Need help with : Balancing oxidation reduction reactions
Mg(s) + HCl(aq) → Mg^2+(aq) + Cl ‾(aq) + H2(g)
Mg + 2HCl ==> MgCl2 + H2 or in ionic form
Mg + 2H^+ + 2Cl^- ==> Mg^+2 + 2Cl^- + H2
or in net ionic form
Mg + 2H+ ==> Mg^+2 + H2
To balance oxidation-reduction reactions, you need to follow a systematic approach. Here's how you can balance the given equation, which involves the oxidation of magnesium (Mg) and the reduction of hydrogen chloride (HCl):
1. Identify the oxidation and reduction half-reactions:
In this equation, Mg is being oxidized (loses electrons) while HCl is being reduced (gains electrons).
Mg --> Mg^2+ + 2e^- (oxidation)
H^+ + Cl^- + 2e^- --> H2 + Cl^- (reduction)
2. Balance the atoms other than hydrogen and oxygen:
Count the number of atoms of each element on both sides of each half-reaction. In this case, the Mg half-reaction is already balanced.
3. Balance the oxygen atoms:
Add water (H2O) to the side that needs oxygen atoms. Since there are no oxygen atoms on either side, we don't need to add water in this equation.
4. Balance the hydrogen atoms:
Add hydrogen ions (H+) to the side that needs hydrogen atoms. Since there are two hydrogen atoms in the Mg half-reaction, we need to add two hydrogen ions (H+) to the other side.
Mg --> Mg^2+ + 2e^- (oxidation)
2H+ + Cl^- + 2e^- --> H2 + Cl^- (reduction)
5. Balance the charges:
Make sure the total charges on both sides are equal. In this case, the charges are already balanced.
6. Balance the electrons:
Multiply one or both half-reactions by a suitable factor to balance the number of electrons. In this case, both half-reactions already have the same number of electrons.
Mg --> Mg^2+ + 2e^- (oxidation)
2H+ + Cl^- + 2e^- --> H2 + Cl^- (reduction)
7. Combine the half-reactions:
Multiply each half-reaction by a factor if necessary so that the electrons cancel out when the two half-reactions are combined. In this case, we don't need to multiply any of the half-reactions.
Mg + 2H+ + Cl^- --> Mg^2+ + H2 + Cl^-
Now, we have a balanced oxidation-reduction equation for the reaction between magnesium and hydrochloric acid.
Please note that the final equation may also be written as:
Mg + 2HCl → MgCl2 + H2