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Chemistry
Acids and Alkalis

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Contents
Acids and Alkalis
Neutralization
Summary activities
What are acids and alkalis?
Indicators and the pH scale

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What is an acid?
Acids are a group of chemicals that donate a proton
in a reaction.
What do you know about acids? Are all acids
dangerous?

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What is an acid?
everyday acids laboratory acids

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What are acids?
Acids are
substances that:
Have a pH
below 7 and
turn universal
indicator yellow,
orange or red.

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Properties of acids
• An acid is a substance that releases
hydrogen ions (H+) into an aqueous (water)
solution.
• are corrosive.
• have a sour taste
• turn blue litmus paper red
• react with some metals, releasing hydrogen
gas and leaving a salt behind
• conduct electricity
• are neutralized by bases, producing water
and a salt.

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What is a strong acid?
Some acids, like those found in the laboratory or a
car battery, dissolve completely in solution. They
are very dangerous (too dangerous to taste or
touch).
These acids are said to be corrosive as they can
damage other materials by eating them away! They
are strong acids.

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What is a weak acid?
Many acids are found in household items such as
food, drink and beauty/skincare products.
These acids do not dissolve completely in solution
and are known as weak acids.

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Wear Safety Glasses!!!

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What is an alkali?
everyday alkalis laboratory alkalis
Alkalis, or bases, are another group of chemicals,
the opposite of acids.

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• A base is a substance that releases
hydroxide ions (OH–) in an aqueous
solution.
• are caustic
• have a soapy, slimy feel
• turn red litmus paper blue
• have a bitter taste
• conduct electricity
• are neutralized by acids, producing
water and a salt.
Properties of Bases

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What is a strong alkali?
Some alkalis, like those in the laboratory or in
cleaning materials such as toilet cleaner, dissolve
completely in solution and are too dangerous to
touch.
These alkalis are said to be caustic because they
can burn skin and damage other materials! They
are strong alkalis, or bases.

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What is a weak alkali?
Alkalis are found in soaps and other materials used
for cleaning. It is safe to handle these alkalis, which
can feel soapy.
These do not dissolve completely in solution and
are known as weak alkalis, or weak bases.

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Contents
Acids and Alkalis
Neutralization
Summary activities
What are acids and alkalis?
Indicators and the pH scale

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How can you test a liquid to find if it is an acid or an
alkali?
An indicator is a special chemical that changes
to a different color in an acid or an alkali.
What is an indicator?
Litmus paper and litmus solution
are examples of indicators.
Litmus is
red in acid.
Litmus is
blue in alkali.

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Litmus test experiment

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Litmus is used to show if a solution is acid or alkali.
Litmus does not show if the acid or alkali is weak or
strong.
What is universal indicator?
Universal indicator has a range of colors that show
how weak or strong the acid or alkali is.
stronger alkalistronger acid
What is the color for a weak acid?
What is the color for a strong alkali?
weak
alkali
weak
acid
strong
alkalineutral
strong
acid

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The strength of an acid or alkali is measured by the
pH scale.
What is the pH scale?
Each universal indicator color is given a number
called the pH value.
Universal indicator can tell you the pH of a solution.
What is the pH of a weak acid?
What is the pH of strong alkali?
weak
alkali
weak
acid
strong
alkali
strong
acid
stronger alkalistronger acid
neutral
1 2 3 4 5 6 7 8 9 10 11 12 13 14

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What is the pH?

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Are these substances acidic or alkaline?
Are they weak or strong?
1 2 14131211109876543
Substance pH Description of acid/alkali
soda water 6
car battery acid 1
soap 8
washing soda 10
stomach acid 2
oven cleaner 14
vinegar 4
very weak acid
very strong acid
very weak alkali
weak alkali
strong acid
very strong alkali
weak acid
alkaliacid
What type of substance?

