Chemistry Module Form 4 (3)

mohd faisol mansor/chemistry form 4/chapter 3

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CHAPTER 3 CHEMICAL FORMULAE & EQUATIONS

Relative Molecular Mass

Average mass of

one molecule

1/12 x mass of an

atom of carbon-12

Relative Atomic Mass

Average mass of

one atom of an

element

1/12 x mass of an

atom of carbon-12

Relative Molecular Mass (RMM)/Relative Formula Mass (RFM) can

be calculated by adding up the Relative Atomic Mass (RAM).

Water, H2O

RMM =

Sodium Chloride, NaCl

RFM =

Relative Formula Mass

Average mass of

one formula unit

1/12 x mass of an

atom of carbon-12

+ -

Example

1) Element mercury is 20 times

heavier than helium. Determine

the relative atomic mass of

element mercury if the relative

atomic mass of helium is 4.

2) The relative atomic mass of helium,

nitrogen and sulphur is 4, 14, and 32

respectively.

a) How many times is one atom of

sulphur heavier than one atom of

helium.

b) Calculate the number of atoms of

helium that have the same mass as two

atoms of nitrogen.


23

1. Calculate relative molecular mass of the following element or compound.

a) Oxygen gas, O2

b) Chlorine gas, Cl2

c) Carbon dioxide, CO2

d) Ammonia, NH3

e) Iodine gas, I2

f) Sulphur dioxide, SO2

g) Sugar, C6H12O6

h) Ethanol, C2H6O

2. Calculate relative formula mass of the following compound.

a) Magnesium oxide, MgO

b) Potassium iodide, KI

c) Calcium carbonate, CaCO3

d) Copper(II) nitrate, Cu(NO3)2

e) Aluminium oxide, Al2O3

f) Zinc Sulphate, ZnSO4

g) Hydrated magnesium sulphate,

MgSO4.7H2O

h) Hydrated copper(II) sulphate,

CuSO4.5H2O

Atom, Molecule & Ion

Example


24

The Mole, Number of Particles, Mass & Volume of Substances.

MOLE

Amount of substance

that contains as many

particles as the number

of atoms in exactly 12 g

of carbon-12

NUMBER OF

PARTICLES

One mole of

substance contains

6.02 x 1023 particles.

MASS OF

SUBSTANCES

The mass of one

mole of the

substance equal to

the mass of 6.02 x

1023 particles.

VOLUME OF GAS

One mole of any gas

always has the same

volume under the

same temperature &

pressure.

Avogadro Constant

NA = 6.02 x 1023

mole = no of particles

NA

No of particles

= mole x NA

Molar Mass

= RAM/RMM/RFM

mole = Mass

Molar Mass

Mass = mole x MM

Molar Volume

1) Room Condition

= 24 dm3 mol -1

2) At S.T.P

= 22.4 dm3 mol -1

mole = Volume

Molar Volume

Volume = mole x MV

Unit conversion

1 dm3 = 1000 cm3


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1. A closed glass bottle contains 0.5 mol of oxygen gas, O2.

a) How many oxygen molecules, O2 are there in the bottle?

b) How many oxygen atoms are there in the bottle?

2. Find the number of moles of hydrogen gas, H2 containing

a) 3.01 x 1024 hydrogen molecule, H2

b) 6.02 x 1023 hydrogen atoms.

3. Find the number of moles of molecules in a sample containing 9.03 x 1023

molecules of carbon dioxide, CO2.

4. A sample contains 6.02 x 1025 molecule of water. How many moles of water

are there in the sample?

Example 1


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5. A container contains 1.806 x 1023 oxygen molecules, O2. A sample of 0.5 mol

of oxygen gas, O2 is added to the container. How many molecules are there

altogether in the container?

6. Calcium is needed for the formation of bones and teeth. How many calcium

ions are there in a serving of cereal that contains 0.007 mol of calcium ions?

7. A beaker contains 0.1 mol of zinc chloride, ZnCl2

a) Calculate the number of moles of chloride ions in the beaker.

b) Find the total number of ions in the beaker.


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1. What is the mass of

a) 0.1 mol of magnesium? [RAM: Mg, 24]

b) 2.408 x 1023 atoms of magnesium? [RAM: Mg, 24 ; NA = 6.02 x 1023]

2. How many moles of molecules are there in 16 g of sulphur dioxide gas, SO2?

[RAM: O, 16 ; S, 32]

3. How many chloride ions are there in 27.2 g of zinc chloride, ZnCl2?

[RAM: Cl, 35.5 ; Zn, 65 ; NA = 6.02 x 1023]

Example 2


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4. What is the mass of carbon that contains 6.02 x 1023 carbon atoms?

