Acids and bases
Teacher: Claudia De Candido
Tutor: Elena Monti
ITC “O.Mattiussi” 2005/06
1
Menu
What is a (n):
acid, base
Acid/ base indicators
Acid/base reactions
Acid rain
Assessment : multiple choice,
true or false, crosswords,
substitution table, interview.
2
Time
10 class periods 50 min. each.
3
Objectives
In this unit the students will:
learn about properties and uses of acids and
alkalis;
use indicators to classify solutions as acidic,
alkaline or neutral ;
use the pH scale to compare the acidity and
alkalinity of different solutions ;
begin to explore neutralisation and other reactions
of acid;
learn about sources and consequences of acid rain;
recognise hazards linked with acids and alkalis .
4
Skills
Knowledge of the new words and the new concepts.
Accurate explanation of the behaviour of acidic and
basic solutions.
Knowledge of the causes and consequences of acid
rain.
Prediction of behaviour through the acquainted
knowledge.
Grade Level : second classes - secondary school.
5
Evaluation
During the lessons the students can evaluate
their own improvements through activities
single or in group.
Assessment:
indicator chart, multiple choice, mistakes maze ,
crosswords, substitution table, interview with acids
and bases.
6
Suggestions
What the students need to do:
Ask, ask, ask if you don’t understand.
During the experiments follow instructions
carefully.
Take notes and take part in the lessons.
Practice and revise even when we don’t tell
you.
7
Safety
Wear chemical splash goggles for the
acidic and basic solutions.
Normal laboratory care is needed.
8
Procedure
Show the students acids and bases used in everyday life. Outline
basic characteristics e.g. acid food is sour tasting; alkalis are often
soapy, bitter and slippery.
Show how they can be tested and determined using indicators
(universal indicator and phenolphthalein ). Students will learn about pH
numbers and colours for varying acid and alkali strengths and neutral,
and fill in the indicator chart. Ask them some questions.
Drop some acid in a base and the base in an acid and observe the
behaviour of added phenolphthalein and explain it. Show the effects of
an acid dropped on limestone and on magnesium.
Collect all observations to describe the acid and bases and formulate
a theory.
Explain what the acid rain is like , how it forms, which effects it
produces.
9
Resources required
Various acids and alkalis, universal indicator
paper /phenolphthalein.
Test tubes, hydrochloric acid, sulphuric acid,
nitric acid, sodium hydroxide, potassium
hydroxide, ammonia,baking soda, wine,
vinegar, limestone, magnesium.
Projector, computer, power point
presentation.
10
Where do we find acids?
Acids are found in :
citrus fruits ( lemon juice, orange juice)
vinegar, wine, coca cola
car batteries ( sulphuric acid)
our stomach (hydrochloric acid)
acid soils
bee stings
acid rain
11
Useful acid facts
Ascorbic acid is another name for vitamin C. this
chemical is found in fresh fruit and prevents a
deadly disease, the scurvy.
Citric acid helps make the taste of the juice.
Salicylic acid is used to make aspirin.
Amino acids are molecules that join to make
proteins.
12
Where do we find alkalis ?
Alkalis are found in :
oven cleaners (sodium hydroxide)
soap
cleaning fluid
milk of magnesia
baking soda
Alkalis are often found in substances for
cleaning.
13
What of these adjectives can be linked to
an acid or to a base?
cleaning
caustic
corrosive
sour
dangerous
soapy
fuming
irritant
harmful
slippery
edible
toxic
bitter
14
Sour and bitter
What part of the
tongue can taste a
lemon or other sour
things?
Where might you
taste
something
bitter like baking
soda?
15
Hazard simbols
These symbols are showing the common
safety hazards of the acids and bases.
Toxic: can cause death, if swallowed,
breathed in or adsorbed through the skin.
Corrosive: attacks and destroys living
tissues, including the eyes and the skin.
Harmful: similar to toxic but less
dangerous.
Irritant: not corrosive but can cause
reddening or blistering of the skin.
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Definition of acid and base
The definition of acid and base is based
on its experimental behaviour.
17
Universal indicator
Indicators are chemicals that have different colours in
acidic and alkaline solutions.
Universal Indicator (pH paper) is a special indicator. It
has many colours that tell us if the solution is acidic,
neutral or alkaline and how strong the solution is.
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Indicators
Indicator
acid neutral alkali
Universal indicator red green purple
Litmus
red
blue
Phenolphthalein colourless colourless pink
19
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pH
Using the Universal Indicator and a chart you can
read off a number - the pH number. The pH number
usually ranges from 1-14. 1-6 means the solution is
acidic, 7 is neutral and 8-14 is alkaline.
