Question

Molecules of oxygen gas have been very difficult to find in space. Recently, the European Space Agency's Herschel Space Observatory has found molecular oxygen in the Orion star-forming complex. It is present at very low concentrations, 1 molecule of oxygen per every million molecules of hydrogen, but it does exist. How many molecules of oxygen would exist in a 3.0 gram sample of hydrogen gas?
(Enter your answer in scientific notation, i.e., 1.00E+10)

Answer 1

Moles of H2 in 3g = weight/molar mass = 3g / 2.016g/mole = 1.488 moles

Each mole contains Na = 6.022*10²³ molecules so, 1.488 moles will have

1.488*6.022*10²³ molecules = 8.96*10²³ molecules of H2

The number of H2 molecules in 3 g sample = 8.96*10²³ molecules of H2

So, 8.96*10²³ = 8.96*10²³ / 10⁶ million molecules of H2

= 8.96*10¹⁷ million molecules of H2

As there is 1 molecule of H2 for every 1 million of H2 we have

8.96*10¹⁷ molecules of O2 in 8.96*10¹⁷million molecules of H2 or 3g of hydrogen sample.

8.96*10¹⁷ = 8.96E+17