O-LevelChemistryChemistry of the Environment5070/21 · May/June 2020 · Q710 Marks

Carbon dioxide is a colourless gas found in air.

(a)The percentage of carbon dioxide in the air is increasing. State one environmental problem caused by this increase.[1]
(b)Carbon dioxide is a product of the complete combustion of octane, C8H18- Construct the equation for this reaction.[2]
(c)(i)Fermentation of glucose produces carbon dioxide. Give the equation for the fermentation of glucose.[1]
(c)(ii)State two essential conditions needed for fermentation.[2]
(d)When warmed, solid carbon dioxide changes directly into a gas. It does not become a liquid. Use the kinetic particle theory to describe the changes in movement and arrangement of the particles during this change of state.[3]
(e)Explain why solid carbon dioxide does not conduct electricity.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] (increased) greenhouse effect / global warming
[2] C8H18 + 12½O2 → 8CO2 + 9H2O correct formulae for reactants and products (1) balanced – dependent on correct formulae for reactants and products (1)
[1] C6H12O6 → 2C2H5OH + 2CO2
[2] Any two from: aqueous / presence of water (1); absence of oxygen / anaerobic (1); yeast (1); temperature between 10 and 40°C (1)
[3] particles change from vibrational to translational motion / change from vibrations to moving very fast (1) change from a set pattern to a random arrangement (1) particles change from touching each other to large distance between particles (1)
[1] electrons cannot move / no mobile electrons

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.