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Indicators
22
pH
23
pH
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Why does the indicator change
colour?
Acids release hydrogen ions in water.
HCl
water
H+(aq) + Cl- (aq)
Bases release hydroxide ions in water.
water
NaOH
Na+(aq) + OH- (aq)
These ions are responsible for the changes
of colour.
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Strong acids and bases
Stronger acids give up more protons
(the positively charged parts of
atoms); stronger bases give up more
OH- (hydroxide). Neutral substances
have an even balance of protons and
OH-.
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Weak and strong acids
The strong acids
have the lowest pH
(pH 0-1).
The strong alkalis
have the highest pH
(pH 13-14)
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pH Scale Worksheet
Use the results of the indicator chart to answer the questions below.
1. Which substances are acidic?
2. Which substances are basic?
3. Which substance is neutral?
4. Which two substances in this activity are the most acidic?
5. Which substance in this activity is the most basic?
6. List the acidic substances shown from the least acidic to the most acidic.
7. List the basic substances shown from the least basic to the most basic.
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pH
The pH scale is a measure of how acidic or
alkaline a solution is. It shows the
concentration of hydrogen ions in a solution.
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Neutralisation
When an acid reacts with a base and
they produce
salt and water, the
reaction is called "neutralisation."
The acid supplies the H+ and the base
supplies the OH- which combine to form
water.
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Neutralisation
The reaction is:
acid +alkali
neutral salt +water
The type of salt produced depends on
the metal in the alkali used and on the
acid used.
HCl(aq) + NaOH(aq)
ClNa+
H+
OH-
NaCl(aq) + H2O(l)
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Reaction with limestone
An acid (hydrochloric acid) reacts with
limestone , producing CO2 .
2HCl (aq) + CaCO3 (s)
CO2(g) + CaCl2(aq) + H2O(l)
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Reaction with metals
An acid (hydrochloric acid) reacts with
magnesium producing hydrogen.
Mg(s) + 2HCl(aq)
MgCl2(aq) + H2(g)
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Typical properties of acids:
sour taste;
corrosive;
react with bases;
turn universal indicator into red;
generate CO2 from limestone;
generate H2 with metals;
release hydrogen ions;
have a pH less than 7.
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Typical properties of bases:
bitter taste;
soapy feeling;
turn universal indicator into blue;
react with acids;
have a pH of more than 7;
are also corrosive;
bases are also called alkalis.
37
Strong acids
The common strongest acids are:
hydrochloric acid (HCl)
sulphuric acid (H2SO4),
nitric acid (HNO3).
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Common bases
Common bases are:
sodium hydroxide (NaOH)
potassium hydroxide (KOH)
calcium hydroxide ( Ca (OH) )
ammonia
The soluble oxides and hydroxide of
metals form alkaline solutions.
2
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If the sentences are correct follow the thick arrow.
If the sentences are wrong follow the thin arrow.
IN 6 is the pH of a neutral solution
1. KOH is a base
2. The acids neutralise salts
3. The bases neutralise the acids
4. Nitric acid is corrosive
5. Sodium choride is a salt
6. Aspirin is a base
7. 14 is pH of a strong alkali
8. 14 is a pH of a strong acid
9. Phenolphtalein is colourless in acid solutions
10. Citric acid is a strong acid
11. H2SO4 is an acid
12. This simbol means toxic X
13. The universal indicator becomes red in basic solutions
14. The pH of basic solution is lower than the PH of acid solution
OUT
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Acids , bases , pH
Fill in the gaps
1. The term _________ refers to concentration of hydrogen in a solution.
2. The pH _________ measures how _________ or basic a substance on a scale of 1 to 14.
_______ measure from 1 to 7, while the _________ measure from 7 to 14.
3. Identify each as an acid (A) or a base (B).
____ Lemon juice ____ Soap ____ Battery acid ____ Hydrochloric acid
____ Bleach____ Vinegar ____ Baking soda ____ Floor cleaner
4. Really strong acids and bases are found at the ____________ of the scale, while those
near the ______________ are weaker. Right in the middle at exactly 7, or pH
______________, you have pure water.
5. Acids contain ________________ ions (H+), while bases contain _______________
(OH-) ions. Ions are atoms that have either lost or gained ___________.
When you put a metal in acid, the metal starts to____________________
6. Bases have the power to _______________ acids. The hydroxyl ion ___________ its
electron with the hydrogen ion. The H+ from the hydrogen ion and the OH- from the
hydroxyl ion bond together to form ____________ with pH neutral.
