Aqueous sodium sulfide reacts with aqueous calcium chloride to make a solid. The % yield is 85%. Calculate the amount of each reactant needed to actually make 3.0g of the solid.
I should point out here that since CaS is soluble in water that extenuation circumstances will be necessary (temperature, saturation points, etc) in order to produce a solid.
% yield = 100*(actual/theoretical)
85% = 100*(3.0/theoretical)
Theoretical = 3.0/0.85 = about 3.6 grams.
CaCl2 + Na2S ==> CaS + 2NaCl
So how much of each reagent is needed to make about 3.6g of CaS.
To calculate the amount of each reactant needed to produce 3.0g of the solid product, we need to use stoichiometry and the percent yield.
Step 1: Write and balance the chemical equation for the reaction:
Na2S(aq) + CaCl2(aq) → CaS(s) + 2NaCl(aq)
Step 2: Determine the molar mass of the solid product, CaS:
The molar mass of CaS is calculated by adding the molar mass of calcium (Ca) and sulfur (S):
Molar mass of CaS = 40.08 g/mol (Ca) + 32.07 g/mol (S) = 72.15 g/mol
Step 3: Calculate the moles of the solid product, CaS:
Moles of CaS = Mass of CaS / Molar mass of CaS = 3.0 g / 72.15 g/mol = 0.0415 mol
Step 4: Determine the limiting reactant:
To find the limiting reactant, we compare the stoichiometric ratio of the reactants to the desired product. From the balanced equation, we can determine that 1 mole of CaS is produced for every 1 mole of Na2S and 1 mole of CaCl2.
As the reaction proceeds, the reactant that produces the least moles of CaS will be the limiting reactant. In this case, we need to compare the moles of Na2S and CaCl2 to determine the limiting reactant.
Step 5: Calculate the moles of Na2S:
Moles of Na2S = moles of CaS = 0.0415 mol
Step 6: Calculate the moles of CaCl2:
Moles of CaCl2 = 2 × moles of CaS = 2 × 0.0415 mol = 0.083 mol
Step 7: Determine the actual yield of CaCl2:
Actual yield = percent yield / 100 × theoretical yield
Actual yield of CaCl2 = 85 / 100 × 0.083 mol = 0.0706 mol
Step 8: Calculate the mass of Na2S using the stoichiometry of the balanced equation:
Mass of Na2S = Number of moles × Molar mass of Na2S
Mass of Na2S = 0.0415 mol × (2 × 22.99 g/mol + 32.07 g/mol) = 2.45 g
Step 9: Calculate the mass of CaCl2 using the stoichiometry of the balanced equation:
Mass of CaCl2 = Number of moles × Molar mass of CaCl2
Mass of CaCl2 = 0.0706 mol × (40.08 g/mol + 2 × 35.45 g/mol) = 7.88 g
Therefore, to actually produce 3.0g of the solid product, you would need approximately 2.45g of Na2S and 7.88g of CaCl2 as reactants.