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Provide the oxidation numbers of the elements which are bolded (and increased in size for clarity)in each of the following compounds or ions (a) KNO₃: N is bolded(b) AlH₃: Al is bolded(c) H₂PO₄⁻: P is bolded

Sagot :

Answer

(a) KNO₃: The oxidation number of the bolded element N is +5

(b) AlH₃: The oxidation number of the bolded element Al is +3

(c) H₂PO₄⁻: The oxidation number of the bolded element P is +5

Explanation

Note: The sum of the oxidation numbers of elements in a neutral compound is zero

(a) KNO₃

Potassium belongs to group 1, and oxygen belongs to group 6 so their oxidation numbers are +1 and -2 respectively.

The oxidation number of the bolded element N is calculated as follows:

KNO₃ = 0

K + N + 3(O) = 0

+1 + N + 3 (-2) = 0

+1 + N - 6 = 0

N = +6 - 1

N = +5

(b) AlH₃

Note: The oxidation state of hydrogen in hydrides is -1.

AlH₃ = 0

Al + 3(H) = 0

Al + 3(-1) = 0

Al - 3 = 0

Al = +3

(c) H₂PO₄⁻

H₂PO₄ = -1

2(H) + P + 4(O) = -1

2(+1) + P + 4(-2) = -1

+2 + P - 8 = -1

P = +8 - 2 - 1

P = +8 - 3

P = +5