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Contents
Acids and Alkalis
Neutralization
Summary activities
What are acids and alkalis?
Indicators and the pH scale

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Mixing an acid and an alkali
What happens when an acid and an alkali are
mixed?
Mixing an acid and an alkali causes a chemical
change.
This chemical change is called a chemical reaction.
How do you know this chemical reaction has taken
place?
?

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What is neutralization?
The chemical reaction between an acid and an
alkali is called neutralization.
What happens to the pH value of the reaction
mixture during neutralization?
acid alkali a salt water
The pH value of the reaction mixture becomes
closer to 7.

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What is neutralization?
The chemical reaction between an acid and an
alkali can be written as:
What are the two new substances produced by a
neutralization reaction?
a saltacid alkali water

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Neutralization and indigestion

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Neutralizing stings
A bee sting
is acidic.
A wasp sting
is alkaline.
Why can
bicarbonate of
soda (pH 9) be used
to treat a bee sting?
Why can vinegar
(pH 3) be used to
treat a wasp sting?

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Neutralizing soil
Soils in different places
can be acidic, alkaline or
neutral.
Many plants do not grow
well in acidic soil.
Why do farmers test
soil to check the pH?
Farmers often add an alkali to acidic soil to make
their plants grow better.
How does the alkali help to treat the acidic
soil?

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Neutralizing acid rain
Gases emitted by cars, power
stations and factories mix with
rainwater in the atmosphere.
This rainwater has a pH <5.5.
Why is it called acid rain?
Acid rain can have a
harmful effect on the
environment killing trees,
polluting lakes and
damaging buildings.
How can the effects of
acid rain be prevented?

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Contents
Acids and Alkalis
Neutralization
Summary activities
What are acids and alkalis?
Indicators and the pH scale

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Glossary
 acid – A chemical that has a pH less than 7.
 alkali – A chemical that has a pH greater than 7 and
dissolves in water.
 indicator – A special chemical that changes into different
colours in acid and alkali solutions.
 neutral – A chemical with a pH of 7 that is not an acid or
an alkali.
 neutralization – The chemical reaction between an acid
and an alkali.
 pH scale – The range of values that shows how strong or
weak an acid or alkali is.
 universal indicator – The indicator that shows the pH
value of a chemical.

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Anagrams

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Word search

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 Weak acids, like lemon juice and vinegar, taste
sour.
 Strong acids are corrosive and can “eat away”
at metal, stone and flesh!
 Acids turns blue litmus paper red.
 Acids have a pH of less than 7.
 Acids can be neutralized with alkalis.
Facts about acids

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 Alkalis feel soapy and are used in household
cleaning materials.
 Strong alkalis are caustic.
 Alkalis turn red litmus paper blue.
 Alkalis have a pH of more than 7.
 Alkalis can be neutralized with acids.
Facts about alkalis

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Multiple-choice quiz

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Guided Notes
Guided Notes for Acids and Alkalis
What is an acid?
Acids are substances that have a pH ____________ 7 and turn universal indicator
yellow, orange or _________.
Properties of Acids
• An acid is a substance that releases ____________ ions (H+) into an ____________ (water) solution.
• are ____________.
• have a ____________ taste
• turn ____________ litmus paper ____________
• react with some ____________, releasing ____________ gas and leaving a ____________ behind
• ____________ electricity
• are neutralized by ____________, producing water and a salt.
What is a strong acid?
Some acids, like those found in the laboratory or a ____________ battery, ____________ completely in solution. They
are very dangerous (too dangerous to taste or touch).
These acids are said to be ________________________ as they can damage other materials by eating them away!
What is a weak acid?
Many acids are found in household items such as food, drink and _________________ /skincare products.
These acids do ____________ dissolve completely in solution and are known as ____________ acids.
What is an alkali?
Alkalis, or ____________ , are another group of chemicals, the ________________________ of acids.
Properties of Bases
• A base is a substance that releases ____________ ions ____________ in an ____________ solution.
• are ________________________
• have a ____________, ____________ feel
• turn ____________ litmus paper ____________
• have a ____________ taste
• ________________________electricity
• are neutralized by ____________, producing water and a salt.