1. Moles and Stoichiometry

2. The Mole OBJECTIVES: Describe the mole concept
Calculate the mass of a mole of any substance.
Convert between moles, grams, liters, and particle number

3. What is a Mole 摩尔? We measure mass in grams. g
We measure volume in liters. L
We count pieces in MOLES. mol

4. The Mole Concept A Carbon-12 atom has a mass of 12amu
A mole of Carbon atoms
has a mass of 12 grams C

5. Gram Atomic Mass Equals the mass of 1 mole of an element
Written on the Periodic Table
12.01 grams of C has the same number of pieces as grams of H and grams of iron.
We can write this as g C = 1 mole C
We can count things by weighing them.

6. The Mole Concept
Atomic Mass
in grams
Mole of atoms
A mole of aluminum =
A mole of gold =
A mole of silver =
A mole of boron =
27.0g
197g
108g
10.8g

7. The Mole Concept So, How many atoms are in a mole?
Does a mole of H have the same number of atoms as a mole of He?

8. If a Helium atom is 4 times heavier than a Hydrogen atom,
then a dozen Helium atoms is 4 times
heavier than a dozen Hydrogen atoms.

9. And a mole of Helium atoms is 4 times
heavier than a mole of Hydrogen atoms.

10. The number of atoms in a mole is called,
So, the number of atoms in a mole
is always the same
The number of atoms in a mole is called,
Avogadro's Number
Avogadro's Number = x 1023

11. Mole – Particle Conversions
The mole concept allows us to count atoms, molecules, formula units and ions.
1 mole of Al = x 1023 atoms of Al
So how many atoms in 3 mol of Al?

12. Mole – Particle Conversions
1 mole of Al = x 1023 atoms of Al
So how many atoms in 3 mol of Al?
3 mol Al
6.022 x 1023 atoms of Al
1 mol Al
= x 1023 atoms of Al

13. Conversions 1 mole of Al = 6.022 x 1023 atoms of Al
So how many moles are 3.0 x 1023 atoms of Al?
3.0 x 1023 atoms Al
1 mol Al
6.022 x 1023 atoms of Al
= .5 mol of Al

14. How many moles of Na atoms are there in 46.0g of Na?
Converting into Moles
How many moles of Na atoms are there in 46.0g of Na?
Na has a mass
of 23.0
46.0g Na
23.0g Na
1 mol Na
= 2 mol Na
23.0
Step 1: Write a grid and place the given number
into the upper left hand part of the grid
Step 3: Place the units you need to cancel on the bottom, and multiply by the top and divide by the bottom
Step 2: Look up the atomic mass
on the periodic table and find out
how many grams = 1mole

15. Mole-Mass Conversations
Dimensional Analysis- converting between physical properties using ratios
How many grams are in 3.5 mol CO2?
How many moles are in 150g in NaBr?
3.5 mol CO2
44.0 g CO2
=154g CO2
1 mol CO2
150 g NaBr
1 mol NaBr
= 1.5 mol NaBr
102.9 g NaBr

16. 28.1 g C 1 mol Mg 8.60 x 1022 atoms Li Examples
How much would 2.34 moles of carbon weigh?
How many moles of magnesium is g of Mg?
How many atoms of lithium is 1.00 g of Li?
28.1 g C
1 mol Mg
8.60 x 1022 atoms Li

17. What about compounds?
In 1 mole of H2O molecules there are 2 moles of H atoms and 1 mole of O atoms
To find the mass of one mole of a compound
determine the moles of the elements they have
Find out how much they would weigh
add them up

18. Types of Molar Mass
Gram Molecular Mass (GMM)- the total number of atoms in a molecular compound
Cl2 = 2 x 35.4 g = 70.8 g
CH4=
Gram Formula Mass (GFM)- the total number of atoms in an ionic compound
NaCl = (1 x 23.0g) + (1 x 35.4g) = 58.4g
Ca(OH)2=
(1 x 12.0g) + (4 x 1.0g) = 16g
(1 x 40.0g) + (2 x (16.0g+1.0g))= 74g

