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7.2. Brønsted–Lowry theory of acids and bases
A subsection of Chemistry, 9701, through 7. Equilibria
Listing 10 of 133 questions
Aqueous solutions of methanoic acid, HCOOH, and propanoic acid, CH3CH2COOH, are mixed together. An equilibrium is set up between two conjugate acid–base pairs. Define conjugate acid–base pair. The pKa of HCOOH is 3.75 and of CH3CH2COOH is 4.87. Complete the equation for the Brønsted–Lowry equilibrium between the stronger of these two acids and water. + H2O + Write an expression for the acid dissociation constant, Ka, for butanoic acid, CH3CH2CH2COOH. Ka = The pKa of CH3CH2CH2COOH is 4.82. A solution of CH3CH2CH2COOHhas a pH of 3.25. Calculate the concentration, in mol dm–3, of CH3CH2CH2COOH in this solution. concentration of CH3CH2CH2COOH = mol dm–3 Define buffer solution. A buffer solution containing a mixture of CH3COOH and CH3COONa is prepared as follows. A solution of 600 cm3 of CH3COOH is mixed with 400 cm3 of 0.125 mol dm–3 CH3COONa. The buffer solution has pH 5.70. The Ka of CH3COOH is 1.78 × 10–5 mol dm–3. Calculate the initial concentration, in mol dm–3, of CH3COOH used. concentration of CH3COOH = mol dm–3 A fuel cell is an electrochemical cell that can be used to generate electrical energy by using oxygen to oxidise a fuel. Methanoic acid, HCOOH, is being investigated as a fuel in fuel cells. When the cell operates, HCOOH is oxidised to carbon dioxide. The half‑equation for the reaction at the cathode is: O2 + 4H+ + 4e– 2H2O. In this fuel cell, the overall cell reaction is the same as that for the complete combustion of HCOOH. Deduce the half‑equation for the reaction at the anode. Calculate the volume, in cm3, of oxygen used when a current of 3.75 A is delivered by the cell for 40.0 minutes. Assume the cell operates at room conditions. volume of oxygen = cm3 , ,
9701_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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Questions Discovered
133