Acids and Bases Written Response January 1999 4. Consider the salt sodium oxalate, Na2C2O4. a) Write the dissociation equation for sodium oxalate. (1 mark) b) A 1.0M solution of sodium oxalate turns pink when a few drops of the indicator phenolphthalein are added. Write a hydrolysis equation and explain why this salt causes the indicator to change colour. (2 marks) c) Calculate the equilibrium constant for the hydrolysis in b). (1 mark) 5. Calculate the ph of 0.50M H3BO3. (4 marks) 6. A 25.0mL sample of Sr(OH)2 is titrated with a standardized solution of HCl to the equivalence point. a) Write the formula equation for the neutralization. (1 mark) b) Write the net ionic equation for the neutralization. (1 mark) c) What is meant by the term standardized solution? (1 mark) d) Define equivalence point. (1 mark)
April 1999 6. Consider the following amphiprotic anions reacting with each other: HC6H5O7-2 + HC2O4? a) Complete the Brönsted-Lowry acid-base equilibrium for the predominant reaction. (1 mark) b) Does the equilibrium above favour reactants or products? Explain. (1 mark) 7. Calculate the ph of a 1.5M H2S solution. (4 marks) 8. Consider the following reaction: 2HCl (aq) + Ba(OH)2 (s) BaCl2 (aq) + 2H2O (l) When 3.16g samples of Ba(OH)2 were titrated to the equivalence point with an HCl solution, the following data were recorded: Using the data above, calculate the original [HCl]. (4 marks) June 1999 6. In aqueous solutions, H3O + is the strongest acid present. This phenomenon is called the levelling effect. Explain why this occurs. (2 marks)
7. A 1.00M OCl solution has an [OH ] of 5.75 10 4 M. a) Calculate Kb for OCl. (3 marks) b) Calculate Ka for HOCl. (1 mark) 8. Calculate the mass of NaOH needed to prepare 2.0 L of a solution with a ph of 12.00. (3 marks) August 1999 6. Consider a Brönsted-Lowry acid-base equation, where HNO2 is a reactant and H2PO4 is a product. a) Complete the following equation. (1 mark) HNO2 + + H2PO4 b) Identify the weaker base in the equilibrium in part a). (1 mark) 7. A chemist prepares a solution by dissolving the salt NaIO3 in water. a) Write the equation for the dissociation reaction that occurs. (1 mark) b) Write the equation for the hydrolysis reaction that occurs. (1 mark) c) Calculate the value of the equilibrium constant for the hydrolysis in part b). (1 mark) 8. Calculate the ph of a solution prepared by adding 15.0mL of 0.500M H2SO4 to 35.0mL of 0.750M NaOH. (4 marks)
January 2000 7. Define the term amphiprotic. Give an example of an ion which is amphiprotic. (2 marks) Definition: Example: 8. A 0.0200M solution of methylamine, CH 3 NH 2, has a ph = 11.40. Calculate the Kb for methylamine. (4 marks) 9. A titration was performed by adding 0.115M NaOH to a 25.00mL sample of H 2 SO 4. Calculate the [H 2 SO 4 ] from the following data. (3 marks) April 2000 7. A sample of a weak acid was found to conduct an electric current better than a sample of a strong acid. Explain these results in terms of ion concentration. (2 marks) 8. Calculate the [OH - ] of 0.10M NH 3. (4 marks)
9. A titration was performed by adding 0.175M H 2 C 2 O 4 to a 25.00mL sample of NaOH. The following data was collected: a) Calculate the [NaOH]. (3 marks) June 2000 6. A 0.100M solution of an unknown weak acid, HX, has a ph = 1.414. What is the K a for HX? (4 marks) 7. Consider the salt ammonium acetate, NH 4 CH 3 COO. a) Write the equation for the dissociation of NH 4 CH 3 COO. (1 mark) b) Write equations for the hydrolysis reactions which occur. (2 marks) c) Explain why a solution of NH 4 CH 3 COO has a ph = 7.00. Support your answer with calculations. (2 marks) August 2000 5. a) Define the term Bronsted-Lowry conjugate acid-base pair. (1 mark) b) Give an example of a conjugate acid-base pair. (1 mark) Acid: Base:
