Moles

Stoichiometry

The study of quantitative relationships between the

amounts of reactants used and products formed by a chemical

reactions; it is based on the law of conservation of mass.

MoleThe SI base unit used to measure the amount of a

substance.

Avogadro’s NumberThe number of representative particles in a mole, and can be

rounded to three significant digits: 6.02 X 1023

molecules/mol (atoms/mol)(formula units/mol)

(electrons/mol)

Molecule Forms when two or

more atoms covalently bond.

A number smaller than 1.0 x 1019 or greater

than 1.0 x 1026 should not be found in front of molecule or atom.

To find the number of molecules it takes to equal a certain number of moles. Take the number of moles

given and multiply by Avogadro’s number.

How many molecules of Sucrose is in 3.50 moles of

Sucrose.

3.50 mol Sucrose X 6.02x1023 molecules/mol =2.11x1024molecules of Sucrose

How many molecules of Sodium Hydroxide is in 4.80 moles of Sodium Hydroxide?

4.80 mol Sodium Hydroxide X

6.02x1023molecules/mol

=2.89x1024 molecules of Sodium Hydroxide

To find the number of moles it takes to equal a

certain number of molecules. Take the

number of molecules given and divide by Avogadro’s

number.

How many moles of Sucrose is in 3.54x1024 molecules of Sucrose.

3.54x1024 molecules of Sucrose ÷

6.02x1023 molecules/mol

=5.88 moles of Sucrose

How many moles of Sodium Hydroxide is in 5.63x1024

molecules of Sodium Hydroxide.

5.63x1024 molecules NaOH ÷6.02x1023 molecules/mol=9.35 moles of NaOH

A number smaller than 0.0001 or greater than

10,000 should not be found in front of grams.

Atomic MassThe weighted average mass of the isotopes

of that element.

Mass Number

The number of protons plus the number of

neutrons found in that element

Molar MassThe mass in grams of one mole of any pure

substance.

g/mol

To find the number of grams of substance. Take the number of moles given

and multiply by the substance’s molar mass.

Find the mass of 3.2 moles of Butane needed to

complete the reaction.

3.2 mol of Butane X

58.14 g/mol

=186.05 g of Butane

Find the mass of 4.5 moles of Pentanol needed to complete the reaction.

4.5 mol Pentanol X86.15 g/mol=387.68 g of Pentanol

To find the number of moles of substance. Take the number of grams given

and divide by the substance’s molar mass.

Find the moles of 23 g of water needed to complete

the reaction.

23 g water ÷18.02 g/mol=1.28 mol of water

Find the moles of 112 g of Hydrochloric Acid needed to complete the reaction.

112 g of Hydrochloric Acid ÷36.46 g/mol=3.07 mol of Hydrochloric Acid

To find the number of moles of an element in a compound, multiply the moles of the compound

with the ratio of number of elements to 1 mol of

compound.

How many moles of Fluorine is found in 5.50 moles of

Freon (CCl2F2).

5.50 mol CCl2F2 X

2 mol F atoms/1 mol CCl2F2 = 11.0 mol F atoms

How many moles of Oxygen is found in 4.75 moles of

Glucose (C6H12O6).

4.75 mol C6H12O6 X 6 mol O atoms/1 mol C6H12O6 = 28.5 mol O atoms

Molecular MassThe mass of the

molecule found by adding the mass of each atom in the

molecule.

To find the molar mass of compound, for each element multiply the

number of element with the ratio of the molar mass of the element to 1 mol of the element. Add all the grams

up.

What is the molar mass of Potassium Chromate K2CrO4.2molK X 39.1gK/1molK=78.2g

1molCr X 52gCr/1molCr=52g

4molO X 16gO/1mol=64g

78.2g + 52g + 64g=194.2g K2CrO4

What is the molar mass of Sodium Hydroxide NaOH.

1molNaX22.99gNa/1molNa

=22.9g

1molH X 1.01gH/1molH=1.01g

1molO X 16gO/1mol=16g

22.9g+1.01g+16g=39.9gNaOH

To find the moles of a compound, take the mass

of the compound and divide by the molar mass of

the compound.

How many moles are there of 47g of water?

47g of water ÷

18.02 g/mol of water

= 2.61 mol of water

How many moles are there of 21g of Benzene?

21g of Benzene ÷

78.12 g/mol of Benzene

= 0.27 mol of Benzene