DSE Chemistry: Redox Reactions, Chemical Cells and Electrolysis — Practice Questions & Answers
Oxidation numbers and redox in terms of electron transfer, displacement reactions, simple and galvanic chemical cells, electrolysis, and electroplating.
456 practice questions available for this topic — here are 10 with full answers and explanations.
What is the oxidation number of Cu in Cu(NH3)4Cl2?
+2
0
+4
+6
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WhyNH3 is neutral and the two Cl contribute -2 in total, so Cu is +2.
2Multiple choice · Medium
What is the oxidation number of Mn in MnO4-?
+7
+6
+4
+2
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WhyFour O at -2 give -8; for an overall -1, Mn is +7.
3Multiple choice · Easy
The oxidation number of oxygen in a peroxide such as H2O2 is
-1
-2
0
+2
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WhyIn peroxides oxygen takes the unusual value of -1.
4Fill in the blank · Medium
In the sulphate ion SO4 2-, the oxidation number of sulphur is +.
Answer:
6 / six
WhyFour O at -2 give -8; overall -2, so S = +6.
5Fill in the blank · Easy
A species is oxidised when its oxidation number during a reaction.
Answer:
increases / rises / goes up
WhyOxidation = increase in oxidation number.
6Fill in the blank · Medium
The oxidation number of hydrogen is +1 in most compounds, but it is in metal hydrides such as NaH.
Answer:
-1 / minus 1
WhyThis is a standard exception to remember.
7Multiple choice · Medium
The tendency of being reduced of six ionic species increases in the order Ba2+(aq) < Na+(aq) < Mg2+(aq) < H+(aq) < Cu2+(aq) < Hg2+(aq). Which statement is correct?
Na(s) has a stronger reducing power than Hg(l)
Hg2+(aq) is the weakest oxidising agent among the six species
Ba(s) does NOT react with H+(aq)
A displacement reaction occurs when Cu(s) is immersed in MgSO4(aq)
Tap an answer to check it.
WhyA species lower in this order (such as Na/Na+) corresponds to a metal with stronger reducing power than Hg.
8Multiple choice · Medium
Which of the following displacement reactions can occur?
Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s)
Cu(s) + MgSO4(aq) -> CuSO4(aq) + Mg(s)
Cu(s) + ZnSO4(aq) -> CuSO4(aq) + Zn(s)
Ag(s) + Cu(NO3)2(aq) -> AgNO3(aq) + Cu(s)
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WhyZinc is more reactive than copper, so it displaces copper from copper(II) sulphate.
9Multiple choice · Easy
In the reaction Mg(s) + Cu2+(aq) -> Mg2+(aq) + Cu(s), the Cu2+ ion acts as
the oxidising agent
the reducing agent
a catalyst
a spectator ion
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WhyCu2+ gains electrons (is reduced), so it is the oxidising agent.
10Fill in the blank · Medium
A reducing agent gives electrons to another species and is itself .
Answer:
oxidised / oxidized
WhyThe reducing agent undergoes oxidation.
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