Recall Sem1: Redox reaction

What is the change in oxidation number of sulfur?

• +6

• +8

• -6

• -8

Which statement is true?

• HI undergoes reduction

• H₂SO₄ is a reducing agent

• HI loses electron

• H₂S undergoes reduction.

Zinc atoms can be oxidised to Zinc ions by dichromate(VI) ions in alkaline solution. Chromium is reduced to Cr³⁺ in this reaction.

Which equation is correct?

• Cr₂O₇^2- + Zn + 14H⁺ → 2Cr³⁺ + Zn²⁺ + 7H₂O

• Cr₂O₇^2- + 3Zn + 14H⁺ → 2Cr³⁺ + 3Zn²⁺ + 7H₂O

• Cr₂O₇^2- + 3Zn + 14H₂O → 2Cr³⁺ + 3Zn²⁺ + 7OH^-

• Cr₂O₇^2- + 3Zn + 7H₂O → 2Cr³⁺ + 3Zn²⁺ + 14OH^-

Which defines reduction?

(Please select all the correct answers.)

• gain electron

• oxidation number increases

• gain hydrogen

• gain oxygen

Write the oxidation number of carbon in C₂O₄^2-.