Describe the rules for assigning the oxidation state.

The oxidation state (also known as oxidation number) is a concept that helps chemists determine the electron distribution in a molecule or ion. There are several rules to assign oxidation states to elements in different compounds or ions. Here are the key rules:

  1. Oxidation state of an element in its free (uncombined) state is zero:

    • Example: O₂, N₂, H₂, P₄, S₈ all have oxidation numbers of 0.

  2. The oxidation state of a monoatomic ion is equal to the charge on the ion:

    • Example: Na⁺ has an oxidation state of +1, Cl⁻ has an oxidation state of -1.

  3. In compounds, hydrogen has an oxidation state of +1, unless it is bonded to a metal in hydrides, where it has an oxidation state of -1:

    • Example: In H₂O, hydrogen has an oxidation state of +1; in NaH (sodium hydride), hydrogen has an oxidation state of -1.

  4. The oxidation state of oxygen is usually -2, except in peroxides (where it is -1) and when it is bonded to fluorine (where it can be positive):

    • Example: In H₂O, oxygen has an oxidation state of -2; in H₂O₂ (hydrogen peroxide), oxygen has an oxidation state of -1.

  5. The sum of the oxidation states of all atoms in a neutral compound is zero:

    • Example: In Na₂SO₄, the sum of the oxidation states of Na, S, and O equals zero.

  6. The sum of the oxidation states of all atoms in a polyatomic ion equals the charge of the ion:

    • Example: In SO₄²⁻, the sum of the oxidation states of S and O equals -2 (the charge on the ion).

  7. Group 1 elements always have an oxidation state of +1, and Group 2 elements always have an oxidation state of +2:

    • Example: Na in NaCl has an oxidation state of +1, Mg in MgCl₂ has an oxidation state of +2.

  8. Halogens typically have an oxidation state of -1, except when they are bonded to oxygen or other halogens, in which case their oxidation state is positive:

    • Example: In NaCl, chlorine has an oxidation state of -1; in Cl₂O (chlorine monoxide), chlorine has an oxidation state of +1.

Related Questions:

  1. What is the difference between valency and oxidation state?
  2. Choose Arrhenius acids from the following compounds: HF, NH₃, H₂SO₄, SO₂, H₂S, H₂O
  3. Which salt is formed when HCl reacts with BaCO₃?
  4. How will you justify that H₂SO₄ is a Bronsted-Lowry acid?
  5. Define oxidation in terms of electrons. Give an example.
  6. Define reduction in terms of loss or gain of oxygen or hydrogen. Give an example.
  7. Differentiate between oxidizing and reducing agents.
  8. Differentiate between strong and weak electrolytes.
  9. How is electroplating of tin on steel carried out?
  10. Why is steel plated with nickel before the electroplating of chromium?
  11. How can you explain that the following reaction is oxidation in terms of increase of oxidation number?
  12. How can you prove with an example that conversion of an ion to an atom is an oxidation process?
  13. Why does the anode carry a negative charge in a galvanic cell but a positive charge in an electrolytic cell? Justify with comments.
  14. Where do the electrons flow from the Zn electrode in Daniel’s cell?
  15. What happens at the cathode in a galvanic cell?
  16. Which solution is used as an electrolyte in Nelson’s cell?
  17. Name the by-products produced in Nelson’s cell.
  18. Why is galvanizing done?
  19. Why is an iron grill painted frequently?
  20. Why is O₂ necessary for rusting?