Multiple Choice
What is the typical oxidation number of oxygen in most compounds?
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6. Chemical Quantities & Aqueous Reactions
Calculate Oxidation Numbers
Multiple Choice
Which of the following compounds contains phosphorus (P) with an oxidation number of -3?
A
PH3
B
Na3P
C
H3PO4
D
PCl3
Verified step by step guidance1
Recall the definition of oxidation number: it is the hypothetical charge an atom would have if all bonds to atoms of different elements were 100% ionic.
Identify the oxidation number of phosphorus (P) in each compound by using the known oxidation states of other atoms and the fact that the sum of oxidation numbers in a neutral compound is zero.
For PH3: Hydrogen (H) usually has an oxidation number of +1. Since there are 3 hydrogens, total +3, phosphorus must be -3 to balance the molecule.
For Na3P: Sodium (Na) has an oxidation number of +1. With 3 sodium atoms, total +3, phosphorus must be -3 to balance the compound.
For H3PO4 and PCl3: Use the known oxidation states of oxygen (-2) and chlorine (-1) respectively to calculate phosphorus oxidation number, which will not be -3 in these cases.
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