chemistry help?

Question

twenty milliliters of a .50M solution of silver nitrate are added to 50 milliliters of a .20M solution of calcium chloride. which reactant is in excess and what is the mass of the precipitate formed in the reaction? when evaporated, what is the mass of the remaining solid?

Answer 1

The reaction is 2AgNO3 + CaCl2 ---> Ca(NO3)2 + 2AgCl. Two moles of AgNO3 react with one mole of CaCl2.

0.02L * 0.5 mole/L = 0.01 moles of AgNO3
0.05L * 0.2 mole/L = 0.01 moles of CaCl2

Since you need half as much CaCl2 as AgNO3, CaCl2 is in excess. The precipitate is AgCl, and the no of moles of it will be the same as the no of moles of AgNO3, or 0.01 moles. The molecular mass of AgCl is 143.3 g/mole, so .01 mole is 1.43 g of precipitate. What is left in solution is half of the CaCl2, or 0.005 moles at 111 g/mole giving 0.55 g of dissolved CaCl2. When the water is evaporated, the mass that remains is that of the precipitate plus the dissolved solids, or 1.43 g AgCl + 0.55 g CaCl2 = 1.98 g