A student adds an alkali gradually to an acid. The measured pH values after successive additions are 2, 4, 6, 7, 9 and 11.
.1
Describe the change and identify the neutral reading.
[2 marks]
.2
Explain neutralisation in terms of the reacting ions.
[2 marks]
5 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
Three repeated demonstrations with equal samples of a group 1 metal collect hydrogen volumes of 47, 49 and 48 cm³. A separate run collects 31 cm³ after the gas tube becomes loose.
.1
Calculate the mean volume from the three valid repeated demonstrations.
[3 marks]
.2
Explain why the low run cannot show that the metal was less reactive.
[2 marks]
6 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
Copper oxide is reduced by hydrogen: CuO+H2→Cu+H2O. A process must produce 12.8 g copper. Ar: Cu = 64, O = 16, H = 1.
.1
Calculate the minimum mass of copper oxide needed if conversion is complete.
[4 marks]
.2
Calculate the mass of hydrogen that reacts with this copper oxide.
[2 marks]
5 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A supply of scrap contains iron and copper pieces. Iron is above copper in the reactivity series. A student proposes using the iron to obtain copper from a copper sulfate solution.
.1
Explain the reaction, its observation and a limitation of the proposed recovery method.
[3 marks]
.2
Suggest why the deposited solid should be washed and why it might still be impure.
[2 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Propane burns completely in oxygen to form carbon dioxide and water. A sample uses 8.0 g oxygen and produces 6.6 g carbon dioxide and 3.6 g water. No products escape before weighing.
.1
Write the balanced equation for complete combustion of propane, C3H8.
