Chemistry Form 4 chapter 3

7/28/2019 Chemistry Form 4 chapter 3

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Matter

Particles Mole

concept

Chemical

formulae

Equations

- Atoms (Relative

atomic mass)

- Ions(Relative Formula

mass)

- Molecules(Relative

molecular mass

- Number of

particles

- Molar mass

- Molar volume

- Empirical

formula

- Molecular

formula

- Balance equations

- Writing equations


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Relative Formula mass,Ff

1) Relative atomic mass is used for substances that are made up of ion. For ioniccompound which made up of positive ion(cation) & negative ion (anion), relative

formula mass is used.

Exp:

Determine the relative formula mass of following:

[ r.a.m of Zn=65 , O=16 , Cu=64 , S=32]

a)Zinc oxide ,ZnO b) Copper(II) Sulphate,CuSO4= 65+16 = 64+32+(16x4)

= 81 = 160


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Number of mole

Mole:

1)A moleis an amount of substance that contains as many particles as the numberof atoms in exactly 12g of carbon-12.

2) 1 mole contains 3.02 x 1023 particlesTherefore

a)1 mol of atomic substance contains 6.02 x 1023 atomsb)1 mol of molecular substance contains 6.02 x 1023 atomsc)1 mol of ionic substance contains 6.02 x 1023 atoms

3)6.02 x 1023 is called Avogadro constant / Avogadro number4)Avogadro constant NA : The number of particles ( atom, molecules / ions)

contained 1 mole of substance.

Formula :

Number of particles =Number of moles xAvogadro constant NA


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Number of moles & mass

1)The mass of 1 mole of element in grams is equivalent ( same) to the relativeatomic mass & relative molecular mass of the element.

Exp:

1 mole of hydrogen = 1 g (relative atomic mass (RAM:1, Mass= 1g)

Number of mole (atoms) = Mass in grams (g)

Relative atomic mass (molar mass)

Number of mole (molecules) = Mass in grams (g)

Relative molecular mass (molar mass)

Therefore:

Mole = Mass(g) n=m

Molar mass mr


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Number of Moles of a Gas & Its Molar Volume

1)Molar volume of a gas defined as the volume occupied by 1 mole of the gas2)Standard temperature& pressure (S.T.P), 1 mole of gas occupies a volume of

22.4dm3

3)Room conditions (R.T.P), 1 mole of gas occupies a volume of24 dm3

Formula:

Number of mole =Volume

Molar Volume(24/22.4dm3)


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Chemical Formulae

1)A chemical formula is used to represent a chemical compound by using letters foratoms & number of atom that are present in the substance.

Exp:

C6H12O6

2)Several covalent compounds & their chemical formulae that are sharing thenumber of atoms of each element making up the compound

Name Chemical Formula

Oxygen O2

Chlorine Cl2

Water H2O

Ammonia NH3

Carbon dioxide CO2

Nitrogen dioxide NO2

Show the symbols

of carbon,

hydrogen &oxygen

Show the numbers of carbon,

hydrogen & oxygen that

combine together


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3 Aluminium Al3+

Iron(III) Fe3+

Chromonium(III) Cr3+

Phosphate PO43-

Nitride N3-

Writing the chemical formula of ionic compound

Xm+

Yn-

= XnYm

Exp:

1)Na+ & Cl-NaCl

2)Al3+ N3-Al3N3 = AlN

3)Al3+

O

2-

Al2O3

4)Mn4+ O2-Mn2O4 =MnO2


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Molecular Formula & Empirical Formulae

1)Relative molecular mass of a substance can be calculated by using chemicalformulae.

Exp:

Calcium carbonate CaCO3 RAM of Ca=40 , C= 12 , O=16

Relative atomic mass = 40+ 12+ (16X3)

= 100

2)2 types of chemical formulaea)Empirical formulab)Molecular formula

3)Empirical formula shows the simplest ratio of atoms of the elements thatcombine to form the compound.

4)The molecular formula shows the actual number of atoms of the elements thatcombine to form compound.


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Steps of determine the empirical formula

Step 1 Write the mass / the mass percentage of each element in the compound.

Step 2 Calculate the number of moles of each element by dividing the mass /mass percentage of each element by its relative atomic mass.

Step 3 Calculate the simplest mole ratio by diving each number with the smallest

number.

Step 4 Write the empirical formula

Exp:

The table below shows the mass of metal M & chlorine that combine to form a

compound. Determine the empirical formula of this compound.

Element M Cl

Mass of the element 2.08 g 4.26 g

Relative atomic mass of the element 52 35.5


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Chemical Equations

1)The steps involved in writing a chemical equation:Step 1 Write the correct formulae of the reactants on the left side of the

equation

Step 2 Write the correct formulae of products on the right side of the

equation

Step 3 Balance the equation by making sure the number of atoms of each

element on the left & on the left & on the right of the equation is the

same. This is done by writing an integer in front of the chemicalformula.

Step 4 When balancing the equation, never alter (change) the formula of the

compounds.


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Step 1 Step 2

Na + O2 Na2O (Change charged Na+O

2-

Na2O)

Step 3 Step4

Na+O2 Na2O To make it balance

4Na + O2 2Na2O

1 atom 1 atom 2 atoms2 atoms

Not balance bcoz in front Na has 1 atom

& O has 2 atoms

but behind Na has 2 atoms 1 O has 1

atom

4 atoms 2 atoms 4 atoms 2 atoms

Balanced bcoz

2x2Na = 4Na

2x1O (oxygen) =2


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Reminder is the formula is mole = mass / molar mass the answer should be 50

mole.

If not mole means wrong.

Same as all the formula.

If forgot g, mole, dm3

all wrong.

Must remember to put the unit.

Except for Relative atomic mass and Relative molecular mass & Relative

Formula mass

Chemistry Form 4 chapter 3

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