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.
HNO2 + ________
(1 mark)
________ + 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, CH3NH2, has a pH =
Calculate the Kb for methylamine.
11.40.
(4 marks)
9. A titration was performed by adding 0.115M NaOH to a 25.00mL sample of H2SO4.
Calculate the [H2SO4] 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 NH3.
(4 marks)
9. A titration was performed by adding 0.175M H2C2O4 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 =
What is the Ka for HX?
1.414.
(4 marks)
7. Consider the salt ammonium acetate, NH4CH3COO.
a) Write the equation for the dissociation of NH4CH3COO.
(1 mark)
b) Write equations for the hydrolysis reactions which occur.
(2 marks)
c) Explain why a solution of NH4CH3COO has a pH =
Support your answer with calculations.
(2 marks)
7.00.
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 [H3O+] of 0.10M HNO2.
(3 marks)
8. Write the formula equation and the net ionic equation for the reaction
between 0.10M H2SO4 and 0.10M Sr(OH)2.
(3 marks)
Formula equation:
Net ionic equation:
January 2001
6. Consider the following Bronsted-Lowry equilibrium:
H2SO3 (aq) + HPO4 -2(aq)
H2PO4- (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 NH3(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:
H3O+
energy + 2H2O
a) Explain how pure water can have a pH =
+
7.30.
b) Calculate the value of Kw for the sample of water with a pH =
OH(2 marks)
7.30. (2 marks)
April 2001
6.a) Write the equation for the predominant reaction of HC2O4 - with HSO3
HC2O4 - + HSO3
. (1 mark)
__________ + ___________
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
CH3COOH in place of the HCl.
(2 marks)
i)___________________________________________________________
ii)___________________________________________________________
8. Calculate the [OH-] in 0.50M NH3(aq).
(5 marks)
June 2001
6. Write the equation for the predominant reaction between HSO4
and H2PO4 .
(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 NH4F.
a) Write both hydrolysis reactions that occur when NH4F is dissolved in water.
(2 marks)
b) Will the above NH4F 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 HC2O4 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)