acids and bases. corrosions and its factors

1. Corrosions
Chemistry Grade 8 - 2021

2. Learning outcomes
• To know what corrosion is.
• How corrosion occurred.
• Know factors affecting rate of corrosions.
• How to prevent corrosions.
• Know the example of corrosion in daily life.

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Corrosion is the gradual destruction of a metal due to
reactions with other chemicals in its environment.
Over time, corrosion
changes the appearance of
the metal as it breaks down
and it becomes weaker.
What is corrosion?
Coating the surface of a metal
with paint and certain chemicals
can protect it from corrosion.
What happens if the protective coating becomes damaged?
Corrosion can seriously damage
metallic objects and structures.

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Salt can increase the rate of rusting. This iron bolt is on a
seaside structure and is nearly completely corroded.
Rusting is the specific name
given to the corrosion of iron.
It is a chemical reaction between
iron, oxygen and water.
What is the word equation for the formation of rust?
What is rusting?
The chemical name for rust is
hydrated iron oxide. Rust can
form on cars and buildings,
making them unsafe. It is an
expensive problem.
hydrated iron oxide
water
+ 
+
iron oxygen

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Rate of corrosion experiment

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How to prevent corrosions?
• Covering with grease
• Attaching a piece of zinc to the iron
• Painting
• Covering the iron in a thin layer of tin

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Quiz time

8. Acid and Base
Chemistry Grade 8 - 2021

9. Learning Objectives
• To know that solutions can be sorted by whether they
are: acid, alkali or neutral.
• To know that indicators show you how acidic or alkaline
a solution is.
• To understand that an alkali reacts with an acid to
cancel it out.
• Understand the application of acid and bases in our daily
life

10. What should I understand in
this topic?
• Define acids, alkali and salts
• Mentions examples of acids and alkalis
• Compare the properties of acids and alkalis
• Identify the pH acidic, alkaline, and neutral solutions
• Use indicators to measure pH

12. What is an acid?
• Acids are a group of soluble chemicals.
everyday acids laboratory acids

13. Are all acids dangerous?
•Weak acids
• Strong acids

16. Base and Alkali
Base is an insoluble compounds
Alkali is a group of soluble chemicals
In our daily life, base is the common term used
Base divided into two
• Weak Base
• Strong base

17. 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 alkalis are known as weak alkalis.

18. What is a strong alkali?
Some alkalis, like those in the laboratory or in cleaning
materials such as toilet cleaner, 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.
Why must strong alkalis always be handled very carefully?

20. How to know whether a substance
is an acids, base or neutral ?

21. Do experiment by using indicators.

22. • An indicator is a special chemical that changes to a
different colour in an acid or an alkali.
• Natural indicators
• Artificial indicators
Indicators

23. Activity 1.
Open your google classroom,
Find the worksheet
Watch the video
Answer the worksheet according to the
information given in the video

24. Litmus paper
Litmus paper and litmus solution are
examples of indicators.
Litmus is
red in acid.
Litmus is
blue in alkali.

25. Classwork 1

26. Activity 2.
Continue watch the video
Answer the worksheet according to the
information given in the video

27. Methyl Orange
Methyl Orange Indicator is used as a pH
indicator. It has clear and distinct colour
change
Methyl
orange is
red/orange
in acid.
Methyl
orange is
yellow in
alkali.

28. Activity 3.
Continue watch the video
Answer the worksheet according to the
information given in the video

29. PP
PP is
colorless in
acid.
Pp is
Purple in
alkali.

30. Activity 4.
Continue watch the video
Answer the worksheet according to the
information given in the video

31. pH scale
The pH scale is a set of numbers used to indicate whether a
solution is acidic, neutral or alkaline.
Acids have pH values less than 7.
Alkalis have pH values greater than 7.
A neutral solution has a pH value of exactly 7.

32. 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 colours that show how weak or strong the acid or
alkali is.
stronger alkali
stronger acid
What is the colour for a weak acid?
What is the colour for a strong alkali?
weak
alkali
weak
acid
strong
alkali
neutral
strong
acid

33. The strength of an acid or alkali is measured by the pH scale.
What is the pH scale?
Each universal indicator colour 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?
Go to slide 7e
weak
alkali
weak
acid
strong
alkali
strong
acid
stronger alkali
stronger acid
neutral
1 2 3 4 5 6 7 8 9 10 11 12 13 14

34. Classwork 2

35. Natural Indicators

36. Red Cabbage Indicator
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

37. Edible Acid-Base Indicators
COLOR CHANGES AS A FUNCTION OF pH
INDICATOR pH 2 3 4 5 6 7 8 9 10 11 12
RED APPLE SKIN
BEETS
BLUEBERRIES
RED CABBAGE
CHERRIES
GRAPE JUICE
RED ONION
YELLOW ONION
PEACH SKIN
PEAR SKIN
PLUM SKIN
RADISH SKIN
RHUBARB SKIN
TOMATO
TURNIP SKIN
*
*YELLOW at pH 12 and above

38. Project - making poster or video
natural indicators to check acid and base
From the previous slide (you may choose from other references also),
choose one of plant which can be used as an indicators.
Find in internet
- Information / background of the plant so it can be used as indicators
- Procedure for making natural indicators
- Procedure testing indicators
- Result and conclusion
- Make an interesting poster which provide all of information above.
- Due : 5 February 2021

39. Neutralisation

40. 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?
?

41. 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.

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

43. Application of acid and base
• Indigestion tablets
• Soil pH
• Wasp sting vs bee sting
• Acid rain from gases emitted from cars and factories

44. • Indigestion: Our stomach carries
around hydrochloric acid.
Too much of this leads to indigestion.
To cure indigestion, you can neutralise the excess
acid with baking soda or specialised indigestion
tablets.
Go to GC find link WS 3

46. Soil Treatment: When soils are too
acidic (often as a result of acid rain)
they can be treated with slaked
lime, chalk or quicklime, all alkalis.
Plants and crops grow best in
neutral soils.

47. 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?

48. • Insect Stings
Bee stings are acidic
and can be neutralised with
baking soda (bicarbonate of soda).
Wasp stings are alkaline and can be
neutralised with vinegar.

49. 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?

50. Factory Waste: Liquid waste from factories is often
acidic. If it reaches a river it will destroy and kill sea
life of many forms. Neutralising the waste with
slaked lime can prevent this.

51. Corrosions

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Corrosion is the gradual destruction of a metal due to
reactions with other chemicals in its environment.
Over time, corrosion
changes the appearance of
the metal as it breaks down
and it becomes weaker.
What is corrosion?
Coating the surface of a metal
with paint and certain chemicals
can protect it from corrosion.
What happens if the protective coating becomes damaged?
Corrosion can seriously damage
metallic objects and structures.

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Salt can increase the rate of rusting. This iron bolt is on a
seaside structure and is nearly completely corroded.
Rusting is the specific name
given to the corrosion of iron.
It is a chemical reaction between
iron, oxygen and water.
What is the word equation for the formation of rust?
What is rusting?
The chemical name for rust is
hydrated iron oxide. Rust can
form on cars and buildings,
making them unsafe. It is an
expensive problem.
hydrated iron oxide
water
+ 
+
iron oxygen

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Rate of corrosion experiment

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Method of preventing corrosions
• Covering with grease
• Attaching a piece of zinc to the iron
• Painting
• Covering the iron with thin layer of tin

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