Experimental Techniques (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

The following paragraph was taken from a student’s notebook.

To make potassium chloride

25.0 cm³ of aqueous potassium hydroxide were placed in a flask and a few drops of indicator were added. Dilute hydrochloric acid was added to the flask until the indicator changed colour. The volume of acid used was 19.0 cm³.

What piece of apparatus should be used to measure the aqueous potassium hydroxide? 

Which solution was more concentrated? Explain your answer.

How could pure crystals of potassium chloride be obtained from this experiment?

Sulfur dioxide gas is denser than air and soluble in water. A sample of sulfur dioxide can be prepared by adding dilute hydrochloric acid to sodium sulfite and warming the mixture.
Study the diagram of the apparatus used.  

Fill in the boxes to show the chemicals used.

Show by using an arrow, on the diagram, where heat is applied.

Identify two mistakes in the diagram. 

Ammonia is produced when aqueous sodium hydroxide is warmed with ammonium sulfate. Ammonia is less dense than air and very soluble in water. The apparatus below was used to prepare a sample of dry ammonia gas.

Name substance C.

Name substance D.

What necessary piece of equipment is missing in the diagram?

Suggest why concentrated sulfuric acid should not be used to dry ammonia.

There are two other mistakes in the apparatus shown in the diagram. Identify and explain these mistakes.

mistake 1 ..........................................................................................................................
explanation .......................................................................................................................
mistake 2 ..........................................................................................................................
explanation .......................................................................................................................

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 sodium thiosulfate and potassium iodate.

Two experiments were carried out.

Experiment 1

A burette was filled up to the 0.0 cm³ mark with sodium thiosulfate solution. By using a measuring cylinder, 20 cm³ of solution A of potassium iodate was placed into a conical flask. Dilute sulfuric acid and potassium iodide were also added to the flask. The flask was shaken to mix the contents and produce a red solution of iodine.

The sodium thiosulfate solution was added to the flask. When the contents of the flask were yellow, 1 cm³ of starch solution was added to the flask. Addition of sodium thiosulfate to the flask was continued until the solution turned colourless.

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

   Experiment 2

   Experiment 1 was repeated using a different solution of potassium iodate, solution B.

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

   Table of results

   Burette readings / cm³ 

   Suggest why the starch was used.

Predict the volume of sodium thiosulfate solution which would be needed to react completely with 10cm³ of solution B.

Explain one change that could be made to the experimental method to obtain more accurate results, without changing the apparatus.

change ....................................................................................................

explanation ....................................................................................................

A student reacted dry ammonia gas with hot copper(II) oxide.

The apparatus used is shown below.

The equation for the reaction is

2NH₃ + 3CuO → 3Cu + N₂ + 3H₂O

Indicate with an arrow where the heat is applied. 

The colour of the copper(II) oxide would change from ............................... to ...............................

Draw a labelled diagram to show how liquid water could be obtained from the water vapour produced.

Suggest the effect of nitrogen on a lighted splint.

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 redox reaction between potassium iodate(V) and iodide ions. Two experiments were carried out.

Experiment 1

A burette was filled up to the 0.0 cm³ mark with the solution A of sodium thiosulphate. By using a measuring cylinder, a 10 cm³ sample of the solution B of potassium iodate(V) was added into a conical flask. A 10 cm³ sample of dilute sulfuric acid was added to the flask followed by 20 cm³ of aqueous potassium iodide.

Solution A was added slowly to the flask until there was a pale yellow colour in the contents of the flask. Starch solution was then added into the flask and the colour changed to blue black. Solution A was added to the flask until the colour just disappeared.

Experiment 2
Experiment 1 was repeated using solution C of potassium iodate(V) instead of solution B.

Use the burette diagrams for experiment 1 and 2 to record the volumes in the table and complete the table.

The reaction of the mixture of potassium iodate(V), sulfuric acid and potassium iodide in the flask produces iodine. Sodium thiosulfate then reacts with the iodine.

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.

Look at the diagrams of common laboratory apparatus.

Complete the empty boxes to identify the pieces of apparatus labelled.

What name is given to the separation method in C?

Which apparatus would be most suitable to obtain crystals from an aqueous solution of copper(II) sulphate?

Hydrogen chloride gas is strong-smelling, denser than air and soluble in water. A sample of hydrogen chloride gas can be prepared by adding concentrated sulfuric acid to sodium chloride. Study the diagram of the apparatus used.

Fill in the boxes to show the chemicals used.

Identify and explain two mistakes in the diagram.

Mistake 1 ....................................................................................................

[2]

Mistake 2 ....................................................................................................

[2]

State one precaution that should be taken when carrying out this experiment.

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?