IB Docs (2) Team MC test: Oxidation & reduction
Multiple choice test on 9.1 Oxidation & reduction
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
Applying IUPAC rules, what is the name of Cu2SO4?
The sulfate ion is SO42− so the copper cation must be Cu+.
What is the oxidation state of manganese in the MnO4− ion?
Oxidation states should be in the form of + or − followed by the number. VII is the oxidation number of Mn in MnO4− and 7+ would refer to the charge on the Mn7+ ion, if it existed in a compound.
Which is a correct statement about reducing agents?
A reducing agent readily loses electrons and in the process the oxidation state of one of its elements must increase.
Which substance cannot act as an oxidising agent?
S is already in its lowest oxidation state (−2) in hydrogen sulfide so it cannot be reduced any further.
In which compound does the metal ion have an oxidation state of +3?
The cyanide ion has a negative charge so the overall charge on iron(III) hexacyanide becomes 3−. Vanadium has an oxidation state of +5 in Na3VO4 and phosphorus, which does have an oxidation state of +3 in P2O3, is not a metal.
What is the sum of all the coefficients in the correctly balanced half-equation for the reduction of the dichromate(VI) ion in acidic solution?
_ Cr2O72−(aq) + _ H+(aq) + _ e− → _ Cr3+(aq) + _ H2O(l)
1 Cr2O72−(aq) + 14 H+(aq) + 6 e− → 2 Cr3+(aq) + 7 H2O(l)
In which reaction is oxygen simultaneously oxidized and reduced?
In the two reactions with oxygen gas, oxygen is reduced from 0 to −2 but it is carbon that is oxidized. In the iodine-thiosulfate reaction the oxidation state of oxygen does not change. In hydrogen peroxide the oxidation state of oxygen is −1 whereas in water and oxygen gas it is −2 and 0 respectively.
The Winkler method can be used to measure biological oxygen demand, BOD.
Three reactions taking place are:
2Mn2+(aq) + 4OH−(aq) + O2(aq) → 2MnO2(s) + 2H2O(l)
MnO2(s) + 2I−(aq) + 4H+(aq) → Mn2+(aq) + I2(aq) + 2H2O(l)
I2(aq) + 2S2O32-(aq) → S4O62−(aq) + 2I−(aq)
What is the ratio of the amount of dissolved oxygen (in mol) in the water to the amount of thiosulfate ions (in mol) required ?
Each mol of O2 produces 2 mol of MnO2. 2 mol of MnO2 react to produce 2 mol of I2 and 2 mol of I2 react with 4 mol of S2O32−.
Consider the following three redox reactions
Fe(s) + Cu2+ (aq) → Fe2+(aq) + Cu(s)
Cu(s) + 2Ag+ (aq) → Cu2+(aq) + 2Ag(s)
Zn(s) + Fe2+(aq) → Zn2+(aq) + Fe(s)
Which row correctly describes the most reactive metal and the best reducing agent?
| Row | Most reactive metal | Best reducing agent |
| 1 | Zn | Zn2+ |
| 2 | Ag | Ag+ |
| 3 | Zn | Ag+ |
| 4 | Zn | Zn |
The activity series ranks metals according to the ease with which they undergo oxidation so the higher a metal is in the activity series the better its reducing ability.
The concentration of iron(II) ions in a solution can be determined by titrating the solution with an acidified solution of potassium manganate(VII). The end-point is reached when one drop of of the manganate(VII) solution causes a faint pink colour to remain.
The equation for the reaction is:
5Fe2+(aq) + MnO4−(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
What volume of 0.020 mol dm-3 potassium manganate(VII) solution will be required to reach the end-point when it is added to 20.0 cm3 of a solution with an Fe2+(aq) concentration of 0.10 mol dm-3?
Amount of Fe2+ in 20.0 cm3 of 0.10 mol dm-3 Fe2+(aq) = (20.0/1000) x 0.1 = 2 x 10−3 mol.
Amount of MnO4− required = 1/5 x 2 x 10−3 = 4.0 x 10−4 mol.
Volume of 0.020 mol dm-3 MnO4− required = (1000/0.02) x (4.0 x 10−4) = 20.0 cm3
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