Question

Na has an atomic mass of 23.0g and O has an atomic mass of 16.0g. How many grams of Na are needed to completely react with 40.0g of O2?

Answer 1

The grams of Na that are needed to complete to react with 40..0 g of O2 is calculated as below

find the moles of O2 used = mass/molar mass

= 40 g/32g/mol = 1.25 moles

write the reacting equation
4Na+ O2 = 2Na2O

by use of mole ratio between Na to O2 which is 4 :1

the moles of Na = 1.25 x 4 = 5 moles

mass of Na = mass x molar mass

= 5 moles x 23 g /mol= 115 moles