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7/25/2019 Quantitative Chemistry Experiments
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How is the mass of atoms measured?
Atoms are so small that their
masses are not measured directly.
ne !rain of sand contains millions of
atoms" so atoms must #e really small.
$ow is the mass of an atom measured%
&nstead" all atoms are com'aredwith the mass of car#on(12.
)he mass of an atom on this scale is
called its relative atomic mass.
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What is relative atomic mass?
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Where are r.a.m. values found?
)he *alues of relati*e atomic mass +r.a.m., are usually
!i*en in a data #ook or found in the 'eriodic ta#le. -o you
dont ha*e to work them out or remem#er them all/
hen lookin! u' relati*e atomic mass in the 'eriodic ta#le"
remem#er that it always the lar!er of the two num#ers !i*en.
atomic number
symbol
relative atomic mass
hat is the other num#er%
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Identifying relative atomic mass
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Why isnt r.a.m. always a whole number?
elati*e atomic mass +r.a.m., is not always a whole num#er.
or eam'le" the r.a.m. of chlorine is 35.5.
hlorine has two isoto'es6
chlorine-35+75, and chlorine-37+25,.
)he standard r.a.m. *alue of each
element is actually the average relati*e
atomic mass" which takes all the
isoto'es of each element into account.
average r.a.m. of chlorine 8 +35 75, 9 +37 25,
8 +35 0.75, 9 +37 0.25,
8 2.25 9 :.25
8 35.5
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alculating average r.a.m. from isoto!es
hat is the a*era!e r.a.m. of naturally(occurrin! #romine%
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What about the mass of com!ounds?
=ost su#stances are made of molecules"not indi*idual atoms. =olecules are really
small too" so can we work out their masses
in the same kind of way%
f course/ )he mass of a molecule is
called the relative formula mass. )his is
calculated #y addin! u' the relati*e atomic
masses of all the atoms in the molecule.
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What is relative formula mass?
$ow is r.a.m. used to find the relati*e formula mass of $2%
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&te! '6 rite down the formula of the molecule.
How is relative formula mass calculated?
&te! (6 ind the r.a.m. of each ty'e of atom in the molecule.
&te! 36=ulti'ly each r.a.m. #y the num#er of atoms of thatelement and add these*alues to!ether.
)o find the relative formula massof a com'ound" add u'
the relati*e atomic masses of all the atoms in its formula.
hat is the relati*e formula mass of water%
-te' 16 formula of water is $2
-te' 26 r.a.m. *alues6 hydro!en 8 1" oy!en 8 1
-te' 36 relati*e formula mass 8 +2 1, 9 +1 1, 8 ')
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*elative formula mass +calculator
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alculating relative formula mass
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What is a mole?
or eam'le" the relati*e
atomic mass of car#on is 12"
so one mole of carbonatoms weighs '( grams.
hat is the mass of one mole of hydro!en atoms%
)he term moleis also used totalk a#out mass. ,ne moleof a
su#stance is its relati*e atomic mass"
or relati*e formula mass" in grams.
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What is the mass of one mole?
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*elative atomic mass true or false?
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an you wor out which fertili/er is best?
=y uncle uses fertili>ers on his allotment
to !row his 'ri>e(winnin! 'um'kins.
?ifferent fertili>ers contain different
com'ounds. @our uncle needs to findout the !ercentage by massof
nitro!en in each com'ound.
$ow can he work out which fertili>er
contains the most nitro!en%
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How is !ercentage by mass calculated?
)he 'ercenta!e #y mass of an element in a com'ound is
sometimes known as the !ercentage com!osition.
ercenta!e #y mass is calculated usin! r.a.m. and r.f.m.
-cientists use !ercentage by masscalculations to hel' them work out how
useful a su#stance is" how 'ure it is or
e*en to identify an unknown su#stance.
