Question

Some hydrogen gas is collected over water at 20 degrees celsius (use R63). The partial pressure of hydrogen is 742.5 torr. What is the total pressure at the time the gas was collected?

Answer 1

Well, you need to know the atomic weight of Platinum (Pt) and the number of atoms per mole. The answer to the former is 195.084 g/mole and the latter is 6.023 * 10^23 atoms/mole. Then, multiply everything as shown below:

Number of atoms = (1 g) * (1/195.084 g/mole) * 6.023 * 10^23 atoms/mole

Number of atoms = 3.087 * 10^21 atoms

Note, I’ve included units on everything and you can see that they all cancel except for atoms. Dragging the units along can be a pain but it is a great way to check that they way the numbers are being combined is correct.