Question

Name or state the following.
1. An efflorescent dehydrate salt
2. A deliquesce salt of a trivalent metal
3. A liquid hygroscopic substance.
4. A salt whose solubility decreases with rise in temperature of the solvent water
5. A substance added to remove both temporary and permanent hardness of water

Answer 1

Hint: adsorption is the phenomenon of increase in concentration at the surface due to molecular surface force occurring in hygroscopic substance.
- Hardness of natural water is generally caused by the presence of bicarbonates, chloride and sulphates of calcium and magnesium.

Complete Solution :
1. $\text{N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\text{.10}{{\text{H}}_{\text{2}}}\text{O}$- An efflorescent substance in chemistry is a hydrated molecule which have water associate with it molecule. When it is exposed to air, it gets dehydrated. $\text{N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\text{.10}{{\text{H}}_{\text{2}}}\text{O}$ Loses nine water molecules and finally becomes completely anhydrous.
2. $\text{AlC}{{\text{l}}_{\text{3}}}\,\text{or}\,\text{AuC}{{\text{l}}_{\text{3}}}$ - a deliquescent salt is a hygroscopic salt, which absorbs water from the surrounding.
3- Glycerine or methanol – a hygroscopic substance makes attachment of water through its surface either through adsorption or absorption.
4- $\text{CaS}{{\text{O}}_{\text{4}}}$ - calcium sulphate is the salt which solubility decreases with increasing the temperature.
5. Washing soda $\text{N}{{\text{a}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}$ - Washing soda removes both temporary and permanent hardness of water by converting calcium and magnesium compound into insoluble carbonates. In place of sodium carbonate, caustic soda or sodium phosphate can also be used.
So, the correct answer is “Option B”.

Note: Normally increase in temperature increases the solubility of salts but in case of calcium sulphate and sodium sulphate on increasing temperature reduces the solubility of salt. In some salt dissolution of salt in water is an exothermic process, so increase in temperature in an exothermic process leads chemical reaction into backward direction.