Which Alkali Metal Carbonate? Imagine you are an analytical chemist and have received a sample of a pure alkali metal carbonate from a newly discovered deposit. Your task is to determine which alkali metal carbonate is present in the sample. You will determine an experimental molar mass for the alkali metal in the carbonate and, from that result, you will determine which alkali metal is present. To identify your unknown, you will employ the Law of Conservation of Mass. This law states that in a chemical reaction the total mass of the reactants must equal the total mass of products. Alkali metal carbonates (X2CO3) react with HCl according to the following equation (X is meant to represent the unknown alkali metal cation)

The alkali metal can be Lithium, sodium or potassium

Explanation:

The alkali metal carbonate has a formula of X2CO3

The alkali metals are: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).

When thhe alkali metal carbonate reacts with HCl it will give the following equation:

2HCl + X2CO3 → 2XCl + CO2 + H2O

If there is 2 moles of HCl consumed, there is needed 1 mole of X2CO3 to produce 1 mole of XCl2 1 mole of CO2 and 1 mole of H2O.

The Law of Conservation of Mass states that in a chemical reaction the total mass of the reactants must equal the total mass of products.

This means the mass of all reactants is the same as the mass of all products.

Calculate moles of CO2

moles of CO2 = mass of CO2/Molar mass of CO2

Calculate moles of X2CO3

Since for 1 mole of CO2 produced, there is needed 1 mole of X2CO3 the amount of moles is the same.

moles of CO2 = moles of X2CO3

Calculate molar mass of X2CO3

Molar mass of X2CO3 = mass of X2CO3 / moles of X2CO3

Calculate molar mass of X

Molar mass of X2CO3 - Molar mass of CO3 (60.01 g/mole) = Molar mass of X2

Molar mass of X = Molar mass of X2 / 2

Since there is no mass given we can't do further calculations.

The alkali metal can be Lithium, sodium or potassium