Study Guide 1d Calculations With Exam Qs and MS

7/24/2019 Study Guide 1d Calculations With Exam Qs and MS

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IGCSE Chemistry

Section 1d:relative formula masses and molar volumes of gases

The relative atomic mass (Ar) of an atom is found of the periodic table.

We usually use relative atomic masses correct to the nearest whole number (or 0.5 in the case

of Cl): ! "# C ! "$# % ! " ' ! "# %a ! $# Al ! $*# + ! $# Cl ! 5.5# Cu ! &

Relative formula mass, Mr

"." calculate relative formula masses (Mr) from relative atomic masses (Ar)

The relative formula mass is the relative mass of compounds and is calculated usin, the relativeatomic masses of the elements in the compound multiplied by the number of particles of thatelement.

C'$ -/ ! "$ $ 1" ! &&Cu(%')$ -/ ! & $ 1 ("& 1")! "22

relative molecular mass of $' ! "2 because ($ 3 ") for (" 3 ") for ' ! "2

relative formula mass of %a' ! &0 because $ " " ! &0

relative molecular mass of Al$(+'&)! because ($ 3 $* ) ( 3 $) ("$ 3 ") ! &$

Cu+'&.5$'

ind the relative molecular mass for each of the followin,. +'W your W'-4%6+

Cl7 /,Cl$78 9i' C& Ca+'& %&' (%&)$+'&

Calculate the relative formula mass of the followin,:

". '$7$$. %$7$2. $'7"2&. C'$7&&5. %7"*. %a'70*. %aCl7522. $+'&8. %'"0.Cl

"".Cu+'&"$.CuCl$".$+"&.C&"5.Ca'".Al$'"*.Cu(%')$"2.CaC'"8./,(%')$$0.Al$(+'&)

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IGCSE Chemistry

-elative ormula /ass Calculations

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IGCSE Chemistry

Calculating percentage by mass of elements in compounds.

The percenta,e by mass is important to mineral prospectors and is also useful in findin,formulae.f the formula is already ;nown it is simply a &&!.*$* "& C CaC'

5 % in %!"&>"*!.2$ "5 %a in %a$C' Cu in CuCl$ " ' in %aC'* Ca in Ca' "* 4 in 4$+'&2 + in +' "2 in %'8 %a in %aCl "8 + in Al$(+'&)"0 Cl in Cl $0 ' in Cu(%')$

'ther li;ely


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IGCSE Chemistry

a) % in %&%' !"!# b) % in 4%' "&>"0" c) % in %&@'&"&>82

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Calculate the percenta,e element in a compound

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$uestions: Relative ormula Mass and % Element in a compound

1. The symbol e


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IGCSE Chemistry

...........................................................e3cess C'$ ,as created.......................................

(. (a) The formula for ammonia is %. What does the formula tell you about each molecule

of ammonia? B"

......................................one nitro,en three hydro,ens......................................................

(b) Ammonia is used to ma;e nitric acid (%'). Calculate the formula mass (/r) for nitric

acid. B"

.....................................................................................................................................

). The formula for the chemical compound ma,nesium sulphate is /,+'&.

Calculate the relative formula mass (/r) of this compound. B"

..........................."$0...................................................................................................................

*. Ammonium chloride %&Cl is made up of nitro,en hydro,en and chlorine atoms.

(i) Complete the table to show the number of atoms of each element present in %&Cl.

Element+umber of atoms in

+&Cl

nitro,en "

hydro,en &

chlorine "

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(ii) Calculate the relative formula mass of ammonium chloride %&Cl. B"

.................................................................5....................................................................

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IGCSE Chemistry

&he mole

"."* understand the use of the term mole to represent the amount of substance

1.1! understand the term mole as the 'vogadro number of particles -atoms, molecules, formulae, ions or electrons in a substance

Gecause atoms and molecules are so small chemists measure or wor; with them in lar,enumbers. Chemists measure amounts of substance in moles.

The mole is the chemists countin, unit used to indicate a certain number Hust li;e a pair adoIen a trio.

A mole is the number .0$ 3 "0$ and is called Avo,adroJs number.

