Oxidation-Reduction (Redox) Reactions - AP Chemistry

1. What is the oxidation state of aluminum in $Al_2O_3$?

   +3. Calculate using: 2(Al) + 3(-2) = 0, so Al = +3.

2. Identify the oxidizing agent: $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$.

   $Cu^{2+}$. $Cu^{2+}$ gains electrons and gets reduced.

3. What is the change in oxidation state for iron in $Fe_2O_3$ during reduction?

   Decreases from +3 to 0. Reduction decreases oxidation state by gaining electrons.

4. What is reduction in a redox reaction?

   Gain of electrons. Reduction involves gaining electrons from another species.

5. Identify the reducing agent: $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$.

   $Zn$. $Zn$ loses electrons and gets oxidized.

6. In redox terminology, what is a half-reaction?

   Reaction showing either oxidation or reduction alone. Shows one part of the complete redox process.

7. What is the sum of oxidation states in an ion?

   Charge of the ion. The sum equals the ion's overall charge.

8. State the oxidation state of chlorine in $Cl_2$.

   0. Diatomic chlorine is in its elemental state.

9. What is the oxidation state of oxygen in most compounds?

   -2. Oxygen typically has -2 oxidation state in compounds.

10. What happens to the oxidation state of an element during reduction?

    Decreases. Reduction involves gain of electrons.

11. Describe a redox reaction in terms of electron transfer.

    Electrons transfer from reducing to oxidizing agent. One species loses electrons while another gains them.

12. What is the role of the reducing agent in a redox reaction?

    Donates electrons. It loses electrons and gets oxidized itself.

13. What is the oxidation state of nitrogen in $NH_3$?

    -3. Calculate using: 3(+1) + N = 0, so N = -3.

14. Identify the oxidizing agent in the reaction: $2H_2 + O_2 \rightarrow 2H_2O$.

    $O_2$. $O_2$ gains electrons, so it's the oxidizing agent.

15. What is oxidation in a redox reaction?

    Loss of electrons. Oxidation involves losing electrons to another species.

16. What is the oxidation state of phosphorus in $PCl_5$?

    +5. Calculate using: P + 5(-1) = 0, so P = +5.

17. Find the oxidation state of nitrogen in $NO_3^-$.

    +5. Calculate using: N + 3(-2) = -1, so N = +5.

18. Identify the element reduced in the reaction: $Fe + CuSO_4 \rightarrow FeSO_4 + Cu$.

    $Cu$. Copper's oxidation state decreases from +2 to 0.

19. What is the role of the oxidizing agent in a redox reaction?

    Accepts electrons. It gains electrons and gets reduced itself.

20. Define 'redox reaction'.

    A reaction involving electron transfer. Involves oxidation and reduction occurring simultaneously.

21. State the oxidation state of chlorine in $NaCl$.

    -1. Chlorine gains one electron to form chloride ion.

22. What is the oxidation state of carbon in $CH_4$?

    -4. Calculate using: C + 4(+1) = 0, so C = -4.

23. Identify the reducing agent in the reaction: $2H_2 + O_2 \rightarrow 2H_2O$.

    $H_2$. $H_2$ loses electrons, so it's the reducing agent.

24. What is the oxidation state of phosphorus in $H_3PO_4$?

    +5. Calculate using: 3(+1) + P + 4(-2) = 0, so P = +5.

25. Identify the element reduced: $2K + Br_2 \rightarrow 2KBr$.

    $Br_2$. Bromine's oxidation state decreases from 0 to -1.

26. What happens to the oxidation state of an element during oxidation?

    Increases. Oxidation involves loss of electrons.

27. What is the oxidation state of sulfur in $SO_2$?

    +4. Calculate using: S + 2(-2) = 0, so S = +4.

28. In $H_2O_2$, what is the oxidation state of oxygen?

    -1. In peroxide, oxygen has unusual -1 oxidation state.

29. What is the oxidation state of carbon in $CO_2$?

    +4. Calculate using: C + 2(-2) = 0, so C = +4.

30. Identify the element oxidized: $2K + Br_2 \rightarrow 2KBr$.

    $K$. Potassium's oxidation state increases from 0 to +1.

31. Find the oxidation state of chromium in $Cr_2O_7^{2-}$.

    +6. Calculate using: 2(Cr) + 7(-2) = -2, so Cr = +6.

32. What is the change in oxidation state for copper in $CuO$ during reduction?

    Decreases from +2 to 0. Reduction decreases oxidation state by gaining electrons.

33. Define the term 'disproportionation reaction'.

    A single element undergoes both oxidation and reduction. Same element has atoms with different oxidation states.

34. What is the oxidation state of sulfur in $H_2SO_4$?

    +6. Calculate using: 2(+1) + S + 4(-2) = 0, so S = +6.

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