Science: Redox Reactions and Electrochemistry
Oxidation, reduction, and electron flow in chemical systems
Science: Redox Reactions and Electrochemistry
Oxidation, reduction, and electron flow in chemical systems
Chemistry - Grade 9-12
- 1
Define oxidation and reduction in terms of electron transfer.
Use the idea of electron loss and gain.
Oxidation is the loss of electrons, and reduction is the gain of electrons. In every redox reaction, one substance loses electrons while another substance gains them. - 2
In the reaction Zn + Cu2+ -> Zn2+ + Cu, identify which species is oxidized and which species is reduced.
Zinc is oxidized because it changes from Zn to Zn2+ by losing electrons. Copper ion, Cu2+, is reduced because it gains electrons and becomes Cu. - 3
Assign the oxidation number of each element in H2O.
Use common oxidation number rules for hydrogen and oxygen.
In H2O, hydrogen has an oxidation number of +1 and oxygen has an oxidation number of -2. The total adds to 0 because water is a neutral compound. - 4
Assign the oxidation number of sulfur in SO4^2-.
Oxygen is usually -2, so four oxygens contribute a total of -8. The ion has an overall charge of -2, so sulfur must be +6 to make the total equal -2. - 5
Determine whether the following reaction is a redox reaction: 2Mg + O2 -> 2MgO. Explain your answer.
Compare oxidation numbers of the elements before and after the reaction.
Yes, this is a redox reaction. Magnesium is oxidized because its oxidation number changes from 0 to +2, and oxygen is reduced because its oxidation number changes from 0 to -2. - 6
Write the oxidation half-reaction for magnesium in the reaction Mg -> Mg2+ + 2e-.
The oxidation half-reaction is Mg -> Mg2+ + 2e-. This shows that magnesium loses two electrons, so it is oxidized. - 7
Write the reduction half-reaction for chlorine in the reaction Cl2 + 2e- -> 2Cl-.
Reduction always includes electrons on the reactant side of the half-reaction.
The reduction half-reaction is Cl2 + 2e- -> 2Cl-. This shows that chlorine gains electrons, so it is reduced. - 8
In a galvanic or voltaic cell, what is the function of the salt bridge?
The salt bridge allows ions to move between the half-cells so charge does not build up. This maintains electrical neutrality and allows the cell to continue operating. - 9
In an electrochemical cell, where does oxidation occur and where does reduction occur?
Remember the pattern anode-oxidation and cathode-reduction.
Oxidation occurs at the anode, and reduction occurs at the cathode. This is true for all electrochemical cells. - 10
Describe the direction of electron flow in a galvanic cell.
Electrons flow through the external circuit from the anode to the cathode. They move from the site of oxidation to the site of reduction. - 11
Explain why rusting of iron is considered a redox process.
Think about what happens to iron and oxygen during corrosion.
Rusting is a redox process because iron atoms lose electrons and are oxidized, while oxygen gains electrons and is reduced. The reaction between iron, oxygen, and water forms iron oxides. - 12
A student says that the reducing agent in a reaction is the substance that gets reduced. Correct this statement and explain the role of a reducing agent.
The statement is incorrect. A reducing agent causes another substance to be reduced by donating electrons, and the reducing agent itself is oxidized in the process.