' mole of any substancecontains the same number of atoms or molecules or ions or

electrons or formula units and al/ays e0uals .# 2 1#(.

The 'vogadro3s +umber or Constantis emol

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IGCSE Chemistry

Calculating moles using molar mass

ind the number of moles of the followin, K show your wor;in,.

a. *, of Cl b. "0, of bromine molecules c. "0, of sodium hydro3ide

$mols %a'$mols .&

d. 25, of % e. 0, of ma,nesium sulphate f. 0.2, of C&5$> .$5 ">$0

,. "8, of $+'& h. ", of @& i. 0.5, of Ca'

ind the mass of the followin, amounts of substanceK show your wor;in,:

a. $ moles of iron b. 0.5 mole of water c. "00 moles of %'""$, 8,

d. 0.005 mole of Cu+'& e. 0." mole of Ca(')$ f. $0 moles of chlorine molecules

,. 0.$5 moles of CaC' i. 0." moles of +2

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m

molmr

Number of moles m!ss of the subst!"#e

m!ss of 1 mole of the subst!"#e

mol m

mr

$o% m!"y moles !re there i" 88& of C'2(

m!ss of 1 mole

molm882 moles

mr44

Example

IGCSE Chemistry

Calculating the Number of Moles from a given Mass

1 o/ many moles are there in . . .4

o/ many moles are there in . . .4

( o/ many moles are there in . . .4

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!) 2& of helium !toms f) 4& of o*y&e" mole#ules

b) 6& of #!rbo" !toms &) 213& of #hlori"e mole#ules

#) 16& of helium !toms h) 254& of io+i"e mole#ules

+) 4& of sul,hur !toms I) 08& of o*y&e" mole#ulese) 4& of hy+ro&e" !toms .) 056& of "itro&e" mole#ules

!) 88& of #!rbo" +io*i+e /C'2) f) 392& of sul,huri# !#i+ /$2S'4)

b) 31& of sul,hur +io*i+e /S'2) &) 120& of m!&"esium o*i+e /&')

#) 73& of hy+ro&e" #hlori+e /$Cl) h) 4& of #o,,er o*i+e /Cu')

+) 4& of so+ium hy+ro*i+e /N!'$) I) 28& of #!rbo" mo"o*i+e /C')

e) 560& of ,ot!ssium hy+ro*i+e /'$) .) 170& of !mmo"i! /N$3)

!) 158& of ,ot!ssium m!"&!"!te /II) /"'4) f) 473& of so+ium sul,h!te/N!2S'4)

b) 405& of i"# o*i+e /"') &) 078& of !lumi"ium hy+ro*i+e /l/'$)3)

#) 16& of bromi"e /r2) h) 8& of !mmo"ium "itr!te /N$4N'3)

+) 56& of #!l#ium o*i+e /C!') I) 298& of !mmo"ium ,hos,h!te //N$4)3'4)

e) 37& of #!l#ium hy+ro*i+e /C!/'$)2) .) 092& of eth!"ol /C2$5'$)


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m

molmr

h!t is the m!ss of 2 moles of #!rbo"(

molm

mr

Example

m!ssmol * mr2 * 12

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IGCSE Chemistry

Calculating the Mass from a number of Moles

1 5hat is the mass of . . .4

5hat is the mass of . . .4

( 5hat is the mass of . . .4

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Number of moles m!ss of the subst!"#e

m!ss of 1 mole of the subst!"#e

mol m

mrherefore:

!ss of subst!"#e "umber of moles * m!ss of 1 mole

which is the same as saying . . .

!ss "umber of moles * ;el!ti


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IGCSE Chemistry

".$5 calculate reactin, masses usin, e3perimental data and chemical e


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IGCSE Chemistry

" Linc o3ide reacts with carbon to form Iinc and carbon mono3ide. ow much Iinc o3ide doyou need to ma;e "0 tonnes of Iinc?

