Acids and Bases
By the end of today’s class you
should be able to:
 Explain what an indicator is
 Know that litmus paper is an indicator
An indicator
• An indicator is chemical that changes
colour if it is in an acid or a base
•Litmus paper is an indicator.
How litmus paper works..
Red litmus stays red
Blue litmus turns red
Red litmus turns blue
Blue Litmus stays blue
Red litmus stays red
Blue Litmus stays blue
Doing the litmus test
Substance
tested
What
happened to
red litmus
What
happened to
blue litmus
Is it acid/
base or
neutral
Litmus test experiment
By the end of today’s class you
should be able to:
• Name some common AND lab acids and
bases
• Know what the pH scale is and how it
works
What is an acid?
Acids are a group of chemicals.
What do you know about acids? Are all acids dangerous?
Some common acids used in the laboratory are:
1. Hydrochloric Acid (HCl)
2. Sulfuric Acid (H2SO4)
What is a base?
Bases are another group of chemicals. Examples…
everyday alkalis
Some common bases used in the laboratory are:
1. Sodium hydroxide - NaOH
2. Limewater – Calcium hydroxide - Ca(OH)2
Bases that are soluble in water are called alkalis.
Can you…
 Explain what an indicator is?
 Give an example of an indicator?
 Use litmus paper to test a variety of
solution and classify these as acidic, basic
or neutral?
 Name some common acids and bases?
Learning objectives for today..
• What the PH scale is
• How universal indocator
• Learn what a neutralisation reaction is
Indicators: how acidic or basic?
Litmus will tell you whether a solution is acidic or basic:
what it won’t tell you is how acid or basic.
Universal indicator is an indicator that tells us how
strong an acid or base is.
Indicators: the pH scale
The pH scale is a scale that runs from 0 to 14 which tells you
how acidic or how basic something is.
•pH7 is neutral
•pH 1 is strongly acid
•pH14 is strongly basic
1 2 3 4 5 6
7 8 9 10 11 12 13 14
Strong acid
Neutral
Strong bases
Weak acid
Weak Bases
Doing the universal indicator test
Substance
tested
What is its
pH?
What type of
substance is
it?
What type of substance?
Are these substances acidic or alkaline?
Are they weak or strong?
Substance
soda water
car battery acid
1
Description of acid/alkali
very weak acid
very strong acid
soap
8
very weak alkali
washing soda
10
weak alkali
stomach acid
2
strong acid
oven cleaner
14
very strong alkali
vinegar
4
weak acid
acid
pH
6
1 2 3 4 5 6
7
8 9 10 11 12 13 14
alkali
Learning check:
• Can you..
• Tell what universal indicator is used for?
• Explain the difference between universal indicator and
litmus paper?
• Explain what the pH scale is?
What is the pH?
Learning objectives
• To learn about what happens in a
neutralisation reaction
What happens when an acid and an alkali are mixed?
?
Mixing an acid and a base causes a chemical reaction.
The chemical reaction between an acid and a base
is called neutralisation.
acid
base
a salt
The pH value of the reaction mixture will turn to 7
water
• When an acid is mixed with a base they react
with each other form a salt and water. This is
called a neutralisation reaction.
The things
that react
are called
reactants
Acid + Base
The things
that are
made are
called
products
Salt + Water
Examples of neutralisation
reactions
The vinegar neutralises
the wasp sting!
Learning check..
• What is a neutralisation reaction?
• What is made during a neutralisation
reaction?
• What is the chemical formula of
hydrochloric acid?
• What is the chemical formula of sodium
hydroxide?
• Give one example of a neutralisation
reaction
By the end of the lesson you
should be able to:
• Know what a burette and pipette are used for
and how they are used
• Learn the word equation and chemical equation
for a neutralisation reaction between sodium
hydroxide and hydrochloric acid
• Know how to titrate HCl against NaOH and
prepare a sample of sodium chloride salt.
A Neutralisation reaction:
The reaction in words (A word equation):
Hydrochloric acid + Sodium Hydroxide
Sodium Chloride + Water
The reaction in chemical formulas (A chemical equation):
HCl
+
NaOH
NaCl
+ H 2O
Homework
Draw diagrams of the four main steps in the
experiment into notes copy
1.Filling pipette,
2.Filling burette,
3.Titration,
4.Evaporating water to get salt
1.
Measure out 25cm3 of sodium hydroxide
into the conical flask!
2. Add some indicator to the solution
3. Fill up the burette with hydrochloric acid (HCl) to
the zero level.
Start the titration!
Do the titration once roughly, twice more and then finally
without an indicator.
Finally repeat the titration without
using an indicator!
Evaporation will separate the salt
and water!
Acids and Bases neutralisation
• Acids react with bases called carbonates
to produce a salt, carbon dioxide gas and
water. This is also a neutralisation
reaction.
Acid + Carbonate  Salt + Carbon
dioxide + Water
A different type of neutralisation
reaction
2. Acid + Carbonate  Salt + Water +
Carbon dioxide
Hydrochloric acid + calcium carbonate 
Calcium chloride + Water+ Carbon dioxide
HCl + CaCO3  CaCl2 + H2O + CO2