Ca + F2 --> CaF2
The mass of CaF2 that results from the reaction of 3.00 g of calcium and 2.00 g of fluorine is 4.02 g. What is the percent yield? (Atomic weights: Ca = 40.08, F = 19.00).
You have a limiting reagent problem here.
1.Convert grams to mols. Mols = g/molar mass.
2. Convert mols Ca to mols CaF2. Convert mols F2 to mols CaF2.
3. The smaller number of mols of CaF2 will be the one to pick and the reagent with that result will be the limiting reagent.
4. Using the smaller number of mols CaF2, convert to grams CaF2. That is the theoretical yield.
5.
%yield = [(actual yield/theoretical yield)]*100
Note that the acutal yield is 4.02 g.
To find the percent yield, we need to compare the actual yield (the mass of CaF2 that results from the reaction) to the theoretical yield (the maximum amount of CaF2 that can be formed based on the balanced equation and the amount of reactants given).
Step 1: Calculate the moles of calcium (Ca) and fluorine (F2) present:
Moles of Ca = mass of Ca / molar mass of Ca = 3.00 g / 40.08 g/mol = 0.0748 mol
Moles of F2 = mass of F2 / molar mass of F2 = 2.00 g / 19.00 g/mol = 0.1053 mol
Step 2: Determine the limiting reactant:
To find the limiting reactant, we compare the mole ratio of Ca to F2 in the balanced equation:
2 moles of F2 are required for 1 mole of Ca.
So, we need to multiply the moles of Ca by 2 to get the equivalent moles of F2: 0.0748 mol x 2 = 0.1496 mol.
Since the moles of F2 (0.1053 mol) are less than the equivalent moles of F2 needed (0.1496 mol), Ca is the limiting reactant.
Step 3: Calculate the theoretical yield of CaF2:
Using the balanced equation, we know that 1 mole of Ca reacts with 1 mole of F2 to produce 1 mole of CaF2.
Therefore, the moles of CaF2 produced will be equal to the moles of Ca (limiting reactant), which is 0.0748 mol.
Next, calculate the mass of the theoretical yield of CaF2:
Mass of CaF2 = moles of CaF2 x molar mass of CaF2
= 0.0748 mol x (40.08 g/mol + 2 x 19.00 g/mol)
= 0.0748 mol x 78.08 g/mol
= 5.83 g (rounded to 3 significant figures)
Step 4: Calculate the percent yield:
Percent yield = (actual yield / theoretical yield) x 100
= (4.02 g / 5.83 g) x 100
= 68.98% (rounded to 3 significant figures)
Therefore, the percent yield of CaF2 in this reaction is approximately 68.98%.