Unit 7 The P Block Elements (Intext Questions-8)
Intext Questions
7.13 List the important sources of sulphur.
Answer Sulphur mainly exists in combined form in the earth’s crust primarily as sulphates [gypsum ( $\left.\mathrm{CaSO_4} \cdot 2 \mathrm{H_2} \mathrm{O}\right)$, Epsom salt $\left(\mathrm{MgSO_4} \cdot 7 \mathrm{H_2} \mathrm{O}\right)$, baryte $\left(\mathrm{BaSO_4}\right)$ ] and sulphides [(galena (PbS), zinc blends ( $\left.\mathrm{ZnS}\right)$, copper pyrites $\left(\mathrm{CuFeS_2}\right)$ ].Show Answer
Answer The thermal stability of hydrides decreases on moving down the group. This is due to a decrease in the bond dissociation enthalpy ( $\mathrm{H}-\mathrm{E}$ ) of hydrides on moving down the group. Therefore, $
\begin{array}{l}
\mathrm{H_2} \mathrm{O} \\
\mathrm{H_2} \mathrm{S} \\
\mathrm{H_2} \mathrm{Se} \\
\mathrm{H_2} \mathrm{Te}^{2} \\
\mathrm{H_2} \mathrm{Po} \\
\end{array} \Bigg \downarrow \text{Thermal stability decreases}
$Show Answer
Show Answer
Answer
$\mathrm{H_2} \mathrm{O}$ has oxygen as the central atom. Oxygen has smaller size and higher electronegativity as compared to sulphur. Therefore, there is extensive hydrogen bonding in $\mathrm{H_2} \mathrm{O}$, which is absent in $\mathrm{H_2} \mathrm{~S}$. Molecules of $\mathrm{H_2} \mathrm{~S}$ are held together only by weak van der Waal’s forces of attraction.
Hence, $\mathrm{H_2} \mathrm{O}$ exists as a liquid while $\mathrm{H_2} \mathrm{~S}$ as a gas.
