The structure of myrcene is shown.
(a) Deduce the formula of myrcene to show the number of atoms of carbon and hydrogen.
(b) Myrcene is found in some plants.
The coloured compounds in plant leaves can be separated by chromatography.
Complete the diagram by putting the correct labels in the boxes.
(c) Myrcene is an unsaturated hydrocarbon.
Describe a chemical test to distinguish between a saturated and an unsaturated hydrocarbon.
(d) Butane is a saturated hydrocarbon.
To which homologous series does butane belong?
Draw a circle around the correct answer.
alcohol alkane alkene carboxylic acid
(e) Large hydrocarbons can be cracked to form smaller hydrocarbons.
Complete the chemical equation for cracking tridecane, $\mathrm{C}_{13} \mathrm{H}_{28}$, to form an alkene and one other hydrocarbon.
$ \mathrm{C}_{13} \mathrm{H}_{28} \rightarrow \mathrm{C}_3 \mathrm{H}_6+\ldots \ldots \ldots \ldots $
(f) Ethene is an alkene.
Draw the structure of ethene showing all of the atoms and all of the bonds.
(g) Complete the sentences about the separation of hydrocarbons from petroleum using words from the list.
bitumen combustion condense crystallisation distillation
evaporate gasoline kerosene melt
Hydrocarbons are separated in a fractionating column by fractional
Hydrocarbons with lower boiling points move further up the column. When the temperature in the column falls below the boiling points of the hydrocarbons they _______. The fraction at the bottom of the column which is used for making roads is called ________ .
▶️ Answer/Explanation
(a) Ans: C10H16
Counting the carbon and hydrogen atoms in the myrcene structure gives 10 carbons and 16 hydrogens.
(b) Ans:
Top box: Chromatography paper / filter paper
Bottom box: Solvent (e.g., ethanol or water)
In chromatography, the stationary phase is the paper, and the mobile phase is the solvent.
(c) Ans:
Test: Bromine water
Saturated hydrocarbon: No color change (stays orange-brown)
Unsaturated hydrocarbon: Decolorizes (turns colorless)
Bromine reacts with C=C double bonds in unsaturated compounds.
(d) Ans: Alkane
Butane (C4H10) is a saturated hydrocarbon with single bonds, characteristic of alkanes.
(e) Ans: C10H22
Balancing the equation: C13H28 → C3H6 (propene) + C10H22 (decane).
(f) Ans:
Ethene (C2H4) has a double bond between the two carbon atoms.
(g) Ans:
1st blank: Distillation
2nd blank: Condense
3rd blank: Bitumen
Fractional distillation separates hydrocarbons by boiling points. Bitumen is the heaviest fraction.
(a) Magnesium is manufactured by the electrolysis of molten magnesium chloride.
(i) The negative electrode is made of iron.
Suggest a non-metal which could be used for the positive electrode.
Give a reason for your answer.[2]
(ii) Predict the products of the electrolysis of molten magnesium chloride at:[2]
the positive electrode
the negative electrode.
(b) The following statements are about the procedure for making crystals of hydrated magnesium chloride from magnesium and dilute hydrochloric acid.
- Leave the mixture until no more bubbles are seen.
- Leave the mixture at room temperature to form more crystals.
- Add an excess of magnesium to dilute hydrochloric acid.
- Warm the filtrate to the point of crystallization.
- Filter off the crystals and dry between filter papers.
- Filter off the excess magnesium.
Put the statements A, B, C, D, E and F in the correct order.
The first one has been done for you.
(c) Magnesium is a metal in Group II of the Periodic Table.
Copper is a transition element.
Copper has a higher melting point and a higher boiling point than magnesium.
Describe two other properties of copper which are different from those of magnesium.[2]
(d) Chromatography can be used to separate a mixture of ions from different transition element compounds.
Four samples, R, S, T and U, each containing transition element ions, were placed on a piece of chromatography paper.
Two solutions, Y and Z, each containing only one type of transition element ion were also placed on the same piece of chromatography paper.
The results of the chromatography are shown.
(i) Which sample, R, S, T or U, contains the same ions as both solution Y and solution Z?[1]
(ii) Which sample, R, S, T or U, does not contain the same ions as either solution Y or solution Z?[1]
(iii) In which sample, R, S, T or U, has the greatest number of transition element ions been separated?[1] [Total: 11]
▶️ Answer/Explanation
(a)(i) Ans: graphite (1)
conducts electricity / inert (1)
Graphite is used as it conducts electricity and is inert to chlorine gas produced at the anode.
(a)(ii) Ans: positive electrode: chlorine (1)
negative electrode: magnesium (1)
Chloride ions (Cl⁻) are oxidized to chlorine gas at the anode, while magnesium ions (Mg²⁺) are reduced to magnesium metal at the cathode.
(b) Ans: (C), A, F, D, B, E (2)
Correct sequence: Add excess Mg (C), wait for reaction completion (A), filter excess Mg (F), concentrate solution (D), crystallize (B), collect crystals (E).
(c) Ans:
1. Copper has higher density (8.96 g/cm³) vs magnesium (1.74 g/cm³)
2. Copper forms colored compounds (blue CuSO₄) while magnesium compounds are white
3. Copper acts as catalyst (e.g., in Fehling’s test) unlike magnesium
4. Copper shows variable oxidation states (+1, +2) vs magnesium’s fixed +2 state
(d)(i) Ans: R
Sample R shows spots aligning with both Y and Z reference solutions.
(d)(ii) Ans: T
Sample T’s spots don’t align with either Y or Z references.
(d)(iii) Ans: R
Sample R shows three distinct spots (including Y and Z components), indicating maximum separation.