19. Molar Mass
Molar mass is the generic term for the mass of one mole of any substance (in grams)
The same as:
1) gram molecular mass
2) gram formula mass
3) gram atomic mass

20. Examples = 78.1 g = 92.0 g = 164.1 g = 180.0 g = 149.0 g Na2S N2O4
Calculate the molar mass of the following and tell what type it is:
Na2S
N2O4
Ca(NO3)2
C6H12O6
(NH4)3PO4
= 78.1 g
= 92.0 g
= g
= g
= g

21. 0.104 mol CO2 178 g H2O 0.425 mol CH4 Examples
How many moles is 4.56 g of CO2?
How many grams is 9.87 moles of H2O?
How many molecules is 6.8 g of CH4?
0.104 mol CO2
178 g H2O
0.425 mol CH4

22. Gases Many of the chemicals we deal with are gases.
They are difficult to weigh.
Need to know how many moles of gas we have.
Two things effect the volume of a gas
Temperature and pressure
We need to compare them at the same temperature and pressure.

23. Standard Temperature and Pressure
0ºC and 1 atm pressure （1个大气压，约为 kPa）
0oC = 32oF= 273 K
1 atm= kPa = 760 mmHg (torr)
abbreviated STP 标准状况
At STP 1 mole of gas occupies 22.4 L
Called the molar volume 摩尔体积
1 mole = 22.4 L of any gas at STP

24. Examples What is the volume of 4.59 mole of CO2 gas at STP?
How many moles is L of O2 at STP?
22.4 L CO2
4.59 mol CO2
=103 L CO2
1 mol CO2
5.67 L O2
1 mol O2
=0.253 mol O2
22.4 L O2

25. Ideal Gas Law
Connection between the number of particles (n) and the pressure (P), volume (V), and temperature (T) of a gas
PV=nRT
R= 8.31 kPa∙L/ mol∙K
T= ALWAYS in Kelvin, so convert oC to K
-50oC = 223K
How many moles of helium are contained in a 5.00-L canister at 101 kPa and 30oC?
n= PV/RT
n= kPa x 5.00-L
8.31 kPa∙L/mol∙K x 303K
n= 0.2 mol

26. Stoichiometry化学计量法 It starts with a balanced equation 2H2 + O2 ® 2H2O
“Stoichiometry” is Greek for “Measuring Elements”
It starts with a balanced equation
2H2 + O2 ® 2H2O
2 moles of hydrogen reacts with
1 mole of oxygen
Forming 2 moles of water.

27. Stoichiometry
The coefficients tell us how many moles of each substance. Not Grams!
For example:
2H2 + O2 ® 2H2O
2 g of H2 + 1 g of O2 = 2 g of H2O
3 g of reactants can’t make only 2 g of products

28. Mass of a Product 2H2 + O2 ® 2H2O 2 moles H2 2.02 g H2 = 4.04 g H2
The Law of Conservation of Mass applies
Convert the moles to grams and the equation does work.
2H2 + O2 ® 2H2O
2 moles H2
2.02 g H2 =
4.04 g H2
1 mole H2
1 mole O2
32.00 g O2 =
32.00 g O2
1 mole O2
36.04 g H2+O2

29. Mass of a Product 2H2 + O2 ® 2H2O 2H2 + O2 ® 2H2O 18.02 g H2O
2 moles H2O
18.02 g H2O
36.04 g H2O =
1 mole H2O
2H2 + O2 ® 2H2O
36.04 g H2 + O2 =
36.04 g H2O

30. 2Na + Cl2  2NaCl 2Na (s) + Cl2(g) 2NaCl (s)
How many grams of sodium are needed to react with .071g of chlorine gas?
2Na (s) + Cl2(g) 2NaCl (s)
Mole Ratio
Mass Ratio
23 x 2= 46
35.5 x 2 x 1= 71
58.5 x 2=
117
1 mol Cl2
2 mol Na
0.071 g Cl2
46 g Na
71 g Cl2
1 mol Cl2
2 mol Na
= g Na

31. Chemical Yield The amount of product made in a chemical reaction.
There are three types:
1.Theoretical yield 理论产量 - the amount of Product that should be made (from calculations)
2. Actual yield 实际产量- the amount of Product formed in the laboratory (always given)