Ln' (s) C(s) Ln (s) C' (,)

$Al$'(s)

&Al (s) '$(,) What mass of silver chloride was produced?

b. Calculate the amount of chromium produced from " tonne of chromium () o3ide

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9 n the thermit reaction aluminium is used to obtain pure iron. ow much aluminium isneeded to obtain $2 tonnes of iron?

e$'(s) $Al (s) $e (s) Al$'(s)

10 What mass of chlorine would be needed to ma;e * tonnes of hydro,en chloride?

$(,) Cl$(,) $Cl (,)

11 Calculate the mass of nitric acid needed to ma;e &00 tonnes of ammonium nitrate

%' % %&%'

12 What mass of aluminium would be produced from $0& tonnes of aluminium o3ide ,iven thereaction?

13 $.*, of aluminium chloride was dissolved in water and silver nitrate was added to ,ivesilver chloride

AlCl A,%' Al(%') A,Cl

"&. Calcium hydro3ide is manufactured by heatin, calcium carbonate stron,ly to producecalcium o3ide and then addin, a controlled amount of water to produce calcium hydro3ide.

CaC'(s) Ca' (s) C'$(,)

Ca' (s) $' (l) Ca(')$ (s)

a. What mass of calcium o3ide would be produced from " tonne of calcium carbonate?b. What mass of water would you need to add to that calcium o3ide?c. What mass of calcium hydro3ide would eventually be produced?

15 Chromium is manufactured by heatin, a mi3ture of chromium () o3ide with aluminium

powder. Cr$'(s) $Al (s) $Cr (s) Al$'(s)

a. Calculate the amount of aluminium needed to react with " tonne of chromium () o3ide.


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IGCSE Chemistry

&he volume of 1 mole of hydrogen gas'ne mole of any ,as occupies the same volume when measured under the same conditions of

temperature and pressure. n this e3periment the volume of one mole of hydro,en is calculated at room

temperature and pressure.

". Clean a piece of ma,nesium ribbon

about .5 cm lon, and wei,h accurately.(Getween 0.0$ and 0.0& ,)

$. /easure $5 cmof dilute hydrochloricacid (6rritant) into the burette. Carefullyadd $5 cmof water on top of this.

. @ush the ma,nesium into the end ofthe burette so it will stay in position with itsown tension.

&. Add 50 cmof water to a $50 cmbea;er.

5. Muic;ly invert the burette into thewater. t is important that the li


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IGCSE Chemistry

Molar volume of gases

1.# understand the term molar volume of a gas and use its values -) dm (and ),###cm( at room temperature and pressure -rtp in calculations

The moles of a ,as can be calculated because " mole of any ,as at room temperature and

normal pressure occupies a volume of $& dmwhich is called the molar volume of ,ases atroom temperature.

number of moles of ,as at r.t.p. !volume of ,as in dm

$& dm

At room temperature and pressure (r.t.p.) one mole of any gas occupies a volume of $& dm($&0cm).

%umber of moles of ,as at r.t.p ! 24000

3cmingasofvolume

as volume of gas at r.t.p 7 -number of moles ) dm(

7 -number of moles )### cm(

e.,. What total olume of gas at rtp can be obtaine* from heating ..3g of lea*#//$ nitrate?#0b12, &1'4, O1'$

2 0b#&O3$2 20bO 5 4&O2 5 O2

-a /olar mass of lead() nitrate ! $0* $("& ") ! ",>mol

Amount of lead() nitrate !&>mol331

99-3&

! 0.00 mol-b rom emol

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IGCSE Chemistry

mass of %a' needed ! 0.02 mol &0 ,>mol ! . ,

ow many moles of ,as are there in (at rtp):

a. $&00 cmof chlorine b. "$0 cmof chlorine c. 8 cmof nitro,en

d. $& cmof methane e. "$ dmof o3y,en ,as f. "$ dmof Cl$

,. ".$ dmof +'$ h. $& 000 cm of '$

Calculate the volumes at -T@

a. ".$ moles of %$ b. $.05 moles of '$ c. * moles of %

d. 0.5 moles of C& e. 0.$5 moles of e f. 0.00" moles of $

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'vogadros 8a/ of 9ases

When two ,ases react the ratio of volumes is the same as the ratio of moles.This is because e


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IGCSE Chemistry

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Study Guide 1d Calculations With Exam Qs and MS

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