MOLESChapter 10

Dimensional Analysis

EXAMPLE 1• What is the mass of 90 average-sized apples if

a dozen apples has a mass of 2.0 kg?• 90 apples x 1 dozen apples x 2.0 kg apples = 15 kg apples 12 apples 1 dozen apples

All you need to know: Conversion factors The process

Given with unit x __________ x ___________

EXAMPLE 2• If a bushel is a dozen apples and a dozen apples

has a mass of 2.0 kg, what is the mass of 0.5 bushel of apples?

0.5 bushel x dozen apples x 2.0 kg = 1.0 kg

1 bushel I dozenEXAMPLE 3• Assume 2.0 kg of apples is a dozen and that each

apple has 8 seeds. How many apple seeds are in 14 kg of apples?

14 kg x 1 dozen x 12 apples x 8 seeds = 672 seeds

2 kg 1 dozen 1 apple

JUST HOW MUCH DO YOU HAVE?

• We measure the amount of something by using one of three different methods

by mass (bird seed) by count (screws) by volume (paint)

• Can you go from one to another?

by MASS: Molar Mass• # of grams of an element in one mole of that element. – atomic mass of the element with the units of g/mol– Get it from the periodic table

Molar mass of compounds: – add the molar mass of every

atom present in the compound

You will use molar mass as a conversion factor to convert between grams and moles.

Elements

CompoundsADD the molar mass

of every atom present in the compound

Find the molar mass on the periodic table round to 0.01 grams/mol

If you know the MOLAR MASS … You can convert between grams and moles!

1 Mole

Mass

Volumeof gas at STP

Representative Particles

Molar mass (g/mol)

By COUNT: Avogadro's NumberHow big is 6.02x1023?

602 000 000 000 000 000 000 000

• If you had Avogadro's number of un-popped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

• If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

• A mole of coke cans would cover the surface of the earth to a depth of over 200 miles.

If you know Avogadro’s number … You can convert between particles and moles!

1 Mole

Mass

Volumeof gas at STP

Representative Particles

Avogadro’s Number

6.02 x 10 23 Molar mass (g/mol)

Atoms – elementsFormula Units - ionic Molecules - covalent

If you know Molar Volume… You can convert between Liters and moles!

1 Mole

Mass

Volumeof gas at STP

Representative Particles

Avogadro’s Number

6.02 x 10 23 Molar mass (g/mol)

Atoms – elementsFormula Units - ionic Molecules - covalent

22.4 L / mol @STP

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