5. What is the mass of

a) 0.01 mol of ammonia gas, NH3?

b) 6.02 x 1024 nitrogen molecules, N2?

6. How many moles of molecules are there in 2.8 g of carbon monoxide, CO?


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1. What is the volume of 1.2 mol of ammonia gas, NH3 at STP?

[Molar volume: 22.4 dm3 mol-1]

2. How many moles of ammonia gas, NH3 are present in 600 cm3 of the gas

measured at room conditions? [molar volume: 24 dm3 mol-1]

3. Calculate the volume of the following gases.

a) 0.3 mol of oxygen gas, O2, at room condition.

b) 4 mol of helium gas measured at STP.

4. Calculate the number of moles of 48 dm3 of chlorine gas, Cl2, at room

condition.

Example 3


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1. What is the volume of 12.8 g of oxygen gas, O2, in cm3, at STP?

[RAM: O, 16 ; Molar volume: 22.4 dm3 mol-1]

2. How many molecules of carbon dioxide, CO2, are produced when 120 cm3 of

the gas is released during chemical reaction between an acid and a

carbonate at room conditions?

[Molar volume: 24 dm3 mol-1 ; NA = 6.02 x 1023]

3. What is the mass of 0.6 dm3 of chlorine gas, Cl2 at room condition?

[RAM: Cl, 35.5 ; Molar volume = 24 dm3 mol-1]

4. 3 dm3 of an unknown gas has a mass of 6.0 g at room conditions. Find the

molar mass of the gas.

Example 4


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CHEMICAL FORMULAE

A representation

of a chemical

substance using

letters and

subscript numbers.

Magnesium Nitrate

Mg(NO3)2

Water

H2O

Empirical Formula

The simplest

number ratio of

atoms in the

compound.

Molecular Formula

The actual number

of atoms that are

present in the

compound.

Molecular Formula = (Empirical Formula)n

Compound Molecular

Formula

Empirical

Formula n

Water H2O

Ethene CH2 2

Glucose C6H12O6

RMM of Molecular Formula

RMM of Empirical Formula

= n

The empirical formula of a compound

is CH2. Its relative molecular mass is 42.

Find its molecular formula. [RAM: H, 1 ; C, 12]

Copper(II) Oxide

Magnesium Oxide

[state the number of particles consist in the substance above]


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To determine Empirical Formulae of Magnesium Oxide

To determine Empirical Formulae of Copper(II) Oxide

1. Why is the magnesium ribbon cleaned with

sand paper before used?

2. Name the white fumes produced.

3. State the reason:

a) covering the crucible with its lid as soon as

the magnesium start burning.

b) raising the lid of the crucible at intervals

during heating.

c) heating, cooling & weighing are repeated

until constant mass is obtained.

4. Why is it important not to let any white fumes

escape from the crucible?

1. Why do we start off with copper(II) oxide instead of allowing copper to react with

oxygen in the air in this experiment?

2. How do you test that the air in the tube has been removed completely?

3. Explain what will happen if we burn excess hydrogen gas without removing the air

completely in combustion tube?

4. Why we need to continue the flow of hydrogen gas after the heating of copper(II)

oxide?

5. Why do we need to repeat heating, cooling and weighing until constant mass is

obtained?


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a) A sample of aluminium oxide contains 1.08 g of aluminium and 0.96 g of

oxygen. What is the empirical formula of this compound? [RAM: O, 16 ; Al, 27]

Element Al O

Mass of Element (g)

Number of Mole

Ratio of Mole

Simplest Ratio

Empirical Formula of Aluminium Oxide =

b) 0.20 g of calcium reacts with fluorine to give 0.39 g of calcium fluoride. Find

the empirical formula of the calcium fluoride produced. [RAM: F, 19 ; Ca, 40]

Example 1


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c) Find the empirical formula of a compound that consists of 32.4% of sodium,

22.6% of sulphur and 45.0% of oxygen. [RAM: O, 16, Na, 23 ; S, 32]

d) 60 g of aluminium sulphide contains 38.4 g of sulphur. Find the empirical

formula of the compound. [RAM: Al, 27 ; S, 32]


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a) Butane has empirical formula of C2H5 and relative molecular mass of 58. Find

its molecular formula.

b) Ethanoic acid is an important ingredient of vinegar. The empirical formula of

this acid is CH2O. Given that its molar mass is 60 g mol-1, find its molecular

formula.

c) 6.24 g of element X combines with 1.28 g of oxygen to produce a compound

with an empirical formula of X2O. What is relative atomic mass of X?

