Question

Why is potassium sulfate K2SO4, but strontium sulfate SrSO4?

Answer 1

The sulphate ion has a charge of 2-, and potassium has a charge of 1+. To fully neutralise the charge on a sulphate ion, you need two potassium ions. 

However, strontium has a charge of 2+. To neutralise the sulphate ion's 2- charge, one strontium ion is enough, so only one bonds to the sulphate.

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