#3 Molar Mass and Grams  Moles
Finding Molar Mass:
1) Using the atomic weight on the periodic table for each element, add up to find the total atomic
weight for each formula.
2) The subscript is only multiplied by the element to its left
3) When you have parenthesis, multiply the number outside the parenthesis times all of the elements
within the parenthesis
Ex. Ni2(SO4)3
Calculate the molar mass of the following:
1. MnCl2
5. Na2CO3
2. N2O5
6. CHCl2COOH
3. K3AsO4
7. Al2(SO4)3
4. Na2B4O7
8. (NH4)3PO4
Using Molar Mass to find grams:
1) Find the molar mass of your substance. For each substance the molar mass = number of grams
1 mole
2) Using your given number of moles, do a conversion and multiply by your molar mass.
3) Make sure that your units cancel!!!
Ex. Find the mass of 0.0240 mole of Ni2(SO4)3
Calculate the mass of 0.354 mole of each of the following:
1. NH3
2. Pt
3. C27H46O
4. Fe3(Fe(CN)6)2
Using Molar Mass to find moles:
1) Find the molar mass of your substance. For each substance the molar mass = ____1 mole_____
Number of grams
2) Using your given number of grams, do a conversion and divide by your molar mass.
3) Make sure that your units cancel!!!
Ex. Find the moles of 3.204 grams of Ni2(SO4)3
Calculate the moles of 50.0 grams of each of the following:
1. BN
2. Tl2SO4
3. Ca(C3H5O2)2
4. C16H18N2O4S
Calculating particles (atoms if an element, molecules if a compound, ions if an ion) from grams:
1) Start with the given grams and using the molar mass, convert to moles using
____1 mole_____
Number of grams
2) Once you have moles, you can go anywhere!!!!! Where do you want to go? To particles.
To convert to particles use Avogadro’s Number 6.02 x 1023 particles (atoms, molecules, etc.)
1 mole
3) Make sure that your units cancel!!!
Ex. Find the molecules (or to be technically correct, the formula units) of 3.204 g of Ni2(SO4)3
Calculate the particles in each of the following grams:
1. 46.0 g Na
2. 68.0 g H2S
3. 46.0 g Na+
4. 117.3 g K+
Calculating mass (grams) from particles:
1) Start with the given particles and using Avogadro’s Number, convert to moles ____1 mole_____
6.02 1023 particles
2) Once you have moles, you can go anywhere!!!!! Where do you want to go? To grams.
To convert to grams, multiply by your molar mass from the Periodic Table: Number of grams
1 mole
3) Make sure that your units cancel!!!
Ex. Find the mass of 9.056 x 1023 formula units of Ni2(SO4)3
Calculate the mass (in grams) in each of the following particles:
1. 6.02 x 1023 atoms Na
2. 3.01 x 1023 formula units Sr(OH)2
3. 1.20 x 1024 molecules CO2
4. 1.50 x 1023 ions Na+