[RAM: O, 16]

Example 2


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d) Element Y react with oxygen to produce a compound with molecular

formula YO3. Given that the mass of 1 mol of the compound is 80 g.

Determine the relative atomic mass of element Y.

e) Determine the percentage composition by mass of water in hydrated

copper(II) sulphate, CuSO4.5H2O. [RAM: H, 1 ; O, 16 ; S, 32 ; Cu, 64]

f) Due to its high nitrogen content, urea, CO(NH2)2 is commercially used as

fertilizers. Calculate the percentage composition by mass of nitrogen in urea,

CO(NH2)2. [RAM: H, 1 ; C, 12 ; N, 14 ;O, 16]


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Metal

Atom

Nonmetal

Atom

Cation

(+ve ion)

Anion

(-ve ion)

IONIC

COMPOUND

Ionic

Formulae

Silver

Chlorine

Silver

Chloride

Ionic

Formulae

Zinc

Zn

Oxygen

O

Zn2+

O2-

Zinc Oxide

ZnO

Ionic

Formulae


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Charge Name of Cation Formula of Cation

1+

Hydrogen ion H +

Lithium ion Li +

Sodium ion Na +

Potassium ion K +

Silver ion Ag +

Ammonium ion NH4 +

2+

Barium ion Ba 2+

Calcium ion Ca 2+

Magnesium ion Mg 2+

Zinc ion Zn 2+

Copper(II) ion Cu 2+

Iron(II) ion Fe 2+

Lead(II) ion Pb 2+

3+ Aluminium ion Al 3+

Iron(III) ion Fe 3+

Charge Name of Anion Formula of Anion

1-

Hydroxide ion OH -

Chloride ion Cl -

Fluoride ion F -

Bromide ion Br -

Iodide ion I -

Nitrate ion NO3 -

2-

Oxide ion O 2-

Sulphate ion SO4 2-

Carbonate ion CO3 2-

3- Phosphate ion PO4 3-


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Name of Cation Formula of

Cation

Hydrogen ion

Lithium ion

Sodium ion

Potassium ion

Silver ion

Ammonium ion

Barium ion

Calcium ion

Magnesium ion

Zinc ion

Copper(II) ion

Iron(II) ion

Lead(II) ion

Aluminium ion

Iron(III) ion


Cation

Hydrogen ion

Magnesium ion

Barium ion

Potassium ion

Iron(II) ion

Ammonium ion

Zinc ion

Aluminium ion

Lithium ion

Iron(III) ion

Sodium ion

Calcium ion

Silver ion

Copper(II) ion

Lead(II) ion

Name of Anion Formula of

Anion

Hydroxide ion

Chloride ion

Fluoride ion

Bromide ion

Iodide ion

Nitrate ion

Oxide ion

Sulphate ion

Carbonate ion

Phosphate ion


Anion

Phosphate ion

Bromide ion

Oxide ion

Carbonate ion

Iodide ion

Chloride ion

Sulphate ion

Nitrate ion

Hydroxide ion

Fluoride ion


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Cation

Hydrogen ion

Lithium ion

Sodium ion

Potassium ion

Silver ion

Ammonium ion

Barium ion

Calcium ion

Magnesium ion

Zinc ion

Copper(II) ion

Iron(II) ion

Lead(II) ion

Aluminium ion

Iron(III) ion


Anion

Hydroxide ion

Chloride ion

Fluoride ion

Bromide ion

Iodide ion

Nitrate ion

Oxide ion

Sulphate ion

Carbonate ion

Phosphate ion


Anion

Hydroxide ion

Chloride ion

Fluoride ion

Bromide ion

Iodide ion

Nitrate ion

Oxide ion

Sulphate ion

Carbonate ion

Phosphate ion


Cation

Hydrogen ion

Lithium ion

Sodium ion

Potassium ion

Silver ion

Ammonium ion

Barium ion

Calcium ion

Magnesium ion

Zinc ion

Copper(II) ion

Iron(II) ion

Aluminium ion

Iron(III) ion

Lead(II) ion


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Cation

Hydrogen ion

Lithium ion

Sodium ion

Potassium ion

Silver ion

Ammonium ion

Barium ion

Calcium ion

Magnesium ion

Zinc ion

Copper(II) ion

Iron(II) ion

Lead(II) ion

Aluminium ion

Iron(III) ion


