OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Exam Questions and Mark Scheme
, OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Exam Questions and Mark Scheme
1. The equation for the reaction of aqueous phosphoric(V) acid, H3PO4, with aqueous sodium
hydroxide, NaOH(aq) is shown below.
H3PO4(aq) + 3NaOH(aq) → Na3PO4(aq) + 3H2O(l)
25.0 cm3 of a 0.200 mol dm−3 H3PO4(aq) is titrated with 0.600 mol dm−3 NaOH(aq).
Which statement is correct?
A. The end point occurs when 25.00 cm3 of NaOH(aq) has been added.
B. The end point occurs when 75.00 cm3 of NaOH(aq) has been added.
C. After titration the final solution contains 0.0150 mol of Na3PO4.
D. After titration the final solution contains 0.0150 mol of H2O.
Your answer
[1]
2. A student carries out a titration. Sodium hydroxide solution is transferred to a conical flask using a
pipette. Methyl orange indicator is added to the flask. Hydrochloric acid is added from a burette
until the indicator changes colour.
Which of the following would lead to the titre being larger than it should be?
A. Rinsing the conical flask with water before adding the sodium hydroxide solution.
B. Rinsing the burette with water before filling it with hydrochloric acid.
C. Rinsing the pipette with water before filling it with sodium hydroxide solution.
D. Adding extra drops of indicator.
Your answer
[1]
3. A student prepares a standard solution and carries out a titration.
Which of the following would result in a titre that is larger than it should be?
1: Water is added to completely fill the volumetric flask, rather than to the graduation line.
2: The conical flask is washed out with water before carrying out each titration.
3: The pipette is washed out with water before carrying out each titration.
A. 1, 2 and 3
B. Only 1 and 2
C. Only 2 and 3
D. Only 1
Your answer
[1]
, 4. A student carries out a titration to determine the molar mass of an unknown acid, A.
• The student dissolves 2.24 g of acid A in distilled water and makes the solution up to 250.0 cm3.
• The student titrates a 25.0 cm3 portion of this solution with 0.120 mol dm−3 NaOH.
• 25.25 cm3 of 0.120 mol dm−3 NaOH are required to reach the end point.
Name the apparatus that the student should use to
• make up the acid solution to 250.0 cm3
• measure the 25.0 cm3 portion of acid solution.
make up the acid solution to 250 cm3:
measure the 25.0 cm3 portion:
[1]
5. A student carries out a titration to determine the molar mass and structure of a weak acid A.
The student follows the method below.
Dissolve a weighed mass of A in 100 cm3 of distilled water and make the solution up to 250
• cm3 in a beaker.
Add the solution of A to a burette.
•
Titrate the solution of A with a standard solution of sodium hydroxide, NaOH.
•
What is meant by the term standard solution?
[1]
PAG 2: Acid-base titration
Exam Questions and Mark Scheme
, OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Exam Questions and Mark Scheme
1. The equation for the reaction of aqueous phosphoric(V) acid, H3PO4, with aqueous sodium
hydroxide, NaOH(aq) is shown below.
H3PO4(aq) + 3NaOH(aq) → Na3PO4(aq) + 3H2O(l)
25.0 cm3 of a 0.200 mol dm−3 H3PO4(aq) is titrated with 0.600 mol dm−3 NaOH(aq).
Which statement is correct?
A. The end point occurs when 25.00 cm3 of NaOH(aq) has been added.
B. The end point occurs when 75.00 cm3 of NaOH(aq) has been added.
C. After titration the final solution contains 0.0150 mol of Na3PO4.
D. After titration the final solution contains 0.0150 mol of H2O.
Your answer
[1]
2. A student carries out a titration. Sodium hydroxide solution is transferred to a conical flask using a
pipette. Methyl orange indicator is added to the flask. Hydrochloric acid is added from a burette
until the indicator changes colour.
Which of the following would lead to the titre being larger than it should be?
A. Rinsing the conical flask with water before adding the sodium hydroxide solution.
B. Rinsing the burette with water before filling it with hydrochloric acid.
C. Rinsing the pipette with water before filling it with sodium hydroxide solution.
D. Adding extra drops of indicator.
Your answer
[1]
3. A student prepares a standard solution and carries out a titration.
Which of the following would result in a titre that is larger than it should be?
1: Water is added to completely fill the volumetric flask, rather than to the graduation line.
2: The conical flask is washed out with water before carrying out each titration.
3: The pipette is washed out with water before carrying out each titration.
A. 1, 2 and 3
B. Only 1 and 2
C. Only 2 and 3
D. Only 1
Your answer
[1]
, 4. A student carries out a titration to determine the molar mass of an unknown acid, A.
• The student dissolves 2.24 g of acid A in distilled water and makes the solution up to 250.0 cm3.
• The student titrates a 25.0 cm3 portion of this solution with 0.120 mol dm−3 NaOH.
• 25.25 cm3 of 0.120 mol dm−3 NaOH are required to reach the end point.
Name the apparatus that the student should use to
• make up the acid solution to 250.0 cm3
• measure the 25.0 cm3 portion of acid solution.
make up the acid solution to 250 cm3:
measure the 25.0 cm3 portion:
[1]
5. A student carries out a titration to determine the molar mass and structure of a weak acid A.
The student follows the method below.
Dissolve a weighed mass of A in 100 cm3 of distilled water and make the solution up to 250
• cm3 in a beaker.
Add the solution of A to a burette.
•
Titrate the solution of A with a standard solution of sodium hydroxide, NaOH.
•
What is meant by the term standard solution?
[1]
