.