Stoichiometry AP Chemistry - PowerPoint Presentation

Slide1

Stoichiometry AP ChemistryMr. GuerreroSlide2

Stoichiometry Homework, due on the day of chapter exam. Zumdahl

Text, 9

th

ed.

page 126:

#10, 13, 18, 38, 40, 46, 50, 66, 74, 84, 86, 88, 100, 106, 122, 124, 126.

Write out all conceptual(non-math) questions & answer in complete sentences.

Box all answers.

Math questions: write out all givens and unknown. Show all work, you do not need to write out these questions.Slide3

IsotopesElement-matter consisting of atoms with the same # of protons. Isotopes- atoms of the same element w/ different # of neutrons.

Most elements are comprised of several isotopes.

Ex: Boron, B-10(10.0129

amu

, 19.80%) & B-11(11.009amu, 80.20%)Slide4

Finding avg atomic mass from isotope abundancies

Find the avg. atomic mass of boron as an element.

AVG. = M

1

F

1

+ M

2

F

2

+ …..

M

1

mass of 1

st

isotope, F

1

fraction of 1

st

isotope=%/100

M

2

mass of 2

nd

isotope, F

2

fraction of 2

nd

isotope=%/100Slide5

BoronB-10(10.0129

amu

, 19.80%) & B-11(11.009amu, 80.20%)

What is the avg. atomic mass of boron?Slide6

Isotope practiceCopper has two natural occurring isotopes:

Cu-63(62.9296

amu

) 69.17% & Cu- 65. What is

the atomic mass of the Cu-65 isotope? Slide7

AntimonySb-121(120.9038 amu

) & Sb-123(122.9042

amu

)

Find the relative abundancy of each isotope:Slide8

Old Pennies/New PenniesOld pennies = 3.07g & New pennies = 2.49g

If 10 pennies have a mass of 26.65 grams, how many

old pennies are in the mix?Slide9

Mass Spectrometer-an instrument that vaporizes, then ionizes a sample. It is then accelerated across a magnetic field. The momentum of the particles determines it’s angle of deflection. The angle determines the atomic mass of the particles.Slide10

Calculate the avg. atomic mass & identify the element:Slide11

Calc. the avg. atomic massSlide12

Calc. the avg. atomic mass:Slide13

One more time…..Iridium has two naturally occurring isotopes: Ir-191(190.9606amu) & Ir-193(192.9629amu) Find the relative percent abundance of each isotope.Slide14

Molar massMolar mass- the mass of 1 mole of substance.1mole= 6.022 x 10

23

particles

What is the molar mass of each?

N

2

(g)

P

4

(s)

O

3

(g)

S

8

(s)

C

(soot)

C

60

(s)

C

6

H

12

O

6

(s)

Mg

3

(PO

4

)

2

(s)

Slide15

Every pure substance has a formula:Molecular Formula- (true formula) the actual # of atoms in a molecule.

Empirical Formula-the Molecular formula in simplest whole number ratio.

Substance Molecular F. Empirical F.

glucose C

6

H

12

O

6

CH

2

O

water H

2

O

H

2

O

butane C

4

H

10

C

2

H

5Slide16

Percent Composition Empirical Formula

A mass spectrometer is a machine that finds the % of each element in a compound. From the experiment results, we can easily find the formula of unknown substances.Slide17

Ex: An experiment yields that a substance is 43.64% phosphorus, and the rest is oxygen.The molar mass is 284 g/mol. Find the empirical and molecular formulas.Slide18

A substance is found to be 49.99%C, 5.61%H, and the rest is oxygen. Find the empirical & molecular formulas, if the molar mass is 216g/mol.Slide19

Empirical FormulaPercent Composition

Find the percent composition of each:

CO

2

Al

2

O

3

Fe

2

O

3

Fe(NO

3

)

3Slide20

20 min. Quiz tomorrowSlide21

Reaction stoichiometry

Law of conservation of mass-during an ordinary chemical reaction, matter is neither created, nor destroyed.

During a chemical reaction, atoms change the way that they are bonded, but they are still the same atoms. Ergo, the mass of all reactants must equal the mass of all products.

For this reason, we must balance chemical equations.Slide22

Balance the following reactions

TYPE of

Rxn

C

5

H

10

+ O

2

 CO

2

+ H

2

O

N

2

+ H

2

 NH

3

NO

2

 N

2

O

4

H

2

O

2

 H

2

O + O

2

K

2

CO

3

+ Ca  CaCO

3

+ K

Na

3

PO

4

+ CuSO

4

 Cu

3

(PO

4

)

2

+ Na

2

SO

4

Slide23

Molar ConversionsX is always the given substance:

Grams X

Mole X

Moles Y

Grams Y

Particles X

Liters X(@STP)

Particles Y

Liters Y(@STP)Slide24

Molar Conversions practice:If 45.8 grams of ammonia reacts with excess oxygen, how many grams of H2

O can form?

Rxn

: NH

3

+ O

2

 NO + H

2

OSlide25

If 16.3 liter of oxygen gas(@STP) react with excess C3H6, how many CO2

molecules can form(assuming 100% yield)?

Rxn

: C

3

H

6

+ O

2

 CO

2

+ H

2

OSlide26

Percent Yield3.50 grams of H2 react with excess O

2

, to form 30.8 grams of water. Find the percent yield.

Slide27

Percent Yield2.8 moles N2 react with excess H

2

. How much NH

3

will form at 88.5 percent yield?Slide28

Limiting ReactantLimiting Reactant-the reactant which runs out first, ending the reaction.Excess Reactant-reactant that has

unreacted

amount left over.Slide29

If 14.5 liters NH3 gas(@STP) react with 50.0 gramsCuO(s)

, how many grams of H

2

O can form? Find the

Limiting reactant and the amount of excess left over.

Rxn

: NH

3(g)

+

CuO

(s)

 N

2(g)

+ Cu

(s)

+ H

2

O

(g)Slide30

If 5.00 x 1023 Fe3O4

formula units react with 98.2 liters CO(@STP). How many grams CO

2

can form? Identify the LR/ER. How much excess is left over?

Rxn

: Fe

3

O

4

+

4

CO



3

Fe +

4

CO

2

Slide31

25.0 grams of C3H8 react with 25.0 grams of O

2

. What mass of H

2

O can form? Identify LR/ER & amount left over.

C

3

H

8

+

5

O

2



3

CO

2

+

4

H

2

OSlide32

Combustion Analysis: Determining the formula of a compound by mass of CO2 & H2O formed.Slide33

A 0.00300 g sample of napthalene, a compound containing only carbon and hydrogen, was burned in excess oxygen to give 0.0103 g of CO

2

. Determine the empirical formula of

napthalene

. The formula weight (molecular weight) of

napthalene

is 128 u, determine the molecular formula.Slide34

Combustion Analysis: Determining the formula of a compound by mass of CO2 & H2O formed

.

Menthol contains carbon, hydrogen and oxygen, 95.6

mg of menthol (molar mass = 156 g/

mol

) are burned in oxygen gas to give 269 mg CO

2

 and 110 mg H

2

O. What is menthol's empirical

and molecular formula

?