How many grams of Cl are in 38.0 g of each sample of chlo- rofluorocarbons (CFCs)?
(a) CF2Cl2
(b) CFCl3
(c) C2F3Cl3
(d) CF3Cl
Solution 67P
First, you need to find how many moles of chlorine are in 38.0g of each of these compounds:
Cl is 35.453 grams/mol
C is 12.011 grams/mol
F is 18.988 grams/mol
Step 1:
(a) CF2Cl2 = 1 Carbon + 2 Fluorine + 2 Chlorine
[1(12.011g/mol)] + [2
(18.988 g/mol)] + [2
(35.453 g/mol)] = 120.893 g/mol
So for this particular compound, one mole weighs 120.893 grams
(or in other words 6.0221413 x 1023 of these molecules would weight 120.893 grams)
Now find how many moles of the compound it takes to weigh 38.0 grams:
38.0 grams x (1 mol /120.893 grams) = grams cancel and we get 0.314 moles
( 0.314 moles means we have 0.314 (6.0221413
1023) molecules of compound
In each molecule of compound (CF2Cl2) we have 2 Chlorine molecules
therefore...
In each mole of compound (6.0221413 1023 molecules of CF2Cl2)
we have 2 moles of Chlorine (2 x [6.02214131023] molecules of Cl)
So,
In 0.314 moles of CF2Cl2 there are (2 x 0.314) moles of Chlorine
2 x 0.314 = 0.628 moles of Chlorine in 38.0 grams of CF2Cl2
Chlorine = 35.453 grams/mole
So...
0.628 moles x (35.453 grams / 1 mole) = 22.3 grams of chlorine in 38.0 grams of CF2Cl2
Just to help clarify...
Because there are 0.314 moles of CF2Cl2, there are 2 0.314 moles of Fluorine and 1
0.314 moles of carbon in the compound as well...
2 0.314 moles = 0.628 moles of Fluorine
Fluorine = 18.988 grams/mol
So...
0.628 moles x (18.988 grams / 1 mole) = 11.92 grams of fluorine in 38.0 grams of CF2Cl2
And 1 0.314 moles = 0.314 moles of Carbon
Carbon is 12.011 grams/mol
So...
0.314 moles (12.011 grams / 1 mole) = 3.77 grams of carbon in 38.0 grams of CF2Cl2
In total, in 38 grams of CF2Cl2 there are:
22.3 grams of chlorine
11.92 grams of fluorine
3.77 grams of carbon
= 38.0 grams total