How to determine oxidation state

General
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how to determine oxidation state

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How to determine oxidation state

Answer:

Determining the oxidation state of an element in a compound involves using a set of rules to assign numbers that reflect the electron distribution in molecules. Here’s a step-by-step guide to help you determine oxidation states:

1. Understand the Concept:

The oxidation state (also called oxidation number) represents the charge an atom would have if the compound was composed of ions. It helps in understanding electron transfer in redox reactions.

2. Basic Rules for Assigning Oxidation States:

  1. Elemental Form: The oxidation state of an element in its elemental form (e.g., N_2, O_2, S_8) is always 0.

  2. Monatomic Ions: For ions consisting of only one atom, the oxidation state is equal to the charge of the ion. For example, the oxidation state of Na^+ is +1, and Cl^- is -1.

  3. Hydrogen: Usually has an oxidation state of +1. However, in metal hydrides like NaH, it’s -1.

  4. Oxygen: Usually has an oxidation state of -2. Exceptions include peroxides (e.g., H_2O_2) where it’s -1, and superoxides (e.g., KO_2) where it’s -0.5.

  5. Alkali Metals (Group 1): Always have an oxidation state of +1.

  6. Alkaline Earth Metals (Group 2): Always have an oxidation state of +2.

  7. Halogens: Usually have an oxidation state of -1, unless bonded with an element with higher electronegativity, like oxygen.

  8. Sum Rule: In a neutral compound, the sum of the oxidation states is 0. In a polyatomic ion, the sum of the oxidation states equals the charge of the ion.

3. Example Steps: Determine the Oxidation State in H_2SO_4

  1. Hydrogen (H): Each hydrogen has an oxidation state of +1. With two hydrogens, the total is +2.

  2. Oxygen (O): Each oxygen has an oxidation state of -2. With four oxygens, the total is -8.

  3. Sulfur (S): Let the oxidation state of sulfur be x.

    Using the sum rule for a neutral molecule:

    $$2(+1) + x + 4(-2) = 0$$

    $$2 + x - 8 = 0$$

    Solving for x:

    $$x = +6$$

So, the oxidation states in H_2SO_4 are +1 for hydrogen, +6 for sulfur, and -2 for oxygen.

Summary: By applying standard rules and balancing the overall charge, you can determine the oxidation states of elements in a compound. Remember that these values help track electron movement in reactions.