540562215-PPT-Cambridge-VII-Stage-7-Unit-7-1-7-3-Material-changes.ppt

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1. Material Changes Cambridge/2122 Of 13
Subject: Chemistry
Standard: VII
Topic: Material Changes
1

2. Material Changes Cambridge/2122 Of 132
Acids
These are substances with particular properties such as
sour , sharp, tangy taste.
They may have a peculiar odour.
Some common acids can be prepared and used in the
laboratory like hydrochloric acid, sulphuric acid and nitric
acid.
All acids are not weak; some are strong, dangerous and
corrosive.
If acids spill on skin, they can harm the skin and cause a
chemical burn. In such cases, water can be added on the area
as water dilutes the acids.

3. Material Changes Cambridge/2122 Of 133
Alkalis
Cleaning products such as soap and bleach contain a
substance called alkali.
Like strong acids, strong alkalis are also corrosiveand
dangerous and have the same effect on skin as acids.
Common alkalis found in the laboratory are
sodium hydroxide, potassium hydroxide and
calcium hydroxide.
Alkalis feel soapy to touch.
Acids and alkalis are chemical opposites.
They can cancel out each other when mixed together.

4. Material Changes Cambridge/2122 Of 134
If an acid and alkali solution are kept in two
jars, how can you identify them as an acid and
an alkali without tasting them?
A B
Is it an acid or alkali ?

5. Material Changes Cambridge/2122 Of 135
What are indicators?
Can you name a few indicators?

6. Material Changes Cambridge/2122 Of 136
•We can use indicatorsto distinguish between acids and
alkalis.
•Indicators are chemical substances that show different
colors for acids and alkalis.
•Natural indicators can be made from juices of berries,
flowers and other plant parts. For eg: red cabbage, china
rose solution, blackcurrant and beetroot juices.
•Turmeric can also be used as an indicator.
What are indicators?

7. Material Changes Cambridge/2122 Of 137
•Litmusis a common indicator dye.
•It turns red in acids and blue in alkalis.
•In the presence of neutral solutions (solutions that are
neither acidic nor alkaline), there is no change in the
colour of litmus.
•It can be used in the form of a paper or a solution.
Litmus

8. Material Changes Cambridge/2122 Of 138
Note the colour change of litmus
paper in both solutions.
Litmus

9. Material Changes Cambridge/2122 Of 1311
Litmus
substance litmus colour type of substance
hydrochloricacid red acid
sodium hydroxide blue alkali
water purple neutral
lemon juice red acid
calcium hydroxide blue alkali

10. Material Changes Cambridge/2122 Of 1312
•Litmus test tells if a substance is acidic or alkaline.
•Universal indicator tells us how strong the acid or alkali
is.
•Depending on the strength of the substance, the
indicator can change to many different colours.
•This strength is measured on a scale called the pH
scale.
•This is the pH scale:
The pH scale

11. Material Changes Cambridge/2122 Of 1313
Quick Review
1.What are acids and alkalis?
2.Name a few acids or alkalis used in daily life.
3.What are indicators?
4.List a few indicators.
5.What is the pH scale?
6.Why universal indicator is a good indicator?
7.What is the pH of a neutral solution?
8.What is the pH of a highly acidic and alkaline solution?
9.Which one is more acidic -Stomach acid or acid rain?

12. Material Changes Cambridge/2122 Of 1314
Observe the pH scale and answer the following questions.
1.Is a substance acidic or alkaline if the indicator changes to
orange?
2.A substance having a pH below 7 is ___________.
3.A substance having a pH above 7 is ___________.
4.A substance having a pH of 7 is ___________.
Quiz time
Acidic
Acidic
Alkaline
Neutral

13. Material Changes Cambridge/2122 Of 1313
5. Is a substance acidic or alkaline if the indicator changes to purple?
6. What will be the colour of the indicator if the substance is strongly
acidic?
Quiz time
Alkaline
Red-orange