S3 Chemistry
Acids and Bases
REVISION
NEW LEARNING
I have demonstrated ways of
measuring and adjusting pH and can
describe the significance of pH in
everyday life.
I can describe the dissociation of water into
H+ and OH- ions and explain how the excess
of these ions produces acids or alkalis
respectively.
SCN 3-18a
National 4/5
Starter Task
Can you sort out the cards in to acids and alkalis and
match them to pH, indicator colour and type?
Starter Questions
1. Name 2 household alkalis.
Bleach, shampoo, toilet cleaner, oven
cleaner etc.
2. Name 2 laboratory acids.
Hydrochloric acid, sulphuric acid, nitric acid,
phosphoric acid.
3. What is the pH scale?
A measure of the acidity of a substance, ranging from 0
to 14.
Lesson 1: pH and Concentration
Today we will learn to
Predict the effect of dilution on the pH of an acid or
alkali.
We will do this by
Doing an experiment to measure pH of different diluted
solutions.
We will have succeeded if
We can describe the effect of adding water on the pH of
any solution.
pH Scale
The indicator turns a different colour at each pH number and so the pH of acids and
alkalis can be found by colour-matching with a chart.
Red
Orange / Yellow
Green
Green/blue
Blue/Purple
Remember that the pH of a substance can only be measured in aqueous solution - any
solids must be dissolved first. A solution is formed when a substance dissolves in
water.
**REMINDER**
Making a solution
Solutions are made when a SOLUTE is dissolved in a SOLVENT.
‘Solute is what you put
Solvent is where it went,
Solution is what you’re producing.’
Diluting Acids and Alkalis
Pupil Experiment – Dilution of acids & Alkalis
Aim: To identify the effect of dilution on pH and ion concentration when acids and alkalis
are diluted
Method: Collect 7 test tubes, test tube rack, acid or alkali, a rubber
stopper, multimeter and safety glasses.
1. Pour 10cm3 of acid (or alkali) into test tube 1.
2. Take 1 cm3 of acid from test tube 1 and add to test tube 2.
3. Add 9cm3 of water to make test tube 2 up to 10cm3.
4. Repeat steps 2 and 3 for the remaining test tubes.
5. Test conductivity, then add 2 drops of universal indicator to
each test tube and record pH by comparing colour to pH chart.
Diluting Acids and Alkalis
Pupil Experiment – Dilution of acids & Alkalis
Aim: To identify the effect of dilution on pH and ion concentration when acids and alkalis
are diluted
Your teacher will help you complete figures for last column!
Diluting Acids and Alkalis
Pupil Experiment – Dilution of acids & Alkalis
Aim: To identify the effect of dilution on pH and ion concentration when acids and alkalis
are diluted
Diluting Acids and Alkalis
ACID
NEUTRAL
more dilute acid
decreasing acidity
increasing pH
ALKALI
more dilute alkali
decreasing alkalinity
decreasing pH
Note that diluting a solution by a factor of 10 (e.g. 1ml of solution diluted with water up
to 10ml) will only change its pH value by 1. In other words a pH 2 solution is TEN times
more acidic than a pH 3 solution.
Consolidation Task
Objective Traffic Lights
How do you feel about the lesson objectives?
Red = don’t think I have grasped this
Amber = feeling OK about this, have just about got there
Green = Confident I have achieved this
Starter Questions
1. What is the solvent when lemonade is made from
lemons, sugar and water?
Water.
2. Describe the effect of dilution on the pH of and acid.
As water is added, the pH will increase.
Lesson 2 :Forming Acids and Bases
Today we will learn to
Describe how acids and bases are made.
We will do this by
Watching a demo of the production of an acid and alkali,
and planning an experiment to make our own alkali
solution.
We will have succeeded if
We can identify the oxides used to make an acid or an
alkali.
Forming Acids and Bases
Non-metal oxides
An element that reacts with oxygen forms an oxide.
Carbon,
nitrogen
and
sulphur
are
all
non-metals.
Carbon forms carbon dioxide (CO2), nitrogen forms
nitrogen dioxide (NO2) and sulphur forms sulphur
dioxide (SO2).
It is not just the oxides of carbon, nitrogen and
sulphur that lower the pH of water …
All non-metal oxides that dissolve in water form
acidic solutions.
Forming Acids and Bases
Metal oxides
When a metal reacts with oxygen, the metal oxide is
formed, e.g. sodium produces sodium oxide, calcium
produces calcium oxide.
Some metal oxides are soluble in water, e.g. sodium oxide
and barium oxide.
It is not just the oxides of sodium and barium that
increase the pH of water …
All metal oxides that dissolve in water form alkaline
solutions.
Forming Acids and Bases
Some metal oxides are insoluble in water, e.g. copper(II) oxide and zinc oxide.
What is the effect of copper(II) oxide and zinc oxide on the pH
of water?
It is not just copper(II) oxide and zinc oxide that have no effect on the pH of water …
All metal oxides that are insoluble in water have no effect on pH.
The solubility of selected metal oxides is shown on page 8 of the Data Booklet.
Only oxides with the letter ‘i’ are sufficiently insoluble to have no effect on the pH of water.
Forming Acids and Bases
Pupil Experiment - Making alkalis
Aim: To make an alkali from magnesium metal.
Method: Burn a piece of magnesium metal in the air following your teacher's
instructions carefully. Once the magnesium has changed colour and cooled down,
add the product to about 5cm3 of water in a test tube. Add some universal
indicator.
Results & Conclusion: Record your observations from your experiment in your
jotter and your overall findings.
Complete the word equation for this reaction
Exit Task
Shape and Colour
Use only shape and colour to create an image of one thing
you have learned today
Then, show it to a partner and see if they can guess what the
learning is.
Starter Questions
1. Name 2 elements which when burned produce an ACIDIC
oxide.
Carbon, Sulphur, Nitrogen etc.
2. Describe how you might prepare an alkaline solution.
Use p8 of the data book to find a soluble metal oxide.
Burn the metal in air then dissolve the product in water.
3. What happens to the pH of water when aluminium oxide is
added to it.
Nothing. It is insoluble.
Starter Questions
Place each of the following metal oxides in the correct column in the table
below.
potassium oxide, nickel oxide, lithium oxide, tin(II) oxide, calcium oxide, iron(III)
oxide
Dissolves to form an alkali
No effect on the pH of water
Lesson 3: Water and Neutral Solutions
Today we will learn to
Identify the ions which produce acids and alkalis.
We will do this by
Writing down the dissociation of water and deducing
which ions are in acids and which are in alkalis.
We will have succeeded if
We can identify the ions which are responsible for acidity
and alkalinity.
Water and Neutral Solutions
The chemical name for water is hydrogen oxide, H2O. With two non-metal elements, water can be expected
to be made up of molecules with the atoms joined together by covalent bonds. Covalent compounds are nonconductors of electricity.
A sensitive meter can be used to show that water does conduct electricity although very poorly. This
indicates that water does not just consist of molecules … a small number of ions must also be present
in water.
This is because a small number of molecules split up as follows:
H2O (l)

