Chemistry: Atomic Mass and Moles

Question

1) Calculate the molar mass (include proper units) for the following compounds.

a) NaCl

b) Al2O3

2) How many molecules are there in a 1.25 mol sample of NO2 ?

3) How many moles are in 24.5g of H2SO4(aq) ?

4) What is the mass of 3.00 x 10 20 atoms of iron?

5) What is the mass in grams, if you have a sample of glucose (C6H12O6) that has 7.224 x 10^24

atoms of Oxygen?

Answer 1

1) Molar mass is the mass of each element multiplied by the subscript and added together.

a) NaCl (Na = 22.990 + Cl = 35.453 = 58.353g/mol)

b) Al2O3 (Al = 2*26.982 + O = 3*16 = 101.96g/mol)

2) To convert from Moles to Molecules we use Avogadros # 6.022x10²³

1.25 mol NO2 x 6.022 x 10²³ molecules = 7.527 x 10²³ molecules

1 mole

3) Find the molar mass of H2SO4 like we did above which is

24.5g H2SO4 x 1 mole = 0.250 moles H2SO4

98.079 g

4) To convert from atoms to mass you need to go to moles using Avogadro's number and then use molar mass.

3.00 x 10²⁰ atoms of iron x 1 mole x 55.845 g = 0.0278 g Fe

6.022x10²³ 1 mole

5) What is the mass in grams, if you have a sample of glucose (C6H12O6) that has

7.224 x 10²⁴ atoms of Oxygen x 1 atom glucose x 1 mole glucose x 180.156 g = 360.19 g glucose

6 atoms O 6.022x10²³ atoms 1 mole glucose