Chemical Calculations
• Moles and Molecules
• Moles and Chemical Reactions
• Moles, Chemical Reactions, and Molarity
• All done as UNIT CONVERSIONS!!!
• …and practice, practice, practice
CHM 1010 - Sinex
Mass-moles-particles conversions
Mass of substance in grams
Molar mass of substance - g/mole
Moles of substance
Conversion factors
Avogrado’s number 6.02 x 1023 particles/mole
Number of particles of substance
(atoms, molecules, or ions)
Molar mass – sum of atomic masses from periodic table
2
How many molecules of aspirin (C9H8O4) in a dose of 1000 mg?
Find MM of aspirin:
MM = 9*12+8*1+4*16 = 180 g/mole
First find moles:
moles = 1000 mg *1g/1000mg * 1mole/180g = 0.0055 moles
Conversion factors in boxes
Now find molecules:
molecules = 0.0055 moles * 6.02x1023 molecules/mole = 3.3 x 1021 molecules
How many atoms of carbon?
atoms C = 9 atoms/molecule * 3.3 x 1021 molecules = 3.0 x 1022 atoms
from the formula
3
For 12.6g NaHCO3, how many moles do you have?
Mass of substance A
MM
Moles of substance A
How many CO2 molecules in 0.17 moles CO2?
Moles of substance A
6.02 x 1023
Molecules of substance A
4
Another way to find moles…
For a solution (homogeneous mixture), there are two components:
solute (substance being dissolved) and solvent (dissolving medium, usually water)
A unit of concentration – amount solute per amount solution or solvent
Molarity = moles of solute/volume of solution in liters (moles/L)
Rearranging the definition of molarity:
moles = M x VL
Another way to find moles!
How many moles NaCl in 50 mL of 0.28 M NaCl?
50 mL x 1L/1000 mL x 0.28 mole/L = 0.014 mole NaCl
5
What is the molarity if 35g KCl are dissolved to make 350 mL of solution?
Molarity
Moles of substance A
Volume of substance A
How many moles are in 300 mL of a 0.23 M NaOH solution?
6
The ratio of moles in a reaction
2C4H10 + 13O2  8CO2 + 10H2O
Mole ratios
2
4
13
26
8
16
10
20
20
1
130
6.5
80
4
100
5
6
1.3
32
50
1.37
1.37
X 13/2
X 8/2
X 10/2
8.91
5.48
6.85
Click for answers
7
Mole-to-mole conversions
This comes from the balanced chemical reaction!
…and it relates substances in the reaction!
Moles of substance A
Mole ratio
Moles of substance B
2HCl + CaCO3  CaCl2 + H2O
How many moles of HCl react with a mole of CaCO3?
1 mole CaCO3 x 2 mole HCl/1 mole CaCO3 = 2 mole HCl
mole ratio
8
Stoichiometry
Mass of substance A
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Moles of substance A
Molarity of solution A
Mole ratio
Moles of substance B
Molarity of solution B
Volume of substance A
Volume of substance B
Conversion factors
Molarity (M) = moles of solute/volume in liters of solution – moles/L
9
Mass of substance A
How many grams of O2 are
required to reaction with
10g C3H8?
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Moles of substance B
Molarity of solution A
Molarity of solution B
Volume of substance A
Volume of substance B
C3H8 + 5O2  3CO2 + 4H2O
10g C3H8 x 1 mole/44g = 0.23 moles C3H8
Conversion factors in boxes
0.23 moles C3H8 x 5 moles O2/1mole C3H8 = 1.15 moles O2
1.15 moles O2 x 32.0g/mole = 37 g O2
This is a classic
stoichiometry problem!
10
1
How many grams of O2 are
required to reaction with
10g C3H8?
3
Mass of substance A
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Molarity of solution A
Another view of solving
Mass of substance B
Volume of substance A
2
Moles of substance B
Molarity of solution B
Volume of substance B
C3H8 + 5O2  3CO2 + 4H2O
Step 1
10g C3H8 x 1 mole/44g = 0.23 moles C3H8
Step 2
0.23 moles C3H8 x 5 moles O2/1mole C3H8 = 1.15 moles O2
Step 3
1.15 moles O2 x 32.0g/mole = 37 g O2
11
Mass of substance A
If 74g O2 react, how many
grams of CO2 will be
produced?
