Calculate the volume for 1 mole of aluminum and strontium using the molar masses.

Question

Calculate the volume for 1 mole of aluminum, Al, and Strontium, Sr, using the molar masses (Al = 26.982 g/mol and Sr = 87.62 g/mol) and the known densities (Al = 2.70 g/mL and Sr = 2.54 g/mL).

Answer 1

The key is to think through the process from moles to volume. If I know I have 1 mole of a substance, then as long as I can find the molar mass I know the mass of that mole (this works for molecules as well as elements). What is the connection between mass and volume? Density is mass/volume. So I need to look up the density of the material. Once I have that number, I do some algebra to get that Volume = mass/density. At this point I can plug in. Always try to use concepts first, then do algebra, and only at the END should you calculate, otherwise solving one problem does not help prepare you for other problems.

Answer 2

Aluminum

1 mol * (26.982 g/mol) = 26.982 g o Use the molecular weight to convert from moles to grams.

26.982 g / (2.7g / 1 mL) = 9.993 mL o Divide the mass by the density to get the volume. Note that density is

mass divided by volume. The density is 2.70 g / mL. In other words, per each mL of Al, there are 2.70 g of Al.

One mole of Al is equal to 26.982 grams of Al. Since the density of Al is 2.70g/mL, one mL of Al weighs 2.70g; so, 9.993 mL of Al weighs 9.993 * 2.70g = 26.982 g.

Strontium

Similar approach here, too.

1 mol * (87.62 g / mol) = 87.62 g

87.2 g / (2.54g / 1mL) = 34.496 mL

1 mol Sr = 87.62 grams Sr. Since each mL of Sr contains 2.54 grams of Sr,

34.496 mL of Sr contains 87.62 grams of Sr. (34.496 mL * 2.54 g/mL = 87.62 g).