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

1 hour14 questions

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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

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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

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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

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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

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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

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