many water molecules
H+ (aq)
+
OH- (aq)
very few ions
Water and Neutral Solutions
Since each water molecule can form one hydrogen ion, H+ (aq), and
one hydroxide ion, OH- (aq), the concentration of hydrogen ions in pure
water is equal to the concentration of hydroxide ions.
Like water, in all neutral solutions, the concentration of hydrogen ions,
H+ (aq) is equal to the concentration of hydroxide ions, OH- (aq).
Acids
In acids, the concentration of hydrogen ions, H+ (aq). is
greater than the concentration of hydroxide ions, OH(aq). When an acid solution is diluted, the concentration of
H+ (aq) decreases.
Alkalis
In alkalis, the concentration of hydroxide ions,
OH- (aq) is greater than the concentration of
hydrogen ions, H+ (aq). When an alkaline solution is
diluted, the concentration of OH- (aq) decreases.
Acid or Alkali?
It is important to remember that all solutions in water contain
both hydrogen and hydroxide ions. It is the relative
concentrations of these ions that decide whether a solution is
acid, alkaline or neutral.
Consolidation Task
Summary Exercise for Lessons 1-4
Exit Task
Question you have about the
lesson
Pyramid
Things you have
been reminded of
today
Things you have
learned today
Starter Questions
1. Write the equation for water dissociating into its ions.
H2O

H+
+
OH-
2. Why is the pH of pure water neutral?
Because there are equal concentrations of H+ and OHions in pure water.
3. Why is water a (very poor) electrical conductor?
Because it contains a small number of ions which are
free to move.
Neutralisation
Today we will learn to
Describe the reaction of an acid with an alkali.
We will do this by
Reacting acid and alkali together and predicting the
results.
We will have succeeded if
We can write a chemical equation for our experiment.
Neutralisation
A base is a substance that reacts with an acid, decreasing the acidity. This kind of reaction is known
as neutralisation (since the pH of the acid moves towards 7, the pH of a neutral solution). Water is
one of the products of a neutralisation reaction and the other is a salt.
ACID
+
BASE

SALT +
WATER
Neutralisation of an acid involves the reaction of H+ (aq) ions with the base.
H+ (aq)
+
base 
salt
+
H2O
salt
+
H2O
An alkali can also be neutralised by an acid.
OH- (aq)
+
acid

Neutralisation
GROUP THOUGHT: What happens when an acid and an alkali are mixed?

