Chapter 3a Chemical Formulae & Equations

8/8/2019 Chapter 3a Chemical Formulae & Equations

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CHEMICAL FORMULAECHEMICAL FORMULAE

& EQUATIONS& EQUATIONS


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Relative Atomic Mass &Relative Atomic Mass &

Relative Molecular MassRelative Molecular Mass

AtomAtom tinytiny impossible toimpossible todetermine its mass by weighing.determine its mass by weighing.

Scientist compare the mass of anScientist compare the mass of an

atom with aatom with a standard atom.standard atom.


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CarbonCarbon--1212 was chosen as thewas chosen as the

standard atomstandard atom ::

Many elements can combine withMany elements can combine with

carboncarbon--12.12.CarbonCarbon--12 exist as a12 exist as a solidsolid at roomat room

temperature.temperature.

CarbonCarbon--12 is the12 is the most abundantmost abundantcarbon isotope ( 98.89 % ).carbon isotope ( 98.89 % ).


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Relative atomic mass & relativeRelative atomic mass & relativemolecular mass hasmolecular mass has no unitno unit

because it is not the actual massbecause it is not the actual massof an atom, its only aof an atom, its only a comparisoncomparisonvalue.value.


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Relative atomic massRelative atomic mass

==

average mass of an atomaverage mass of an atom

1/121/12 xx mass of one carbonmass of one carbon--12 atom12 atom


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Atomic substancesAtomic substances are :are :MetalsMetals

Noble gases ( Group 18 elements )Noble gases ( Group 18 elements )

CarbonCarbon


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Given the relative atomic mass ofGiven the relative atomic mass ofpotassium ispotassium is 3939..

Thus, the average mass of oneThus, the average mass of onepotassium atom ispotassium atom is 39 times39 times moremorethan the mass of 1/12 of a carbonthan the mass of 1/12 of a carbon

atom.atom.


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Example 1Example 1

How many times heavier is aHow many times heavier is a kryptonkrypton

atom compared to aatom compared to a heliumhelium atom ?atom ?

[ Relative atomic mass : He, 4 ; Kr,[ Relative atomic mass : He, 4 ; Kr,84 ]84 ]


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Example 2Example 2

Calculate how many times heavierCalculate how many times heavier

areare 3 calcium atoms3 calcium atoms compared tocompared to 55

carbon atoms ?carbon atoms ?[ Relative atomic mass : C, 12 ; Ca,[ Relative atomic mass : C, 12 ; Ca,

40 ]40 ]


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Example 3Example 3

Calculate how manyCalculate how many magnesiummagnesium

atomsatoms will have thewill have the same mass as 2same mass as 2

silver atoms ?silver atoms ?[ Relative atomic mass : Mg, 24 ;[ Relative atomic mass : Mg, 24 ;

Ag, 108 ]Ag, 108 ]


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Relative Molecular Mass ( MRelative Molecular Mass ( Mrr ))

==

the average mass of one moleculethe average mass of one molecule

1/121/12 XXmass of one carbonmass of one carbon--12 atom12 atom


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CO2The symbol for theelement carbon

The symbol for theelement oxygen

Shows that there are 2oxygen atoms for everycarbon atom


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Example 1Example 1

Calculate theCalculate the relative molecularrelative molecular

massmass ofofammonia, NHammonia, NH33..

[ Relative atomic mass : H, 1 ;[ Relative atomic mass : H, 1 ;N, 14 ]N, 14 ]


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Relative Formula Mass ( FRelative Formula Mass ( Frr ))

ForFor ionic compoundsionic compounds ( metals( metalscombine with noncombine with non--metals )metals )..

Calculated byCalculated by adding up theadding up therelative atomic masses of allrelative atomic masses of all

atomsatoms shown in the formula.shown in the formula.


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Example 1Example 1

Calculate theCalculate the relative formula massrelative formula mass

ofofsodium chloridesodium chloride..

[ Relative atomic mass : Na,23 ;[ Relative atomic mass : Na,23 ;

Cl, 35.5 ]Cl, 35.5 ]


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Example 2Example 2

Calculate theCalculate the relative formula massrelative formula mass

ofofcopper (II) sulphate.copper (II) sulphate.

[ Relative atomic mass : Cu, 64 ; S,[ Relative atomic mass : Cu, 64 ; S,32 ; O, 16 ]32 ; O, 16 ]


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Example 3Example 3

TheThe relative formula massrelative formula mass of aof a

compound with the formulacompound with the formulaYY22SOSO44 isis

142.142. Calculate theCalculate the relative atomicrelative atomic

mass of element Y.mass of element Y.

[ Relative atomic mass : O, 16 ;[ Relative atomic mass : O, 16 ;S, 32 ]S, 32 ]


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AA kind wordkind word is likeis like perfume ,perfume ,if you spray on others,if you spray on others,

a couple of drops will staya couple of drops will stayon you.on you.

~ Still Thoughts~ Still Thoughts


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MoleMole

1 mole1 mole is defined as the amountis defined as the amountof substance containingof substance containing

6.02 X 106.02 X 102323 particles.particles.

( 6.02 x 10( 6.02 x 102323 is known asis known as

Avogadro constant, NAvogadro constant, NAA ))Symbol of mole isSymbol of mole is mol.mol.


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1 mole of1 mole ofatomic substancesatomic substances

== 6.02 X 106.02 X 102323 atomsatoms

1 mole of1 mole ofmolecular substancesmolecular substances

== 6.02 X 106.02 X 102323 moleculesmolecules1 mole of1 mole ofionic substancesionic substances

== 6.02 X 106.02 X 102323

formula unitsformula units


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Mole & Number of particlesMole & Number of particles

x Nx NAA

Number ofNumber of Number ofNumber ofmolesmoles particlesparticles

NNAA


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Example 1Example 1

Find theFind the numbers of atomsnumbers of atoms inin

(a)(a) 0.4 mole of iron.0.4 mole of iron.