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Molarity of solution A
Volume of substance A
Moles of substance B
Molarity of solution B
Volume of substance B
C3H8 + 5O2  3CO2 + 4H2O
12
Mass of substance A
What volume of stomach
acid, 0.16 M HCl, reacts
with 1.0 g CaCO3?
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Molarity of solution A
Volume of substance A
Moles of substance B
Molarity of solution B
Volume of substance B
2HCl + CaCO3  CaCl2 + H2O
1.0 g CaCO3 x 1 mole/100g = 0.010 mole CaCO3
0.010 mole CaCO3 x 2 mole HCl/1 mole CaCO3 = 0.020 mole HCl
0.020 mole HCl x 1L/0.16 moles = 0.13 L = 130 mL stomach acid
13
Mass of substance A
What volume of 0.25 M
CH3COOH will reaction
with 25.0 mL of 0.37M
NaOH?
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Molarity of solution A
Volume of substance A
Moles of substance B
Molarity of solution B
Volume of substance B
CH3COOH + NaOH  CH3COONa + H2O
25.0 mL x 1L/1000 mL x 0.37 mole/L = 0.0093 moles NaOH
0.0093 moles NaOH x 1 mole CH3COOH/1 mole NaOH = 0.0093 mole CH3COOH
0.0093 mole x 1L/0.25 moles = 0.037 L = 37 mL CH3COOH
This is a classic titration
problem!
14
Could you find one of
the conversion factors?
Suppose 2.0g CaCO3
reacted with 25.0 mL of
HCl. What is the
molarity of the HCl?
Mass of substance A
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Molarity of solution A
Volume of substance A
Moles of substance B
Molarity of solution B
Volume of substance B
2HCl + CaCO3  CaCl2 + H2O
2.0 g CaCO3 x 1 mole/100g = 0.020mole CaCO3
0.020 mole CaCO3 x 2 mole HCl/1 mole CaCO3 = 0.040 mole HCl
Molarity = moles/ VL = 0.040 mole HCl / (25.0 mL x 1L/1000mL) = 1.6 M HCl
Moles of substance B
Volume of substance B
15
Mass of substance A
How many grams of
Al(OH)3 will react with
100 mL of 0.15 M HCl?
Mass of substance B
Molar mass of substance B
Molar mass of substance A
Mole ratio
Moles of substance A
Molarity of solution A
Volume of substance A
Moles of substance B
Molarity of solution B
Volume of substance B
Al(OH)3 + 3HCl  AlCl3 + 3H2O
16
For a 1.0 kg of Al2O3, how much aluminum metal, in grams, can be produced?
2Al2O3 (l) + 3C (s)  4Al (l) + 3CO2 (g)
How many atoms of carbon are consumed for the problem above?
17
How many grams of CH3COOH are needed to react with 27.3 mL of 0.21 M NaOH?
CH3COOH + NaOH  CH3COONa + H2O
If 0.121g HX react with 26.2 mL of 0.229 M NaOH, what is the molar mass of HX?
HX + NaOH  NaX + H2O
What is element X?
18
What if two reagents are added, how much product do you get?
Suppose 10 g Na and 10 g Cl2 are mixed together. How much NaCl can be produced?
2Na + Cl2  2NaCl
2Na + 1Cl2
First find the moles of each reactant:
10 g Na x 1 mole/23.0 g = 0.43 mole Na
10 g Cl2 x 1 mole/71.0 g = 0.14 mole Cl2
Find the moles of NaCl produced for each reactant:
2
1
Have
0.43
Need
0.22
Need
0.28
Have
0.14
0.43 mole Na x 2 mole NaCl/2 mole Na = 0.43 mole BrCl
0.14 mole Cl2 x 2 mole NaCl/1 mole Cl2 = 0.28 mole NaCl
 This is what can
be produced! Cl2
is limiting reagent.
19
A chemical analysis problem
A chemist decides to check the molarity of H2SO4 in her car battery. A 10.0 mL
sample is reacted with 31.03 mL of 2.73M NaOH. What is the molarity of
H2SO4?
H2SO4 + 2NaOH  Na2SO4 + 2H2O
20
21
Answers to problems by slide number:
4- 0.15 mole NaHCO3; 1.0 x 1023 molecules CO2
6- 1.3 M KCl; 0.069 mole NaOH
12- 61g CO2
16- 0.39g Al(OH)3
17- 5.3 x 102g Al; 8.9 x 1024 atoms C
18- 0.34g CH3COOH; MM = 20.2 g/mole; X = F
20- 4.2M H2SO4