Different types of ___________ are formed depending on the types of acids and bases involved in the
reaction.
7. When we poured an acid into the limestone, a reaction occurred. Salt, water, and
___________ _____________ were produced by the reaction.
8. Most science labs have pH paper, which is paper that has been soaked in a special chemical
____________________. They turn _________ in an acid and __________ in a base. By comparing
the color of the pH paper to a chart, you can determine how _______ or ________ an acid or base is.
9. Constant reactions between acids and bases keep our ________________________ from being too
acidic or too alkaline.
Word Bank:
Acidic Acids Atoms Bases Blue Carbon dioxide Dissolve Electrons Ends Environment
Hydrogen Hydroxyl Indicator Neutral Neutralize pH Red Salts Scale Shares Strong
Water Weak
42
Multiple choise . Choose the right answer from A to D.
1. Which one of the following substances is an acid?
A. Lemon juice
C. Salt solution
B. Bleach
D. Water
2. Acids and alkalis can cause some dyes to change colour. These dyes are called:
A. solutions
C. indicators
B. mixtures
D. solvents
3.What colour does Universal indicator turn in strong acid?
A. Orange
C. Blue
B. Green
D. Red
4. The pH scale can be used to tell the strength of an acid or alkali. What pH number indicates an
alkali?
A. Less than 7
C. Exactly 7
B. Greater than 7
D. Any number
5. Neutralisation can be described as:
A. an acid an alkali cancelling each other out
C. salt dissolving in water
B. an acid becoming clearer in colour
D. bubbles of gas appearing
6. Indigestion is caused by too much acid in the stomach. It can be cured by taking antacids.
These work because:
A. they neutralise the acid
C. they lower the pH in the stomach
B. they taste nice
D. they make the acid more concentrated
7. Some acids should be treated very carefully. This is because:
A. they are red
C. they taste sour
B. they are corrosive
D. none of these
8. Hydrochloric acid has a pH of 1. If just enough sodium hydroxide was added to
neutralise some of the acid, the final pH would be:
A. 1
C. 5
B. 7
D. 9
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9. When an acid is added to an alkali what happens to the pH?
A. It goes up
C. It stays the same
B. It goes down
D. None of these
10. One strong alkali that can be used at home is:
A. bleach
C. soap
B. vinegar
D. lemon juice
11. A weak acid will have a pH of:
A. 0-3
C. 7
B. 4-6
D. 8-14
12. Which piece of equipment should always be used when handling acids and alkalis?
A. tongs
C. gauze
B. tripod
D. safety goggles
13. What is the pH of a neutral substance?
A. 6
C. 8
B. 9
D. 7
14. A bee sting is acidic. To stop the pain, which of these substances could you put onto it?
A. Vinegar
C. Lemon juice
B. Baking soda
D. Water
15. What colour would a neutral solution go if Universal indicator was added to it?
A. Red
C. Green
B. Purple
D. Blue
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Solutions
1-a
2-c
3-d
4-b
5-a
6-a
7-b
8-b
9-b
10-a
11-b
12-d
13-d
14-b
15-c
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46
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48
for cleaning
kitchen
it is irritant
for popular fertilisers:
ammonium nitrate and
ammonium sulphate
49
50
You are to be interviewed as if you are hydrochloric
acid. Read the information below to answer.
Hydrochloric acid (HCl)
•It is corrosive for some metals
(magnesium).
•It dissolves limestone.
•Part of gastric juice, it aids in
the digestion of protein.
•Sold commercially as “Muriatic
acid”.
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52
You are to be interviewed as if you are acetic
acid. Read the information below to answer.
The formula is CH3COOH
Acetic acid is:
used in the manufacture of plastics ;
used in making pharmaceuticals;
the acid present in vinegar;
a weak acid.
It has sharp smell.
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54
You are to be interviewed as if you are phosphoric acid.
Read the information below to answer.
Phosphoric Acid is:
The formula is H3PO4
ºa flavouring agent in sodas;
ºused in the manufacture of
detergents;
ºused in the manufacture of
fertilisers;
ºused to dissolve calcium
carbonate in the taps.
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You are to be interviewed as if you are nitric acid.
Read the information below to answer.
The formula is HNO3
Nitric acid
•It is used in the production of
fertilisers.
•It is used in the production of
explosives.
•Nitric acid is a volatile acid – its
reactive components evaporate
easily and are irritant.
•It is a strong acid.
•It stains proteins (including skin!).
