Ch. 10- The Mole

Why- Within the next 2 months we will be working with chemical quantities. Determining what a reaction will produce or how much we need to go into a reaction with. These math skills can be applied across all science, ALL

professions and many day to day life activities.

Measuring MatterCount, Mass, Volume……

Units indicating a specific number of itemsExamples????

Remember your dimensional analysis….well lets get those gears agrindingWhat is the mass of 90 apples if 1 dozen of the

apples has a mass of 2.0kg

Jan 25- “Mole Day”Hey you….don’t be miserable today…you don’t

want to be labeled as being dismole

Why is it hard to count atoms, ions, or molecules 1x1?

We as chemists use the mole (mol) in the same way we use dozen1 mole = 6.02 x 1023 representative particles

Avogadro’s number- named after him to honor his work on molecular theories

How big is a mole?

If you count to 6.02 x 1023, one number per second, how long will it take?

6.02 x 1023 x 1min/60sec x 1hr/60min x 1 day/24 hr x 1 yr/365 days =

1.9 x 1016 years = 19 quadrillion years!

The earth is 4.6 billion years old, so that’s 4 million times the earth’s age!

Representative particlesRefers the the species present in a substance

Na = atomsCO2 = molecules

NaCl = formula unit

So……

1 mole of Na = 6.02 x 1023 atoms1 mole of CO2 = 6.02 x 1023 molecules

1 mole of NaCl = 6.02 x 1023 formula units

Mole Calculations

Cont.

Practice1. What is Avogadro’s #?

2. What is the representative particle for MgS?

3. How many formula units are in 2.34 moles of NaNO3?

4. How many moles are in 3.48 x 1024 atoms of Li?

Remember our friend amu?Decimal from periodic table

Relative values based on the mass of Carbon-12 isotopeSince ratio is relative, changing the unit will not

change the ratioGrams is convenient to use in lab so….lets us it

Molar Mass (IMPORTANT)

Molar mass of CompoundsSimply…add the masses of all the elements in

the compound togetherEx. SO3

EX. C9H11NO2

On your own…try

1.) K3PO4

2.) Al2(SO4)3

Mole Land…. Where the fun is multiplied by 6.02 x 1023 times

Mole Mass problems

Mass Mole Problems

Molar VolumeAvogadro’s hypothesis- equal volumes of

gases at the same temp. and pressure contain equal number of particles

Volume measured at STP (Standard Temp. and Pressure)0°C and 101.3kPa (1 atm)

Molar volume = At STP, 1 mole or 6.02 x 1023 representative particles, of any gas occupies a volume of 22.4 L.

Mole Volume Problems

Volume Mole Problems

% CompositionRelative amounts of the elements in a

compoundHow important in the real world

% mass of element = _mass of element_ x 100%

mass of compound

% Composition from mass data When a 13.60g sample of a compound containing only Mg

and O is decomposed, 5.40g of O is obtained. What is the % composition of this compound?

% O = _mass of O_ x 100% = 5.40 g x 100% = 39.7 %

mass of MgO 13.60g

% Mg= _mass of Mg__ x 100% = 8.20 g x 100% = 60.3%

mass of MgO 13.60g

% Composition from Chemical Formula

% mass = mass of element in 1 mol compound molar mass of compound

Propane (C3H8) is commonly used in gas grills. What is the percent composition of Propane?

% C = 36.0g x 100% = 81.8%

44.0g

% H = 8.0g x 100% = 18%

44.0g

% PracticeWhat is the percent composition for each

element in the following compounds

C11H12N2O2 -Tryptophan

C6H8O6 – Vitamin C

Magnesium Phosphate

Empirical FormulaThe lowest whole number ratio of the atoms of

the elements in a compoundBasic ratio (ie 1:2:1)May or may not be the same as the molecular

formulaTells the actual # of each kind of atom in the

compound

Determining empirical formula of a compound A compound is found to contain 25.9% N and 74.1% O.

What is the empirical formula of the compound Since % means part per 100, we can assume that 100.0g of

the compound contains 25.9g and 74.1g.

Step 1 – convert to moles

25.9g N x 1 mol = 1.85 mol N

14.0g

74.1g O x 1 mol = 4.63 mol O

16.0g

Step 2- Divide each molar quantity by the smaller molar quantity

1.85 mol N = 1.00 mol N 4.63 mol O = 2.50 mol

1.85 1.85

Step 3- Multiple each part of the ratio by the smallest whole # that will convert both subscripts to whole #’s

1 mol N x 2 = 2 mol N

2.5 mol O x 2 = 5 mol O

Cont

Calculate the empirical formula for a compound containing 67.6% Hg, 10.8% S, and 21.6% O.

Step 1

67.6g Hg x 1 mol Hg = 0.337 mol Hg

200.6g Hg

10.8g S x 1 mol S = 0.336 mol S

32.1g S

21.6g O x 1 mol O = 1.35 mol O

16.0 g

Step 2

0.337mol Hg = 1.00mol Hg 0.336mol S = 1.00mol S 1.35mol O =4.02mol O

0.336 0.336 0.336