quantitative chemistry experiments

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%



&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 ')



*elative formula mass +calculator



alculating relative formula mass



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.



What is the mass of one mole?



*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



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



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



How much o$ygen?



How much nitrogen?



om!aring fertili/ers



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



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/

quantitative chemistry experiments

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