Question

COMPREHENSION # 1

The name 'Silica' covers an entire group of minerals, which have the general formula $Si{O}_2$, The most common of which is quartz. Quartz is a framework silicate with $Si{O}_4$ tetrahedral arranged in spirals. the spirals can turn in a clockwise or anticlockwise direction a feature that results in there being two mirror images, optically active, varieties of quartz.

The following pictures represent various silicate anions. Their formulae are respectively :

• A. ${SiO}_3^{2-}S{i}_3{O}_7^{2-}$
• B. ${SiO}_4^{4-}S{i}_3{O}_{10}^{8-}$
• C. ${SiO}_4^{2-}S{i}_3{O}_9^{2-}$
• D. ${SiO}_3^{4-}S{i}_3{O}_7^{8-}$

Answer 1

The correct option is B ${SiO}_4^{4-}S{i}_3{O}_{10}^{8-}$

One silicon is bonded to four oxygen ions. No. of edges represents no. of oxygen ions.

The basic unit of silicates is $Si{O}_4^{4-}$ in which number of shared $O_2$ units is 0.

The second silicate anion has 2 shared $O_2$ units. Therefore, its formula will be $S{i}_3{O}_{10}^{-8}$.