chy 115 moles
TRANSCRIPT
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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