Define conjugate acid-base pair.

1. (a)(i)Define conjugate acid-base pair.[1]
2. (a)(ii)Give the formulas of the conjugate acid and the conjugate base of the hydrogen phosphate ion, HPO42–. conjugate acid of HPO42– conjugate base of HPO42–[1]
3. (b)(i)The Ka of propanoic acid, CH3CH2COOH, is 1.35 × 10–5 mol dm–3 at 298 K. Solution C is a solution of CH3CH2COOH with a pH of 3.60 at 298 K. Calculate the concentration of CH3CH2COOH in solution C. [CH3CH2COOH] = mol dm–3[2]
4. (b)(ii)Calculate the concentration of hydroxide ions in solution C. [OH–] = moldm–3[1]
5. (b)(iii)Calculate the concentration of a solution of hydrochloric acid with the same pH as solution C. concentration = .moldm–3[1]
6. (b)(iv)Table 3.1 shows three possible values of the Ka of dimethylpropanoic acid, (CH3)3CCOOH. Place a tick in Table 3.1 to show the correct value. Explain your answer. Table 3.1 value of Ka /moldm–3 place one tick (✔) in this column 9.33 x 10–6 1.35 x 10–5 3.35 x 10–5 explanation[3]
7. (c)(i)Solution D is made by mixing 100cm³ of 0.100 mol dm–3 CH3CH2COOH and 100 cm³ of 0.100 mol dm–3 NaCl. The pH of solution D is measured as small amounts of H2SO4(aq) are added to it, and when small amounts of NaOH(aq) are added to it. Solution D only acts as a buffer solution when one of these solutions is added to it. Complete the sentence and write an equation for the reaction that occurs. Solution D acts as a buffer when is added to it. equation[1]
8. (c)(ii)Complete the sentence and explain why solution D does not act as a buffer when the other solution is added. Solution D does not act as a buffer when explanation[1]
9. (d)(i)Manganese(II) hydroxide, Mn(OH)2, is only slightly soluble in water. The solubility of Mn(OH)2 in water is 3.28 × 10–3 g dm–3 at 298 K. Calculate the concentration of a saturated solution of Mn(OH)2 at 298 K. [Mn(OH)2] = moldm–3[1]
10. (d)(ii)Write an expression for the Ksp of Mn(OH)2. Give the units of Ksp. Ksp = units[2]
11. (d)(iii)Use your answers to (d)(i) and (d)(ii) to calculate the value of Ksp of Mn(OH)2 at 298 K. Ksp =[1]

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