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ACID + BASE
SALT + WATER
Complete the following equations in both words and formulae:
1. Hydrochloric +
Acid
Sodium
Hydroxide
Sodium
Chloride
+
Water
+
Na OH
_______
+
_______
+
Sodium
Hydroxide
Sodium
Nitrate
+
Water
+
Na OH
_______
+
_______
+
Zinc
Hydroxide
_______
+
_______
H NO3
+
Zn (OH)2
_______
+
_______
4. Sulphuric
Acid
+
Calcium
Hydroxide
_______
+
_______
H2 SO4
+
Ca (OH)2
_______
+
_______
Calcium
Hydroxide
_______
+
_______
+
Ca (OH)2
_______
+
_______
6. Sulphuric
Acid
+
Ammonium
Hydroxide
_______
+
_______
H2 SO4
+
NH4 OH
_______
+
_______
H Cl
2. Nitric
Acid
H NO3
3. Nitric
Acid
5. Hydrochloric +
Acid
H Cl
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Indigestion and antacids
The stomach produces hydrochloric
acid to help digest food. The pH
ranges from 0.9 to 1.5. When too
much food is eaten, too much acid
can be produced and the pH can
become too low. This is called
indigestion.
Antacids are bases that neutralise
the excess acid. Many contain
bicarbonate or carbonate salts,
which are basic.
62
Hydrangea
You can use flowers to detect acid and
bases.Hydrangea plants produce pink and
white flowers when the soil is alkaline and
blue flowers when it’s acid.
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Treating stings
Bee stings are acid. You
can ease the pain with a
weak alkali (bicarbonate of
soda)
Wasp stings are alkaline.
You can neutralise them
with vinegar (ethanoic acid)
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Making predictions
Which substance do you think can clean
this penny better?
65
Acids are better penny cleaners. In fact, if you were to leave a
penny in vinegar or lemon juice for several days, small pieces of
the penny would eventually start to come off. Drain cleaners, on
the other hand, are mostly bases. Bases do not damage metal
pipes like an acid cleaner would.
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Other experiments
An egg in acid (acid dissolves the shell).
A bone in acid (acid dissolves salts of calcium).
Milk + lemon juice (milk curdles, because its
molecules are broken down by the citric acid of the
lemon).
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ACIDS AND BASES
is
A
/an
acid /base
turns
neutralizes
reacts/
doesn’t react
with
has
releases
sour
slippery
soapy
harmful
corrosive
bitter
irritant
cleaning
caustic
like
Universal indicator/
phenolphthalein
an acid / a base
limestone
marble
calcium carbonate
metals
a pH
hydrogen/
hydroxyde
red/blue
colourless/pink
to form
to form
lower/ higher
ions
soap
hydrochloric acid
lemon juice
bleach
ammonia
oven cleaner
viakal
acetic acid
milk of magnesia
baking soda
a salt and water
carbon dioxide/
hydrogen
than 7
in water
Read in pairs¸ choosing the right sentence.
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Acid rain
Most combustions give off sulphur
dioxide and nitrogen oxides which
cause acid rain.
69
Consequences on vegetation
Increased acidity in the soil leaches
important nutrients.
Many trees have been seriously affected by
acid rain.
70
Consequences on lakes and
rivers
Aquatic life is also highly
sensitive to pH. Below pH 6
the number of sensitive fish
declines and below pH 5.0
many microscopic species
disappear. Below pH 4.0
lakes are effectively dead.
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Consequences on buildings
Stone, such as marble, that contain calcium
carbonate is eroded by acid rain.
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Consequences on human health
The acids irritate the mucus membranes and
increase the risk of respiratory illnesses, such as
asthma, bronchitis, and emphisema.
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Consequences of the pH change
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Acid soil
If the soil is too acid , most crops will
not grow well. Farmers can spread
limestone on the soil to neutralise it.
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Questionnaire - Write down the answers after power
point presentation.
What gases cause acid rain?
What pH is rain naturally?
Where do the acid rain gases come from?
How are the acid rain gases formed?
What specific problems does acid rain cause in the
environment?
How can acid rain be reduced?
Give 3 different ways.
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Look at the pictures below and fill in the gaps.
is
is produced by
because it
contains
emitted
Acid rain
leaches
causes
erodes
develops
sulphuric acid
and nitric acid
by cars
the ions of
the disappearance
of
marble, stones
which contain
allergies and
in the
breathing
problems
by burning of
coal and fuels
in the soil
in the lakes and
in the rivers
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Reducing acid rain and its effects
It is much better to reduce the sources of acid rain than to treat
the effects
Use less electricity at home and at work, so that less fossil fuel
is needed to generate it.
