1. KNOW, calculations based on…..
CHAPTER 3
Mole
Molar Mass
Avogadro’s Number
Calculations
- mass, mole, particle
- mass %
- determining formulas
Emperical/Molecular
- Molarity (mols/L)
- Dilution
Stoichiometry
Limiting Reagent
KNOW, calculations based on…..
Formulas
Balance Eqn
Subst Mass
TERMS:
formula/molar/molecular weight or mass
- sum total of all atoms in chem formula
- CaCl2; 1 Ca + 2 Cl = 1(40.1) + 2(35.5) = g/mol
states: (s) - (l) - (g) - (aq)

2. FORMULA--MOLECULAR WEIGHT
The sum of the Atomic Weights of all atoms present
in one formula unit or molecule
Formula Wt: ionic cmpd
Molecular Wt: covalent molecule

3. What is the formula weight of sodium carbonate,
PROBLEM
What is the formula weight of sodium carbonate,
Na2CO3. This is an industrial chemical used in
making glass.
Also, equivalent to 1mole
of a substance
SOLUTION
2 * =
2 Na
1 C
3 O
1 * =
3 * = + g 3

4. What is the % composition of chloroform,
CHCl3, anesthetic?
PROBLEM
SOLUTION
1 C
1 H
3 Cl
1 * = 12.0
1 * 1.0 =
3 * = 106.5
1. Identify # each element
2. Calculate formula weight +
119.5 g
3. Calculate % Composition by each element

5. % Composition +
100.0 %

6. MOLES Mole: A collection of objects
A collection of Avogadro’s number of objects
Avogadro’s number
6.02 * 1023
Atoms
Particles
Ions
Cations
Anions
Molecules
Formula
Units
MOLES
mass = 1 mole
Multiply by
Divide by
MASS

7. Given mass, find moles
How many moles are in g NaNO3 ?
Step 1: find formula wt. of NaNO3
1 Na = g
1 N = g
3 O = 3 * 16.0 = 48.0 g
1 mole of NaNO3 = g
Step 2 : Find # of moles
Use factor-label method
4.07 moles NaNO3

8. How many grams are in 0.6 moles N2O ?
Given moles, find mass
How many grams are in 0.6 moles N2O ?
Step 1: find molecular wt. of N2O
2 N = 2 * 14.0 = 28.0 g
1 O = g
1 mole of N2O = g
Step 2 : Find mass
Use factor-label method
26.4 g N2O 8

9. Given moles, find # molecules
Divide by
MOLES
NUMBER of
PARTICLES by
Multiply
Avogadro’s Number
6.02*1023
Given moles, find # molecules
How many molecules are in 1.6 moles oxygen?
Step 1: Recognize that mass does not apply here.
But Avogadro’s # is used
Step 2 : Find # molecules
Use factor-label method
9.63 * 1023 molecules O2 9

10. Given # atoms, find moles
How many moles are in 3.01 *1012 atoms of Chromium?
Step 1: Recognize that mass does not apply here.
But Avogadro’s # is used
Step 2 : Find # moles
Use factor-label method
5.00 * mols Cr 10

11. There is not a direct relationship between MASS and PARTICLES
MOLES
6.02*1023
mass = 1 mole
Multiply by
Divide by
Avogadro’s Number
Multiply by
Divide by
MASS
NUMBER of
PARTICLES
There is not a direct relationship
between MASS and PARTICLES 11

12. 2 Step Conversion Problem
Will need to use MASS at some
point in the problem
Given # formula units, find grams
How many grams are in * 1024 formula units AgCl ?
Step 1: find formula wt. of AgCl
1 Ag = g
1 Cl = g
1 mole of AgCl = g
Step 2 : Find moles
Step 3 : Find mass
Use factor-label method
288 g AgCl
Converts formula units
to MOLES
Converts moles
to MASS 12

13. 2 Step Conversion Problem
Will need to use MASS at some
point in the problem
Given grams, find # atoms
How many atoms are in grams of Mercury ?
Step 1: find molar mass of Hg
1 mole of Hg = g
Step 2 : Find moles
Step 3 : Find atoms
Use factor-label method
3.84*1023 atoms Hg
Converts mass
to MOLES
Converts moles
to ATOMS 13

14. EMPERICAL FORMULA Problem: Determine the formula for a cmpd that is
26.6% potassium, 35.4% chromium, and 38.1% oxygen.
Solution:
step1) assume, using 100 g sample, thus the percentages
can be used as your masses for each diff. element
26.6% -- 26.6 g K % --- 35.4 g Cr % --- 38.1 g O
step 2) convert your masses to moles of each diff. element
Determine Formulas
Convert mols of parts into whole # subscripts
STEPS
1. Determinemolefraction for each element
2. Divide each subscript by the smallest value
3. If not all # are whole #, find smallest factor to multiple
all subscripts by to obtain a whole # 14

15. step 3) Divide each value by the smallest “mole” number
from step 2
step 4) calculate whole # subscripts
Potassium Dichromate 15

16. MOLECULAR FORMULA Problem:
An unknown substance containing 82.7% carbon
and 17.4% hydrogen has a molar mass of 58.2 grams.
Find the molecular formula.
Solution:
step1) assume, using 100 g sample, thus the percentages
can be used as your masses for each diff. element
82.7% -- 82.7 g C % --- 17.4 g H
step 2) convert your masses to moles of each diff. element 16

