Measurement of Matter: The Mole

How do you measure matter?

What are the three different ways weCan measure things?

countmassvolume

CONVERSIONSA pair Equals

A dozen equals1 minute equals how

many seconds?1 hour equals how

many minutes

21260

60

CHEMICAL QUANTITIES

http://www.youtube.com/watch?v=1R7NiIum2TI

THE MOLEHow do we count matter?

Composed of atoms, molecules and ionsThe mole is an equality that describes the

number of particles in a substance

6.02 x 10 23 particles,atoms ect.. = 1 mole ( avogadro’s number)

Practice ProblemHow many moles of magnesium is 1.25 x 1023

atoms of magnesium

1. Start with what you know

1.25 x 10 23 atoms of Mg 1 mole of Mg6.02 X 10 23 atoms of mg

= 0.208 mol Mg

REVIEW1. How many atoms are in 1.14 mol of SO3

2. How many moles are in 4.65 x10 24 molecules of NO2

How many atoms are in 1.50 mols of Na

determine the number of moles in 4.96 x 10 24 molecules glucose

Mass of a Mole in an elementThe atomic mass of an element expressed in

grams is the mass of a mole of the element = molar mass

Ex. Carbons molar mass = 12.0g Hydrogens molar mass = 1.0 g

The molar masses of any two elements contains the same number of atoms

12.0 g of carbon = 1 mol = 6.02 x 10 23 particles

1.0 g of hydrogen = 1 mol = 6.023 x 10 23 particles

Mass of a mole of a compoundMust know the formula of the compound firstEx. SO3

1 sulfur ( 1 x 32.1) 32.1 amu3 oxygen ( 3 x 16.0) = 48.0 amu

molar mass = 48.0 + 32.1 = 80.1 amu1 mol has a mass of 80.1 amu

Review

What is the molar mass of PCl3

How many atoms are in 1.50 mols of Na

MASS/MOLE RELATIONSHIPSRemember: to calculate molar mass you

must know the number of grams of each element in one mole of the compound and add the masses of all the elements of the compound

You can use molar mass of an element or compound to convert between the mass of a substance and the moles of a substance

calculationsCalculate the mass of 3.00 mol of NaClMolar Mass of NaClNa = 23.9Cl = 35.4Total = 53.9 g

3.00 mol 54.9 g NaCl

1 mol NaCl

Converting mass to molesHow many moles of Iron (III) oxide are

contained in 92.2 g of Fe2O3

92.2 g of Fe2O3 X 1 mol of Fe2O3

160 g Fe2O3

= .58 mol Fe2O3

GRAMS TO MOLECULESHow many grams are in 4.65 x10 24 molecules

of NO2

Review QuizHow many grams are in 4.65 x10 24 molecules

of NO2

What is the molar mass of PCl3

What is the mass of 2.25 mol of NaCl

QUIZ

How many grams does 4.3 x 1021 molecules of MgCl2 have

PERCENT COMPOSITIONPercent Composition – the relative amounts

of the elements in a compound

Consists of a percent value for each different element in a compound

CALCULATIONSThe percent by mass of an element in a

compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%

% mass of element = mass of element x 100

mass of compound

PracticePropane (C3H8), the fuel commonly used in

gas grills, is one of the compounds obtained from petroleum. Calculate the percent composition of propane

%C = 36.0g (3 X 12) x 100 = 81.8% 44.0g

%H = 8.0g x 100 = 18% 44.0g

REVIEW QUIZPropane (C3H8), the fuel commonly used in

gas grills, is one of the compounds obtained from petroleum. Calculate the percent composition of propane

Calculate the number of moles in 0.50 g of sodium bromide (NaBr)

Review Quiz; % compositionWhat is the percent composition of baking

soda NaHCO3

Empirical/Molecular FormulasThe lowest whole number ratio of the atoms

of the elements in a compound

Molecular formula H2O2Empirical formula HO

Determining empirical formulasA compound is analyzed and found to contain

70.9% potassium and 29.1%sulfer. What is the empirical formula of the compound?

Percent you can assume 100

70.9 g x 1 mol K = 1.8molK 39 g K

29.1 g x 1 mol S = .91 mol S

32 g S

HINT:% TO MASSMASS TO MOLEDIVIDE BY SMALLESTMULTIPLY TILL WHOLE

Divide each molar quantity by the smaller number of moles 1.85/.91 = 2 K 1. = .91/.91 = 1 S

K2S

MOLECULAR FORMULASMolecular formulas can be determine by

empirical formulas.

First calculate the empirical formula massDivide molecular mass by formula massMultiply each subscript in your formula by

the factor

Practice problemA compound with an empirical formula of

CH2O has a molecular mass of 90 amu. What is it’s molecular formula

Determine empirical formula massC = 12 x1 H = 1 x 2O = 16 x 1

30

Divide the molecular mass by the empirical formula mass to determine the multiple

90/30 = 3

Multiply the empirical formula by the multiple to find the molecular formula

[CH2O] X 3 = C3H6O3

REVIEW QUIZA compound has 67.6% Hg, 10.8% S, and

21.6% O. Determine the empirical formula

Find the molecular formula of ethylene glycol (antifreeze). The molar mass is 62g/mol and the empirical formula is CH3O