Finding the number of moles

Finding the number of moles

Open Ended

Find the gram formula mass of KBr?

Multiple Choice

How many units are present in a dozen?

• 3

• 6

• 12

• 24

Multiple Choice

Use google to determine how many units are represented in a ream.

• 100

• 500

• 50

• 1000

A mole represents units in chemistry

• the quantity of anything that has the same number of particles found in 12.000 grams of carbon-12.  A mole is a unit of measurement just like a dozen or a ream.  It means 6.02 x 10^23 unit

Steps to finding the number of moles

Step 1: Find the gram formula mass (either calculate or obtain from the problem) Step

2: Label the knowns provided by the problem (including the gram formula mass)

Step 3: Determine the unknown

Step 4: Substitute

Step 5: Solve

Example #1

• What is the mass of 3 moles of potassium nitrate [KNO3]? (gram formula mass = 101 g/mol)

• mole = 3 moles (we know this because its unit is moles.

• gram formula mass (gfm) = 101 g/mol

• unknown = mass

• Substitute and Solve:

Multiple Choice

How many moles are in 270. g of dinitrogen pentoxide [N2O5]? (gram formula mass = 108 g/mol)

What is the number of moles?

• 270

• 108

• unknown

Multiple Choice

How many moles are in 270. g of dinitrogen pentoxide [N2O5]? (gram formula mass = 108 g/mol)

What is the gram formula mass?

• 270

• 108

• unknown

Multiple Choice

How many moles are in 270. g of dinitrogen pentoxide [N2O5]? (gram formula mass = 108 g/mol)

What it the unknown?

• mass

• moles

• gram formula mass (gfm)

Example #2

• How many moles are in 270. g of dinitrogen pentoxide [N2O5]? (gram formula mass = 108 g/mol)?

• gram formula mass = 108

• mass = 270

• unknown = moles