OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Practice Exam Questions and Mark Scheme
This resource includes exam questions from both Chemistry A and Chemistry B. It is not designed as a
topic test but is instead intended as a document to support the teaching and learning of Module 1 –
Development of practical skills in chemistry.
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]
Created in ExamBuilder 1 © OCR 2020
, OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Practice Exam Questions and Mark Scheme
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]
6. A student carries out an experiment to identify an unknown carbonate.
The student weighs a sample of the solid carbonate in a weighing bottle.
Created in ExamBuilder 2 © OCR 2020
, OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Practice Exam Questions and Mark Scheme
The student tips the carbonate into a beaker and weighs the empty weighing bottle.
The student prepares a 250.0 cm3 solution of the carbonate.
The student carries out a titration using 25.0 cm3 of this solution measured using a pipette
with 0.100 mol dm−3 hydrochloric acid in the burette.
The sample of carbonate is dissolved in approximately 100 cm3 of distilled water in a beaker and
the solution transferred to a volumetric flask. The volume of the solution is made up to 250.0 cm3
with distilled water.
Another student suggests two possible sources of error:
A small amount of solid remained in the weighing bottle.
A small amount of solution remained in the beaker.
State whether the other student’s statements are correct.
How could the procedure be improved?
[2]
7(a). 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.
Created in ExamBuilder 3 © OCR 2020
PAG 2: Acid-base titration
Practice Exam Questions and Mark Scheme
This resource includes exam questions from both Chemistry A and Chemistry B. It is not designed as a
topic test but is instead intended as a document to support the teaching and learning of Module 1 –
Development of practical skills in chemistry.
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]
Created in ExamBuilder 1 © OCR 2020
, OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Practice Exam Questions and Mark Scheme
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]
6. A student carries out an experiment to identify an unknown carbonate.
The student weighs a sample of the solid carbonate in a weighing bottle.
Created in ExamBuilder 2 © OCR 2020
, OCR A Level Chemistry A (H432) Chemistry B (H433)
PAG 2: Acid-base titration
Practice Exam Questions and Mark Scheme
The student tips the carbonate into a beaker and weighs the empty weighing bottle.
The student prepares a 250.0 cm3 solution of the carbonate.
The student carries out a titration using 25.0 cm3 of this solution measured using a pipette
with 0.100 mol dm−3 hydrochloric acid in the burette.
The sample of carbonate is dissolved in approximately 100 cm3 of distilled water in a beaker and
the solution transferred to a volumetric flask. The volume of the solution is made up to 250.0 cm3
with distilled water.
Another student suggests two possible sources of error:
A small amount of solid remained in the weighing bottle.
A small amount of solution remained in the beaker.
State whether the other student’s statements are correct.
How could the procedure be improved?
[2]
7(a). 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.
Created in ExamBuilder 3 © OCR 2020