$ '001 element 2r.a.m. of element $ number of atoms
r.f.m of com!ound
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alculating !ercentage by mass e$am!le '
hat 'ercenta!e #y mass of nitrogenis in ammonia +H3,%
+r.a.m.6 $ 8 1" < 8 14,
&te! '6 ork out the relati*e formula mass +r.f.m., of
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alculating !ercentage by mass e$am!le (
hat 'ercenta!e #y mass of hydrogenis in ammonia +H3,%
+r.a.m.6 $ 8 1" < 8 14,
&te! '6 ork out the relati*e formula mass +r.f.m., of
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How much o$ygen?
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How much nitrogen?
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om!aring fertili/ers
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Which fertili/er is the best?
lant(B(#i!" which contains urea" has
the hi!hest 'ercenta!e of nitro!en.
351
('1
471
68 !um!in
&u!ergro
9lant-:-big
;ertili/er 1 nitrogen
-o" if my uncle 'uts the same amount
of each fertili>er on his 'um'kins"
lant(B(#i! will 'ro*ide the most nitro!en.
om!ound
H4,3
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Introduction to reacting masses
=y asthma inhaler uses a chemical
called sal#utamol. =illions of 'eo'le ha*easthma" so how do manufacturers work
out how to make enou!h sal#utamol%
=any useful su#stances are made
#y chemical reactions. -cientists decide how
much 'roduct they want to make and then work
out the amount of reactants needed.
)he first ste' is to write a balanced
symbol e>uationfor the reaction.
& b l i b l d ?
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&ymbol e>uations balanced or not?
: l i b l ti
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:alancing symbol e>uations
Wh b l d ti f l?
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Why are balanced e>uations useful?
)he #alanced eCuation for a
chemical reaction shows the ratio of
reactants and !roductsin*ol*ed.
)hese amounts are called the relative reacting masses.
)his ratio can #e used to calculate the masses of reactants
needed and the mass of 'roduct that will #e made.
)he #alanced eCuation for this chemical reaction shows
that the ratio of g ,(
g,is ( ' (.
(g @ ,( A (g,magnesium @ o$ygen Amagnesium o$ide
B i ti l '
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Bsing reacting masses e$am!le '
&f you ha*e 4; !rams of ma!nesium" what mass of oy!en
will react with this%
)he #alanced eCuation shows the ratio of g ,(is ( '.
om#inin! these two sets of information !i*esthe ratio of reactin! masses.
g ,(2
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Bsing reacting masses e$am!le (
&f you ha*e 4; !rams of ma!nesium" what mass of
ma!nesium oide will #e 'roduced%
)he #alanced eCuation shows the ratio of g g,is ((.
om#inin! these two sets of information !i*esthe ratio of reactin! masses.
g g,2
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*eacting masses
B i ti l 3
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Bsing reacting masses e$am!le 3
&f you ha*e 4;0 !rams of ma!nesium" what mass of
ma!nesium oide will #e 'roduced%
(g @ ,( A (g,
magnesium @ o$ygen Amagnesium o$ide
rom 're*ious calculations" the ratio of reactin! massesfor g g,2
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What are the rules for reacting masses?
)he rules for workin! out reacting massesare6
&te! '. rite down the #alanced sym#ol eCuation.
&te! (. rite down the relati*e atomicDformula
masses of the reactants and 'roducts.
&te! 3. Ese the #alanced eCuation to write down
the ratios of reactants and 'roducts.
&te! 4. on*ert to ratio of reactin! masses.
&te! 5. alculate the scale factor and a''ly this
to the ratio of reactin! masses.
*eacting masses wored e$am!le
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*eacting masses wored e$am!le
&f 2; ! of iron reacts with co''er sul'hate solution" what
mass of co''er will #e made%
&te! '. rite down the #alanced sym#ol eCuation.
;e @ u&,4 u @ ;e&,4&te! (. rite down the relati*e atomicDformula masses.
;e 2 5C u 2 C4
&te! 3. rite down the ratio of reactants and
'roducts.
;e u 2 ' ' &te! 4. on*ert to ratio of reactin! masses.
;e u 2 ' ' 2 5C g C4 g&te! 5. alculate the scale factor and a''ly this to the
ratio of reactin! masses.scale factor 2 () g E 5C g 2 0.5
mass of u made 2 C4 g $ 0.5 2 3( g
*eacting masses and scale factors
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*eacting masses and scale factors
What about reacting masses in industry?