17. step 3) Divide each value by the smallest “mole” number
from step 2
step 4) calculate whole # subscripts
step 5) Find formula wt. of C2H5 and the ratio to the molar mass
C2H5: C = 2 * 12.0 = 24.0 g
H = 5 * = g
29.0 g
step 6) Determine the molecular formula
There are 2 empirical
formula units
2(C2H5) = C4H10
C4H10 = 4(12.0) + 10(1.0) = 58.0 g 17

19. Sample Exercise 3.10 Converting Grams to Moles
Calculate the number of moles of glucose (C6H12O6) in g of C6H12O6.
Solution
Analyze We are given the number of grams of a substance and its chemical formula and asked to calculate the number of moles.
Plan The molar mass of a substance provides the factor for converting grams to moles. The molar mass of C6H12O6 is g/mol (Sample Exercise 3.9).
Solve Using 1 mol C6H12O6=180.0 g C6H12O6 to write the appropriate conversion factor, we have
Check Because g is less than the molar mass, a reasonable answer is less than one mole. The units of our answer (mol) are appropriate. The original data had four significant figures, so our answer has four significant figures.
How many moles of sodium bicarbonate (NaHCO3) are in 508 g of NaHCO3?
Answer: 6.05 mol NaHCO3
Practice Exercise

20. Sample Exercise 3.11 Converting Moles to Grams
Calculate the mass, in grams, of mol of calcium nitrate.
Solution
Analyze We are given the number of moles and the name of a substance and asked to calculate the number of grams in the sample.
Plan To convert moles to grams, we need the molar mass, which we can calculate using the chemical formula and atomic weights.
Solve Because the calcium ion is Ca2+ and the nitrate ion is NO3–, calcium nitrate is Ca(NO3)2. Adding the atomic weights of the elements in the compound gives a formula weight of amu. Using 1 mol Ca(NO3)2 = g Ca(NO3)2 to write the appropriate conversion factor, we have
Check The number of moles is less than 1, so the number of grams must be less than the molar mass, g. Using rounded numbers to estimate, we have 0.5  150 = 75 g. The magnitude of our answer is reasonable. Both the units (g) and the number of significant figures (3) are correct.
What is the mass, in grams, of (a) 6.33 mol of NaHCO3 and (b) 3.0  10–5 mol of sulfuric acid?
Answer: (a) 532 g, (b) 2.9  10–3 g
Practice Exercise

21. TERMS Solution A homogeneous mixture of 2 or more pure substances
Solute
The substance that is dissolved in solution
Solvent
The substance that does the dissolving

22. MOLARITY --CONCENTRATION
mols
liter M
Label
moles of solute
liter of solution
[H+]
[OH-]
Concentration of ACID
Symbol
Concentration of BASE
Brackets indicate CONCENTRATION

23. DILUTION A single solution (homogeneous mixture) of a known
concentration needs to be diluted to a lower concentration.
This is accomplished by adding a known quantity of
water (distilled) to the original solution volume.
The terms used indicate:
Mo; Vo Initial – Original -- Beginning
M1; V1; Mi; Vi concentration & volume
Md; Vd Final – Diluted -- Ending
M2; V2; Mf; Vf concentration & volume
Equation:
M1 * V1 = M2 * V2

24. 290.0 mL of a 0.560 M Fe(OH)3 solution is required
to make a M solution by dilution. What is the
final volume.
Step #1: Identify the parts for equation
M1 = M
V1 = 290.0
M2 = M
V2 = X ml
650 ml
Step #2: Set up and solve equation
(0.560 M) (290.0 mL) = (X ml) (0.250 M)
0.250 M
Notice: Dilution problems are not volume specific

25. 1.25 L of H2O is added to 750 ml of 0.75 M HCl
solution. What is the resulting molarity?
Step #1: Identify parts for equation
M1 = 0.75 M
V1 = 750 ml
M2 = X
V2 = 2.0 L
So, final vol. is amount
Start + Added
or ml
or L
Step #2: Set up & solve equation
1.25 L is added to ….
(0.75 M) (0.75 L) = (X) (2.0 L)
2.0 L OR
0.28 M

26. Given mass & volume, find molarity
Determine the M of g Barium
Chloride in 575 ml of solution.
Step 1: Need to change 575 ml to L
Step 2: Find formula wt. of CMPD.
BaCl2 = g/mol
Step 3 : Find moles of CMPD.
g * 1 mol . g
3.6 moles
Step 4 : Find molarity of solution
M = 3.6 moles L
6.3 M

27. Given molarity & volume, find moles & mass
How many moles of NaCl are in
36.7 ml of a M solution?
Step 1: Need to change 36.7 ml to L
Step 2: Convert M label to mols/L
0.256 mols
1 L
Using given concentration
& volume, find moles
Step 3 : Find moles of NaCl
or 9.4*10-3 moles NaCl

28. Continuing, next we need to find
the MASS of NaCl in moles
Step 1: find formula wt. of NaCl
58.5 g /mol
Step 2 : Find mass
0.55 g NaCl
MOLES
MASS
Multiply by
Divide

29. DILUTION MOLARITY PRACTICE PROBLEMS
1. What is the molarity of a solution containing 2.50 moles of KNO3
dissolved in 5.00 L?
2. How many moles of KCl are present in mL of M solution?
DILUTION
1. What is the molarity of 50.0 mL of a 0.50 M NaOH solution after it has
been diluted to mL?
2. If mL of water is added to mL of a M Na2CrO4
solution, what is the molarity of the resulting solution?