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QUESTION 22 (7 marks) The structures of phenol red when in either an acidic or a basic solution are shown in the equation. on 0 OHÔøΩ OO am & OTs Ht Se se Yellow Red a) Identify the species that acts as the conjugate base by circling it in the equation. [1 mark] Note: If you make a mistake draw a line through this equation and use the additional equation provided on page 13 of this question and response book. b) A solution of phenol red at equilibrium and 50 ÔøΩC was found to contain 2.0 x 10-4 M of the conjugate base and 0.034 M of the acid. Determine the pK for the system assuming all the protons present come from dissociation of the acid. [3 marks] (to two significant figures) c) Explain the relationship between the pH range of phenol red and its pK value. [3 marks]
QUESTION 5 (17 marks) Compound A reacts with water to produce compound B and hydroxide ions. a) b) c) d) e) CH CH NH (aq) +H O(l) f C HsNH{ (aq) + OH (aq) A B Apply IUPAC rules to name compound A. Identify the Brensted-Lowry acids in the equation. A small amount of hydrochloric acid is added to the equilibrium mixture. Predict the effect of this on the concentration of compound A in the mixture. Explain your reasoning. Calculate the pH of a 2.0 M solution of compound A. State any assumptions. Show your working. (K =5.6x10-*) (to one decimal place) Describe using a balanced chemical equation how Compound A could be made from bromomethane. Include relevant conditions and reagents in your response. [1 mark] [2 marks] [3 marks] [6 marks] [5 marks]
QUESTION 1 (11 marks) Phosphoric acid (H3PO ) is a common triprotic acid that dissociates fully in three stages. The dissociation equations are shown in the table. to H;PO (aq) +H 0(1) = H PO (aq) +H30*(aq) 71 x103 20 H PO (aq) +H 0(1) = HPO 2-(aq) + H30* (aq) 6.5x10ÔøΩ8 HPO 2 (aq) +H 0(1) = PO 2-(aq)-+ Hy0*(aq) 45x 1073 a) Use the information to determine the strongest Brensted-Lowry acid and its conjugate base. Explain your reasoning. [3 marks] Acid: Conjugate base: Reasoning: b) Identify an amphiprotic species from the dissociation reactions. Explain your reasoning. = /2 marks] c) Determine the Aj value for the strongest conjugate base formed when H3PO has fully dissociated. Show your working. [2 marks] Ky = (to two significant figures) d) Calculate the pH of a 0.05 M solution of dihydrogen phosphate (H PO ). Show your working and state any assumptions made. [4 marks] pH = (to one decimal place)
QUESTION 3 (9 marks) A 50.0 mL solution of ethanoic acid (CH;COOH) was titrated with 15.0 mL of 0.10 M sodium hydroxide (NaOH) solution to reach the equivalence point (pK ethanoic acid = 4.76). a) b) Cc) d) Write a balanced chemical equation to indicate how ethanoic acid acts as a Bronsted-Lowry acid during the titration and identify its conjugate base. Determine the Ky of the conjugate base of ethanoic acid. (to two decimal places) Calculate the concentration of the conjugate base at the equivalence point. Show your working. Concentration = M (to three significant figures) Calculate the pH at the equivalence point. Show your working. (to one decimal place) [2 marks] [1 mark] [2 marks] [4 marks]
QUESTION 15 Predict how a buffer solution consisting of carbonic acid (H CO;) and hydrogen carbonate ions (HCO ) would react to resist a change in pH when a small amount of hydrochloric acid is added. HCO3(aq) = HCO; (aq) + H” (aq) = CO” (aq) + 2H (aq) (A) Equilibrium shifts to the right and the [H ](aq) increases. (B) Equilibrium shifts to the left and the [CO;* ](aq) increases. (C) Equilibrium shifts to the left and the [H CO; ](aq) increases. (D) Equilibrium shifts to the right and the [HCO3 ](aq) increases.
QUESTION 5 (13 marks) The table gives the properties of four monoprotic acids. (a) (b) (Cc) (d —_ (e) a 0.100 4.20 x 102 1.80 x 1074 CH COOH(aq) 0.100 ae 1.78 x 107° HCl(aq) 0.010 1.00 x 102 Determine the relative strength of acids 1 and 2 by contrasting their K values. Write a balanced chemical equation for the dissociation of ethanoic acid (CH ; COOH) in water. Identify whether the conjugate base of ethanoic acid (CH;COOH(aq)) is amphiprotic. Explain your reasoning. Calculate the pH of the aqueous solution of ethanoic acid (CH;COOH). Show your working. Determine the volume of water that would need to be added to 100.0 mL of HCl(aq) to change the pH from 2.00 to 3.00. Explain your reasoning. [3 marks] [2 marks] [2 marks] [3 marks] [3 marks]
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