O LevelChemistryCambridge (CIE)Exam Questions12. Experimental Techniques & Chemical Analysis12.2 Acid-Base Titrations

Acid-Base Titrations (Cambridge (CIE) O Level Chemistry): Exam Questions

Exam code: 5070

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12.2 Acid-Base Titrations

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1
1 mark

A student carries out a titration to determine the concentration of a dilute acid using a standard alkali.

Five actions in this acid-base titration are shown in the table.

step

action

P

record the final burette reading after the end-point is reached

Q

transfer a measured volume of alkali into a conical flask using a volumetric pipette

R

add a few drops of a suitable indicator to the flask

S

note the initial burette reading before starting the titration

T

carefully run the acid from the burette into the flask while swirling until a permanent colour change occurs

  • Q → R → S → T → P

  • Q → S → T→ P→ R

  • S → T → P→ Q→ R

  • Q → R → T → S → P

Choose your answer

2
1 mark

A student carries out an acid-base titration using thymolphthalein as the indicator.

Which row shows the colour of thymolphthalein in an acid and in an alkali?

in an acid

in an alkali

A

colourless

blue

B

blue

colourless

C

yellow

red

D

red

yellow

    Choose your answer

    3
    1 mark

    A student titrates dilute hydrochloric acid against aqueous sodium hydroxide.

    A volumetric pipette is used to add 25.0 cm3 of the aqueous sodium hydroxide to a conical flask. The dilute hydrochloric acid is added from a burette.

    Where should the indicator be added?

    • to the dilute hydrochloric acid in the burette

    • to the aqueous sodium hydroxide in the conical flask

    • to the dilute hydrochloric acid in the burette and to the aqueous sodium hydroxide in the conical flask

    • to the conical flask once the end point has been reached

    Choose your answer

    4
    1 mark

    A student carries out a titration and records the burette readings shown.

    final burette reading / cm3

    27.5

    initial burette reading / cm3

    4.0

    What is the volume of solution used?

    • 4.0 cm3

    • 23.5 cm3

    • 27.5 cm3

    • 31.5 cm3

    Choose your answer

    5
    1 mark

    A student fills a burette with dilute nitric acid, exactly to the zero mark, and records the initial reading in a results table.

    All of the other readings in the table are recorded to one decimal place.

    Which initial reading is recorded in the same way as the other readings in the table?

    • 0

    • zero

    • 0.0

    • 0.00

    Choose your answer

    1
    1 mark

    A student carries out a titration four times, adding dilute hydrochloric acid from a burette to 25.0 cm3 of aqueous sodium hydroxide, and then calculates a mean titre.

    Why does the student carry out the titration four times rather than once?

    • So that a mean titre can be calculated

    • To check that the results are consistent with one another

    • Because a single titration always gives a titre that is too large

    • So that any anomalous result can be included in the mean

    Choose your answer

    2
    1 mark

    A student uses a volumetric pipette to add 25.0 cm3 of aqueous potassium hydroxide to a conical flask, then adds a few drops of thymolphthalein indicator.

    Dilute sulfuric acid is run in from a burette until the end point is reached.

    What colour change is seen in the conical flask?

    • blue to colourless

    • colourless to blue

    • blue to yellow

    • colourless to pink

    Choose your answer

    3
    1 mark

    Part of a student's titration method is shown.

    Add the acid from the burette, swirling the flask after each addition. Near the end point, add the acid one drop at a time.

    Why is the acid added one drop at a time near the end point?

    • to make sure the solution in the flask is mixed after each addition

    • to stop the reaction in the flask becoming too exothermic

    • to avoid adding more acid than is needed to reach the end point

    • to give the indicator time to dissolve in the solution

    Choose your answer

    4
    1 mark

    During a titration a student stands the conical flask on a white tile.

    Why is the white tile used?

    • to reflect light through the solution so the indicator reacts faster

    • to insulate the flask from the bench so the temperature does not change

    • to hold the conical flask steady while it is swirled

    • to make the colour change at the end point easier to see

    Choose your answer

    5
    1 mark

    A student carries out four titrations, adding dilute hydrochloric acid from a burette to 25.0 cm3 of aqueous sodium hydroxide.

    Between titrations the conical flask is emptied and rinsed.

    Which liquid should be used to rinse the conical flask?

    • the aqueous sodium hydroxide

    • distilled water

    • the dilute hydrochloric acid

    • The flask should be emptied but not rinsed.

    Choose your answer

    1
    1 mark

    A student performed a titration to find the volume of hydrochloric acid required to neutralise 25.0 cm3 of sodium hydroxide using the following method.

    • Add a fixed volume of sodium hydroxide to a conical flask using a measuring cylinder

    • Add methyl orange indicator

    • Record the initial volume of hydrochloric acid in the burette 

    • Add hydrochloric acid from the burette into the conical flask until the indicator changes colour

    • Record the final volume of hydrochloric acid in the burette

    Another student suggested the following changes:

    1. Use a pipette to measure the sodium hydroxide

    2. Use universal indicator as the indicator

    3. Repeat the experiment until the results are concordant

    4. Ensure that the initial volume of hydrochloric acid reads 0.00 cm3 on the burette

    Which suggestions would improve the experiment?

    • 1 and 2

    • 1 and 3

    • 2 and 3

    • 3 and 4

    Choose your answer

    2
    1 mark

    A student titrated sodium carbonate solution against 25 cm3 of hydrochloric acid.

    They used methyl orange as an indicator.

    What is the colour change observed at the end point?

    • red to yellow

    • yellow to orange

    • yellow to red

    • red to orange

    Choose your answer

    3
    1 mark

    Before beginning a titration, a student opens the burette tap briefly so that the space below the tap fills with acid.

    Why is this important?

    • Because the solution that fills the space is recorded as delivered but never reaches the conical flask

    • Because air trapped in the space would dissolve in the acid and lower its concentration

    • Because the tap cannot be opened fully until the space below it is filled

    • Because the space holds a fixed 0.5 cm3 that must be subtracted from every titre

    Choose your answer

    4
    1 mark

    A burette is to be filled with a dilute acid for a titration.

    The burette is washed immediately before it is filled.

    Which washing gives an accurate volume of acid used?

    • distilled water only

    • distilled water, then the dilute acid

    • the aqueous alkali only

    • distilled water, then the aqueous alkali

    Choose your answer

    5
    1 mark

    A student uses this method to find the concentration of an acid.

    • Use a volumetric pipette to add 25.0 cm3 of the acid to a conical flask

    • Add a few drops of thymolphthalein

    • Run aqueous sodium hydroxide into the flask from a burette until the end point is reached

    For which acid would this method not give a reliable value for the volume of sodium hydroxide used?

    • a colourless solution of ethanoic acid

    • a colourless solution of sulfuric acid

    • a dark brown vinegar, which contains ethanoic acid

    • a colourless solution of nitric acid

    Choose your answer