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Chapter 10

Acids, Bases and Salts
LEARNING OUTCOMES
nDefine acid and acid anhydride
nInvestigate the reactions of non-oxidising acids

with metals, carbonates, hydrogen carbonates and
bases
nDefine base and alkali
nInvestigate the reaction of bases with ammonium
salts
nRelate acidity and alkalinity to the pH scale
nDiscuss the strength of acids and alkalis on the
basis of their completeness of ionisation
nDefine acidic, basic, amphoteric and neutral oxides

Chapter 10

Acids, Bases and Salts
LEARNING OUTCOMES
nDefine salt
nIdentify an appropriate method of salt preparation

based on the solubility of the salt
nDistinguish between acidic and normal salts
nInvestigate neutralisation reactions using indicators
and temperature changes

Chapter 10

Acids, Bases and Salts

What are acids?
n

Fruits like apples, oranges and pineapples taste sour because
they contain acids
...


n

Acids produce hydrogen ions H + in water
...
e they conduct an electric current

Chapter 10

Acids, Bases and Salts
n

Acids in their anhydrous form , a composed of covalent molecules
and they may be solid liquid or gases at room temperature
...
g nitric acid (HNO 3)
sulfuric acid ( H2SO4)

4

Chapter 10

Acids, Bases and Salts
Definition of An Acid
An acid is a substance which produces hydrogen ions, H+(aq) in water
...


Acids, Bases and Salts
Ionization of Acids in water
n
n
n

When an acid is added to water, the acid molecule will ionize i
...

All acids will ionize to produce protons( hydrogen ions) and a
negative ion
...


6

Acids, Bases and Salts
Ionization of Acids in Water
The overall reaction for the ionization of HCl(g) can be summarised
as:
HCl(g) + H2O (l) - H3O+ (aq) + Cl- (aq)

n

Which can be simplified :
HCl (aq)  H+(aq) + Cl - (aq)

n

See page 122 for examples
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Acids, Bases and Salts
When an acid reacts, the hydrogen ions or protons formed when it
dissolves in water, can be given to the other reactant
...
g
...
g
...
g
...

n E
...
sulphuric acid reacts with copper(II) oxide to form a salt
called copper(II) sulphate and water:
H2SO4 + CuO  CuSO4 + H2O
n

This reaction is called neutralisation
...
This means that all the
acid molecules become ions
in the water
...


Chapter 10

Acids, Bases and Salts
A Weak Acid
Weak acid

n

A weak acid is an acid that is
only partially ionised in water
...


n

E
...
s
...


Acids, Bases and Salts
Organic and Inorganic acids
Inorganic Acids
n An inorganic acid contains a
non metallic element or
polyatomic group as well as
hydrogen

Acid

Formula

Hydrochloric acid

HCl

Nitric acid

HNO3

Sulfuric acid

H2SO4

Nitrous acid

HNO2

Carbonic acid

H2CO3

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Acids, Bases and Salts
Organic and Inorganic acids
Organic Acids
n

Most organic acids contain the
COOH group
...


Acid

Formula

Methanoic acid

HCOOH

Ethanoic acid

CH3COOH

Lactic acid

CH3CH(OH)COO
H

Citric acid

C6H8O7

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Acids, Bases and Salts
Monobasic, dibasic and tribasic acids
Basicity is the number of H+ ions produced per molecule
of acid when dissolved in water
...
g HCl ,
HNO3
n A dibasic acid:
Produces two H+ ions per molecule when it dissolves in water e
...
g H 3PO4
n

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Acids, Bases and Salts
Organic and Inorganic acids

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Chapter 10

Acids, Bases and Salts

Uses of Acids
n

Hydrochloric acid is used in the industry to remove
rust from metals before they are painted
...


n

Ethanoic acid is used in vinegar for cooking and
to preserve food such as vegetables
...


Chapter 10

Acids, Bases and Salts

Quick check 1
1
...

3
...

5
...

Explain what is meant by a strong acid
...

Explain what is meant by a weak acid
...

Some dry citric acid crystals are placed on a dry piece of
litmus paper
...

Solution

Chapter 10

Acids, Bases and Salts

Solution to Quick check 1
1
...


