Question

1.A sample of the male sex hormone testosterone, C19H28O2, contains 3.28×10²¹ atoms of hydrogen.

Q) What is the mass of this sample in grams?

2. The octane rating of gasoline is a relationship of the burning efficiency of the given gasoline mixture to the burning efficiency of octane (C8H18). (Figure 1)Like most hydrocarbons, octane reacts with oxygen gas to produce carbon dioxide and water. The unbalanced equation for this reaction is

C8H18(g)+O2(g)→CO2(g)+H2O(g)

Q) After the reaction, how much octane is left? Express your answer with the appropriate units.

Answer 1

1)

use:

number of mol of H atoms = number of atoms / Avogadro’s number

= 3.28*10^21 / 6.022*10^23 mol

= 5.447*10^-3 mol

1 mol of C19H28O2 has 28 moles of H

So,

moles of C19H28O2 = 5.447*10^-3 mol / 28

= 1.945*10^-4 mol

Molar mass of C19H28O2,

MM = 19*MM(C) + 28*MM(H) + 2*MM(O)

= 19*12.01 + 28*1.008 + 2*16.0

= 288.414 g/mol

use:

mass of C19H28O2,

m = number of mol * molar mass

= 1.945*10^-4 mol * 2.884*10^2 g/mol

= 5.61*10^-2 g

Answer: 5.61*10^-2 g

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