1. Chemistry SM-1131 Week 8 Lesson 1
Dr. Jesse Reich
Assistant Professor of Chemistry
Massachusetts Maritime Academy
Fall 2008

2. Class Today Poem Quiz Correction Grams, atoms, mols, avogadro’s number
“Moles,” g-> molecules, molecules  atoms, grams molecule  gram element, mass percent, mass percent from a chemical formula
Take Worksheets on moles Wednesday (each completed packet is worth 5 test points)
Test Friday: Nomenclature and formula writing (Ionic, molecular, acids) mole and gram conversions.

3. When I was one-and-twenty
By A. E. Housman ( )
When I was one-and-twenty I heard a wise man say, 'Give crowns and pounds and guineas But not your heart away; Give pearls away and rubies But keep your fancy free.' But I was one-and-twenty, No use to talk to me.
When I was one-and-twenty I heard him say again, 'The heart out of the bosom Was never given in vain; 'Tis paid with sighs a plenty And sold for endless rue.' And I am two-and-twenty, And oh, 'tis true, 'tis true.

4. Quiz Correction Put away your pens Take out your quizes
Switch quizes with your neighbor
Print your name in red ink on their quiz
Put a big X by a wrong answer
Put a check by a correct one
Grade your neighbors quiz:
8-0.1(wrong answers)= quiz grade

5. Molecular Mass
To figure out molecular mass you have to know the atomic mass.
Let’s start easily
Ne- it exists by itself and doesn’t form molecules. It’s mass is just the atomic mass of Ne, which is 20.18

6. Simple Molecule Mass
The mass of N2 is going to be twice the mass of 1 atom of N
So, if N has an atomic mass of 14.01, then N2 must have a mass of 2x14.01 or 28.02

7. Molecular Mass Ozone has the formula O3, what is it’s molecular mass
1 Oxygen has a mass of 16.00
3x(16.00) has a mass of amu

8. More Complex Masses Water has the formula H2O
The molecular mass is going to be from 2H atoms and 1 O atom, so
2x(1.0079) + 1x(16.00)= amu

9. Sugar
C6H12O6
6(12.01) + 12(1.0079) + 6(16.00)= ???

10. Moles Dozen: 12 somethings Baker’s Dozen: 13 Somethings
A Score: 20 Somethings
Avogadro’s number: 1 mol= 6.022e23 somethings

11. See how it works A dozen atoms = 12 atoms
A baker’s dozen atoms = 13 atoms
A score of atoms = 20 atoms
A mole of atoms = 6.022e23 atoms

12. Moles It just means a big number. 602,200,000,000,000,000,000,000,000
But we do this because it converts amu to grams

13. Moles 1 mole of atoms = 6.022e23 atoms
2 moles of atoms= 2(6.022e23)atoms= e24 atoms
3 moles of atoms = 3(6.022e23)atoms= e24

14. Moles 1 mole of kittens = 6.022e23 kittens
2 moles of kittens= 2(6.022e23)kittens= e24 kittens
3 moles of kittens = 3(6.022e23)kittens= e24

15. Why a 6.022e23
1 amu = 1.66e-24 grams
So, 1.66e-24gx6.022e23= g which is very similar to 1g.
The point is that if you multiply the mass of something in amu you can convert amu into a mass in grams
We don’t weigh anything in amu, but we do in grams so this is useful.
So, if we multiply the atomic mass of something by 1 mol it turns from amu into grams.

16. If you have 1 mole of N2 how much would it weigh?
Atomic Mass of N= amu
Molecular Mass of N2= amu
6.022e23 atoms of N2 x amu x 1.66e-24g =
1 atom amu
Which equals 28.02g.
So, 1 mol x molecular mass = # of grams

17. What do we do with this? Chemists generally convert moles into atoms.
Atoms into Moles
Moles into grams
Grams into Moles

18. Moles into atoms 1 mole has 6.022e23 atoms in it 1 mole
5 moles of Ne x 6.022e23 atoms = 3.011e24 atoms
1 mole
24.00 moles of He 6.022e23 atoms = 1.445e25 atoms

19. Atoms into Moles
You have e23 atoms of Cu many many moles of Cu do you have?
18.066e23 atoms x mol = mol
6.022e23 atoms

20. So Atoms x 1 mole = moles 6.022e23 atoms
Moles x 6.022e23 atoms = atoms
1 mole

21. Moles to grams We also convert moles into grams
You can’t weigh a mole, you weigh a gram
Moles x molecular mass in grams = grams
1 mole

22. Grams to Moles
Grams -> Moles
Xgrams x moles = moles
Atomic mass

23. New Material
“Moles,” grams molecule  gram element, mass percent, mass percent from a chemical formula

24. Mole 1 mole of something means 6.022e23 somethings
Remember 1 mole of a compound = the molecular mass in grams

25. Grams molecules  moles of an element
Grams of a molecule  moles of a molecule  moles of an element
25 g H2O has how many moles of Oxygen in it?
25g H2O x 1 mole H2O x mole O = 1.4 moles
18 gram H2O 1 moles H2O
25 g H2O has how many moles of hydrogen in it?
25g H2O x 1 mole H2O x mole H = 2.8 moles

