THE MOLE

Chapter 10: Chemical Quantities

10.1 Measuring Matter

What is a mole? It is the SI unit that measures the amount of substance.

Mole

Masss

Volume

Number of

Particles

Avogadro’s number Simply multiply by 6.02 x 1023

How many moles of magnesium is 1.25 x 1023 atoms of magnesium?

How many atoms are in 2.12 mol of propane? (C3H8)

Multiply by the molecular mass of the substance.

Molar mass: mass (in grams) of one mole

of the substance

The Mass of 1 mole (in grams)

› Molecular mass, molecular weight, formula mass,

formula weight

Equal to the numerical value of the average

atomic mass (get from periodic table)

1 mole of C atoms = 12.0 g

1 mole of Mg atoms = 24.3 g

1 mole of Cu atoms = 63.5 g

Find the molar mass (usually we round to the tenths place)

A. 1 mole of Br atoms = 79.9 g B. 1 mole of Sn atoms = 118.7 g

Mass in grams of 1 mole is numerically equal to the sum of the atomic masses

1 mole of CaCl2 = 111.1 g/mol

1 mole Ca x 40.1 g/mol

+ 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl2

How many grams are in 9.45 mol of dinitrogen trioxide (N2O3)?

How many moles in 92.2 g of iron (III) oxide (Fe2O3)?

The Special Number

22.4

volume varies with changes in temperature and pressure› usually measured at STP (0oC; 101.3 kPa)› at STP, one mole of any gas occupies a

volume of 22.4 L

Determine the volume, in liters, of 0.60 mol SO2 gas at STP.

The density of a gaseous compound containing carbon and oxygen is 1.964 g/L at STP. Determine the molar mass of the compound.

Mass / molecular mass Volume / 22.4 Number of particles /

Avogadro’s number

How many molecules are in 5.0 g of N2O5?

What is the volume of 10.0 g of CO2?

What is the mass of 1.5 x 1025 molecules of C3H8?

Percent by mass of each element in a compound

% mass of element =

Grams of element X

Grams of compoundX 100

9.03 g Mg combine completely with 3.48 g N to form a compound. What is the % composition of this compound?

Calculate the % composition of ethane (C2H6).

Calculate the mass of hydrogen in 350 g C3H8.

Lowest whole number ratio of atoms of an element in a compound.› May or may not be the same

as the molecular formula!› If not given an amount, you may assume it is a 100g.

1. Find moles of each element2. Divide by the smallest number of

moles3. If not a whole number, multiply to

obtain a whole number.

Give the empirical formula for a compound which is 25.9% Nitrogen and 74.1% Oxygen.

Assume it is a 100g sample, so 25.9g N and 74.1g of O

25.9/14 =1.85 moles of N 74.1/16 = 4.63 moles of O 1.85/1.85 = 1 4.63/1.85 = 2.5Double both numbers to get a whole

number ratio…N2O5

Calculate the empirical formula of a compound that is 79.8% C and 20.2% H.

Calculate the molecular formula of a

compound whose molecular mass is 62 g/mol and empirical formula is CH3O.

Compounds with specific numbers of water molecules bound to their atoms are called hydrates.

In the formula, a dot is used to show that water is bonded. Use a prefix to name the hydrate.› Na2CO3 ∙ 10H2O

Sodium carbonate decahydrate

In order to analyze a hydrate, you must first find the number of moles of water associated with one mole of the hydrate. › Heat the sample to drive off the water,

then you can mass the anhydrous compound and determine the moles of water.

A mass of 2.50 g of blue, hydrated copper sulfate (CuSO4· xH2O) is placed in a crucible and heated. After heating, 1.59 g of white anhydrous copper sulfate (CuSO4) remains. What is the formula for the hydrate? Name the hydrate.

An 11.75g sample of a common hydrate of cobalt (II) chloride is heated. After heating, 0.0712 mol of anhydrous cobalt chloride remains. What is the formula and the name of this hydrate?

THE END