Anion

Hydroxide ion

Chloride ion

Fluoride ion

Bromide ion

Iodide ion

Nitrate ion

Oxide ion

Sulphate ion

Carbonate ion

Phosphate ion


Anion

Hydroxide ion

Chloride ion

Fluoride ion

Bromide ion

Iodide ion

Nitrate ion

Oxide ion

Sulphate ion

Carbonate ion

Phosphate ion


Cation

Hydrogen ion

Lithium ion

Sodium ion

Potassium ion

Silver ion

Ammonium ion

Barium ion

Calcium ion

Magnesium ion

Zinc ion

Copper(II) ion

Iron(II) ion

Aluminium ion

Iron(III) ion

Lead(II) ion


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Construct the chemical formula for each of the following ionic compound.

a)Magnesium hydroxide

b) Silver iodide c) Potassium Bromide

d) Zinc nitrate

e) Sodium carbonate f) Aluminium oxide

g) Copper(II) iodide

h) Iron(II) sulphate i) Magnesium oxide

j)Calcium carbonate

l) Ammonium phosphate m) Sodium hydroxide

n) Zinc bromide

o) Lead(II) nitrate p) copper(II) sulphate

Example


43

1. Write the formula of the following substances.

a) Potassium iodide =

b) Magnesium oxide =

c) Carbon dioxide =

d) Copper(II) oxide =

e) Lead(II) bromide =

f) Calcium chloride =

g) Hydrochloric acid =

h) Copper(II) sulphate =

i) Hydrogen gas =

j) Water =

k) Sulphuric acid =

l) Silver chloride =

m) Potassium nitrate =

n) Calcium carbonate =

o) Aluminium oxide =

p) Oxygen gas =

q) Oleum =

r) Ammonium sulphate =

s) Sodium chloride =

t) Zinc oxide =

Example

1) Nitric acid =

2) Lead(II) iodide =

3) Copper(II) nitrate =

4) Zinc sulphate =

5) Iron(II) chloride =

6) Iron(III) chloride =

7) Chlorine gas =

8) Potasium nitrate =

9) Silver nitrate =

10) Magnesium bromide =

11) Zinc chloride =

12) Sodium hydroxide =

13) Ammonia =

14) Iron(II) sulphate =

15) Lead(II) oxide =

16) Carbon monoxide =

17) Magnesium sulphate =

18) Ammonium nitrate =

19) Potassium hydroxide =

20) Lithium oxide =


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c) Carbon dioxide =






i) Hydrogen gas =

j) Water =

k) Sulphuric acid =





p) Oxygen gas =

q) Oleum =



t) Zinc oxide =

1) Nitric acid =



4) Zinc sulphate =



7) Chlorine gas =


9) Silver nitrate =


11) Zinc chloride =


13) Ammonia =







20) Lithium oxide =

Example


45




c) Carbon dioxide =






i) Hydrogen gas =

j) Water =

k) Sulphuric acid =





p) Oxygen gas =

q) Oleum =



t) Zinc oxide =

1) Nitric acid =



4) Zinc sulphate =



7) Chlorine gas =


9) Silver nitrate =


11) Zinc chloride =


13) Ammonia =







20) Lithium oxide =

Example


46

Name the following ionic compound by using their IUPAC name.

Ionic

Formula Name

Ionic

Formula Name

NaCl KI

MgO BaSO4

Cu(NO3)2 CaCO3

Al2O3 FeCl3

ZnCl2 LiOH

CuO FeSO4

AgNO3 NaOH

MgBr2 ZnO

PbSO4 PbI2

Example

NaBr

Sodium Bromide

Br -

Bromide

Na +

Sodium


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CHEMICAL EQUATIONS

a) Qualitative Aspect

For each equation, identify the reactant(s), product(s) and the state of each

of them. Then, balance the equation.

a) H2 (g) + O2 (g) H2O (l)

b) CuO (s) + HCl (aq) CuCl2 (aq) + H2O (l)

c) Cl2 (g) + NaBr (aq) NaCl (aq) + Br2 (l)

d) Mg (s) + HCl (aq) MgCl2 (aq) + H2 (g)

K(S) + H2O(l) KOH(aq) + H2(g)

Reactant

Product

Meaning: Solid Potassium react with water liquid to give

potassium hydroxide solution and hydrogen gas

p/s: 1) Able to classify reactant and product.

