What does the little number below each

Element mean?

What are its’ units?

amu/atom

What is an amu

one amu is defined as 1/12th

of 12C

Average atomic mass or atomic weight is determined by a mass spectroscope.

example: Analysis of a sample of carbon was found to have the following isotopes

12C – 11.999 97.3%13C – 12.998 2.6%14C – 13.966 0.10%What is the atomic weight of Carbon

12C – (11.999) (.973) = 11.67513C – (12.998) (.026) = .3379514C – (13.966) (.0010)

= .013966

12.0269

How much is a mole?

How high could you stack a mole of sheets

of paper?

How much would a mole of iron weigh?Could you lift it?

Look on the back inside cover for amu and mole6.02214 x 1023 atoms of Fe 1atom of Fe

55.85 amu1 amu

1.66054 x 10-24 g*=55.85 g

What is the Mole?What is the Mole?

One mole is equal to the number of carbon atoms in exactly 12.00 grams of

C-12: 6.02 x 1023 atoms

Mole

# of atoms or molecules

volume of gasMass of atomor molecule

The Shopping Mole

6.02 x 10 23 atoms or molecules/mole

22.4 L / molex g/ mole

• Calculate the numbers of atoms of cesium found in 3.57 moles of cesium

• Calculate the numbers of atoms of cesium found in 3.57grams of cesium

• Calculate the mass of 4.82 x 1023 atoms of cesium

Calculating the molar mass of a compound (NH4)2S

1. Calculate the mass of 4.65 moles of (NH4)2S 2. Calculate the numbers of atoms of nitrogen found in 3.57grams (NH4)2S

3. Calculate the mass of nitrogen in 3.76 x 1024 formula units of (NH4)2S

Determining Percent Composition of Compounds

Given the compound: Al(HPO3)3

What are the percent compositions of each of the atoms from which the above compound is constructed?

Mass of Aluminum= 1 mol Al mole of Al

26.9 grams

Mass of hydrogen = 3 mols H mole of H

1.01 gram

Mass of Phosphorus = 3 mols P mole of P

30.9 gram

Mass of oxygen = 9 mols O mole of P

16.0 gram

= 26.9g Al

= 3.03 H

= 92.7 g P

= 144 g O

266 g

Al(HPO3)3

Mass percent of Al:mass of Al

mass of Al(HPO3)3

26.9 g26.9 g

266 g266 g==x 100x 100 == 10.1%10.1%

Mass percent of H:mass of H

mass of Al(HPO3)3

3.03 g3.03 g

266 g266 g==x 100x 100 == 1.13%1.13%

Mass percent of P:mass of P

mass of Al(HPO3)3

92.7 g92.7 g

266 g266 g==x 100x 100 == 34.8%

Mass percent of O:

mass of O

mass of Al(HPO3)3

144 g266 g

=x 100 = 54.1%

Empirical formula

A compound is composed of Cl 71.65% and C 24.27% and H

4.07% what is the empirical formula? The Molar mass is

98.96g/mole, what is the molecular formula?

Determining the Empirical Formula of a Determining the Empirical Formula of a Compound Using Combustion AnalysisCompound Using Combustion Analysis

Combustion AnalysisCombustion Analysis

mass difference of H2O absorber = 0.306 g

mass difference of CO2 absorber = 0.561 g

0.255 g isopropyl alcohol is combusted

mass difference of H2O absorber = 0.306 g

mass difference of CO2 absorber = 0.561 g

grams of H: 0.306 g H2O 18 g H2O1 mole H2O

1 mole H2O

2.02 g H = 0.0343 g H

grams of C: 0.561 g CO2 44 g CO2

1 mole CO2

1 mole CO2

12 g C = 0.153g C

grams of O: 0.255 g - 0.153 g - 0.0343 g H = 0.0677 g

C: 0.153 g C 12 g C

1 mol C= 0.0128 mol C

H: 0.0343 g H1.01 g H

1 mol H= 0.0340 mol C

O: 0.0677 g O16 g O

1 mol O= 0.0043 mol O

0.0043

1

0.00431

0.0043

1

= 2.97= 2.97

= 7.91= 7.91

= 1.00= 1.00

Assume that the empirical formula for the compound is C3H8O

Ascorbic acid (Vitamin C) contains 40.92 percent C, 4.58 percent H, and 54.50 percent O by mass. What is the empirical formula of ascorbic acid?

Ethylene glycol, the substance used in automobile antifreeze, is composed of 48.7 % C, 9.7 percent H, and 51.6 percent O by mass. Its molar mass is 62.1 g/mol. (a) What is the empirical formula of ethylene glycol? (b) What is the molecular formula

So What is Stoichiometry?

mass of A in g mole 3(moles C) C g = mass C A g 1(moles A) mole

1A + 2B → 3C + 4D

Na2SO3(aq) + 2AgNO3(aq) Ag2SO3(s) + 2NaNO3(aq)

If 3.4 g of silver nitrate is mixed w/ excess sodium sulfite, what would be the theoretical yield for silver sulfite?

a) in moles

b) in formula units

c) in L at STP

d) in grams

Na2SO3(aq) + 2AgNO3(aq) Ag2SO3(s) + 2NaNO3(aq)

• If 3.4 g of silver nitrate is mixed sodium sulfite, how many grams of sodium sulfite would you need to react completely?

Na2SO3(aq) + 2AgNO3(aq) Ag2SO3(s) + 2NaNO3(aq)

If 4.5 g of sodium sulfite is mixed w/ excess silver nitrate, what would be the theoretical yield for silver sulfite?

What would be the percent yield if 4.1g was produced in the lab?

Na2SO3(aq) + 2AgNO3(aq) Ag2SO3(s) + 2NaNO3(aq)

If 4.3 g of silver nitrate is mixed w/ 3.2g sodium sulfite, what would be the theoretical yield for silver sulfite?

How much of the excess reagent is left over?

Using Stoichiometry in the LaboratoryUsing Stoichiometry in the Laboratory

Na2SO3(aq) + 2AgNO3(aq) Ag2SO3(s) + 2NaNO3(aq) 20 ml0.35 M

20 ml0.12 M

1. How many grams of silver sulfite would be produced?2. What would be the molarity of the sodium nitrate?