mohd faisol mansor/chemistry form 4/chapter 7
CHAPTER 7
ACIDS AND BASES
Arrhenius Theory
A base defined as a
chemical substance
that can neutralise an
acid to produce a
salt and water.
An acid is a chemical
compound that
produces hydrogen ions,
H+ or hydroxonium ions
H3O+ when dissolve in
water.
An alkali is defined as
a chemical
compound that
dissolve in water to
produce hydroxide
ions, OH- .
Example
HCl (g)
H2O
H+ (aq) + Cl- (aq)
NaOH(s)
H2O
Na+(aq) + OH-(aq)
The role of water
In the presence of water an acid will ionise to form hydrogen ion and
alkaline will dissociate into hydroxide ions, OH-.
Therefore, water is essential for the formation of hydrogen ions, H+
that cause acidity and hydroxide ions, OH- that cause alkalinity.
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mohd faisol mansor/chemistry form 4/chapter 7
BASICITY OF AN ACID
Is the number of ionisable hydrogen atoms per molecule of an
acid.
Monoprotic Acid
Diprotic Acid
Triprotic Acid
Acid which produces
1 hydrogen ion when
one molecule of an
acid ionises in H2O.
Example: a) CH3COOH? (ethanoic acid) =
b) H2SO4? (sulphuric acid )
c) HNO3? (Nitric acid)
d) H3PO4? (Phosphoric acid)
STRENGTH OF ACID & ALKALI
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mohd faisol mansor/chemistry form 4/chapter 7
STRONG ACID
WEAK ACID
Strong acid will dissociate or ionize
completely in water to produce
hydrogen, H+ ions.
Degree of dissociation is higher.
Thus, higher concentration of
hydrogen ions in aqueous acid
solution.
Therefore, low pH value of the acid
solution.
STRONG ALKALI
WEAK ALKALI
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mohd faisol mansor/chemistry form 4/chapter 7
PHYSICAL PROPERTIES OF ACID & ALKALI
pH Value
Conduct
electricity
Litmus paper
ALKALI
Litmus paper
pH Value
ACID
Taste
Corrosive
Corrosive
Taste
Conduct
electricity
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mohd faisol mansor/chemistry form 4/chapter 7
CHEMICAL PROPERTIES OF ACID & ALKALI
Acids can react with,
i) bases to produce salts and water
eg :
ii) metal to produce salts and hydrogen gas
eg :
iii) metal carbonates to produce salts, carbon dioxide
and water
eg :
iv) alkali to produce salts and water (neutralization)
eg :
Alkali can react with,
i) acid to produce salts and water (neutralization)
eg :
ii) ammonium salt to produce salts, water and ammonia
gas
eg :
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mohd faisol mansor/chemistry form 4/chapter 7
The concentration of acid and alkali
Concentration are measurement of the quantity of solutes dissolved
in a quantity of solvent.
Moles per dm3
( mol dm-3)
dm3
Grams per
( g dm-3)
*known as Molarity
Concentration
Unit Conversion
Grams per
dm3 ( g dm-3)
molar mass
molar mass
Moles per dm3
( mol dm-3)
Example
1. The molarity of a bottle of nitric acid, HNO3 solution is 2.0 mol dm-3.
What is the concentration of the solution in g dm-3?
[RAM: H, 1 ; N, 14 ; O , 16]
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mohd faisol mansor/chemistry form 4/chapter 7
2. Calculate the molarity of a sodium sulphate, Na2SO4 solution with
a concentration of 28.4 g dm-3. [RAM: O, 16 ; Na, 23 ; S, 32]
Calculating Involving Concentration and Molarity
3
No of mole = Molarity x Volume ( cm )
1000
MV
n=
1000
1.
5.00 g of copper (II) sulphate is dissolved in water to form 500
cm3 solution. Calculate the concentration of copper (II) sulphate
in g dm-3.
2.
A 250 cm3 nitric acid solution contains 0.4 moles. Calculate the
molarity of the nitric acid.
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mohd faisol mansor/chemistry form 4/chapter 7
3.
What is the mass of sodium carbonate required to dissolve in
water to prepare 200 cm3 solution contains 50 g dm-3.
4.
Calculate the number of moles of ammonia in 150 cm3 of 2 mol
dm-3 aqueous ammonia.
5.
Calculate the volume in dm3 of a 0.8 mol dm-3 sulphuric acid
that contains 0.2 mol.
6.
4.0 g sodium carbonate powder, Na2CO3 is dissolved in water
and made up to 250 cm3. What is the molarity of the sodium
carbonate solution. [RAM: C,12;O,16;Na,23]
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mohd faisol mansor/chemistry form 4/chapter 7
7.
Dilute hydrochloric acid used in the school laboratories usually
has a concentration of 2.0mol dm-3. Calculate the mass of
hydrogen chloride that found in 250 cm3 of the hydrochloric
acid? [RAM : H,1; Cl,35.5]
8.
The concentration of a potassium hydroxide solution is
84.0 g dm-3. Calculate the number of moles of potassium
hydroxide present in 300 cm3 of the solution. [RAM: K,39,H,1 O,16]
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mohd faisol mansor/chemistry form 4/chapter 7
9.
