Question

The shell of a chicken’s egg makes up 5% of the mass of an average egg. An average egg has a mass of 50g. Assume the egg shell is pure calcium carbonate. How many complete chicken’s egg shells would be needed to neutralise 50cm3 of 2.0 moldm–3 ethanoic acid? A 1 B 2 C 3 D 4

Answer 1

B 2
Form the balanced equation for the reaction of ethanoic acid with calcium carbonate.
2CH3COOH+CaCO3-->(CH3COO)2Ca+CO2+H2O
For an average egg, the shell is 0.05 x 50=2.5g. The Mr of CaCO3 is 100.1. Hence a chicken's egg shell contains 2.5/100.1=0.025 mol of CaCO3. 50cm3 of 2.0moldm-3= 50 x 2/1000=0.1mol of ethanoic acid. From the balanced equation, 2 mols of ethanoic acid reacts with 1 mol of CaCO3. Hence, 0.05 mols of calcium carbonate would be required to react with the amount of ethanoic acid stated in the question. 
Therefore, number of chicken's egg shells=0.-05/0.025= 2.