Question

Calculate the mass in gram of calcium chloride formed when 20 g of calcium combines with 35.5 g of chlorine gas.

Answer 1

start off by writing the equation:
Ca+ 2 Cl-> CaCl2

M Ca= 20 g/mol. M Cl= 35.5 g/mol
therefore u have 1 mol of calcium and 1 mol of chloride but u have to take ratios into consideration to find the limiting reactant

number of mol of Ca/ 1 (1 being the # of Ca in the equation) = 1 (since u have 1 mol of Ca from the given).
number of mol of Cl /2 = 0.5 ====> Cl is the limiting reactant

u then proceed by saying that number of mol of Cl/2 = number of mol of CaCl2 formed/1 (1 equivalent of CaCl2 is formed in the equation) therefore u have 0.5 mol of CaCl2 formed in total.

since n= m/M => 0.5= m/91 (91 being the molar mass of CaCl2 35.5*2 + 20)
u get m= 91*0.5= 45.5 g