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&ndustrial 'rocesses use tonnes of reactants" not !rams.
Balanced eCuations and relati*e atomicDformula masses arestill used to calculate the masses of reactants and 'roducts F
#ut the unitsof !rams are swa''ed for tonnes or kilo!rams.
or eam'le" what mass of calcium oide +r.f.m.8 5, can #e
made from 200 tonnes of calcium car#onate +r.f.m.8 100,%
r.f.m. valuesgive ratio of
reacting masses
-o" #y eCui*alence" 100 tonnes of calcium car#onate
'roduces 5 tonnes of calcium oide" and" therefore"
(00 tonnes'roduces ''( tonnesof calcium oide.
What about reacting masses in industry?
a,3 a, ,(@
'00
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*eacting masses in industry
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Introduction to yield and atom economy
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Introduction to yield and atom economy
&m worried a#out the en*ironment and
usin! u' resources. $ow do manufacturersmake sure they dont waste chemicals%
All manufacturers want reactions to #e
as efficientas 'ossi#le. )hey dont want
to waste resources or ener!y" and they want
to make as much 'roduct as 'ossi#le.
)o work out how efficient reactions are"
scientists use yieldand atom economy.
What are the different ty!es of yield?
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What are the different ty!es of yield?
)he theoretical yieldis the maimum mass of 'roduct
e'ected from the reaction" usin! reactin! masses.
)o calculate the 'ercenta!e yield" you need to work out
the theoretical yieldand the actual yield.
)he actual yieldis the mass of the 'roduct that isactually o#tained from the real chemical reaction.
)he !ercentage yieldof a chemical reaction shows
how much 'roduct was actually made com'ared withthe amount of 'roduct that was e'ected.
hy is the actual yield usually less than the theoretical yield%
What factors affect the actual yield?
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What factors affect the actual yield?
How is !ercentage yield calculated?
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How is !ercentage yield calculated?
)he 'ercenta!e yield of a reaction is
the actual yield written as a 'ercenta!e
of the theoretical yield.
)he 'ercenta!e yield is always less than 100.
)he eCuation for workin! out the 'ercenta!e yield is6
hy is the 'ercenta!e yield ne*er 100%
hat does it mean if the 'ercenta!e yield of a reaction is 0%
!ercentage yield 2 $actual yield
theoretical yield'00
alculating !ercentage yield e$am!le
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alculating !ercentage yield e$am!le
& reacted co''er sul'hate solution
with some iron. Esin! reactin! masses"& worked out that the theoretical yield of the
reaction was 50 !rams of co''er.
& lost some co''er when & filtered thesolution and ended u' with 40 !rams. hat
is the !ercentage yieldof my reaction%
!ercentage yield 2 $ '00actual yieldtheoretical yield
!ercentage yield 2 $ '00 2 )0140g
50g
alculating !ercentage yield
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alculating !ercentage yield
What is atom economy?
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What is atom economy?
8tom economyis another measure
of the efficiency of a chemical reaction.
&t is the amount of startin! materials
that end u' as useful 'roducts.
&n an ideal chemical 'rocess" all the startin! materials end
u' as useful 'roducts and no atom is wasted.
&f most of the startin! materials end u' as useful 'roducts"
the reaction is said to ha*e a high atom economy.
hy is it im'ortant for sustaina#le de*elo'ment and for
economicalreasonstousereactionswithhi!hatomeconomy%
Why is high atom economy im!ortant?
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Why is high atom economy im!ortant?
A chemical reaction with a high !ercentage yieldhas a
high atom economy.
to minimise waste of non(renewa#le reactants
)his is im'ortant for the chemical industry for many reasons6
to make as much useful 'roduct as 'ossi#le
to minimise ener!y use in runnin! factories
to minimise ener!y use in heatin! chemical reactions
to reduce use of water for coolin! chemical reactions.
to reduce 'ollution from waste 'roducts
8tom economy true or false?
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8tom economy true or false?
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lossary
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lossary
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lossary
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8nagrams
ulti!le-choice >ui/
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ulti!le choice >ui/
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