(b)(b) 0.1 mole of oxygen gas.0.1 mole of oxygen gas.


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Example 2Example 2

How manyHow many molesmoles of water containof water contain

3.01 x 103.01 x 102222 water molecules ?water molecules ?


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Example 3Example 3

0.3 mole of0.3 mole ofzinc bromide, ZnBrzinc bromide, ZnBr22 isis

dissolved in a beaker of water.dissolved in a beaker of water.

FindFind(a) the number of(a) the number offormula unitsformula units,,

(b) the(b) the total number of ionstotal number of ions presentpresentin the beaker.in the beaker.


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Mole & Mass of particlesMole & Mass of particles

x molar massx molar mass

Number ofNumber of Mass inMass in

molesmoles gramsgrams

molar massmolar mass


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Molar massMolar mass is theis the mass of 1 molemass of 1 moleof the substance in grams.of the substance in grams.

Unit :Unit : g molg mol--11

Is numerically equal to theIs numerically equal to the RAM,RAM,RMM or RFMRMM or RFM of a substance.of a substance.


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Example 1Example 1

Find theFind the massmass ofof

(a)(a) 0.5 mole of copper0.5 mole of copper

(b)(b) 1.5 moles of carbon dioxide1.5 moles of carbon dioxide

[ Relative atomic mass : C, 12 ;[ Relative atomic mass : C, 12 ;

O, 16 ; Cu, 64 ]O, 16 ; Cu, 64 ]


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Example 2Example 2

Find the number ofFind the number ofmoles of sodiummoles of sodium

hydroxidehydroxide with the mass ofwith the mass of2.0 g.2.0 g.

[ Relative atomic mass : H, 1 ;[ Relative atomic mass : H, 1 ;

O, 16 ; Na, 23 ]O, 16 ; Na, 23 ]


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Example 3Example 3

What is theWhat is the mass of goldmass of gold that has thethat has the

same number of atoms in 4 g ofsame number of atoms in 4 g of

oxygen ?oxygen ?

[ Relative atomic mass :[ Relative atomic mass :O, 16 ;O, 16 ;

Au, 197 ]Au, 197 ]


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Example 4Example 4

What is theWhat is the mass of hydrogen gasmass of hydrogen gas

that hasthat has twice the number oftwice the number of

molecules as in 1.6 g of oxygen gas ?molecules as in 1.6 g of oxygen gas ?[ Relative atomic mass :[ Relative atomic mass :H, 1 ;H, 1 ;

O, 16 ]O, 16 ]


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Mole & Volume of gasMole & Volume of gas

x molar volumex molar volume

Number ofNumber of VolumeVolume

molesmoles of gasof gas

molar volumemolar volume


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Molar volumeMolar volume of a gas is theof a gas is the volumevolumeof 1 mole of the gas.of 1 mole of the gas.

Unit :Unit : dmdm33 molmol--11

Equal toEqual to 22.4 dm22.4 dm33

molmol--11

at STPat STP oror24 dm24 dm33 molmol--11 at room conditions.at room conditions.

STPSTP standard temperature (0standard temperature (0 C )C )

& pressure (1 atm)& pressure (1 atm)Room condition : 25Room condition : 25 C & 1 atmC & 1 atm


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Example 1Example 1What is theWhat is the volumevolume of 0.4 mole ofof 0.4 mole of

carbon dioxide gascarbon dioxide gas atatSTPSTP ??

[ Molar volume : 22.4 dm[ Molar volume : 22.4 dm33 molmol--11

at STP ]at STP ]


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Example 2Example 2Find theFind the number of moles ofnumber of moles of

ammonia gasammonia gas contained in a samplecontained in a sample

ofof60 cm60 cm33 of the gas at roomof the gas at room

conditions.conditions.

[ Molar volume : 24 dm[ Molar volume : 24 dm33 molmol--11

at room conditions ]at room conditions ]


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Mole & number of particles,Mole & number of particles,mass & volumemass & volume

MassMass NumberNumber NumberNumber

of molesof moles of particlesof particles

VolumeVolume


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Example 1Example 1

A sample ofA sample of120 cm120 cm33 of COof CO22 isis

collected at room conditions.collected at room conditions.

Calculate theCalculate the massmass of the sample COof the sample CO22[ Relative atomic mass : C, 12 ; O, 16[ Relative atomic mass : C, 12 ; O, 16

Molar volume : 24 dmMolar volume : 24 dm33

molmol--11

atatroom conditions ]room conditions ]


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Example 2Example 2How manyHow many hydrogen moleculeshydrogen molecules areare

there inthere in 6 dm6 dm33 of hydrogen gas atof hydrogen gas at

room conditions ?room conditions ?

[ Molar volume : 24 dm[ Molar volume : 24 dm33 molmol--11 atat

room conditions. Avogadro constantroom conditions. Avogadro constant: 6.02 x 10: 6.02 x 102323 molmol--11 ]]


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Example 3Example 3

Find theFind the volume of nitrogenvolume of nitrogen gas ingas in

cmcm33 at STP that consists ofat STP that consists of2.408 x2.408 x

10102323 nitrogen molecules.nitrogen molecules.[ Molar volume : 22.4 dm[ Molar volume : 22.4 dm33 molmol--11 atat

STP. Avogadro constant : 6.02 xSTP. Avogadro constant : 6.02 x10102323 molmol--11 ]]


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Getting angry is actuallyGetting angry is actuallypunishing yourself with otherspunishing yourself with others

faults.faults.~ Still Thoughts~ Still Thoughts

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Chapter 3a Chemical Formulae & Equations