Practical Skills (OCR Gateway GCSE Chemistry: Combined Science)

A laboratory experiment to separate crude oil is shown below.

Which row is correct? 

Below are five steps in the preparation of a soluble salt. The sentences are not in the correct order.

1. Heat to evaporate most of the water
2. Add solid copper(II) oxide until no more dissolves
3. Measure out 25 cm³ of dilute sulfuric acid
4. Leave in a warm place to cool and crystallise
5. Filter to remove the excess solid

What is the correct order of the sentences?

What is the correct expression for calculating the R_f value in chromatography?

A student wants to investigate the effect of surface area on the rate of reaction between marble chips and dilute acid.

What pieces of apparatus would be essential to this investigation?

A student sets up the following laboratory apparatus.

Which reaction could the student be investigating?

A student investigates the reaction between sodium thiosulfate and hydrochloric acid.

Look at the diagram below. It shows the apparatus he uses.

• After a time he cannot see the cross because the liquid in the conical flask goes cloudy. The student measures the time taken until the cross cannot be seen.
• He does the experiment four times. For each experiment he uses a different concentration of sodium thiosulfate solution.

Which of the following must not be changed to do a fair test?

A student wants to test the purity of a liquid by testing its boiling point.

The actual boiling point of the pure liquid is 85 °C.

Which equation represents the percentage (%) difference between the student’s value and the actual value?

On a chromatogram, a substance has an R_f value of 0.68.  

If the solvent front travels 9 cm from the baseline, at what distance from the baseline will the spot be found.