How many molecules are in 13 moles of oxygen?

What substance has a mass of 9.5g and volume of 2.1cm^3

Use the periodic table to find the molar mass of each element. molar mass h = g/mol molar mass s = g/mol molar mass o = g/mol

If 22.5 of nitrogen at 748 mm hg are compressed to 725 mm hg at constant temperature. what is the new volume?