1. Chemical Quantities and Dimensional Analysis
Avogadro’s Number and the Mole
Percent Composition
Empirical Formulas
Molecular Formulas

2. Welcome Back!!

3. The Mole: What does it have to do with Chemistry???

4. Conversion Factors >Also called dimensional analysis
>Technique used to change one unit to another
When conversion factors are used properly, all units will cancel out except for the unit being converted to.
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5. Writing Conversion Factors
Example: Take the equality that states the relationship between seconds and minutes:
1 minute = 60 seconds
Two conversion factors can be formed from this equality. They are:
The first conversion factor will convert time from seconds to minutes. The second conversion factor will convert from minutes to seconds.
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6. Conversions Factors Conversion factors are equal to 1. Why?
The numerator equals the denominator.
A conversion factor does not change the value of a measurement. It only changes the way the measurement is expressed.
For example, 30 minutes, 0.5 hr, and 1800 seconds all express the same amount of time.
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7. Get out a calculator!! (not your phone)

8. Dimensional Analysis
Dimensional analysis is a technique of problem-solving that uses conversion factors to help solve the problem.
We will use dimensional analysis throughout this semester to solve problems. HOORAY!!!!!!!
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9. How many hours are in 3467 seconds?
This time we will need to convert from seconds to minutes and then minutes to hours. We will need two conversion factors.
To get the answer, you multiply what is on top and divide by what is on the bottom.
The answer is hr.
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10. The answer is 11.25 cases. Therefore, you should buy 12 cases of soda.
You are planning a party for 135 guests. You have been told to buy two colas for each guest. You know that there are 24 colas in a case. How many cases of cola should you buy?
The answer is cases. Therefore, you should buy 12 cases of soda.
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11. The answer is 50.6 pizzas. Therefore, you should buy 51 pizzas.
You also need to order pizza for the party. If each guest can eat three slices of pizza and there are 8 slices per pizza, how many pizzas should you order?
The answer is 50.6 pizzas. Therefore, you should buy 51 pizzas.
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12. Your mother should make 15 batches of cookies.
Your mother has agreed to make cookies for the party. If each guest can eat four cookies and there are 3 dozen cookies in a batch, how many batches of cookies should your mother make?
Your mother should make 15 batches of cookies.
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13. No, the bag is not within the weight limit.
The weight limit on most airlines for checked baggage is 23 kg. If your bag weighs 55 pounds, is it within the weight limit?
No, the bag is not within the weight limit.
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14. The Mole
The mole (mol) is the SI unit for the amount of substance that contains as many particles as there are in exactly 12 g of carbon-12.
1 mole of Cu = 63.55g
1 mole of Al = g
1 mole of Zn = 65.39g
1 mole of Fe = 55.85g

15. Molar Mass The total mass in grams of one mole of that substance.
Mrs. K-- shut up!
The total mass in grams of one mole of that substance.
The units for molar mass are g/mol.

16. Molar Mass of an Element
The molar mass of an element is equal to the atomic mass of an element in atomic mass units, or AMU (which can be found on the periodic table).
What is the molar mass of lithium?
6.94 g/mol
What is the molar mass of carbon?
12.01 g/mol

17. Molar Mass of a Compound or a Diatomic Element

19. Molar Mass Calculations
What is the molar mass of oxygen gas?
O2 = 2 ×16.00 = g/mol

20. Molar Mass Calculations
What is the molar mass of calcium nitrate?
Ca2+, NO3- = Ca(NO3)2
Ca = 1×40.08 g/mol = g/mol
N = 2×14.01g/mol = g/mol
O = 6×16.00 g/mol = g/mol
40.08 g/mol g/mol g/mol=
g/mol

21. ROUND ROCK CSI Benzoyl methyl cocaine – 303.36 g/mol
3methyl ether morphine – g/mol
Diacetyl morphine (heroin) – g/mol
Magnesium sulfate (epsom salt) – g/mol
Sodium Chloride (table salt) – g/mol
Sodium Bicarbonate (baking soda) – g/mol
Sucrose (sugar) – g/mol

22. Warm up
Complete the 8 problems on the molar mass practice you picked up by the door!
This will be a daily grade.
Turn in your CSI lab from last class.
This is a lab grade.

23. Percent Composition
Percent composition is the percent by mass of each element in a compound.

24. Find the percent by mass of carbon in carbon dioxide.
First determine the chemical formula for carbon dioxide.
Carbon Dioxide = CO2
Next determine the mass of each element present in the compound and the molar mass of the compound.
C = 1×12.01 = g/mol
O = 2×16.00 = g/mol
12.01 g/mol g/mol = g/mol
Finally, determine the percent of carbon.

25. Find the percent composition of aluminum sulfate.
First determine the chemical formula for aluminum sulfate.
Al3+, SO = Al2(SO4)3
Next determine the mass of each element present in the compound and the molar mass of the compound.
Finally, determine the percent by mass of each element present in the compound.

