Question

Calculate molecular weight of the following with help of criss – cross
method

a) Magnesium carbonate b) Sodium sulphate​

Answer 1

Explanation:

Magnesium bicarbonate:

Valency of magnesium = 2

Valency of carbonate = 2

By applying criss-cross method:

Formula: MgCO3

(ii) Cupric oxide:

Valency of cupric = 2

Valency of oxide = 2

By applying criss-cross method:

Formula: CuO

(iii) Ferric oxide:

Valency of ferric = 3

Valency of oxide = 2

By applying criss-cross method:

Formula: Fe2O3

(iv) Ammonium hydroxide

Valency of ammonium = 1

Valency of hydroxide = 1

By applying criss-cross method:

Formula: NH4OH

(v) Calcium carbonate

Valency of calcium = 2

Valency of carbonate = 2

By applying criss-cross method:

Formula: CaCO3

(vi) Potassium carbonate

Valency of potassium = 1

Valency of carbonate = 2

By applying criss-cross method:

Formula: K2CO3

Answer 2

Answer:

An alternative way to writing a correct formula for an ionic compound is to use the crisscross method. In this method, the numerical value of each of the ion charges is crossed over to become the subscript of the other ion. Signs of the charges are dropped