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CH 3: Stoichiometry

Moles

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Mole Defined

Mole = number equal to the # of carbon

atoms in exactly 1 !rams of "ure C1$

% Mole = &$' x 1'3

% Called ()o!adro*s number

+ne mole of "rotons = 1!

+ne mole of neutrons = 1! +ne mole of an element = atomic mass in

!rams

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Molar Mass and related terms

Molar mass % mass in !rams of one mole of a

substance

% molecular ,ei!ht- mass of 1 molecule in amu

%.ormula ,ei!ht- mass of 1 formula unit for an ioniccom"ound in amu

Calculate by summin! the masses of the

com"onent atoms- units:

%molar mass % !rams or !rams/mole

%molecular ,t 0 formula ,t amu

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Moles- mass and # "articles

Molar mass lins the mass of a substance

to the number of "articles "resent

1 mole M! = 2$31! = &$' x 1'3M! atoms

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Molar Mass elated Calculations:

1$ Molar mass of a substance$

$ Moles "resent in a !i)en mass of

substance$3$ Mass of a !i)en number of moles of a

substance$

2$ 4umber of "articles in a !i)en mass or a!i)en number of moles of a substance$

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1$ 5hat is the molar mass of !lucose$ 6he

formula for !lucose is C&H1+&$

$ 5hat is the mass of '$'3 moles of

!lucose7

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3$ Ho, many !lucose molecules are

"resent in '$'3 moles of the

com"ound7

2$ Ho, many moles of !lucose are "resent

in 3$8 x 1'#3!rams of the substance7

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Mass 9ercent

Com"ounds are ty"ically described by

either their chemical formula or their

"ercent by mass of the com"onent

elements$

Mass ; = n

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Mass 9ercent Calculations

Calculate the mass "ercent of each

element in C&H1+&%(ssume one mole of the substance$

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>m"irical and Molecular .ormulas

Molecular formula % ratio of atoms in a

molecule

>m"irical formula % sim"lest ratio of

elements in a molecule

?lucose:

% Molecular formula: C&H

1+

&

% >m"irical .ormula:

Molecular formula = n

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Mass >m"irical .ormula

?i)en mass "ercent data:

1$ @CalculateA mass in !rams of each element in1'' ! of com"ound$

$ Con)ert each mass into moles of the element$3$ Di)ide each molar ans,er by the smallest ofthe )alues$

2$ Bf the numbers obtained in ste" 3 are not ,holenumbers- multi"ly all by an inte!er so theresults are ,hole numbers

8$ 5hole numbers obtained in ste" are thesubscri"ts in the em"irical formula$

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>m"irical .ormulaMolecular

.ormula

Molar mass needed

Calculate mass of one mole of the

em"irical formula$

Molar Mass = inte!er

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Caffeine

Molar mass = 12 !/mol

2$2 C

8$1 H

E$E8 4

1&$2E +

5hat is the em"irical and molecular formulaof caffeine7

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(cetamino"hen

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CH 3: #E&

Grea: Molar Mass &' !/mol

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3$F/3$E Chemical eactions

5ritin! chemical reactions

% 5rite the correct chemical formula for each

reactant and "roduct$

% Gse a subscri"t after each formula to indicate

the state of each substance

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Chemical equations must obey the la, of

conser)ation of matter % balancin! does

this$

alance the equation by addin!

coefficients in front of reactants and

"roducts as needed

% D+ 4+6 CH(4?> 6H> .+MGI(S .+

6H> C+M9+G4DS

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+ne of my fa)orite chemical reactions:

M!la, of conser)ation of matter % reactionneeds to be balanced

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M!

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alance the eactions

4

4a9b

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Meanin! of the alanced eaction

(tomic le)el

Molar le)el

Stoichiometry relationshi" bet,een

moles- the balanced reaction and mass

% 9a!e 1'7 outlines the needed ste"s

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4a J Cl 4aCl

mol 4a J 1 mol Cl mol 4aCl

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Cooie exam"leK

e!!s J 1 ba! chi"s 8' cooies

Ho, many cooies could you mae if youhad only one e!!7

Ho, many cooies could you mae if youhad ba!s of chi"s7

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Molar atios

alanced reactions lead to molar ratios

4 J 3 H

4H3

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4

1$ Bf 3$8 !rams of 4 to react- ho, many

moles and ho, many !rams of 4H3,ould be made7

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4

1$ Ho, many !rams of H are needed to

mae3F$E !rams of 4H37

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Ii+H J C+IiC+3 J H+

1$ Ho, many !rams of Ii+H are needed to

react F8'$ !rams of C+7

$ Ho, many !rams of IiC+3 ,ill be made

if F8'$ !rams of C+ react7

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Iimitin! ea!ent

eactants are not al,ays combined in

stoichiometric quantities$

+ften one reactant is used u" before

others$

6his reactant is said to be the limitin!

rea!ent

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Iimitin! ea!ent Calculations

5hen you are !i)en masses for each

reactant you must determine ,hich

reactant is limitin!$

1$ Con)ert !rams of each reactant to moles$

$ Gse the molar ratios to determine ,hich

reactant is limitin!$

3$ ase the amount of "roduct that can be

made on the limitin! rea!ent$

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(nother (""roachL

1$ Con)ert !rams of each reactant to moles$

$ Calculate the moles

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4

1$8 !rams of nitro!en is combined ,ith

$3' !rams of hydro!en$

5hich reactant is in excess and ,hich is

limitin!7

Ho, many !rams of ammonia ,ill be

made7

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9ercent ield

ield = actual yield x 1''

theoretical yield