Show me how to calculate the mass of 20.0 moles of He?
1 mole He has the mass of 4.003 g (from the periodic table). So 20 moles will have a mass of ???
To calculate the mass of a certain number of moles of a substance, you need to know its molar mass. The molar mass is the mass of one mole of a substance and is usually given in grams per mole (g/mol).
To find the molar mass of helium (He), you can look it up in the periodic table. The atomic mass of helium is approximately 4.00 g/mol.
Once you have the molar mass of helium, you can use the following formula:
Mass (g) = Number of Moles × Molar Mass (g/mol)
For your case, you have 20.0 moles of helium. Plugging this value into the formula, we get:
Mass (g) = 20.0 moles × 4.00 g/mol
Now, we can calculate the mass:
Mass (g) = 80.0 g
Therefore, the mass of 20.0 moles of helium is 80.0 grams.