Question

Calculate the formality of solution when { 4.78g } potash alum is dissolved in a { 2L } solution.

Answer 1

Hint: Formality of a solution is defined as the number of formula weights of solute per liter of solution. In place of molarity, formality is used.

Complete step-by-step answer:
- Potash alum is a chemical compound of potassium double sulfate of aluminium. Its chemical formula is: ${ KAl(SO_{ 4 }) }_{ 2 }{ .12H }_{ 2 }{ O }$
- Molar mass of potash alum = { 39\times 1+27+2\times 32 }
                                             = { 474g/mol }
It is given that,
Volume = { 2L } = { 2000mL }
Weight = { 4.78g }
By using the formula,
Formality = { 1000\times wt.\div F\times volume }
Now, put the values in the above formula, we get
Formality = { 1000\times 4.78\div 474\times 2000 }
                = { 0.005F }
Hence, the formality of solution when { 4.78g } potash alum is dissolved in { 2L } solution.= { 0.005F }.

Additional Information: Uses of potash alum:
- To reduce bleeding in a minor cut.
- It is used as an additive in baking powder.
- It is used in the tanning of leather.
- Formality is used only for ionic compounds.
- Double salts are molecular compounds that are formed by the evaporation of a solution containing { 2 } or more salts in stoichiometric proportions. They dissociate into their constituent ions in solution].
- It is used to express the concentration of the ionic solids which do not exist as molecules.