Gravimetric Analysis - Practice Questions & MCQ

Gravimetric Analysis:
It is an analytical technique based on the measurements of the mass of solid substances or the volume of the gaseous species. It is divided into three categories: 

• Mass-Mass (weight-weight) relation

  This relationship relates to the mass of a reactant or product with the mass of another reactant or product.

  1. Write down the balanced equation to represent the chemical change.

  2. Write the number of moles below the formula of reactants and products.

  3. Finally, apply the unitary method to calculate the unknown factor.

• Mass-volume relation
  This relationship relates the mass of a reactant or product with the volume of another gaseous reactant or product involved in a chemical reaction.

1. Write down the relevant balanced chemical equation.

2. Write the weights of various solid reactants and products.

3. Gases are normally expressed in terms of volume. In case the volume of the gas is measured at room temperature and pressure, convert it into N.T.P. by applying gas laws.

4. The volume of a gas at any temperature and pressure can be converted into its weight and vice versa by using the relation,
   PV = (g/M) x RT
   Here g is the weight of the gas, M is the molecular weight of gas and R is the gas constant.

5. Finally, calculate the unknown factor (n or s) by unitary method.

• Volume-Volume relation
  This relationship relates the volume of a gaseous reactant or product with the volume of another gaseous reactant or product involved in a chemical reaction.

1. First,  write down the relevant balanced chemical equation.

2. Now write down the volume of the reactants and the products below the formula to each reactant and product using the fact that one gram molecules of every gaseous substance occupies 22.4 liters at N.T.P. (22.7 Litre at STP)

3. If the volume of the gas is measured under particular or room temperature, convert it to N.T.P. with the help of the ideal gas equation.

4. Now use Avogadro’s hypothesis gases under similar conditions of temperature and pressure contain the same number of molecules. Thus under similar conditions of temperature and pressure, the number of moles of the gases in the balanced equation.