Oxidation Numbers in Chemical Compounds: Examples with Ca(OH)2, MnO2, KNO3, and NO2

Assign oxidation numbers to each element in the following compounds:a. Ca(OH)2b. MnO2c. KNO3d. NO2

a. Ca=+2, O2, H=+1b. Mn=+4, O2c. K=+1, N=+5, O2d. N=+4, O2

a. Ca(OH)2
– The oxidation number of calcium (Ca) is +2 since it is an alkaline earth metal and typically has a +2 oxidation state.
– The oxidation number of oxygen (O) is -2 since it usually has a -2 oxidation state in compounds.
– The oxidation number of hydrogen (H) is +1 since it typically has a +1 oxidation state in compounds.
Therefore, the oxidation numbers for each element in Ca(OH)2 are: Ca(+2), O(-2), and H(+1).

b. MnO2
– The oxidation number of oxygen (O) is -2 since it usually has a -2 oxidation state in compounds.
– We know that the overall charge of MnO2 is neutral (since there is no charge indicated), so the sum of all the oxidation numbers must equal zero.
– Let the oxidation number of manganese (Mn) be x. Therefore, we have: x + 2(-2) = 0.
– Solving for x, we get x = +4.
Therefore, the oxidation numbers for each element in MnO2 are: Mn(+4) and O(-2).

c. KNO3
– The oxidation number of potassium (K) is +1 since it typically has a +1 oxidation state in compounds.
– The oxidation number of nitrogen (N) is +5 since there are 3 oxygen atoms surrounding the nitrogen, each with a -2 oxidation state. Therefore, we have 3(-2) + x = 0, solving for x gives us x = +5.
– The oxidation number of oxygen (O) is -2 since it usually has a -2 oxidation state in compounds.
Therefore, the oxidation numbers for each element in KNO3 are: K(+1), N(+5), and O(-2).

d. NO2
– The oxidation number of nitrogen (N) is +4 since there are 2 oxygen atoms surrounding the nitrogen, each with a -2 oxidation state. Therefore, we have 2(-2) + x = 0, solving for x gives us x = +4.
– The oxidation number of oxygen (O) is -2 since it usually has a -2 oxidation state in compounds.
Therefore, the oxidation numbers for each element in NO2 are: N(+4) and O(-2).

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