1. Mole and Stoichiometry

2. Measuring Matter A mole is an amount of a substance
Similar to: 12 in a dozen, 100 pennies in a dollar, etc.
A mole of any substance represents 6.02 x particles of that substance
6.02 x 1023 = Avogadro’s Number
6.02 x 1023 X atoms OR 1 mol X
1 mol X x 1023 X atoms
NOTE: the words atoms/molecules/particles are all the same

3. Problem 1: If you had 1 mole of donuts, how many donuts would you have?
6.02 x 1023 
Problem 2: In 4.0 moles of glucose (C6H12O6), how many molecules/particles are there?
4.0 mol glucose x 6.02 x 1023 particles
1 mole glucose
= 2.4 x 1024 particles

4. Molar Mass (formula mass)
Must know how to determine molar mass (formula mass)
Molar mass measures the mass of one mole of any element or compound
The molar mass can be calculated using the atomic masses of each element (1 amu = 1 gram) from the periodic table
1 bromine atom = amu
Molar mass can be used to convert grams of a substance into moles or vice versa

5. Calculating the Molar Mass
Molar Mass: add up all the amu values (make sure you look at subscripts!)
What is the molar mass of 1 mole of H2O
H: 2 x 1.01 = 2.02
O: 1 x = 16.00
1 mole H2O = g
What is the molar mass of 1 mole of Cu(OH)2
Cu: 1 x = 63.55
O: 2 x = 32.00
1 mole Cu(OH)2 = g

6. YOU TRY! Find the molar mass of the following: A) H3PO4 B) N2O5
(don’t forget to make sure neutral!)
C) copper (II) nitrate
D) potassium hydroxide

7. Calculations with mass/grams (amu)
Mass of sample x conversion factor = number of moles in sample
Calculate the mass of a sample that contains 23 moles of nitrogen (given: 23 moles N, unknown: N mass)
1 mol N= grams
23 mole N x grams = grams N =
1 mol N 320g
Calculate the number of oxygen gas moles (O2) present in a sample that has a mass of 290 grams.
1 mol O2 = grams
290 grams x 1 mol O2 = moles O2 =
32 grams moles

8. More molar mass problems
YOU TRY!
A) How many moles are in 250 grams of water?
B) How many grams are in 3.21 moles of C12H22O11?

9. Calculations with moles and particles
particles x conversion factor = number of moles
Chromium is a metal that is added to steel to improve its resistance to corrosion. Calculate the number of moles in a sample of chromium containing 5.00 x 1020 atoms.
5.00 x 1020 atoms Cr x 1 mol Cr = 8.31 x 10-4 mol Cr
6.02x1023atoms Cr

10. More molar mass problems
YOU TRY!
A) How many molecules are in 2.32 moles of HNO3?
B) How many moles are in 3.60 x 1024 molecules of Li2O?

11. Calculations with grams to particles
grams x conversion factor = moles; moles x conversion factor = particles
Calculate the number of salt molecules present in a sample of grams of salt
63.2 g NaCl x 1 mol NaCl x x 1023 molecules
58.44 g NaCl mol NaCl
= x = 6.51 x 1023 molecules

12. More molar mass problems
YOU TRY! (two steps!)
A) Calculate the number of iron (Fe) atoms present in a sample that has a mass of grams.
B) If a sample of sodium chloride (NaCl) contains 8.2 x particles, how many grams of NaCl are in the sample?

13. Percent by Mass Composition
When given a sample of a compound, you can determine how much of each element is present
Percent composition is the percent by mass of each element in a compound
The following formula is used to calculate percent composition:
% Mass of Element  = 
(grams of element/grams of compound) x 100%

14. Percent Composition
Example: Calculate the percentage of carbon in ethane, C2H6
grams of carbon = 2 x 12 = 24 grams
grams of compound = 24 + (6 x 1) = 30 grams
(24 /30)  x 100  =  80%
Example: Find the percentage composition of a compound that contains g of chlorine, g of oxygen, and g of phosphorus in a g sample of the compound
Cl ( g/ g) x 100 = 69.4%
O ( g/ g) x 100 = 10.4%
P ( g/ g) x 100 = 20.2%

15. Percent Composition
Example: A sample of an unknown compound with mass of g has the following composition: 66.07% carbon, 6.71% hydrogen, 4.06% nitrogen, 23.16% oxygen. What is the mass of each element?
Equation: (% Mass x grams compound) *you can use other methods
100%
C (66.07x2.876 g)/100 = 1.90g
H (6.71x2.876 g)/100 = .193g
N (4.06x2.876 g)/100 = .117g
O (23.16x2.876 g)/100 = .66g

16. YOU TRY!
A) Calculate the percent by mass composition of dimethylether, CH3OCH3
B) What is the percent composition in each element of Iron (III) oxide?

