Purity & Separating Mixtures (OCR GCSE Chemistry A (Gateway))

Which of the following is not a pure substance?

A student was investigating the colours in black food colouring. 

Chromatography was carried out on samples A-E and compared to the black food colouring. 

The following chromatogram was produced. 

Which of the following conclusions is not true for this chromatogram?

A student set up the following apparatus to investigate the colours in three different food colourings.  

What are the stationary and mobile phases for this experiment? 

A student making copper sulfate crystals used the method below. 

Unreacted copper carbonate was left over as it had been added in excess.

Which separation technique could be used to separate the unreacted copper carbonate and solution into different containers?

A mixture contains methanol and ethanol. They have different boiling points. 

Which method could be used to separate this mixture?

A student carried out chromatography on a sample of green ink. 

The distance moved by the solvent front is 5.8 cm. 

The distance moved by the yellow dye is 4.5 cm.

Calculate the R_f value of the yellow dye to 2 significant figures. 

The diagram below shows a heating curve for a pure substance.

Which part of the curve shows a change of state happening?

A student separates the colours in a sample of black ink using paper chromatography.

• He puts a spot of black ink onto a piece of filter paper.

• He dips the filter paper into ethanol in a beaker.

What phase describes ethanol in this experiment?

Look at the chromatogram.

What is the R_f value of the green spot? Use a ruler to help you.

What is the relative formula mass of sodium carbonate, Na₂CO₃?

The formula of magnesium chloride is MgCl₂.

What is the relative formula mass of magnesium chloride?

(A_r: Mg = 24.3, Cl = 35.5)

The molecular formula of decene is C₁₀H₂₀.

What is the empirical formula of decene?

R_f values are used to compare the different spots on a chromatogram.

What is the formula used to calculate an R_f value?

The formula of sulfuric acid is H₂SO₄.

What is the relative formula mass, M_r, of sulfuric acid?

The relative atomic mass, A_r, of H is 1, of S is 32 and of O is 16.

In some remote islands, drinking water is made from sea water.

What is the name of the process for making drinking water from sea water?

Butane has the molecular formula C₄H₁₀.

What is the empirical formula of butane?

Which statement correctly describes a pure substance?

A student separates the colours of black ink using paper chromatography.

• He puts a spot of black ink onto a piece of filter paper.

• He dips the filter paper into ethanol in a beaker.

What phase describes ethanol in this experiment?

Paper chromatography can be used to separate the colours in ink.

Water is the solvent used to separate the colours in water soluble ink.

What name is given to the water used in paper chromatography?

The molecular formula of hydrogen peroxide is H₂O₂.

What is the empirical formula of hydrogen peroxide?

A gas chromatogram is a chart that represents different substances in a mixture.

Which of the following statements about a gas chromatogram is not correct?

The gas chromatogram shows the different substances in a gas mixture. 

Which statement below is not true? 

The formula of ammonium carbonate is (NH₄)₂CO₃.

What is the relative formula mass of ammonium carbonate?

(A_r: C = 12, H = 1, N = 14, O = 16)

A student separates a dye using thin layer chromatography.

She puts a thin layer of solid alumina onto a glass plate. She puts the dye on the pencil line. She puts the glass plate into a tank containing water.

Which of the following is the stationary phase?

The empirical formula of a compound is CH₂O.

The relative formula mass of the compound is 180.0.

What is the molecular formula of the compound?

Relative atomic mass (A_r): C = 12.0 H = 1.0 O = 16.0

The diagram shows the displayed formula of succinic acid. 

What is the empirical formula for this compound?