Pupil sheet · Redox
Oxygen in, oxygen out — questions
Name ______________________ Date ____________
Try every question before you use a nudge. Write in full sentences where you are asked to explain.
1. identify
Tin is extracted by heating tin(IV) oxide with carbon: SnO2 + C → Sn + CO2. Which row is correct?
| Row | Substance oxidised | Substance reduced |
|---|---|---|
| A | tin(IV) oxide | carbon |
| B | carbon dioxide | tin |
| C | carbon | tin(IV) oxide |
| D | carbon | no substance is reduced |
Circle one answer.
- A
- B
- C
- D
Nudge (only if you are stuck): Follow the oxygen atoms from the left side of the equation to the right.
2. identify
Steam is passed over hot magnesium ribbon, and white magnesium oxide and hydrogen gas form: Mg + H2O → MgO + H2. Fill in the gaps. Magnesium (1) ___ oxygen, so magnesium is (2) ___. Water (3) ___ oxygen, so water is (4) ___. Both happen at once, so this is a (5) ___ reaction.
(1)
(2)
(3)
(4)
(5)
Nudge (only if you are stuck): What does each reactant become on the right of the equation?
3. identify
Manganese(IV) oxide, MnO2, is a black powder. What does the (IV) in its name tell you?
Circle one answer.
- Each manganese atom is joined to four oxygen atoms
- Each formula unit has four manganese atoms
- The oxidation number of manganese is +4
- Manganese has four electrons in its outer shell
Nudge (only if you are stuck): The numeral in the name belongs to the metal.
4. name
Name these compounds, with a Roman numeral where one is needed. (a) PbO2 (b) CuCl (c) CrCl3 (d) MgCl2
(a) PbO2
(b) CuCl
(c) CrCl3
(d) MgCl2
Nudge (only if you are stuck): An oxide ion is O2− and a chloride ion is Cl−. What charge must the metal ion have to balance them?
5. identify
Which of these reactions are redox? Choose all that apply.
Tick every correct statement.
- NH3 + HCl → NH4Cl
- Pb(NO3)2 + 2KI → PbI2 + 2KNO3
- 2NiO + C → 2Ni + CO2
- 2Al + Cr2O3 → Al2O3 + 2Cr
Nudge (only if you are stuck): In each equation, look for a substance that gains oxygen and one that loses it.
6. identify / explain
A catalytic converter in a car exhaust removes two harmful gases: 2CO + 2NO → 2CO2 + N2. (a) Which substance is oxidised? Give a reason. (b) Which substance is reduced? Give a reason. (c) Explain why this is a redox reaction.
(a) Substance oxidised, and why
(b) Substance reduced, and why
(c) Why redox
Nudge (only if you are stuck): Count the oxygen atoms in each reactant and in what it becomes.
7. explain
A pupil says: "ZnO + C → Zn + CO is a reduction, not a redox reaction, because zinc oxide is reduced." Explain why the pupil is incorrect.
Nudge (only if you are stuck): Zinc oxide loses its oxygen. Where does that oxygen go?
8. calculate
Lead(II) oxide, PbO, is a yellow powder. A sample of 4.46 g is heated in a stream of hydrogen until no more water forms, and 4.14 g of lead is left. What mass of oxygen did the lead(II) oxide lose? Give your answer to 2 significant figures.
Mass of oxygen lost: ______________ unit ________
Lead(II) oxide lost its oxygen to the hydrogen: lead(II) oxide was reduced and hydrogen was oxidised.
Nudge (only if you are stuck): All the lead stays in the tube. Only the oxygen leaves, in the water.