Why is potassium sulfate k2so4, but strontium sulfate srso4?

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.

Hope I helped! xx

10.063g / 10.00 ml = 1.0063 g/ml which rounds off to 4 sig figs as: 1.006 g/ml