6. Consider the acids HCl and HF. a) Only one of the following reactions occurs. Complete the equation for the reaction which does occur. (1 mark) i) HCl + F - ii) HF + Cl - b) For the reaction that occurs, are reactants or products favoured? Explain. (1 mark) c) Explain why the other reaction will not occur. (1 mark) 7. Calculate the [H 3 O + ] of 0.10M HNO 2. (3 marks) 8. Write the formula equation and the net ionic equation for the reaction between 0.10M H 2 SO 4 and 0.10M Sr(OH) 2. (3 marks) Formula equation: Net ionic equation: January 2001 6. Consider the following Bronsted-Lowry equilibrium: H 2 SO 3 (aq) + HPO 4-2 (aq) H 2 PO 4 - (aq) + HSO3 - (aq) a) Identify the two Bronsted-Lowry acids in the above equilibrium. (1 mark) b) Define the term conjugate acid. (1 mark)
7. A 250.0mL sample of HCl with a ph of 2.000 is completely neutralized with 0.200M NaOH. a) What volume of NaOH is required to reach the stoichiometric point? (4 marks) b) Write the net ionic equation for the above neutralization reaction. (1 mark) c) If the HCl were titrated with a 0.200M NH 3 (aq) instead of 0.200M NaOH, how would the volume of base required to reach the equivalence point compare with the volume calculated in part a)? Explain your answer. (1 mark) 8. Consider the following equilibrium: energy + 2H 2 O H 3 O + + OH - a) Explain how pure water can have a ph = 7.30. (2 marks) b) Calculate the value of Kw for the sample of water with a ph = 7.30. (2 marks) April 2001 6.a) Write the equation for the predominant reaction of HC 2 O 4 - with HSO 3. (1 mark) HC 2 O 4 - + HSO 3 + B Identify a Br nsted-lowry conjugate acid base pair from the above reaction. (1 mark) Acid: Base:
7.a) In the space below, sketch the titration curve for the reaction when 0.10M HCl is added to 10.0mL of 0.10M NaOH. (3 marks) b) Describe two changes in the titration curve that would result from using 0.10M CH 3 COOH in place of the HCl. (2 marks) i) ii) 8. Calculate the [OH - ] in 0.50M NH 3(aq). (5 marks) June 2001 6. Write the equation for the predominant reaction between HSO4 and H 2 PO 4. (2 marks) 7. A 0.20M solution of a weak acid, HA, has a ph 1.32. Use calculations and the table of Relative Strengths of Brønsted-Lowry Acids and Bases from the Data Booklet to determine the identity of the acid. (5 marks) The Acid is:.
8. Calculate the ph of a solution prepared by mixing 15.0mL of 0.50M HCl with 35.0mL of 1.0M NaOH. (4 marks) 9. Identify a gas which causes acid rain, and write an equation showing this gas reacting with water. (2 marks) August 2001 6. Consider the 0.10M solutions of the following two acids: a) What can you conclude about the acids that will explain these different ph values? (1 mark) You can conclude that acid HA: You can conclude that acid HB: b) Compare the volume of 0.10M NaOH needed to neutralize equal volumes of each of these acid samples. (1 mark)
7. Consider a 1.0M solution of NH 4 F. a) Write both hydrolysis reactions that occur when NH 4 F is dissolved in water. (2 marks) b) Will the above NH 4 F solution be acidic, basic, or neutral? Support your answer with calculations. (2 marks) 8. An indicator is often used during acid-base titrations. a) Define the term transition point for an indicator. (1 mark) b) Calculate the Ka value for methyl red. (1 mark) c)a mixture of indicators is made by combining equal amounts of methyl orange and bromthymol blue. Complete the following table, showing the colour of each indicator and the mixture at ph of 5 and ph of 9. (2 marks) 9. Will HC 2 O 4 act predominantly as an acid or as a base in solution? Support your answer with calculations. (3 marks)
Acids and Bases Written Response Answers January 1999
April 1999
June 1999
8. August 1999 6a) b) 7a) b)
c) 8) January 2000 7)
8) 9) April 2000 7)
8) 9a) b)
June 2000 6) 7a) b)
c) August 2000 5a) b) 6a) b) c)
7) 8) January 2001 6a) b)
7a) b) c) 8a) b)
April 2001 6a) b) 7a) b)
8) June 2001 6)
7) 8)
9) August 2001 6a) b) 7a)
b) 8a) b) c)
9)