26. Grams molecules  grams of an element
Grams of a molecule  moles of a molecule  moles of an element
25 g H2O has how many grams of Oxygen in it?
25g H2O x 1 mole H2O x mole O x g O = 22 grams O
18 gram H2O 1 moles H2O mole O
25g H2O x 1 mole H2O x mole H x g H = 2.8 grams H

27. Grams molecules  grams of an element
Grams of a molecule  moles of a molecule  moles of an element
88 g Fe(II)Cl2 has how many grams of Fe(II) in it?
88g Fe(II)Cl2 x mole Fe(II)Cl x 1 mole Fe(II) x g Fe(II) = 39 grams Fe(II)
gram Fe(II)Cl2 1 moles Fe(II)Cl mole Fe(II)
88 g Fe(II)Cl2 has how many grams of Cl in it?
88g Fe(II)Cl2 x 1 mole Fe(II)Cl2 x mole Cl x g Cl = 25 grams Cl
g Fe(II)Cl2 1 moles Fe(II)Cl mole Fe(II)

28. Mass Percent
Mass percent describes how much of a compound 1 element makes up
A high mass percent means it makes up most of the mass of the compound.
A low mass percent means it makes up just a little mass of the compound.
Whenever we talk about a percent we mean
Little Number x 100 = percent
Big Number

29. Mass percent CO2 1x(12) amu x 100 = 27% carbon 44 amu SF6
For Element A of compound AB
Atomic Mass A x # of A atoms x 100 = mass percent
Molecular mass of AB
CO2
1x(12) amu x 100 = 27% carbon
44 amu
SF6
100xMass of 6 F atoms or 114 amu x 100=88% Molecular Mass amu

30. Percent Composition
Percent Composition is when you figure out the mass percent for every element in the compound.
Sodium chloride has the formula NaCl. What is the percent composition of all elements?
23 amu / 58 amu x 100 = 39 % Na
35 amu / 58 amu x 100 = 61 % Cl

31. You can do this backwards too
Racecar is a palandrome, but it’s harder going backwards
Cl makes up 61% of sodium chloride. What’s the formula?
1- convert % to gram
2- Write the number of grams of element A
3- Convert from grams to moles by multiplying by 1 mole per molecular mass (in grams)
4- repeat steps 2 and 3 for every element
5- divide all number of moles by the smallest number of moles
6- reduce, double, or triple until all atoms are expressed as whole numbers, then write the formula

32. Go through the steps 1- 61% Cl 61g Cl 2- 61g Cl
3- 61g Cl x 1 mole Cl = 1.7 moles Cl
35 g Cl
4- 39% Na  39g Na
5- 39g Na x 1 mole Na = 1.7 moles Na
Decide which number is smaller. Divide both numbers by 1.7 moles. You get 1 mole of Na and Cl. So the formula must be Na1Cl1

33. Iron(II) Carbonate
In class right now. Figure out the formula (carbonate is (CO3)2-).
Figure out the percent composition of every element.
Use the percent composition to back out the formula.

34. Empirical Formula
What you are actually finding is the empirical formula. It’s the “reduced” form of a molecular formula. For ionic compounds the “reduced” form is always the molecular formula. For molecular compounds they are usually different.

35. Ethylene and butadiene C2H4 and C4H8
Perform a percent composition for both formulas
Compute the empirical formula for both
How are they related? Is the empirical formula the same thing as either molecular formula? How would the molecular formula of either relate to the empirical formula?

36. Emipirical Formula to molecular formula
Molecular formula = n x empirical formula
Molecular mass = n x empirical formula mass
Molecular mass/empirical formula mass = n
In a typical quiz/test problem you’ll usually have to calculate molecular mass from a formula, and you’ll be given either n or empirical formula mass and have to find the last variable.

37. Ethylene and butadiene C2H4 and C4H8
Calculate the n term for both of the above compounds.

38. Wednesday Wednesday is a working class day
Come to class, be prepared with the moles packets, your book, a syllabus for homework problems, and a calculator
I may or may not be here on Wednesday. You are expected to be in class. One of you will take attendance if I’m not here. Anyone missing class without sending me a note prior to class will be docked a letter grade from their final grade (B+  B).

39. Test Friday You will have a test Friday
There will be formula writing questions
There will be nomenclature questions
There will be ionic vs acid vs molecular qs
There will be mol -> gram, gram -> mol, gram  mol  atom, gram  mol  element  gram
I will ask you for percent composition, empirical formula, molecular formula for either CH2O & C6H12O6, C2H2 & C6H6, or C2Cl2 & C6Cl6
If you can’t do some of those question get help!