Acid- Base titrations (Cambridge O Level Chemistry)

A student investigated the reaction between aqueous sodium carbonate and two different solutions of dilute hydrochloric acid, A and B.

The reaction is:

Na₂CO₃ (aq) + 2HCl (aq) → 2NaCl (aq) + H₂O (l) + CO₂ (g)

Three experiments were carried out.

Experiment 1

Using a measuring cylinder, 25 cm³ of aqueous sodium carbonate were poured into a conical flask.
Thymolphthalein indicator was added to the conical flask.
A burette was filled up to the 0.0 cm³ mark with solution A. Dilute hydrochloric acid A was added to the flask, until the solution just changed colour.
Use the burette diagram to record the reading in the table.

Experiment 2

Experiment 1 was repeated using methyl orange indicator instead of thymolphthalein.
Methyl orange is red-orange in acidic solutions and yellow in alkaline solutions.
Use the burette diagrams to record the readings in the table and complete the table. 

What colour change was observed in the flask in experiment 2?

 from .......................................... to ........................................ 

Experiment 3

Experiment 1 was repeated using solution B of acid instead of solution A.
Use the burette diagrams to record the readings in the table and complete the table.

Suggest one observation, other than colour change, that is made when hydrochloric acid is added to sodium carbonate.

Complete the sentence below.

Experiment .......... needed the largest volume of hydrochloric acid to change the colour of the indicator.

What would be the effect on the results, if any, if the solutions of sodium carbonate were warmed before adding the hydrochloric acid? Give a reason for your answer.

effect on results ...............................................................................................
reason ..............................................................................................................

Suggest a different method, using standard laboratory chemicals, to determine which of the solutions of dilute hydrochloric acid, A or B, is more concentrated.

A student investigated the reaction between two different solutions of dilute hydrochloric acid, A and B, and solution C which is alkaline.

Two experiments were carried out

Experiment 1

A burette was filled with solution A of dilute hydrochloric acid to the 0.0 cm³ mark. Using a measuring cylinder, 20 cm³ of solution C was poured into a conical flask. A few drops of methyl orange were added to the flask.

Solution A was added to the flask, with shaking, until the mixture just changed colour. Use the burette diagram to record the burette reading in the table and complete the table.

Experiment 2

The burette was emptied and rinsed, first with distilled water, and then with a little of solution B. The burette was filled with solution B of dilute hydrochloric acid to the 0.0 cm³ mark.

Experiment 1 was repeated using solution B.

Use the burette diagram to record the burette reading in the table and complete the table.

[1]

[1]

Why was the burette rinsed, first with distilled water and then with solution B, before starting Experiment 2?

[1]

[1]

[2]

Describe a method other than titration, using a different reactant, that could be used to compare the concentrations of the two solutions of dilute hydrochloric acid, A and B.

A student investigated the reaction between aqueous sodium hydroxide and acid K.
Two experiments were carried out. 

Experiment 1

Using a measuring cylinder, 25 cm³ of acid K was poured into a conical flask.
Phenolphthalein indicator was added to the flask. A burette was filled with aqueous sodium hydroxide to the 0.0 cm³ mark. Aqueous sodium hydroxide was added from the burette to the flask and the mixture shaken until the solution showed a permanent colour change.
The final volume was measured. Use the burette diagram to record the final volume in the table and complete the table.

Experiment 2
The solution was poured away and the conical flask rinsed.
Using a measuring cylinder, 50 cm³ of acid K was poured into the conical flask. 0.3 g of powdered calcium carbonate was added to the flask and the flask shaken until no further reaction was observed.
Phenolphthalein was added to the mixture in the flask.
A burette was filled with the same aqueous sodium hydroxide and the initial volume measured. Aqueous sodium hydroxide was added from the burette to the flask and the mixture shaken until the solution showed a permanent colour change.
Use the burette diagrams to record the initial and final volumes in the table and complete the table.

What type of chemical reaction occurred when acid K reacted with sodium hydroxide?

If Experiment 1 were repeated using 50 cm³ of acid K, what volume of sodium hydroxide would be required to change the colour of the indicator?

[2]

[2]

[1]

What would be the effect on the results if the solutions of acid K were warmed before adding the sodium hydroxide? Give a reason for your answer.

A student investigated an aqueous solution of calcium hydroxide and water.

Two experiments were carried out.

Experiment 1

By using a measuring cylinder 25 cm³ of the aqueous solution of calcium hydroxide was placed in a flask. Phenolphthalein indicator was added to the flask. A burette was filled to the 0.0cm³ mark with solution M of hydrochloric acid.

Solution M was added slowly to the flask until the colour just disappeared.

Use the burette diagram to record the volume in the table and complete the column.

Experiment 2

 

Experiment 1 was repeated using a different solution, N, of hydrochloric acid.

Use the burette diagrams to record the volumes in the table and complete the table.

Table of results

What type of chemical reaction occurs when hydrochloric acid reacts with calcium hydroxide?