+
acid
alkali
What will be the outcome of mixing dilute hydrochloric acid with the alkali sodium hydroxide?
HCl (aq)
+
NaOH (aq)

NaCl (aq)
+
How do you know this chemical reaction has taken place?
The pH of the mixture will become closer to pH7.
The reaction of an acid and an alkali is, therefore, an example of neutralisation.
H2O (l)
Neutralisation
What are the products of the reaction between hydrochloric acid and sodium hydroxide?
HCl (aq)
hydrochloric
acid
+
NaOH (aq)

NaCl (aq)
+
H2O (l)
+
sodium
hydroxide

sodium
chloride
+
water
Sodium chloride and water are produced.
Sodium chloride is a salt.
A salt is a substance in which the hydrogen ion of an acid has been replaced by
a metal or other positive ion.
In this reaction the hydrogen ion of hydrochloric acid has been replaced by a sodium ion.
Neutralisation
Neutralisation
NaOH
Everyday Neutralisations
VW
Acid
+
Alkali
Everyday Neutralisations
Acid
+
Alkali
Mind Map
Produce a mind map to summarise the lesson today.
Starter Questions
1. What is ‘neutralisation’?
When an acid reacts with a neutraliser to produce a salt and
water.
2. What happens to the pH of an acid when it is
neutralised?
It increases towards pH 7.
3. Give 3 everyday examples of neutralisations.
Treating stings, indigestion remedies, gardener’s
lime, rebreathers.
Everyday Neutralisations
Acid
+
Alkali
Acid Rain
Today we will learn to
Explain the causes and effects of acid rain.
We will do this by
Reading about the chemistry involved and summarising it in
our own words
We will have succeeded if
We can correctly identify the chemicals which form acid
rain and what their effects are.
Burning fossil fuels also causes pollution in the form of ACID
RAIN.
*sulfur
Coal contains a small amount of ________.
When coal burns the sulfur forms ______ _______ gas.
The sulfur dioxide reacts with _______ in the air to form _______
________.
The sulfur trioxide _________ in water in the clouds to form an acid.
The _____ _____ that falls can kill tress and _____ and damage
buildings and statues.
Do not copy straight from the
paragraph on side 1 of your
worksheet – write an
explanation in your own words!
Acid Rain
Today we will learn to
Explain the causes and effects of acid rain.
We will do this by
Reading about the chemistry involved and summarising it in
our own words
We will have succeeded if
We can correctly identify the chemicals which form acid
rain and what their effects are.
Starter Questions
1. What common foods do you know that contain acids?
Most fruits, coffee, tea, milk.
2. What health effects do you know of that acid foods
might cause?
Tooth erosion, indigestion.
3. Can you think of any benefits to using acids in foods?
Preservation, flavouring.
Acids in Food and Drink
In this lesson we will learn to…
Carry out research on an acid or alkali and report on it to show
the effect of its use on society.
We will do this by…
Choosing an application of acids or alkalis in our diet and writing a report
on it.
We will have been successful if…
We can explain what a good report on acids or alkalis would
include.
Where can I find information on Acids?
Acids are common chemicals and are found commonly in food and drinks.
1. Which acids are used and what are they used for?
2. What are their effects on our health and diet?
Use the factsheets provided to inform your research.
The following books would be useful:
Standard Chemistry
Chemistry Counts
National 5 Chemistry
Class Notes booklet on rates
You have been given a list of websites to help you.
The following websites would also be useful:
Evans2Chemweb
BBC Bitesize chemistry
Chemistry about.com
What should my report look like?
Your report must
•
Be 50-100 words long. A shorter report will only be assessed as National 4 level.
•
Include a description of the chemical or area you have picked, what it is used for and
why it is useful.
•
Include the effect this acid (and its use) have had on society or the environment.
This might be a good effect, or a bad effect, or a mixture of both.
Give your report a clear structure e.g. titles and subtitles. You can use your own version
of diagrams if you want, but DO NOT cut and paste, or you will not pass.
NB This slide contains 101 words.
Starter :Rainbow Reaction
Naming Salts
Today we will learn to
Name the possible products of neutralisation reactions
We will do this by
Investigating the acids used and predicting names using
page 8 of the Data Book
We will have succeeded if
We can correctly identify the salts in given examples.
Naming Salts
In salt formation, the aqueous hydrogen ions in the acid, H+ (aq), are replaced by the
positive metal ions (or ammonium ions) from the base. This gives the first part of the name
of the salt.
The second part of the name comes from the name of the negative ion in the acid.
Acid
hydrochloric
sulphuric
nitric
carbonic
phosphoric
Negative ion
chloride
sulphate
nitrate
carbonate
phosphate
Naming Salts
Complete the worksheet on hydroxide bases, then try the different bases below:
Name of acid
sulphuric acid
hydrochloric acid
Name of base
sodium oxide
calcium hydroxide
nitric acid
copper(II) oxide
phosphoric acid
potassium carbonate
carbonic acid
magnesium oxide
Name of salt
Acids and Carbonates
Metal hydroxide solutions (alkalis), metal oxides and metal carbonates are all bases … they react with
acids in a neutralisation reaction.
If the base is a metal carbonate then carbon dioxide is also produced.
metal
carbonate
+
acid

