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# Mass-Mole Stoichiometry

## Calculations involving conversions of mass to moles and moles to mass

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Molar Mass and Conversions

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#### Molar Mass

Molar mass is the mass of one mole of representative particles of a substance in grams per mole (g/mol). Based on the periodic table, what's the molar mass of carbon? How many atoms of carbon does that contain?

You can also find the molar masses, or molecular mass, of compounds. Take CO2, for example - you can use the molar masses of carbon and oxygen atoms to find the total mass. What is the molecular mass of carbon dioxide?

#### Conversions between Mass and Moles

You can easily convert mass to moles and moles to mass using molar mass!

For example, the molar mass of CaCl2 is 110.98 g/mol. How many grams are there in 2.00 moles of calcium chloride? (Highlight the following to check your answer: 222 grams)

What is the molar mass of chromium if 0.560 moles has a mass of 29.1 grams?

Using the following balanced equation, how many moles of hydrogen fluoride are required to react completely with 75.0 g of tin (Sn)? The molar mass of tin is 118.69 g/mol.

$\text{Sn}(s)+2\text{HF}(g) \rightarrow \text{SnF}_2(s)+\text{H}_2 (g)$

#### Conversions between Mass and Number of Particles

[Figure1]

Now we can pull together a number of conversion factors - we know how to convert between moles and the number of representative particles (i.e. atoms, molecules, ions) and between moles and mass. So now, we can convert from particles to mass!

How many molecules is 20.0 g of chlorine gas (Cl2)? The molar mass of chlorine gas is 70.90 g/mol.

What is the mass of 1.70 x 1023 molecules of water? The molar mass of water is 18.02 g/mol. (Highlight the following to check your answer: 5.089 g)