Experimental Design (Cambridge O Level Chemistry)

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 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 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.

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.