What is the charge on a sulfate ion?

What is the charge on a sulfate ion?

• A. 2-
• B. 1-
• C. 2+
• D. -2

Answer: (A)

For a polyatomic ion, the overall charge comes from summing the oxidation states of all the atoms inside it. In sulfate, there are four oxygen atoms, each with an oxidation state of -2, contributing -8 in total. The sulfur must then have an oxidation state that makes the whole ion carry a -2 charge, so sulfur is +6. Adding them up gives +6 + (-8) = -2. Therefore, the sulfate ion has a charge of -2. This means it can balance with a +2 cation, like in magnesium sulfate, where MgSO4 is formed.

For a polyatomic ion, the overall charge comes from summing the oxidation states of all the atoms inside it. In sulfate, there are four oxygen atoms, each with an oxidation state of -2, contributing -8 in total. The sulfur must then have an oxidation state that makes the whole ion carry a -2 charge, so sulfur is +6. Adding them up gives +6 + (-8) = -2. Therefore, the sulfate ion has a charge of -2. This means it can balance with a +2 cation, like in magnesium sulfate, where MgSO4 is formed.