Calculate the number of moles of hydrogen ions present in
200 cm3 of 0.5 mol dm-3 sulphuric acid.
Preparation of Standard Solution
A solution in which its concentration is accurately known is a
standard solution.
Preparation of a solution by dilution method
Adding water to a concentrated solution changes the concentration
of the solution but does not change the amount solutes ( number of
moles)of solution present in solution.
Stock solution
Add water
Dilute solution
Moles of stock solution = moles of dilute solution
n1 = n2
M1V1 = M2V2
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mohd faisol mansor/chemistry form 4/chapter 7
Exercise
1.
Find the volume of 2.0 mol dm-3 sulphuric acid, H2SO4 needed to
prepare 100 cm3 of 1.0 mol dm-3 sulphuric acid, H2SO4.
2.
Calculate the volume of a concentrated solution needed to
prepare each of the following dilute solution:
a)
50 cm3 of 0.1 mol dm-3 sodium hydroxide, NaOH solution
from 2.0 mol dm-3 sodium hydroxide, NaOH solution.
b)
100 cm3 of 0.5 mol dm-3 potassium manganate(VII),
KMnO4 solution from 1.0 mol dm-3 potassium
manganate(VII), KMnO4 solution.
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mohd faisol mansor/chemistry form 4/chapter 7
3.
Calculate the volume of 2.0 mol dm-3 sulphuric acid, H2SO4
needed to prepare 2.5 dm3 of 0.5 mol dm-3 of the same acid
solution.
4.
Calculate the molarity of potassium hydroxide, KOH, solution if
200 cm3 of 2.0 mol dm-3 potassium hydroxide, KOH, solution is
added to 200 cm3 of water.
5.
60 cm3 of 0.5 mol dm-3 sodium hydroxide, NaOH, solution is
diluted with 30 cm3 of water. Calculate the molarity of the
solution produced.
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mohd faisol mansor/chemistry form 4/chapter 7
The pH Values and Molarity
As the molarity of an acid increases, the pH value of the acid
decreases, however the pH value of an alkali increases when the
molarity of the alkali increases.
Neutralisation
Acid-base titration
Reaction of an acid
and a base that
produce salt and
water.
Titration is a very useful
laboratory technique in
which one solution is
used to analyse another
solution.
Acid-base indicator is
used to detect the end
of titration.
Eg: methyl orange,
phenolphthalein and
litmus.
An acid of known
concentration is
carefully delivered from
burette to completely
neutralise a known
volume of an alkali in a
conical flask.
The point at which the
colour of the solution
change is called the
end point.
Titration using
phenolphthalein
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mohd faisol mansor/chemistry form 4/chapter 7
NEUTRALISATION
ACID-BASE
TITRATION
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mohd faisol mansor/chemistry form 4/chapter 7
Example
1.
Write a balanced equation for the neutralization of each of the
following:
a) Sulphuric acid, H2SO4 and barium hydroxide, Ba(OH)2
solution.
b) Nitric acid, HNO3 and calcium hydroxide, Ca(OH)2 solution.
c) Ethanoic acid, CH3COOH and potassium hydroxide, KOH
solution.
Acid-base Indicator
Indicator
Colour in
alkalis
Colour in neutral
solution
Colour in
acids
Methyl orange
phenolphthalein
litmus
The end-point of neutralisation also can determined by another two
method:i) Measurement of pH values by computer
ii) Measurement of electrical conductivity during titration
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mohd faisol mansor/chemistry form 4/chapter 7
Numerical Problem involving Neutralisation
Say the balance equation is
aA + bB
product
which,
A = acid
a = no of mole of acid
B = base
b = no of mole of base
MAVA = a
Therefore
and
MAVA
MBVB
MBVB = b
a
b
Exercise
1.
In an experiment, 25.0 cm3 of a sodium hydroxide solution of
unknown concentration required 26.50 cm3 of 1.0 mol dm-3
sulphuric acid to complete a reaction in titration. Calculate the
molarity of sodium hydroxide.
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mohd faisol mansor/chemistry form 4/chapter 7
2.
What is the volume of 0.5 mol dm-3 sulphuric acid, H2SO4 needed
to neutralize 25.0 cm3 of 0.8 mol dm-3 ammonia, NH3 solution?
3.
A sample of copper(II) oxide, CuO was found to completely
neutralize 100 cm3 of 0.5 mol dm-3 hydrochloric acid, HCl.
Calculate the mass of the sample. [RAM: O, 16 ; Cu, 64]
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mohd faisol mansor/chemistry form 4/chapter 7
4.
The volume of 0.15 mol dm-3 sulphuric acid, H2SO4 required to
completely neutralize 25.0 cm3 of potassium hydroxide, KOH
solution is 30.5 cm3. Calculate the molarity of the potassium
hydroxide, KOH solution.
5.
A student dissolved 3.65 g of hydrogen chloride gas, HCl in water
to make 1.0 dm3 of solution. Calculate the volume of a 0.1 mol
dm-3 barium hydroxide, Ba(OH)2 solution required to completely
neutralize 25.0 cm3 of the acid solution. [RAM : H, 1 ; Cl, 35.5]
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