Question

Which of the following is the formula of water glass?
(a) $Na_{ 2 }SiO_{ 3 }$
(b) $Mg_{ 2 }Si$
(c) $SiCl_{ 4 }$
(d) $Ca(H_{ 2 }PO_{ 4 })_{ 2 }$

Answer 1

Hint: You should know that water glass compounds are colorless glassy or crystalline solids or white powders. Except for the most silicon-rich ones, they are readily soluble in water, producing alkaline solutions. Now use this hint to find your answer.

Complete step by step answer:
We will identify all the compounds given in the question one by one -
1. In option A the compound $Na_{ 2 }SiO_{ 3 }$ is sodium silicate. Sodium silicate is also the technical and common name for a mixture of such compounds, chiefly the metasilicate also called water glass or liquid glass. The product has a wide variety of uses, including the formulation of cement, passive fire protection, textile and lumber processing, manufacture of refractory ceramics, as adhesives, and in the production of silica gel.
2. In option B the compound $Mg_{ 2 }Si$ is magnesium silicate. Magnesium silicide is a narrow-gap semiconductor. Its as-grown crystal exhibits n-type conductivity, but it can be changed to p-type by doping with Ag, Ga, Sn, and possibly Li (at high doping level). The major potential electronic application of $Mg_{ 2 }Si$ is in thermoelectric generators.
3. In option C the compound $SiCl_{ 4 }$ is Silicon tetrachloride. Silicon tetrachloride or tetrachlorosilane is a colorless volatile liquid that fumes in the air. It is used to produce high purity silicon and silica for commercial applications.
4. In option D the compound $Ca(H_{ 2 }PO_{ 4 })_{ 2 }$ is Calcium Dihydrogen Phosphate. It is used in the food industry as a leavening agent, i.e., to cause baked goods to rise. Because it is acidic, when combined with an alkali ingredient, commonly sodium bicarbonate (baking soda) or potassium bicarbonate, it reacts to produce carbon dioxide and salt.

Hence, we can conclude that the correct answer to this question A.

Note: You should know that sodium silicates are stable in neutral and alkaline solutions. In acidic solutions, the silicate ions react with hydrogen ions to form silicic acids, which tend to decompose into hydrated silicon dioxide gel.
Heated to drive off the water, the result is a hard translucent substance called silica gel, widely used as a desiccant.
It can withstand temperatures up to $1100^{o}C$.