BNO2−[1]
x + 2(−2) = −1, so x = +3.
NO2 is +4, NH4+ is −3 and N2O is +1.
Bthe acid and carbonate[1]
An acid reacting with a carbonate: calcium stays +2, carbon +4, oxygen −2, hydrogen +1 and chlorine −1.
Each of the others has an element uncombined on one side, so its oxidation state changes.
AThe gas is an oxidising agent.[1]
Iodide ions lose electrons to form iodine, so they are oxidised.
The gas takes those electrons, so it is an oxidising agent.
Bchlorine with sodium hydroxide[1]
Chlorine goes from 0 to −1 in NaCl and to +1 in NaClO.
In A two different elements change, C is ordinary redox and D is not redox.
A2.0 × 10−4[1]
Each MnO4− takes 5 electrons and each Fe2+ gives 1, so MnO4− : Fe2+ = 1 : 5.
1.0 × 10−3 ÷ 5 = 2.0 × 10−4 mol. Option D multiplies instead of dividing.
Na → Na+ + e− and Cl2 + 2e− → 2Cl−[1]
Sodium, because it loses electrons.[1]
Copper(II) oxide, because it loses oxygen.[1]
+6[1]
+2[1]
−1, because NaH is a metal hydride[1]
+5[1]
Not redox: nitrogen stays −3 and +5.[1]
Not redox: copper stays +2, carbon +4 and oxygen −2.[1]
Redox: nitrogen falls from +5 to +4 and some oxygen rises from −2 to 0.[1]
Sulfur dioxide is a reducing agent.
Potassium manganate(VII) and potassium dichromate(VI) are oxidising agents, and both are reduced.[2]
2Fe3+ + 2I− → 2Fe2+ + I2[1]
Cr2O72− + 14H+ + 6e− → 2Cr3+ + 7H2O and Fe2+ → Fe3+ + e− (× 6)
Cr2O72− + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O[2]
nNH₂OH = 2.50 × 10−3 mol and nMn³⁺ = 5.00 × 10−3 mol, each Mn3+ gaining 1 electron.
So each N loses 2 electrons: −1 + 2 = +1[2]
Yes.
Nitrogen is +4 in NO2, and goes up to +5 in HNO3 and down to +3 in HNO2.[2]
nMnO₄⁻ = 4.000 × 10−4 mol. MnO4− + 5Fe2+, so nFe²⁺ = 2.000 × 10−3 mol
c = 2.000 × 10−3 ÷ 0.0250 = 0.0800 mol dm−3[2]
nCr₂O₇²⁻ = 5.100 × 10−4 mol, so nFe²⁺ = 3.060 × 10−3 mol in 25.0 cm3
0.03060 mol in 250 cm3, so Mr = 12.0 ÷ 0.03060 = 392.2
284.0 + 18.0x = 392.2, so x = 6[3]
DHNO3[1]
In HNO3: +1 + x + 3(−2) = 0, so x = +5.
NO2 and N2O4 are +4 and NH4+ is −3.
ANF3[1]
In HNO2 nitrogen is +3. In NF3 each F is −1, so nitrogen is also +3.
NH4+ is −3, NO is +2 and NO2+ is +5.
Brow B[1]
In CaSO4: +2 + x + 4(−2) = 0, so sulfur is +6.
Nitrogen in HNO3 is +5, iron in FeO is +2 and carbon in NaHCO3 is +4.
BK2SO3[1]
Sulfur is +4 in SO2. In K2SO3: 2(+1) + x + 3(−2) = 0, so x = +4.
H2SO4 is +6, Na2S is −2 and Na2S2O3 is +2.
Dno change[1]
In FeTiO3 iron is +2 (iron(II)), so +2 + x + 3(−2) = 0 gives titanium +4.
In TiO2 titanium is also +4.
Bthe oxide with hydrochloric acid[1]
Iron is +3 in Fe2O3 and +3 in FeCl3: an acid–base reaction.
In A, C and D iron changes between 0, +2 and +3.
Amagnesium with the acid[1]
Magnesium rises from 0 to +2 and hydrogen falls from +1 to 0.
B, C and D are acid–base reactions with no change in oxidation state.
DSO3 + H2O[1]
Sulfur is +6 in SO3 and in H2SO4, and no other oxidation state changes.
A, B and C each have an element whose oxidation state changes.
D3 and 4 only[1]
Each Fe2+ loses an electron, so it is oxidised, and Cl2 gains electrons to become Cl−, so it is reduced.
Chlorine is therefore the oxidising agent, not the reducing agent.
CCu loses electrons.[1]
Copper rises from 0 to +2, so it loses electrons.
Nitrogen falls from +5 to +4 in NO2, so HNO3 is the oxidising agent. Nitrogen in nitrate is +5, and oxygen stays −2.
AEthanol has been oxidised.[1]
Decolourising acidified manganate(VII) shows a reducing agent: manganate(VII) is reduced.
So ethanol is the reducing agent and is itself oxidised.
Brow B[1]
Manganese falls from +7 to +2, so MnO4− is reduced.
Sulfur rises from +4 to +6, so SO32− is oxidised: it is the reducing agent. H+ does not change.
DMnO4− to Mn2+[1]
Manganese falls from +7 to +2: reduction, purple to colourless.
A is not redox, and in B and C iodine and iron are oxidised.
Drow D[1]
Cl2 is an element, 0. In HCl chlorine is −1.
In HClO: +1 + x − 2 = 0, so chlorine is +1. Chlorine disproportionates.
Bchlorine with sodium hydroxide[1]
Chlorine goes from 0 to −1 in NaCl and to +1 in NaOCl.
In A and D two different elements change, and C is not redox.
A1 only[1]
Brown iodine formed, so iodide ions were oxidised and X is an oxidising agent.
Any oxidising agent strong enough could do this, such as chlorine, and iodide is oxidised, not reduced.
BI and IV only[1]
pH measures the H+ concentration, and with a metal each H+ gains an electron (it is reduced to hydrogen).
Strength is how far an acid ionises, not its concentration, and a strong acid turns Universal Indicator red, not orange.