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 (6.02214131023) 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

Step 2:

(b) CFCl3 = 1 Carbon + 1 Fluorine + 3 Chlorine

[1(12.011 g/mol)] + [1(18.988 g/mol)] + [3(35.453 g/mol)] = 137.358 g/mol

38.0 grams (1 mol /137.358 grams) = 0.277 moles CFCl3

0.277 moles CFCl3 (3 moles Cl / 1 mole CFCl3) = 0.830 moles Cl

Chlorine = 35.453 grams/mole

0.830 moles (35.453 grams / 1 mole) = 29.4 grams of chlorine in 38.0 grams of CFCl3