1. Chemical Quantities Chemistry Tracy Bonza Sequoyah High School
Chapter 11
Chemical Quantities
Chemistry
Tracy Bonza
Sequoyah High School

2. How do you measure how much?
You can measure mass,
or volume,
or you can count pieces.
We measure mass in grams.
We measure volume in liters.
We count pieces in MOLES.

3. Moles
Defined as the number of carbon atoms in exactly 12 grams of carbon-12.
1 mole is 6.02 x particles.
Treat it like a very large dozen
6.02 x is called Avogadro's number.

4. Measuring Moles Remember relative atomic mass?
The amu was one twelfth the mass of a carbon 12 atom.
Since the mole is the number of atoms in 12 grams of carbon-12,
the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.

5. Representative particles
How many oxygen atoms in the following?
CaCO3
Al2(SO4)3
How many ions in the following?
CaCl2
NaOH

6. Molar Mass The mass of 1 mole of an element in grams.
12.01 grams of carbon has the same number of pieces as grams of hydrogen and grams of iron.
We can write this as g C = 1 mole
We can count things by weighing them.

7. What is the molar mass of:
Potassium
Zinc
Neon
39g
65.4g
20.2g
What does that mean?
It means that 39g of K is 1 mole of potassium
How many particles of potassium is that?
6.02 x 10 23
See…….we can count particles without counting them
……….we weighed them!!!

8. What about compounds?
in 1 mole of H2O molecules there are two 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

9. What about compounds? What is the mass of one mole of CH4?
1 mole of C = g
4 mole of H x 1.01 g = 4.04g
1 mole CH4 = = 16.05g
The Molar mass of CH4 is 16.05g
The mass of one mole of a molecular compound.

10. Molar Mass The generic term for the mass of one mole.
The same as gram molecular mass (for molecules/covalent compounds), gram formula mass (for formula units/ionic compounds), and gram atomic mass (for atoms).
I will use the generic molar mass (sometimes I slip up and call it gram formula mass so work with me here!!!!!)

11. Examples
Calculate the molar mass of the following and tell me what type it is.
Na2S
N2O4 C
Ca(NO3)2
C6H12O6
(NH4)3PO4

12. Finding moles of compounds Counting pieces by weighing
Using Molar Mass
Finding moles of compounds
Counting pieces by weighing

13. Molar Mass The number of grams of 1 mole of atoms, ions, or molecules.
We can make conversion factors from these.
To change grams of a compound to moles of a compound.

14. For example
How many moles is 5.69 g of NaOH?

15. For example
How many moles is 5.69 g of NaOH?

16. For example How many moles is 5.69 g of NaOH?
need to change grams to moles

17. For example How many moles is 5.69 g of NaOH?
need to change grams to moles
for NaOH

18. For example How many moles is 5.69 g of NaOH?
need to change grams to moles
for NaOH
1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g

19. For example How many moles is 5.69 g of NaOH?
need to change grams to moles
for NaOH
1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g
1 mole NaOH = g

20. For example How many moles is 5.69 g of NaOH?
need to change grams to moles
for NaOH
1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g
1 mole NaOH = g

21. For example How many moles is 5.69 g of NaOH?
need to change grams to moles
for NaOH
1mole Na = 22.99g 1 mol O = g 1 mole of H = 1.01 g
1 mole NaOH = g

22. Examples How much would 2.34 moles of carbon weigh, in grams?
How many moles of magnesium in g of Mg?
How many moles is 4.56 g of CO2 ?
How many grams is 9.87 moles of H2O?

23. Moles and Molecules 6.02 x 1023 =1 mole too!
So we can convert from moles to molecules too!
Try it:
How many molecules are there in 3.6 moles of sodium hydroxide?
How many moles is 3.6x 1034 molecules of gold?

24. 3 Step Problems
Converting from grams to molecules/atoms and molecules/atoms to grams
How many atoms of silver are in 2.3g of silver?

25. Examples How many molecules in 6.8 g of CH4?
49 molecules of C6H12O6 weighs how much?
How many atoms of lithium in 1.00 g of Li?
How much would 3.45 x 1022 atoms of U weigh?

27. Gases and the Mole

28. 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
Compare at the same temp. and pressure.

29. Standard Temperature and Pressure
0ºC and 1 atm pressure
abbreviated STP
At STP 1 mole of gas occupies 22.4 L
Called the molar volume
Avogadro’s Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles.

30. Examples What is the volume of 4.59 mole of CO2 gas at STP?
How many moles is L of O2 at STP?
What is the volume of 8.8g of CH4 gas at STP?

31. Density of a gas D = m /V for a gas the units will be g / L
We can determine the density of any gas at STP if we know its formula.
To find the density we need the mass and the volume.
If you assume you have 1 mole than the mass is the molar mass (PT)
At STP the volume is 22.4 L.

32. Examples Find the density of CO2 at STP.
Find the density of CH4 at STP.

33. The other way
Given the density, we can find the molar mass of the gas.
Again, pretend you have a mole at STP, so V = 22.4 L.
m = D x V
m is the mass of 1 mole, since you have 22.4 L of the stuff.
What is the molar mass of a gas with a density of g/L?
2.86 g/L?

34. All the things we can change

35. We have learned how to change moles to grams moles to atoms
moles to formula units
moles to molecules
moles to liters
molecules to atoms
formula units to atoms
formula units to ions

36. Mass
Moles

37. Mass ?g
Moles

38. Mass
Volume ?g
Moles

39. Mass
Volume
22.4 L ?g
Moles

40. Mass
Volume
22.4 L ?g
Moles
Representative
Particles

41. Mass
Volume
22.4 L ?g
Moles
6.02 x 1023
Representative
Particles

42. Mass
Volume
22.4 L ?g
Moles
6.02 x 1023
Representative
Particles
Atoms

43. Mass Volume Moles 6.02 x 1023 Representative Particles molecules Atoms?g
Moles
6.02 x 1023
Representative
Particles
molecules
Atoms

44. Percent Composition Like all percents Part x 100 % whole
Find the mass of each component,
divide by the total mass.

45. Example
Calculate the percent composition of a compound that is 29.0 g of Ag with 4.30 g of S.

46. Getting it from the formula
If we know the formula, assume you have 1 mole.
Then you know the pieces and the whole.

47. Examples Calculate the percent composition of C2H4?
Aluminum carbonate.

48. From percentage to formula
Empirical Formula
From percentage to formula

49. The Empirical Formula
The lowest whole number ratio of elements in a compound.
The molecular formula the actual ration of elements in a compound.
The two can be the same.
CH2 empirical formula
C2H4 molecular formula
C3H6 molecular formula
H2O both

50. 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.

51. Calculating Empirical
Means we can get ratio from percent composition.
Assume you have a 100 g.
The percentages become grams.
Can turn grams to moles.
Find lowest whole number ratio by dividing by the smallest.

52. 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 gC
16.22 g H x 1mol H = mole H gH
45.11 g N x 1mol N = mole N gN

53. Example The ratio is 3.220 mol C = 1 mol C 3.219 molN 1 mol N
The ratio is mol H = 5 mol H molN mol N
C1H5N1
A compound is % P and % O. What is the empirical formula?
Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?

54. 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 the mass of one mole of the empirical formula.
Caffeine has a molar mass of 194 g. what is its molecular mass?

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