Chemistry 9701 · AS & A Level · Carboxylic acids and derivatives
Carboxylic acids and derivatives — practice question
Methanoic acid, $\text{HCO}_2\text{H}$, was once called formic acid, because it occurs in ant stings and the Latin word for ant is $\textit{formica}$. John Ray first isolated it in 1671 after collecting a large number of dead ants and extracting the acid from them by distillation. In this question, all numerical answers should be given to two significant figures. At room temperature, pure methanoic acid is a liquid that is completely soluble in water. When a ‘typical’ ant stings us, a solution of methanoic acid, $A$, is injected into the skin. Solution $A$ contains 50% by volume of pure methanoic acid. A ‘typical’ ant contains $7.5 \times 10^{-6}\,\text{dm}^3$ of solution $A$.
(a(i))
Calculate the volume, in $\text{cm}^3$, of solution $A$ in one ant.
(a(ii))
Use your answer to (i) to calculate the volume, in $\text{cm}^3$, of pure methanoic acid in one ant.
(a(iii))[3]
Use your answer to (ii) to calculate how many ants would need to be distilled to produce $1\,\text{dm}^3$ of pure methanoic acid.
(b(i))
Calculate the volume, in $\text{cm}^3$, of pure methanoic acid injected in one ant sting.
(b(ii))[3]
Use your answer to (i) to calculate the mass of methanoic acid present in one ant sting.
(c(i))
Construct a balanced equation for the reaction of methanoic acid with sodium hydrogencarbonate, $\text{NaHCO}_3$.
(c(ii))[3]
In a typical bee sting, the mass of methanoic acid injected is $5.4 \times 10^{-3}\,\text{g}$. Calculate the mass of $\text{NaHCO}_3$ needed to neutralise one bee sting.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The volume of solution A in one ‘typical ant’ is found from $7.5 \times 10^{-6} \times 1000 = 7.5 \times 10^{-3}\,\text{cm}^3$” …