salt
+
carbon
dioxide
+
water
 When a metal carbonate reacts with hydrochloric acid, the salt
produced is a metal chloride.
 When a metal carbonate reacts with sulfuric acid, the salt
produced is a metal sulfate.
 When a metal carbonate reacts with nitric acid, the salt produced
is a metal nitrate.
Acids and Carbonates
Tell me three things...
you have done well
you would like to find out more about
you know now that you didn’t know 50 minutes ago
Starter Questions
1. What is the test for carbon dioxide gas
It turns limewater chalky/cloudy.
2. If CO2 dissolves in water, is the solution
acid, alkali
or neutral?
Acidic.
3. Write a chemical equation for the reaction of calcium
carbonate and hydrochloric acid.
CaCO3 + HCl  CaCl2 + CO2 + H2O
Metal Oxides and Acid
Today we will learn to
Name the products from metal oxide neutralisations
We will do this by
Reacting an oxide with acid and writing a balanced
equation.
We will have succeeded if
We can correctly identify the salts in given examples.
Metal Oxides and Acid
The reaction of an acid with a metal oxide
ACID
+ METAL OXIDE

SALT
+
WATER
This method of making a salt can be used when the metal oxide is insoluble in water, e.g. copper(II)
sulphate can be prepared by the reaction of copper(II) oxide with sulphuric acid.
The metal oxide will react with the acid but will not dissolve in the neutral solution. If excess metal oxide
is added (more than what is needed to react with all the acid), then the unreacted metal oxide can be
removed from the neutral solution by filtering. The solution (the filtrate) is evaporated to dryness to
obtain a solid sample of the salt.
Preparing a soluble salt from an acid and insoluble
base
Metal Oxides and Acid
Pupil as Teacher
One pupil is the teacher.
You have to summarise the lesson (unit) and/or question the class on what
was studied.
Starter Questions
1. What is the test for hydrogen gas
It burns with a squeaky pop.
2. Which metals react with acid?
All metals above H in the electrochemical series.
3. What would I see if I put magnesium in acid?
Effervescence and the Mg would disappear quite quickly.
Metals and Acid
Today we will learn to
Name the products from the reactions of SOME metals
with acid.
We will do this by
Reacting 4 metals with acid and investigating the results.
We will have succeeded if
We can correctly identify the products in given examples.
Metals and Acid
Acids react with (some) metals to form a salt. The other product is hydrogen gas.
ACID
+
METAL

SALT
+
HYDROGEN
In this reaction, the hydrogen ions, H+ (aq), react by gaining electrons and hydrogen molecules are formed.
2H+ (aq)
+
2e-

