Question

Statement 1 : Crystals of hydrated calcium sulphate gypsum: $(CaSO_4 .2H_2O)$ are soft and easily cleaved.
Statement 2 :Crystals of anhydrous calcium sulphate (anhydride: $CaSO_4)$ are very hard and very difficult to cleave.

• A. If both Statement $1$ and Statement $2$ are true and the statement $2$ is the correct explanation of the statement $1$
• B. If both Statement $1$ and Statement $2$ are true but statement $2$ is not the correct explanation of the statement $1$
• C. If Statement $1$ is true but Statement $2$ is false
• D. If Statement $1$ is false but Statement $2$ is true

Answer 1

Answer: (B)

Within the $Ca^{2+}/SO_4^{2-}$ layers, the ions are held together by strong electrovalent bonds. But these separated $Ca^{2+}/SO_4^{2-}$ layers are linked by relative weak $H$ - bond. The weaker $H$ - bonds link $SO_4^{2-}$ ions in the intermediate region. Consequently, the gypsum can be readily cleaved and stretched along the layer of water molecules. Anhydride has a completely ionic structure involving only $Ca^{2+}$ and $SO_4^{2-}$ ions.