3
...

5
...

(b) Acids turn blue litmus to red
...

A strong acid is an acid that is completely ionised in water
...
g
...

A weak acid is an acid that is only partially ionised in water
...
g
...

There will be no colour change because there is no water, so
the citric acid cannot form hydrogen ions
...

n A base is any substance which can accept the
H+ donated by acids
...

n Examples of bases are:
MgO, CuO, Mg(OH)2 , Cu(OH)2, NaOH, KOH etc
n Ammonia (NH3) is also considered a base
...


An alkali is a soluble base which
produces hydroxide ions, OH− (aq)
in water
...

n

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Chapter 10

Acids, Bases and Salts

Difference between base and alkali
TRUE OR FALSE?
n All alkalis are bases but not all bases are alkalis
n

CuO is a base
CuO is insoluble in water
Will CuO produce OH- in
aqueous solution?
n Is CuO an alkali?
n
n
n

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Chapter 10

Acids, Bases and Salts

Difference between base and alkali
All alkalis are bases,
but not all bases are alkalis
...

Alkalis turns red litmus to blue
...
e they can conduct
electricity

n

They have a pH value of more than 7

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Chapter 10

Acids, Bases and Salts
Chemical Reactions of alkalis
Alkalis react with ammonium salts to produce ammonia gas
...

n Ammonia gas is basic, thus it turns red litmus paper blue
...

n

E
...
1: NaOH + NH4Cl  NaCl + NH3 + H2O

NH3 gas produced turns
red litmus blue
Sodium hydroxide +
ammonium chloride

E
...
2: Ca(OH)2 + 2NH4Cl  CaCl2 + 2NH3 + 2H2O

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CuO(s) +NH4NO3 
n Cu(OH)2 + NH4SO4
n

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Acids, Bases and Salts
Amphoteric Oxides and hydroxides
n
n

What is an amphoteric substance?
An amphoteric substance is one which can act as both an acidic
substance and a basic substance
...
g

134-135
¨ Answer Summary questions on page 135

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Chapter 10

Acids, Bases and Salts

Types of Oxides
n
n
n
n
n
n

Elements burn or react with oxygen to form oxides
...

An acidic oxide is an oxide of a non-metal
...
Acidic oxides react with alkalis to form salts
...
If soluble, it will dissolve in water to
form an alkali
...

An amphoteric oxide is an oxide which can react with both acids and
alkalis to form salts
...

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Chapter 10

Acids, Bases and Salts

Types of Oxides
4 TYPES OF OXIDES

Acidic Oxides

Basic Oxides

Amphoteric Oxides

Neutral Oxides

CO2 , SO2
NO2 , NO

Na2O, CaO, K2O,
MgO, CuO

Al2O3 , PbO ,
ZnO

H2O, CO ,
N2O

React with acids to
form salts

React with both
acids & alkalis to
form salts

Do not react with
both acids &
alkalis

React with
alkalis to form
salts

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Chapter 10

Acids, Bases and Salts

Uses of Bases
Sodium hydroxide and potassium hydroxide are used in
making soaps
...

n

Magnesium hydroxide is used in toothpastes to neutralise
the acid produced by bacteria
...

n

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Chapter 10

Acids, Bases and Salts

Some Common Alkalis
Name

Chemical formula

Sodium hydroxide

NaOH

Potassium hydroxide

KOH

Calcium hydroxide

Ca(OH)2

Ammonia solution
(ammonium hydroxide)

NH3(aq)
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Acids, Bases and Salts
n
n
n
n
n
n

An acid turns ________ litmus to _____, while an alkali turns ______
litmus to _______
...

An acid produces ______ ions in water, while an alkali produces _______
ions in water
...

Acids react with metals to produce ______ gas and with carbonates to
produce ______ gas
...


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Chapter 10

Acids, Bases and Salts

Quick check 2
1
...

3
...

5
...

Define what is an alkali
...

State 3 properties of alkalis
...

Write balanced chemical equations for the following
reactions:
(a) potassium hydroxide + ammonium chloride
(b) calcium hydroxide + ammonium chloride
Solution

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Chapter 10

Acids, Bases and Salts

Solution to Quick check 2
1
...

