How to Calculate Molar Mass
Molar Mass = the mass of 1 mole of a compound.
➞ often referred to as "molecular weight" or "formula mass."
➞ just like an element's atomic mass (i.e. 12.01 g/mol for C), compounds and molecules have a molar mass.
Let's do a molar mass calculation example...
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How Do You Find Molar Mass?
We'll see how to calculate the molar mass in the following example...
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ex: A chemical dye has the formula C10H6O3
Calculate the molar mass of this compound.
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answer:
➞ we'll need to use the Periodic Table:
10 C = 10 (12.01) = 120.10
6 H = 6 (1.01) = 6.06
3 O = 3 (16.00) = 48.00
So, the total amounts to the molar mass of C10H6O3 =
= 174.16 g/mol
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How to Find Moles from Grams
What if we wanted to learn how to find moles from grams?
Let's take a look below...
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ex: A chemical dye has the formula C10H6O3
How many moles of C10H6O3 are contained in 1.56 x 10-2 g of the dye?
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answer:
➞ "start with what you're given, and put it over 1" (remember?)...
(1.56 x 10-2 g / 1) . (1 mole / 174.16 g) =
= 8.96 x 10-5 mol C10H6O3
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Grams to Molecules Calculations
Though not as common as grams-to-moles and moles-to-grams conversions, knowing how to do grams-to-molecules calculations is also extremely important.
Check out the grams-to-molecules example below.
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ex: Isopentyl acetate, C7H14O2 , gives bananas their smell.
If a bee sting releases 1 µg of the compound, how many molecules is this?
How many carbon atoms is this?
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answer:
➞ Before we start, we'll need the molar mass:
7 C = 7 (12.01) = 84.07
14 H = 14 (1.01) = 14.14
2 O = 2 (16.00) = 32.00
So, the total amounts to the molar mass of C7H14O2 =
= 130.21 g/mol
➞ Next, we'll convert 1 µg to molecules in 3 steps.
"Start with what you're given, and put it over 1..."
Okay, lastly we just have to count the number of carbon atoms contained in a single molecule of isopentyl acetate (I.A.):
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How to Calculate Mass Percent
Mass Percent = an element's percentage of the total mass of a compound containing the element.
➞ also called percent composition or mass percent composition.
➞ let's use Isopentyl Acetate, C7H14O2 , from the previous example.
See the image below.
Here's how we calculate mass percent:
As you can see, isopentyl acetate is:
64.6% carbon by mass,
24.5% oxygen by mass, and
10.9% hydrogen by mass.
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100% total
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Next time, in our 3rd set of video notes from SECTION 3 - Chemical Quantities and Stoichiometry,
We'll talk about How to Determine Empirical and Molecular Formula...