H2 (g)
The electrons come from the metal atoms as the atoms lose electrons to form metal ions.
This type of reaction is similar to neutralisation reactions since the H+ (aq) ions are ‘cancelled out’ and, as a
result, the pH of the solution increases towards 7 as the reaction proceeds. However, the H+ (aq) ions
form hydrogen gas, not water.
Metals and Acid
Metals and Acid
Metal
reactions
with
acids
Many metals react with acids. When this happens, effervescence or bubbling occurs.
What do the bubbles indicate?
A gas is produced. Where might this gas have come from?
How can you test to find out if the gas produced is hydrogen?
Place a burning splint next to the mouth of the test tube.
A ‘squeaky pop’ as the gas ignites shows that hydrogen is the gas produced in this reaction.
Metals and acid – equations
What are the products of each reaction?
magnesium
+
hydrochloric
acid

magnesium
chloride
+
hydrogen
Mg
+
2HCl

MgCl2
+
H2
aluminium
+
hydrochloric
acid

aluminium
chloride
+
hydrogen
2Al
+
6HCl

2AlCl3
+
3H2
zinc
+
sulfuric
acid

zinc
sulfate
+
hydrogen
Zn
+
H2SO4

ZnSO4
+
H2
Aide Memoire
Make up a rhyme, story or picture that helps you
remember the order of reactivity of the metals, or
which ones react with acids.
Starter Questions
1. Write down 3 types of substance which react with an acid.
Metal, metal oxide, metal carbonate, base, alkali.
2. Name a compound which would produce CO2 when added to
hydrochloric acid.
Any metal carbonate.
3. Write an equation for the reaction of magnesium hydroxide with
nitric acid.
Magnesium Hydroxide Magnesium Nitrate
+ Nitric Acid
+ Water
Volumetric Titration
Today we will learn to
Titrate an unknown concentration of acid with alkali.
We will do this by
Using a burette and pipette to accurately titrate an
unknown concentration of acid.
We will have succeeded if
We can use get a concordant result for the volume
required.
Volumetric Titration
Burette containing Alkali (known
concentration)
Conical flask with known
volume of acid (unknown
concentration) with few drops
of indicator
Volumetric Titration
Volumetric Titration
Acids and alkalis react to form a salt plus water in a neutralisation reaction.
Neutralisation is complete when all of the H+ (aq) ions from the acid have been
“cancelled out” with exactly the same number of OH- (aq) ions from the alkali.
H+ (aq)
+
OH- (aq)
→
H2O (l)
An indicator can be used to detect the end-point of the reaction.
The number of moles of H+ (aq) that react will equal the number of moles of OH- (aq)
that react.
Volumetric Titration
Using balanced equation
NaOH + HCl
→
NaCl + H2O
1 mole + 1 mole
So 1 mole of acid reacts with 1 mole of alkali.
If the acid is the same concentration as the alkali, it will need exactly
25cm3 to reach the endpoint.
If it is more concentrated, it will need more than 25cm3 to reach the
endpoint.
If it is less concentrated, it will need less than 25cm3 to reach the
endpoint
Volumetric Titration
Definition
Choose three new words you have learnt today or in the last few lessons and write
dictionary definitions.
Starter Questions
Starter Questions
Precipitation Reactions
Today we will learn to
Produce insoluble salts in precipitation reactions.
We will do this by
Mixing solutions and naming the products formed.
We will have succeeded if
We can predict the solubility of a product from the Data
Booklet.
Precipitation Reactions
Insoluble Products - Precipitation Reactions
Some ionic solids are soluble in water. The combination of positive and negative
ions separate as the solid dissolves, e.g. A + X- (s) and B+ Y- (s). When solutions of
these ions are mixed, the combination of A+ (aq) and Y- (aq) is insoluble in water
and the ions come together to form a solid, A + Y- (s).
A+ (aq)
X- (aq)
B+ (aq)
Y- (aq)
B+ (aq) X- (aq)
A+ Y- (s)
The insoluble solid that settles out of the solution is called a precipitate. This
can be separated from the solution by filtration. The kind of reaction that takes
place is known as precipitation.
Precipitation Reactions
Precipitation Reactions
The idea of spectator ions can also be applied to precipitation
reactions.
In any precipitation reaction,
A+ X- (aq)
+
B+ Y- (aq)

A+ Y- (s)
the spectator ions can be cancelled out to leave:
A+ (aq)
+
Y- (aq)

AY (s)
+
B+ X- (aq)
Precipitation Reactions
In any precipitation reaction,
A+ X- (aq)
+
B+ Y- (aq)
 A+ Y- (s)
+
B+ X- (aq)
the spectator ions can be cancelled out to leave:
A+ (aq)
+
Y- (aq)
AY (s)

Apply this to the reaction of sodium chloride solution with silver nitrate solution to produce a
precipitate of silver chloride:
The balanced equation with state symbols is:
NaCl (aq)
+
AgNO3 (aq) 
NaNO3 (aq) +
AgCl (s)
Explain what you have learnt today and how you have learnt it
?