Chem I
Atomic and Molecular Mass/ Molar Mass in-class notes
Atomic mass (atomic weight)
Molecular mass (molecular weight)
both can be expressed in amu, or g/mol
When it is expressed in g/mol, it is called Molar Mass (mass of 1mole in grams)
Atomic mass of Al = 27.0 amu; Molar mass of Al = _________g/mol
Molecular mass of H2O = 18.02 amu; Molar mass of H2O = _________ g/mol
Practice Problems
1. What is the atomic mass of an element if 3.457mol of it weighs 355.72g? Check with the
periodic table what this element is.
____________
______
2. What is the molecular mass of a compound if 0.3148mol of it weighs 20.1472g?
____________
Molecular formula of a compound can be used to find the mole ratio of elements in it.
H2O – the mole ratio of H to O = 2 : 1; for every 2mol of H there is 1mol of O in water
P2O5 – the mole ratio of P to O = _____ : _____
3. Element “X” is 60.0% of the oxide XO2 by mass. What is the atomic mass of X?
_____________
4. 19.334g of element “Y” react with 2.4395g of oxygen to make a compound Y2O3.
What is the atomic mass of “Y”?
_____________