17. Empirical Formula
The empirical formula gives the simplest whole number ratio of the elements in a compound
Example: empirical formula for hydrogen peroxide, H2O2, is HO. The ratio is 1:1
To determine:
1) convert mass of each element given into moles using molar mass (from periodic table)
2) divide each mole value by the smallest # of moles
3) round the mole ratio of the elements to the nearest whole # (NOTE: if something rounds to .5 then you have to multiply everything by 2)
NOTE: Sometimes instead of mass it gives you a percent. Just call it grams.

18. Empirical Formula
Example: A compound was found to contain 7.30 g Na, 5.08 g S,
and 7.62 g O. Determine the empirical formula.
7.30 g Na x 1 mol Na = .317 mol Na 5.08 g S x 1 mol S = .158 mol S
23.0 g Na g S
7.62 g O x 1 mol O = .476 mol O
16.0 g O
SMALLEST # MOLES = .158
Na .317/.158 = S .158/.158 = 1.0
O .476/.158 = 3.0
Answer: Na2SO3 (Also accept: Na2O3S)

19. Empirical Formula
Example: Determine the empirical formula of a compound containing 20.23% aluminum and 79.77% chlorine
Al 20.23%: g Al x 1 mol Al = .750
26.98 g Al
Cl 79.77%: g Cl x 1 mol Cl = 2.25
35.45 g Cl
SMALLEST # MOLES = .750
Al .750/.750 = 1.0
Cl 2.25/.750 = 3.0
Answer: AlCl3

20. Empirical Formula YOU TRY!
A hydrocarbon (a compound containing only hydrogen & carbon) is found to be 7.690% H and 92.31% C by mass. Calculate its empirical formula.
A g sample of an unidentified compound contains g sodium, g chromium, and g oxygen. What is the compound’s empirical formula?

21. Molecular Formula The actual number of atoms in a compound
A whole-number multiple of the empirical formula
CH2O; C6H12O6; C12H24O12
First find the empirical formula, then divide the molar mass of the entire compound by the mass of the empirical formula to determine the multiple

22. Molecular Formula
Example: Ribose has a molar mass of 150 g/mol and a chemical composition of 40.0% carbon, 6.67% hydrogen, and 53.3% oxygen What is the molecular formula for ribose?
C: 40.0 gC x 1 mol C = 3.33 mol C H: 6.67 gH x 1 mol H = 6.60 mol H
12.0 g C g H
O: 53.3 gO x 1 mol O = 3.33 mol O
16.0 g O
Empirical Formula= C1H2O1
empirical formula mass   30.0 g/mol ( )
molar mass = 150 g/mol
molecular formula = 150 / 30 = 5 x empirical
C5H10O5

23. Molecular Formula YOU TRY!
A) A hydrocarbon (a compound containing only hydrogen & carbon) is found to be 7.690% H and 92.31% C by mass. The molar mass is g/mol. Calculate its molecular formula (use the previous empirical formula of CH).

24. Balancing Chemical Equations
Balancing equations is done to satisfy the Law of Conservation of Mass to make the # of atoms the same on both sides of the equation
Add coefficients but leave the subscripts alone
Step by Step Instructions (until you become a professional):
Draw a vertical line down from below the arrow in the equation.
On EACH side of the line, list all of the elements that appear. Do not repeat elements on the same side.
For EACH side of the line, count the number of atoms for each element.
Add coefficients in front of formulas so that the number of atoms on each side matches.
Once all element counts match, make sure all coefficients are reduced to their lowest whole-number ratio.

25. Balancing equations
This process in rather unscientific and is essentially a process of trial and error
TIP #1: If an element appears in only one compound on each side of the equation, try balancing that first.
TIP #2: If one of the reactants or products appears as the free element, try balancing that last.
TIP #3: Remember that you can only change the coefficient.
NOTE: coefficients should be whole numbers

27. YOU TRY! Balance the following:
A) Fe + Br2  FeBr3
B) C4H8 + O2  CO2 + H2O
C) Pb(NO3)2  PbO + NO2 + O2

28. Mole Ratios Balanced equation: C3H8 +5O2  3CO2 + 4H2O is really
(1 mol C3H8 +5 mol O2 yields 3 mol CO2 + 4 mol H2O)
What number of moles of CO2 will be produced by the decomposition of 3.5 mol of C3H8?
Unknown = moles of CO2 Given = 3.5 moles C3H8
Also, 1 mol C3H8 = 3 mol CO2
3.5 mol C3H8 x 3 mol CO2 = 10.5 mol CO2 = 11 mol
1 mol C3H8

29. Another example
Solid iron reacts with oxygen to produce iron(III) oxide. If you wanted to produce 2.5 moles of iron(III) oxide, what mass of oxygen must react?
4Fe + 3O2  2Fe2O3
Unknown = Grams of O2 Given = 2.5 Moles Fe2O3
2.5 moles Fe2O3 3 mol O2 32 grams O mol Fe2O3 1 mol O2
Answer: 120 grams O2 (2.5 x 3 x 32) / 2

30. Mole Ratios YOU TRY! CH4 + 2O2  CO2 + 2H2O
Calculate the grams of O2 required to produce mol of carbon dioxide.
Calculate the mass of water produced when 34.0 g of CH4 is burned.