Generate electricity using alternative methods that don’t release
the acid rain gases e.g. nuclear power station, wind turbines,
hydroelectric schemes
Use vehicles less, walk or cycle more, especially for short
journeys.
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Name
Date
1. Identify each as an acid (A) or a base (B).
____ Lemon juice ____ Soap ____ Battery acid ____ Hydrochloric acid
____ Bleach____ Vinegar ____ Baking soda ____ Floor cleaner
2.____________ are chemicals that have different colours in acidic and alkaline
solutions.
Universal Indicator (pH paper) is a special indicator. It has many colours that tell us if
the solution is acidic, neutral or _______________and how strong or _______the
solution is.
3. The pH _________measures how ________ or basic a substance on a scale of 1 to 14.
_______ measure from 1 to 7, while the _________ measure from 7 to 14.
4. Bases release_________________ in solution.
5 .When an acid reacts with a base and they produce salt and water, the reaction is
called __________.
6. When an acid is added to an alkali the pH__________.
7 .Complete the following reactions
H2 SO4
+
K(OH)
_______
+
_______
H Cl
+
Mg (OH)2
_______
+
_______
NH4 OH
_______
+
_______
H NO3
+
turn the universal indicator into___________
generate ___________from limestone;
generate H2 with____________;
release ________ions;
have a pH____________.
9. Answer to these questions.









The acid of our stomach____________
The adjective for the soap____________
The taste of alkaline medicine____________
The smell of ammonia___________
Salycilic acid is used to make….
A strong acid___________
An acid reacts with marble producing _____________
Is ammonia an acid or a base?________________
What kind of acid does coca cola contain?__________________
10. It is a reaction that releases energy:___________________
12 In an endothermic reaction ____________ are higher in energy than the reactants.
In this case making the bonds gives you less energy than ______________them.
13. What kind of compounds are ammonium nitrate and calcium chloride?___________
14. Is the condensation of rain an endothermic or an exothermic reaction?___________
15. Does cooking food adsorb or release heat energy?________________
16. Substance that changes in a reaction:_______________
8.Complete the properties of the acids.
The acids
Have ______taste;
17. A yellow lamp contains this element._____________
18. The most stable energy state.______________
19.The instable energy state.______________
20.Why do the electrons jump from the ground state to the excited state? What happens
when they return to the ground state ?
are _________;
react with________to make salt and water;
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Name
Date
1. Identify each as an acid (A) or a base (B).
____ Wine ____ Soap ____ Baking soda ____ Phosphoric acid
____ Bleach____ Vinegar ____ Battery acid ____ Oven cleaner
have a pH ___________ if they are strong;
2 .When an acid neutralises a base produces ________ and __________
9. Answer to these questions.
3. The pH _________measures how ________ or basic a substance on a scale of 1 to 14.
_______ measure from 1 to 7, while the _________ measure from 7 to 14.
4. Acids release_____________ _________ in solution.
5. Indicators are chemicals that have different ________in acidic and alkaline solutions.
Universal Indicator (pH paper) is a special indicator. It has many colours that tell us if
the solution is_________, neutral or alkaline and how strong or _______the solution is.
6. When a base is added to an acid the pH__________.









The taste of alkaline medicine____________
The smell of ammonia___________
Ascorbic acid is called ….
A strong base ___________
The adjective for the soap____________
An acid reacts with metal producing _____________
Is the orange juice an acid or a base?________________
What kind of acid does a soft drink contain?__________________
The acid of our stomach____________
7 .Complete the following reactions
10. It is a reaction that takes in heat energy:___________________
H NO3 +
KOH
H Cl
NH4 OH
+
H2 SO4 +
Mg (OH) 2
_______
+
_______
_______
_______
8.Complete the properties of the bases .
+
+
_______
_______
12 In an exothermic reaction the ____________ are higher in energy than the products.
In this case making the bonds gives you more energy than ______________them.
13. What kind of compounds are ammonium nitrate and calcium chloride?___________
14. Is the snow formation an endothermic or an exothermic reaction?___________
15. Does a combustion adsorb or release heat energy?________________
16. Substance that changes in a reaction:_______________
The bases:
have ______taste;
are (an adjective linked to the touch)_______________-
are _________;
react with________to make salt and water;
turn the universal indicator into___________
release ________ions;
have a pH____________.
17. The blue-green fireworks contain this element._____________
18. The instable energy state.______________
19. The most stable energy state.______________
20.Why do the electrons jump from the ground state to the excited state? What happens
when they return to the ground state ?
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