More exercises

A) What is the mass of 0.25 mol aspirin (C9H8O4)?
The formula mass of aspirin is 180 g/mol.
Thus, 0.25 mol ´ 180 g/mol = 45 g
i.e., mass = number of mol ´ molar mass

How many aspirin molecules are in 500 mg aspirin?
There are 6.02 ´ 1023  molecules in 1 mol.
500 mg aspirin is 2.78 ´ 10–3 mol, and thus has 6.02 ´ 1023 molecule/mol ´ 2.78 ´ 10–3 mol = 1.67 ´ 1021 molecules.

B) What is the mass of 2.30 mol acetominophen (Tylenol) (C8H9NO2)?
The formula mass of acetominophen is 151 g/mol.
Thus, 2.30 mol ´ 151 g/mol = 347 g

How many molecules are in 500 mg acetominophen? How many moles are there?
500 mg acetominophen is 3.31 ´ 10–3 mol, and thus has 6.02 ´ 1023 molecule/mol ´ 3.31 ´ 10–3 mol = 1.99 ´ 1021 molecules
0.5 g ¸ 151 g/mol (or ´ D mol/g) = 3.31 ´ 10–3 mol

C) How many Pb molecules are in 1.000 g Pb mass?
1.000 g  ¸ 207.19 g/mol = 4.826 ´ 10–3 mol, which has 6.02 ´ 1023 molecule/mol ´ 4.826 ´ 10–3 mol = 2.91 ´ 1021 molecules.

D) 1 mol oxygen gas is 22.4 L at 1 atm and 0 ºC. How many L does 32 g oxygen gas occupy at 1 atm and 0 ºC? How about 32 g ozone gas? (Hint: How many moles are there in 32 oxygen gas and ozone gas?)
32 g oxygen gas is 1.0 mol, which is thus 22.4 L.
32 g ozone gas (O3) is 0.67 mol, which is 0.67 mol ´ 151 L/mol = 15 L