Question

1) A sample of C3H8 has 7.76 × 1024 H atoms. How many carbon atoms does the sample contain? What is the total mass of the sample?

2) Calculate the molar mass of each compound given below. Keep at least one decimal place in atomic masses from the periodic table.

a. KBr g/mol:

b.Na2s g/mol:

3) A chemist requires 0.885 mol Na2CO3 for a reaction. How many grams does this correspond to?

Answer 1

3 C atoms --------------------------------> 8 H atoms

X C atoms -------------------------------> 7.76 × 10^24 H atoms

X = 3 x 7.76 × 10^24 / 8

X = 2.91 x10^24

number of carbon atoms = 2.91 x10^24

moles of C3H8 = ( 7.76 × 10^24 / 6.023 x 10^23 ) x 1/ 8

                       = 1.61

total mass of the sample = 1.61 x 44

                                      = 70.9 g

2)

KBr molar mass = 119.0 g / mol

Na2S molar mass = 78.0 g / mol

3)

mass = 0.885 x 106

        = 93.8 g