Answer:
Step 1: CCl4 + 2(HF) --> CCl2F2 + 2(HCl)
Step 2: CCl2F2: 121 g/mol CCl4: 154 g/mol
Step 3: 25.1 g
Step 4: 50.6%
Explanation:
Step 1: Write a balanced equation
The unbalanced form of the equation is just what the problem tells you in the beginning: Freon is synthesized from CCl4 with HF. HCl is also made as a byproduct. This means that our equation will be:
CCl4 + HF --> CCl2F2 + HCl
This equation is clearly unbalanced, as there are different numbers of atoms on either side.
Starting Atoms:
(The arrow shows what is on either side of the reaction arrow)
C: 1 --> 1
Cl: 4 --> 3
H: 1 --> 1
F: 1 --> 2
Let's first try adding a coefficient of 2 to HCl.
Coefficient One:
C: 1 --> 1
Cl: 4 --> 4
H: 1 --> 2
F: 1 --> 2
However, now the H (as well as the F) are out of balance on the left side of the arrow. Luckily, putting a coefficient of 2 in front of HF balances the equation completely.
Coefficient Two:
C: 1 --> 1
Cl: 4 --> 4
H: 2 --> 2
F: 2 --> 2
This means that the balanced equation is:
CCl4 + 2(HF) --> CCl2F2 + 2(HCl)
Step 2: Calculate the Molar Masses
To find the molar masses, we simply add up all of the individual atomic masses.
CCl2F2: (12.0)+2(35.5)+2(19.0) = 121 g/mol
CCl4: (12.0)+4(35.5) = 154 g/mol
Step 3: Calculate the Theoretical Yield in Grams
We can now put together the previous steps. You typically need to figure out which molecule is the limiting reactant, but as they have only given you one initial mass, we can assume that CCl4 will be the LR. Essentially, the next step is to do several conversions to turn this reactant gram value into a product value. We will go from g of reactant to moles of reactant (using its molar mass), then to moles of product (with the balanced equation), and finally, to grams of product (using the other molar mass):
[tex]\frac{31.9g}{1} *\frac{1molCCl4}{154g} *\frac{1molproduct}{1molCCl4} *\frac{121g}{1molproduct}=25.1g[/tex]
This results in 25.1 g of product as our theoretical yield. This amount is the absolute maximum amount of product that could possibly be made from the amount of starting materials that we put in.
Step 4: Calculate the Percent Yield
This is probably the easiest step. All we have to do is use the following equation, and we will have our answer:
[tex](\frac{created}{expected})*100=yield[/tex]
The created value is what is given in the problem itself: 12.7 g
The expected amount is our theoretical yield value that we just calculated: 25.1 g
Substituting this into the equation, our percent yield is just over half at about 50.6%. Keep in mind that a yield of 100% is just about impossible due to human error, things being left on glassware, etc.