26. Calculations involving Moles
Let’s make a chart to help us calculate.

27. 1. Calculate the number of moles of NaCl in 175.5 g of the salt.
First determine the molar mass of NaCl.
23.00 g/mol g/mol = g/mol
= mol NaCl

28. 2. Calculate the mass of 0.800 mol of H2SO4
First determine the molar mass of H2SO4.
2.02 g/mol g/mol g/mol = g/mol
= 78.5 g H2SO4

29. *READ THE PROCEDURE CAREFULLY BEFORE STARTING!!*
1. Unwrap one piece of Dubble Bubble bubble gum. Do NOT throw away the wrapper.
2. Place the wrapper on the electronic balance.
3. Record the mass of the wrapper in the data table below.
4. Press the “Zero” button on the balance. The electronic balance should read 0.0g after you have pressed this button.
5. Place your un-chewed piece of Dubble Bubble on the wrapper on the electronic balance.
6. Record the mass of the piece of Dubble Bubble bubble gum in the data table below.
7. Chew the gum for several minutes until you believe that all of the sugar has been dissolved by your saliva.
8. Place the chewed gum in the wrapper.
9. Using the electronic balance, weigh the wrapper and the chewed gum.
10. Record the mass of wrapper and chewed gum in the data table below.
11. Repeat steps 1 – 10 using Wrigley’s Winterfresh gum

30. the smallest whole-number ratio of the different atoms in the compound.
Examples: CH4, NH3, CO,
Why aren’t N2H4 or C2H6 examples of empirical formulas?
They are not in the smallest whole-number ratio.
Empirical Formulas

31. Steps for Determining the Empirical Formula
Determine the number of moles of each element present.
Divide each value of the number of moles by the smallest value.

32. A compound is found to be 79. 8% carbon and 20. 2% hydrogen
A compound is found to be 79.8% carbon and 20.2% hydrogen. What is the empirical formula of the compound?
First determine the number of moles of each element.
CH3
Next divide each answer by the smallest number of moles.

33. What is the empirical formula of a compound that is 25
What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen?
N2O5

34. HOORAY IT’S FRIDAY!
We will start today with notes, then practice problems the rest of the period… but don’t worry, you will get up and move around!

35. So… what are we doing today?
Let’s start here:

36. Molecular Formulas
A molecular formula is a formula that shows the types and numbers of atoms combined in a single molecule of a molecular compound.
It is either the same as the empirical formula or a whole-number multiple of it.
Which of the following are possible molecular formulas for CH4?
C2H8 C4H C5H C6H24
C2H8, C5H20 and C6H24 are possible molecular formulas.

37. Steps for Determining the Molecular Formula
Determine the empirical formula of the compound.
Calculate the molar mass of the empirical formula.
Divide the molar mass of the molecular formula (given) by the molar mass of the empirical formula to determine the ratio of the molecular formula to the empirical formula.
Multiply each subscript in the empirical formula by the ratio calculated in step three.

38. A compound has an empirical formula of CH3
A compound has an empirical formula of CH3. The molar mass of the compound is 30. g/mol. What is the molecular formula of the compound?
We already know that the empirical formula of this compound is CH3.
Now we must calculate the molar mass of the empirical formula.
(1.01) = g/mol
Next divide the molar mass of the molecular formula by the molar mass of the empirical formula.
Finally, multiply each subscript in the empirical formula by the ratio obtained from the previous step.
C2H6

39. A compound has a molar mass of 324 g/mol and contains 25
A compound has a molar mass of 324 g/mol and contains 25.9% nitrogen and 74.1% oxygen. What is its molecular formula?
The empirical formula is N2O5.
The molar mass of N2O5 = 2(14.01) + 5(16.00) = g/mol
The ratio of the molar mass of the molecular formula to the molar mass of the empirical formula is
The molecular formula is N6O15

40. INCLUDING UNITS! Like… “100 g NaCl”)
2nd Period:
You are completing 1-15
(SHOWING ALL YOUR WORK,
INCLUDING UNITS! Like… “100 g NaCl”)

41. The percent composition of a compound is 40.0%C, 6.7% H, and 53.3% O. The molar mass of the compound is 90.0 g/mol. Determine the molecular formula.
Once again, we must first find the empirical formula.
The empirical formula is CH2O. CH2O = 30.0 g/mol
The molecular formula is C3H6O3.

42. Representative Particles
A representative particle is the smallest particle of a substance that has all of the properties of that substance.

43. Representative Particles
Different substances are made up of different types of representative particles.
For example:
Elements are made up of atoms.
Molecular compounds and diatomic elements are made up of molecules.
Ionic compounds are made up of formula units.

44. Avogadro’s Number
A mole of any substance contains 6.02×1023 representative particles of that substance.
This is known as Avogadro’s Number.

45. Avogadro’s Number 1 mole = 6.02×1023 atoms
1 mole = 6.02×1023 molecules
(molecular compound or diatomic molecule)
1 mole = 6.02×1023 formula units
(ionic compound)

46. 4. A sample of nitrogen gas contains 1. 20×1025 molecules
4. A sample of nitrogen gas contains 1.20×1025 molecules. Determine the number of moles of nitrogen in the sample.
= mol N2

47. 3. How many sodium atoms are in 2.5 mol of sodium metal?
= 1.5×1024 atoms Na

48. 4. A sample of nitrogen gas contains 1. 20×1025 molecules
4. A sample of nitrogen gas contains 1.20×1025 molecules. Determine the number of grams of nitrogen in the sample.
=558 g N2

49. 5. How many calcium atoms are in a 10.0 g sample of calcium metal?
= 1.50×1023 atoms Ca