math of chemistry

Math Of Chemistry

In the laboratory you will be dealing with masses and volumes, but in chemistry problems you will be dealing with moles, and molecules. You need a way to connect the two!

This unit is about finding the “# of things” (molecules/moles) by using macroscopic means:Volume and mass!

How does this relate to real life:

Lets take the following example. I ask you to bake me 10 apple pies. Each apple pie requires 6 whole apples. You must get the correct amount of apples but without counting them atthe supermarket!!! How do you do it??? HINT: Each apple weighs 100grams

We can use the same approach with elements in compounds. Since we can’t count individual elements we need to have a system that will allow us to determine how much of each element/compound we have without direct counting.

We can use the concept of a MOLE!!!

Just like we set 1 dozen = 12Just like we set 16 ounces = 1 lbsJust like we set 1 year = 365 daysJust like we set 1 day = 24 hours

You get the point. A mole is equal to a certain quantity of something. Lets get more specific…

What is a mole?

How does it relate the following quantities:

1. Volume of a gas

2. Molecules/atoms of a substance

3. Gram formula mass (this one is tricky, and we need to go into moredetail on what GFM is!)

Gram formula mass

In the laboratory we measure mass in grams. We are UNABLE to measure individual masses of atoms in our high school laboratory. When we measure the mass of compounds/elements we are actually measuring 1020 to 1023 units of these substances.

There is a standard for measurement for each element:

6.02 x 1023 units of a substance = gram formula mass6.02 x 1023 units of a substance = 1 mole of a substanceTherefore: 1 mole of a substance = gram formula mass

Definition of Gram Formula Mass:

How do I find the gram formula mass of a substance (compound or element)?

Practice finding gram atomic masses of Different substances

Review So Far: Key points

One set of problems you will see in this unit will ask you to find the number of moles, the volume, the mass, or the number of moleculesof a substance based on a piece of information given. For example you may be asked to find the volume of 1 mole of a gas. Or the mass of 3 moles of a substance. Finally you may be asked to find the number of moles of 5 x 1015 molecules. (These are just a few examples). Thereare two methods to do this. One of them is on the next page. YOU MUST MEMORIZE THIS OR THE CONCEPT BEHIND THIS CHARTIN ORDER TO MASTER THE REST OF THIS UNIT!

Mole Conversions

Grams Moles

Liters Moles

Molecules Moles

Grams Liters

Molecules Grams

Mole CrutchVolumeIn Liters

VolumeIn Liters

Mass ingrams

Mass ingrams

molecules

molecules

MOLECentral station

Divide by 22.4 Liters

Divide by formula mass

Divide by 6.02 x 1023

Multiply by 22.4 Liters

Multiply by formula mass

multiply by 6.02 x 1023

You must always go through the mole center to get anywhere!!!!!

Using gram formula mass for percent composition problems

Percent Composition and hydrates

Finding the Empirical Formula of a Substance

Finding the Molecular formula of a Substance

The mole ratio in balanced equations, never forget it!!!

Moles of AUse mole Ratio inBalancedequation

Moles of B

Using the mole ratio and the mole crutch:Putting everything together!

Grams of A

Use mole conversion

Moles of AUse mole Ratio inBalancedequation

Moles of B

Use mole conversion

Grams of B

Limiting Reagent Problems

Limiting Reagent Problems

Percent Yield

Molarity and Solution Terms

Solution Stoichiometry