Warmup: 5 minutes

1. Why do we use moles?

Makes it easier to measure chemical quantities because atoms and molecules are very small.

2. Define the following ‘molecabulary’ words

demoleition molearchy molectomy

3.

a. What is a mole's favorite movie?

b. What did Avogadro teach his students in math class?

c. What kind of fruit did Avogadro eat in the summer?

Molar Mass Conversions and Empirical Formulas

*need calculator and PTdemoleition - the destruction which moles bring about in your yard.

molearchy - government in which moles are in complete control; under this government Mole Day is celebrated twice a year and chemistry is the only scientific subject taught in school

molectomy - the process of removing a mole's insides

a. What is a mole's favorite movie?

b. What did Avogadro teach his students in math class?

c. What kind of fruit did Avogadro eat in the summer?

The Green Mole

Moletiplication

Watermolens

1: What is the molar mass of Na2SO4?

Na: 2 mole x 22.99 = 45.98 S: 1 mole x 32.07 = 32.07 O: 4 mole x 16.00 = 64.00 = 142.05 g/mole

Calculating Molar Mass

1) Find the atomic mass of each element

2) Multiply the number of moles times the atomic mass of for each element

3) Add values, round to the hundredths place, and report your answer in g/mole

2. Calculate the molar masses of the following compounds:

a. Zr(SeO3)2 b. NH4OH c. Ca2Fe(CN)6.12H20

14.01

+ 1.01(5)

+ 16.00

35.06 g/mole

91.22

+ 78.96(2)

+ 16.00(6)

345.14 g/mole

40.08(2)

+ 55.85

+ 12.01(6)

+ 14.01(6)

+ 1.01(24)

+ 16.00(12)

508.37 g/mole

Ex 3: What is the molar mass of Pb(NO3)2?Pb: 1 mole x 207.20 = 207.20 N: 2 mole x 14.01 = 28.02 O: 6 mole x 16.00 = 96.00 = 331.22 g/moleEx 4: Find the mass % of each element in Pb(NO3)2

Pb207.20 g/mole

331.22 g/mole

= 0.6256or 62.56%

N

28.02 g/mole

331.22 g/mole

= 0.0846

or 8.46%

O

96.00 g/mole

331.22 g/mole

= 0.2898

or 28.98%

5. What are the mass percents of iron and oxygen in Fe22O3?

Iron: (2 x 55.85 g/mole) x 100= 69.94 %

(159.7 g/mole)

Oxygen: (3 x 16.00 g/mole) x 100 = 30.06 %

(159.7 g/mole)

Conversions using Molar Mass

Ex 6: How many moles is 5.69 grams of CH4 ?

5.69 g CH4 ( ) =

( )

1 mole CH4

16.05 g CH4

0.355 mole CH4

Ex 7: How many moles is 4.56 g of CO2 ?

4.56 g CO2 ( ) =

( )

You need the molar mass of carbon dioxide

1 mole CO2

44.01 g CO2

0.104 mole CO2

Ex 8: Find the mass (in grams) of 9.8 moles of lithium fluoride

9.8 mole LiF ( ) =

( )

You need the formula and molar mass of this compound FIRST!

25.94 g LiF

1 mole LiF

250 g LiF

Empirical formula: shows the relative numbers of atoms of each element using the smallest whole numbers.

Molecular formula: tells us actual numbers of atoms of each element in the molecule.

They CAN BE the same.

CH2OFormaldehyde!Emp. formula for lots of organic molecules, ex. C6H12O6

C3H4O3

Does not exist; emp. formula for ascorbic acid: C6H8O6

Molar mass must be known.

9. The empirical formula of styrene is CH; its formula weight (‘molar mass’) is 104.1 g/mole. What is the molecular formula of styrene?

molecular formula = multiple of the empirical formula* molar mass of the compound is needed

Molar mass styrene = 104.1 g/mole Molar mass emp.form. = 13.02 g/mole

= 7.995391… = 8

molecular formula = C8H8

10. A 25.0 gram sample of a compound contains 6.64 grams potassium, 8.84 g chromium, 9.52g oxygen. Find the empirical formula of this compound.

Step 1: Convert each mass to moles0.170 mole K 0.170 mole Cr 0.595 mole O0.170 0.170 0.170

Step 2. Get ratio of moles (by dividing each # moles by smallest # moles)

Mole ratio: 1 mole K: 1 mole Cr: 3.50 moles O

Step 3: If the numbers in the ratio are not integers, double, triple, etc each number until they are all integers….you may want to round slightly (ex. 2.98 can be 3 but 2.49 should be doubled to 4.98, then rounded to 5)

New ratio: 2 : 2 : 7 K2Cr2O7, potassium dichromate

11. Phenol is a compound which contains 76.57% carbon, 6.43% hydrogen, and 17.0% oxygen. What is the empirical formula of phenol?

If you are given percents of elements instead of actual masses, turn each percent into a gram amount out of a 100g sample

Step 1: Convert each mass to moles76.57g C/12.01 g C 6.43 g H/1.01g H 17.0 g O/16.00 g O

6.376 mole C 6.366 mole H 1.06 mole O1.06 1.06 1.06

Step 2. Get ratio of moles (by dividing each # moles by smallest # moles)

Mole ratio: 6 mole C: 6 mole H: 1 moles O

C6H6O = phenol!

12. A 5.00 gram sample of an acid contains 2.00 g carbon, 0.336 g hydrogen, and 2.66 g oxygen. Find the molecular formula of this acid and give the proper name if its molar mass = 60.06 g/moleTry this yourself. It is acetic acid. We will do the work on the board in a bit for 12 and 13.13. Monosodium glutamate (MSG), a food flavor

enhancer, has been blamed for "Chinese restaurant syndrome", the symptoms of which are headaches and chest painsMSG has the following composition by mass:35.51% carbon4.77 % hydrogen 37.85 % oxygen 8.29 % nitrogen 13.60 % sodiumWhat is its molecular formula it its molar mass is 169 g?