4. Redox Equations

Question 1

what happens in a redox reaction

Answer 1

electrons are transferred

Question 2

Oxidation is ___ of electrons

Answer 2

loss of electrons

OIL

Question 3

Reduction is ____ of electrons

Answer 3

gain of electrons

RIG

Question 4

what happens simultaneously in a redox reaction

Answer 4

reduction and oxidation

Question 5

a oxidising reagent 1.____ electrons and gets 2._____

Answer 5

1. accepts
2. reduced
   RIG

Question 6

a reducing agent 1._____ electrons and gets 2._____

Answer 6

1. donates

2. oxidised

Question 7

e.g. of redox reaction
Na + 1/2Cl2 -> Na+Cl-
what is being reduced what is being oxidised?

Answer 7

Na is oxidised

Cl is reduced

Question 8

separating redox reactions into half-reactions

a redox reaction is made up of an

Answer 8

oxidation half-reaction

reduction half-reaction

Question 9

writing ionic half equations for half reactions

e.g oxidation of sodium and reduction of chlorine

Answer 9

Na -> Na+ + e-

Cl2 + 2e- -> 2Cl-

Question 10

why are electrons shown in half-equations

Answer 10

so the charges on each side of the equation balance

Question 11

an oxidation half-equation can be combined with a reduction half-equation to make a full redox equation

e.g ZINC METAL displaces SILVER IONS from SILVER NITRATE solution to form ZINC NITRATE and a deposit of SILVER METAL

Answer 11

1. zinc oxidised Zn(s) -> Zn2+(aq) + 2e-
   silver reduced Ag+(aq) + e- -> Ag(s)
2. 2 silver ions needed to accept 2 electrons. need to double Ag half equation.
   2Ag+(aq) + 2e- -> Ag(s)
3. number of electrons lost and gained balance, half equations can combine.
   Zn(s) + 2Ag+(aq) + 2e- -> Zn2+(aq) + 2Ag(s) + 2e-
4. electrons cancel out. not included in overall equation.
   Zn(s) + 2Ag+(aq) -> Zn2+(aq) + 2Ag(s)

tip- the charges on each side of the equation should be balanced.

Question 12

what can you add to balance half equations (atoms and charge need to balance)

Answer 12

e-
H+
H2O

Question 13

using e-, H+ and H2O to balance half equations

e.g Acidified manganate (VII) ions (MnO4-) can be reduced to MN2+ by Fe2+ ions
write the 2 half equations for this reaction

Answer 13

iron is being oxidised Fe2+(aq) -> Fe3+ e-

1. Manganate is being reduced MnO4-(aq) -> Mn2+(aq)
2. to balance oxygens need to add H2O
   MnO4- -> Mn2+(aq) + 4H2O(l)
3. need to add H+ ions to balance hydrogens
   MnO4- + 8H+ -> Mn2+(aq) + 4H2O(l)
4. balance charges by adding some electrons
   MnO4-(aq) + 8H+(aq) + 5e- -> Mn2+(aq) + 4H2O(l)
   charges now add to 2+ on each side