KS3 Chemistry. 7E Acids and Alkalis. Contents. 7E Acids and Alkalis. What are acids and alkalis?. Hazard symbols. Indicators and the pH scale. Neutralization. Summary activities. What is an acid?. Acids are a group of chemicals.
Acids are a group of chemicals.
What do you know about acids? Are all acids dangerous?
Acids are a group of chemicals.
Which of these items contains an acid?
Can you think of other examples of acids?
Acids are found in household items such as food, drink
and beauty/skincare products.
It is safe to handle these acids and even taste them, if they
are for eating! These acids are known weak acids.
Some acids, like those found in the laboratory or a car
battery, are very dangerous (too dangerous to taste or touch).
These acids are said to be corrosive as they can damage
other materials by wearing them away!They are strong acids.
Why must strong acids always be handled very carefully?
Alkalis are another group of chemicals, the opposite of acids.
Which of these items contains an alkali?
Can you think of other examples of alkalis?
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.
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?
How can you tell which chemicals are safe and which are dangerous?
Special symbols are used on bottles and vehicles that
contain dangerous chemicals.
These hazard symbols show why the chemical is dangerous.
Why is it important that these symbols can be recognised by
people from other countries?
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 colour in an acid or an alkali.
Litmus paper and litmus solution are examples of indicators.
Litmus is red in acid.
blue in alkali.
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.
Universal indicator has a range of colours that show how weak or strong the acid or alkali is.
What is the colour for a weak acid?
What is the colour for a strong alkali?
The strength of an acid or alkali is measured by the pH scale.
Each universal indicatorcolour is given a number called the pH value.
Universal indicator can tell you the pH of a solution.
1 2 3 4 5 6 7 8 9 10 1112 1314
What is the pH of a weak acid?
What is the pH of strong alkali?
Are they weak or strong?What type of substance?
very weak acid
very strong acid
very weak alkali
very strong 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?
The chemical reaction betweenan acidandan alkali
What happens to the pH value of the reaction mixture during neutralization?
The pH value of the reaction mixture becomes closer to 7.
The chemical reaction between anan acidandan alkalican be written as:
What are the two new substances produced by a neutralization reaction?
A wasp sting
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?
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?
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?
7E Acids and Alkalis
What are acids and alkalis?
Indicators and the pH scale
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
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