What quantity of potassium phosphate, in grams, is required to prepare 500.0 ml of solution where you the concentration of potassium is 0.100 M.

I did this problem and I got 10.6 grams but my computer says I did wrong. what steps am I missing. I'm confused now because I converted potassium to potassium phosphate.

Solutions of sodium carbonate and silver nitrate react to form solid silver carbonate and a solution of sodium nitrate. a solution containing 3.50 g of sodium carbonate is mixed with one containing 5.00 g of silver nitrate. how many grams of sodium carbonate, silver nitrate, silver carbonate, and sodium nitrate are present after the reaction is complete?