3
...

5
...

E
...
sodium oxide, copper(II) oxide, calcium hydroxide
...

E
...
sodium hydroxide, potassium hydroxide, calcium hydroxide
...

(ii) Alkalis react with acids to produce a salt and water
...

Iron(II) hydroxide is a base, but not an alkali because it is
insoluble in water, so it cannot produce hydroxide ions in water
...

n A strong acid has a very high concentation
of H+ ions
...
g
...

This means the solution contains a mixture of
acid molecules which have not been ionized as
well as acid molecules which have been ionized
...
e the strength of the acid or alkali
...

The pH scale ranges from 0 to 14
...

DO you think the solution will be more acidic or less acidic if
the hydrogen ion concentration is high?
49

Chapter 10

Acids, Bases and Salts

The pH Scale
The lower the pH, the more acidic the solution is
...

n pH 7 is neutral
...

n

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Acids, Bases and Salts
The pH meter
The pH meter is a quantitative instrument used for
measuring pH
...

n The pH meter will give an exact value for the pH of the
solution
n This is a more accurate method for determining the pH of a
solution
...

Using the Apparatus and Materials given, fill out the following table
Substance

Observations

pH

Strong/Weak
Acid/ base

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Chapter 10

Acids, Bases and Salts

Indicators
n

Indicators are substances which show different
colours in acidic and alkaline solutions
...
It is red in acidic
solutions and blue in alkaline solutions
...

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Chapter 10

Acids, Bases and Salts

The Universal Indicator
The Universal Indicator consists of a mixture of dyes which
changes its colour in different pH solutions
...

n The Universal Indicator or pH paper changes its colour
according to the pH shown in the chart below
...

2
...

4
...

What is meant by the pH of a solution? What is the pH of :
(a) hydrochloric acid, (b) citric acid, (c) sodium chloride
solution, (d) sodium hydroxide solution?
What are the 4 types of oxides? Give one example of each
type of oxide
...


2
...


4
...
(a) 0 – 1, (b) 3 – 4, (c) 7, (d) 13 – 14
...
E
...
sulphur dioxide, sodium oxide, aluminium oxide,
water
...

n A salt contains two parts:
n Metal part : cation (comes from the
base)
n Non-metal part : anion (comes from
the acid)
Salt
n

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Chapter 10

Acids, Bases and Salts
Examples of Salts

Notice that the metal cation from the base replaces the Hydrogen ion
in the acid
...

n Sodium chloride is electrolysed to obtain sodium and
chlorine in the industry
...

n Magnesium sulphate, commonly called Epsom salt, is
used as a bath-salt
...
Action of acid on alkali ( Titration)
ACID + ALKALI  SALT + WATER
n This process is called neutralisation
...


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Chapter 10

Acids, Bases and Salts

Methods of Preparing Salts

1
...

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Chapter 10

Acids, Bases and Salts
To prepare sodium nitrate by neutralisation (titration method)

burette

Pipette
Sodium nitrate and water
(phenolphthalein as indicator)

67

Chapter 10

Acids, Bases and Salts
To prepare sodium nitrate by neutralisation (titration method)

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Chapter 10

Acids, Bases and Salts

Methods of Preparing Salts
2
...

n Examples of salts prepared by this method:

* copper(II) sulphate from copper(II) oxide and sulphuric acid:
CuO + H2SO4  CuSO4 + H2O
* zinc chloride from zinc oxide and hydrochloric acid:
ZnO + 2HCl  ZnCl2 + H2O
69

Chapter 10

Acids, Bases and Salts
Preparation of copper(II) sulphate (acid on insoluble base)
Step 1 Place about 50 cm³ of dilute
sulphuric acid in a beaker and gently
warm the acid
...

Equation: CuO + H 2SO4  CuSO4 + H2O

Step 2 Filter off the excess copper(II) oxide
using a filter paper and funnel
...

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Chapter 10

Acids, Bases and Salts
Preparation of copper(II) sulphate (acid on insoluble base)

Step 3 Evaporate the copper(II) sulphate solution until it is saturated
...

