7.2. Brønsted–Lowry theory of acids and bases
A subsection of Chemistry, 9701, through 7. Equilibria
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Methanoic acid, HCO2H, was formerly known as formic acid because it is present in the sting of ants and the Latin name for ant is formica. It was first isolated in 1671 by John Ray who collected a large number of dead ants and extracted the acid from them by distillation. In this question, you should give all numerical answers to two significant figures. At room temperature, pure methanoic acid is a liquid which is completely soluble in water. When we are stung by a ‘typical’ ant a solution of methanoic acid, A, is injected into our skin. Solution A contains 50% by volume of pure methanoic acid. A ‘typical’ ant contains 7.5 × 10–6 dm3 of solution A. Calculate the volume, in cm3, of solution A in one ant. volume = cm3 Use your answer to to calculate the volume, in cm3, of pure methanoic acid in one ant. volume = cm3 Use your answer to to calculate how many ants would have to be distilled to produce 1 dm3 of pure methanoic acid. number = When we are stung by an ant, the amount of solution A injected is 80% of the total amount of solution A present in one ant. The density of pure methanoic acid is 1.2 g cm–3. Calculate the volume, in cm3, of pure methanoic acid injected in one ant sting. volume = cm3 Use your answer to to calculate the mass of methanoic acid present in one ant sting. mass = g Bees also sting us by using methanoic acid. One simple treatment for ant or bee stings is to use sodium hydrogencarbonate, NaHCO3. Construct a balanced equation for the reaction between methanoic acid and sodium hydrogencarbonate. In a typical bee sting, the mass of methanoic acid injected is 5.4 × 10–3 g. Calculate the mass of NaHCO3 needed to neutralise one bee sting. mass = g
9701_s11_qp_23
THEORY
2011
Paper 2, Variant 3
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