1. 2g of calcium carbonate was added to 40 cm3 of hydrochloric acid of concentration 2 moldm-3. Write a balanced equation for the reaction. (2 mrks)

The balanced equation :

CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

Equalization of chemical reaction equations can be done using variables. Steps in equalizing the reaction equation:

1. gives a coefficient on substances involved in the equation of reaction such as a, b, or c etc.

2. make an equation based on the similarity of the number of atoms where the number of atoms = coefficient × index between reactant and product

3. Select the coefficient of the substance with the most complex chemical formula equal to 1

CaCO₃ (s) + HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)

Give coefficient :

CaCO₃ (s) + aHCl (aq) → bCaCl₂ (aq) + cH₂O (l) + dCO₂ (g)

Ca, left=1, right=b⇒b=1

C, left=1, right=d⇒d=1

O, left=3, right=c+2d⇒3=c+2d⇒3=c+2.1⇒c=1

H, left=a, right=2c⇒a=2c⇒a=2.1⇒a=2

the equation becomes :

CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)