32. Chemical Yield
3. Percent yield – a percentage/ratio between the actual yield and the theoretical yield.
% Yield =
% yield tells us how “efficient” a reaction is.
% yield can not be bigger than 100 %.
Actual Yield
x 100
Theoretical Yield

33. Example 11.8 g NaCl x 100 13.6 g NaCl Answer = 86.7 %
According to your calculations the theoretical yield for the production of NaCl is 13.6 grams. In the laboratory your actual yield is 11.8 grams of NaCl. What is the percent yield?
11.8 g NaCl
x 100
13.6 g NaCl
Answer = 86.7 %

34. Calculating Percent Composition质量分数of a Compound
Like all percent problems:
Part whole
Find the mass of each component,
then divide by the total mass.
x 100 %

35. Calculating Percent Composition质量分数of a Compound
Find the mass percent for the elements in Sodium hydrogen carbonate:
NaHCO3
-molar mass is 84 g/mol
-mass of: Na= 23g H= 1g
C= 12g O= 3 x 16= 48g
%C = (12g/84g) x 100= 14.3%
%Na = (23g/84g) x 100= 27.4%
%H = (1g/84g) x 100= 1.2%
%O = (48g/84g) x 100= 57.1%

36. The Empirical Formula 经验式
The lowest whole number ratio of elements in a compound.
The molecular formula = the actual ratio of elements in a compound.
The two can be the same.
CH2 is an empirical formula
C2H4 is a molecular formula
C3H6 is a molecular formula
H2O is both empirical & molecular

37. Calculating Empirical
Just find the lowest whole number ratio
C6H12O6
CH4N
It is not just the ratio of atoms, it is also the ratio of moles of atoms.
In 1 mole of CO2 there is 1 mole of carbon and 2 moles of oxygen.
In one molecule of CO2 there is 1 atom of C and 2 atoms of O.

38. Calculating Empirical
We can get a ratio from the percent composition.
Assume you have a 100 g.
The percentages become grams.
Convert grams to moles.
Find lowest whole number ratio by dividing by the smallest mole value

39. Example
Calculate the empirical formula of a compound composed of % C, % H, and %N.
Assume 100 g so
38.67 g C x 1mol C = mole C g C
16.22 g H x 1mol H = mole H g H
45.11 g N x 1mol N = mole N g N

40. Example The ratio is 3.220 mol C = 1 mol C 3.219 mol N 1 mol N
The ratio is mol H = 5 mol H mol N mol N
= C1H5N1 = CH5N
Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

41. Empirical to molecular
Since the empirical formula is the lowest ratio, the actual molecule would weigh more.
By a whole number multiple.
Divide the actual molar mass by the empirical formula mass.
Caffeine has a molar mass of 194 g. what is its molecular formula?
C4H5ON2 = 97.11g
Ratio= 194g/ 97.11g = 2
2(C4H5ON2) = C8H10O2N4; molecular formula

42. Example
A compound is known to be composed of % Cl, 24.27% C and 4.07% H. Its molar mass is known (from gas density) to be g. What is its molecular formula?

43. Final Exam What is matter?
Compounds; elements; substances vs. mixtures (Homogeneous and Heterogeneous)
Atomic symbols; Naming compounds
Periodic table trends: Electronegativity, Atomic Radius, Ion Size, etc…
Reaction energy; exothermic vs. endothermic; activation energy
Solvents, solutes, and solutions
Balancing Equations
Valence electrons
Structure of an Atom; Molecular structures
Alpha, Beta, and Gamma Decay
Group names: Halogens, transition metals, alkali metals, etc…
Properties of metals, non-metals, metalloids, and semiconductors

44. Final Exam Lewis Dot Structures Types of reactions
Orbitals and sub-orbitals
Ionic vs. Covalent bonding
Temperature and Kinetic motion
Equilibrium and shifting the direction of reactions
Calculate:
Density
Wavelength and Frequency
Atomic Mass
Half life
Radioactive decay
Moles; Mass percent, Percent yield, Mass-Mole conversions