Group Properties & Trends (Cambridge (CIE) IGCSE Chemistry): Alternative to Practical Questions

Students add aqueous chlorine to aqueous potassium iodide and record what they see.

One student records the result as "a reaction happened".

Explain why this is not acceptable as an observation.

A second student records the appearance of the potassium iodide solution before the reaction as "clear".

Explain why this is not accepted.

A third student records the colour of the iodine formed in the test tube as purple.

Explain why purple is not accepted as the colour of the iodine in this experiment.

Suggest how a student should record the result of a test in which no reaction occurs.

A student is provided with:

• aqueous solutions of chlorine, bromine and iodine

• aqueous solutions of potassium chloride, potassium bromide and potassium iodide

• the apparatus normally found in a school laboratory

No other chemicals are available.

Plan an investigation to establish the order of reactivity of chlorine, bromine and iodine.

Your plan must include:

• the apparatus you would use

• the method you would follow

• the observations you would expect

• how your observations would establish the order of reactivity

A student compares the reactivity of chlorine, bromine and iodine by adding each halogen solution to each of three halide solutions.

The student uses 10 cm³ of halide solution in every test tube.

State why the same volume of halide solution is used in every test tube.

State two other variables that the student should keep the same in every test tube.

The student carries out each test once.

Explain why repeating each test would improve the investigation.

A student investigates the reactivity of the halogens.

The student is provided with aqueous solutions of chlorine, bromine and iodine, and with aqueous solutions of potassium chloride, potassium bromide and potassium iodide.

The student needs to put 10 cm³ of a halide solution into each of several test tubes.

Name a suitable piece of apparatus for measuring 10 cm³ of a solution.

The student wants to measure the 10 cm³ of halide solution as accurately as possible.

Explain why a pipette is more suitable than a measuring cylinder for this.

The student uses the same dropping pipette to transfer all three halogen solutions, without washing it between solutions.

Explain why this could lead the student to an incorrect conclusion.

Suggest one improvement to the student's method.