Step 4 Filter off the copper(II) sulphate crystals formed and dry them
by pressing them between sheets of filter paper
...
Action of acid on (b) a carbonate
ACID + CARBONATE  SALT + WATER + CO2
Eg
...
2 Hydrochloric acid on calcium carbonate
2HCl + CaCO3  CaCl2 + H2O + CO2
This method is similar to the previous method; instead of the
oxide, the carbonate is added in excess to the acid
...

n

Chapter 10

Acids, Bases and Salts

Methods of Preparing Salts
4
...
1

Sulphuric acid on zinc
H2SO4 + Zn  ZnSO4 + H2
Eg
...
Metals
like sodium, potassium and calcium are explosive with acids;
while metals like lead and copper are unreactive with acids
...

n

ne
...

75

Preparation of
Insoluble salts

Chapter 10

Acids, Bases and Salts

Methods of Preparing Salts
5
...

n Two solutions are mixed together to produce a precipitate of
the insoluble salt which can then be filtered off from the mixture
...
g
...

AB (aq) +CD(aq)  CB (aq) + AD (s)
Two aqueous solutions AB and CD are mixed together
...


n

Examples:
...

2
...

4
...
Give an example of a soluble and insoluble
salt
...

State whether the following salts are soluble or insoluble:
(a) sodium carbonate, (b) calcium chloride, (c) barium sulphate,
(d) lead(II) nitrate, (e) lead(II) chloride
...

For each method, state the chemicals you will need and
write a balanced chemical equation for the reaction
...


2
...

4
...

E
...
soluble salt: sodium chloride
E
...
insoluble salt: calcium sulphate
(a) Acid on metal, (b) acid on base, (c) acid on carbonate,
(d) precipitation method
Soluble: sodium carbonate, calcium chloride, lead(II) nitrate; Insoluble: lead(II)
chloride, barium sulphate
(a) potassium nitrate: titration method; potassium hydroxide and
nitric acid;
KOH + HNO3  KNO3 + H2O
(b) zinc nitrate: acid on carbonate; nitric acid and zinc carbonate;
2HNO3 + ZnCO3  Zn(NO3)2 + H2O + CO2
(c) magnesium sulphate: acid on metal; magnesium and sulphuric acid;
Mg + H2SO4  MgSO4 + H2
(d) copper(II) carbonate: precipitation method;
copper(II) sulphate and sodium carbonate;
CuSO4(aq) + Na2CO3(aq)  CuCO3(s) + Na2SO4(aq)
Return
82

Chapter 10

Acids, Bases and Salts

State symbols in equations
The state symbols in a chemical equation tell us about the state of each reactant
and product
...

n

83

Chapter 10

Acids, Bases and Salts

Writing ionic equations
Ionic equations are general equations which can apply to
any particular reaction
...

n They contain state symbols
...

n

84

Chapter 10

Acids, Bases and Salts

Writing ionic equations
Steps in writing ionic equations
EXAMPLE 1
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
Step 1: Break substances with (aq) into its ions:
H+(aq) + Cl-(aq) + Na+ (aq) + OH-(aq)  Na+ (aq) + Cl- (aq) + H2O (l)
Step 2: Remove similar ions from both sides of equation
...

Step 3: Rewrite the equation with the ions left:
2H+(aq) + CaCO3(s)  Ca2+(aq) + H2O(l) + CO2(g)
86

Chapter 10

Acids, Bases and Salts

Writing ionic equations
Steps in writing ionic equations
EXAMPLE 3
Pb(NO3)2(aq) + 2NaCl (aq)  PbCl2 (s) + 2NaNO3 (aq)
Step 1: Break those with (aq) into its ions:
Pb2+(aq) + 2NO3-(aq) + 2Na+(aq) + 2Cl- (aq)  PbCl2(s) + 2Na+(aq) + 2NO3- (aq)
Step 2: Remove similar ions on both sides
...


H2SO4(aq) + 2KOH(aq)  K2SO4(aq) + 2H2O(l)
H+(aq) + OH-(aq)  H2O(l)

2
...


AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)
Ag+(aq) + Cl-(aq)  AgCl(s)

4
...


Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
Mg(s) + 2H+(aq)  Mg2+(aq) + H2(g)

Return

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