7.2. Brønsted–Lowry theory of acids and bases
A subsection of Chemistry, 9701, through 7. Equilibria
Listing 10 of 133 questions
Valine (Val) and lysine (Lys) are amino acids. The structures of these amino acids can be found in the DataBooklet. The isoelectric point of an amino acid is the pH at which it exists as a zwitterion. The isoelectric point of valine is 6.0. The isoelectric point of lysine is 9.7. Draw the structure of valine at pH 6.0.  A solution of lysine is produced with pH 9.7. Dilute sulfuric acid is added slowly until the pH of the solution is 1.0. The sulfuric acid reacts with lysine to produce different organic ions that are not present in significant concentrations at pH 9.7. Draw the structures of three of the organic ions that form during the addition of sulfuric acid in the boxes. Draw the organic ion present at pH 1.0 in box C. A B C (pH 1.0)  Draw the structure of the dipeptide Val-Lys. The peptide bond should be shown fully displayed.  
9701_w21_qp_41
THEORY
2021
Paper 4, Variant 1
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Valine (Val) and lysine (Lys) are amino acids. The structures of these amino acids can be found in the DataBooklet. The isoelectric point of an amino acid is the pH at which it exists as a zwitterion. The isoelectric point of valine is 6.0. The isoelectric point of lysine is 9.7. Draw the structure of valine at pH 6.0.  A solution of lysine is produced with pH 9.7. Dilute sulfuric acid is added slowly until the pH of the solution is 1.0. The sulfuric acid reacts with lysine to produce different organic ions that are not present in significant concentrations at pH 9.7. Draw the structures of three of the organic ions that form during the addition of sulfuric acid in the boxes. Draw the organic ion present at pH 1.0 in box C. A B C (pH 1.0)  Draw the structure of the dipeptide Val-Lys. The peptide bond should be shown fully displayed.  
9701_w21_qp_43
THEORY
2021
Paper 4, Variant 3
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Define Kw mathematically by completing the expression. Kw = Two solutions, V and W, are described. • V is HCl . • W is NaOH. • The concentration of HCl in V is the same as the concentration of NaOH in W. • The pH values of V and W differ by exactly 11.00 at 298 K. Calculate the concentration of HCl in V. concentration of HCl in V = mol dm−3 Equal volumes of the two solutions V and W are mixed, giving solution X. Name solution X and state its pH. solution X pH A 1 cm3 sample of 1.0 mol dm−3 HNO3 is added to 100 cm3 of solution X, forming mixture Y. A 1 cm3 sample of 1.0 mol dm−3 KOH is added to 100 cm3 of solution X, forming mixture Z. Estimate the pH of mixtures Y and Z. No calculations are required. mixture Y mixture Z CH3CH2COOH, CH3CCl2COOH and H2SO4 are all acidic. Suggest the trend in the relative acid strength of these three compounds. Explain your answer. strongest acid weakest acid explanation When concentrated H2SO4 is added to water a series of acid-base reactions occurs. There are three conjugate acid-base pairs that can be identified during this series of reactions. Write the formulae of these three conjugate acid-base pairs. conjugate acid 1 conjugate base 1 conjugate acid 2 conjugate base 2 conjugate acid 3 conjugate base 3 The partition coefficient, Kpc, of a substance, Q, between hexane and water is 7.84 at 298 K. Q is more soluble in hexane than it is in water. Define partition coefficient, Kpc. 5.00 g of Q is shaken with a mixture of 100.0 cm3 of water and 100.0 cm3 of hexane at 298 K and left until there is no further change in concentrations. Calculate the mass of Q dissolved in the water. mass of Q = g A sample of Q is shaken with a different mixture of water and hexane and left until there is no further change in concentrations. It is found that the mass of Q dissolved in each solvent is the same. Use the Kpc value to suggest possible values for the volume of water used and the volume of hexane used. volume of water = cm3 volume of hexane = cm3 Q is more soluble in hexane than it is in water. It is suggested that Q is one of KCl, CH3(CH2)4OH or HCOOH. Identify Q. Explain your answer.
9701_w23_qp_41
THEORY
2023
Paper 4, Variant 1
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Define Kw mathematically by completing the expression. Kw = Two solutions, V and W, are described. • V is HCl . • W is NaOH. • The concentration of HCl in V is the same as the concentration of NaOH in W. • The pH values of V and W differ by exactly 11.00 at 298 K. Calculate the concentration of HCl in V. concentration of HCl in V = mol dm−3 Equal volumes of the two solutions V and W are mixed, giving solution X. Name solution X and state its pH. solution X pH A 1 cm3 sample of 1.0 mol dm−3 HNO3 is added to 100 cm3 of solution X, forming mixture Y. A 1 cm3 sample of 1.0 mol dm−3 KOH is added to 100 cm3 of solution X, forming mixture Z. Estimate the pH of mixtures Y and Z. No calculations are required. mixture Y mixture Z CH3CH2COOH, CH3CCl2COOH and H2SO4 are all acidic. Suggest the trend in the relative acid strength of these three compounds. Explain your answer. strongest acid weakest acid explanation When concentrated H2SO4 is added to water a series of acid-base reactions occurs. There are three conjugate acid-base pairs that can be identified during this series of reactions. Write the formulae of these three conjugate acid-base pairs. conjugate acid 1 conjugate base 1 conjugate acid 2 conjugate base 2 conjugate acid 3 conjugate base 3 The partition coefficient, Kpc, of a substance, Q, between hexane and water is 7.84 at 298 K. Q is more soluble in hexane than it is in water. Define partition coefficient, Kpc. 5.00 g of Q is shaken with a mixture of 100.0 cm3 of water and 100.0 cm3 of hexane at 298 K and left until there is no further change in concentrations. Calculate the mass of Q dissolved in the water. mass of Q = g A sample of Q is shaken with a different mixture of water and hexane and left until there is no further change in concentrations. It is found that the mass of Q dissolved in each solvent is the same. Use the Kpc value to suggest possible values for the volume of water used and the volume of hexane used. volume of water = cm3 volume of hexane = cm3 Q is more soluble in hexane than it is in water. It is suggested that Q is one of KCl, CH3(CH2)4OH or HCOOH. Identify Q. Explain your answer.
9701_w23_qp_43
THEORY
2023
Paper 4, Variant 3
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