2) Able to balance the equation.

Example 1


48

Write a balanced equation for each of the following reactions.

a) Carbon monoxide gas + oxygen gas Carbon dioxide gas

b) Hydrogen gas + nitrogen gas Ammonia gas

c) Aluminium + iron(III) oxide Aluminium oxide + iron

d) Ammonia gas react with oxygen gas to yield nitrogen monoxide gas and

water.

e) Silver nitrate solution is added to calcium chloride solution. Silver chloride

precipitate and calcium nitrate solution are produced.

f) When solid zinc carbonate is heated, it decomposes into zinc oxide powder

and carbon dioxide gas.

Example 2


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1. Construct balanced chemical equations:

a) Magnesium react with oxygen will produce magnesium oxide.

b) Sodium metal react with chlorine gas will produce sodium

chloride.

c) Potassium oxide react with water will produce potassium

hydroxide.

d) Lithium metal react with water will produce lithium hydroxide

and hydrogen gas.

e) Zinc metal react with water will produce zinc oxide and

hydrogen gas.

f) Calcium carbonate react with hydrochloric acid will produce

calcium chloride, water and carbon dioxide.

g) Hydrochloric acid react with sodium hydroxide will produce

sodium chloride and water.

h) Potassium oxide react with nitric acid will produce potassium

nitrate and water.

Example 3


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i) Iron metal react with chlorine gas will produce iron(III) chloride.

j) Magnesium metal react with nitric acid with produce

magnesium nitrate and hydrogen gas.

k) Zinc metal dissolved in copper(II) chloride will produce zinc

chloride and copper metal.

l) Chlorine gas react with potassium bromide will produce

potassium chloride and bromine gas.

m)Copper(II) carbonate when heated will produce copper(II)

oxide and carbon dioxide.

n) Lead(II) nitrate when heated will produce lead(II) oxide,

nitrogen gas and oxygen gas.

o) Potassium iodide react with lead(II) nitrate will produce lead(II)

iodide and potassium nitrate solution.

p) Sodium hydroxide react ammonium chloride will produce

sodium chloride, water and ammonia gas.

q) Zinc metal react with hydrochloric acid will produce zinc

chloride and hydrogen gas.

r) Magnesium oxide react with sulphuric acid will produce

magnesium sulphate react with water.


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b) Quantitative Aspect

1. Copper(II) oxide, CuO reacts with aluminium according to the following

equation.

3CuO (s) + 2Al (s) Al2O3 (s) + 3Cu (s)

Calculate the mass of aluminium required to react completely with 12 g of

copper(II) oxide, CuO. [RAM: O, 16 ; Al, 27 ; Cu, 64]

2H2 (g) + O2 (g) 2H2O(l)

2 molecule

Or

2 mol

Note: The coefficient in the reaction tell the exact proportions of

reactant and product in chemical reaction.

Example

1 molecule

Or

1 mol

2 molecule

Or

2 mol


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2. A student heats 20 g of calcium carbonate, CaCO3 strongly. It decomposes

according to the equation below.

CaCO3 (s) CaO (s) + CO2 (g)

a) If the carbon dioxide produced is collected at room conditions, what is its

volume?

b) Calculate the mass of calcium oxide, CaO produced.

[RAM: C, 12 ; O, 16 ; Ca, 40 ; Molar volume = 24 dm3 mol-1]


53

3. Hydrogen peroxide, H2O2 decomposes according to the following equation.

2H2O2 (l) 2H2O (l) + O2 (g)

Calculate the volume of oxygen gas, O2 measured at STP that can obtained

from the decomposition of 34 g of hydrogen peroxide.

[RAM : H, 1 ; O, 16 ; Molar volume = 22.4 dm3 mol-1]

4. 16 g of copper(II) oxide, CuO is reacted with excess methane, CH4. Using the

equation below, find the mass of copper that is produced.

4CuO (s) + CH4 (g) 4Cu (s) + CO2 (g) + 2H2O (l)

[RAM : H, 1 ; C, 12 ; O, 16 ; Cu, 64]

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Chemistry Module Form 4 (3)