Molar mass = grams per mole (g / mol) Molar mass (M) - mass of one mole of an element or compound
Eg. mass of one atom C = 12 u (atomic mass units) mass of one mole of C = 12 g (grams)
- Every element has it’s own molar mass
- We can use molar mass to convert moles to mass and vise versa
Calculations with molar mass
Formula: m = M * n
Reminder: LOWERCASE AND UPPERCASE MATTERS
m = mass M = Molar mass n = # of moles
Ex. Calculate the mass of 0.50 mol of sulfur
m = 32.06 g / mol * 0.50 mol
= 16.03 g = 16 g (rounded to 2 sig digs)
Round using Significant Digits Ex. How many moles are present in a 10.0 g sample of iron?
n = m / M = 10.0 g / 55.845 g / mol
= 0.17906706 mol Fe
= 0.179 mol
Round using Significant Digits
Molar mass of Compounds
- get the mass of a molecule by adding up the mass of each atom in the molecule
Ex. Find the molar mass of aluminum nitrate, Al(NO)
1 Al = 1 * 26.982 g / mol = 26.982 g/mol
3 N = 3 * 14.007 g/mol = 42.021 g/mol
9 O = 9 * 15.999 g/mol = 143.991 g/mol
To find the total molar mass u need to add all of them up
molar mass = 212.994 g/mol
Ex. Find the molar mass of HSO
2 H = 2 * 1.008 g / mol = 2.016 g/mol
1 S = 1 * 32.076 g / mol = 32.076 g/mol
4 O = 4 * 15.999 g / mol = 63.996 g/mol
Total molar mass = 98.08 g/mol
Homework p234 # 8 - 13 p235 # 31 - 40** p237 # 41 - 50** p239 # 51 - 60** p242 # 61 - 70** p243 # 1 - 16**