© boardworks ltd 2004 1 of 20 © boardworks ltd 2004 1 of 34 ks3 chemistry 7e acids and alkalis

© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20041 of 34

KS3 Chemistry

7E Acids and Alkalis


Contents


Neutralization

Summary activities

What are acids and alkalis?

Indicators and the pH scale

Hazard symbols


What is an acid?

Acids are a group of chemicals. What do you know about acids? Are all acids dangerous?


What is an acid?

everyday acids laboratory acids

Acids are a group of chemicals.

Can you think of other examples of acids?

Which of these items contains an acid?


What is a weak acid?

Acids are found in household items such as food, drinkand beauty/skincare products.

It is safe to handle these acids and even taste them, if theyare for eating! These acids are known weak acids.


What is a strong acid?

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?


What is an alkali?

everyday alkalis laboratory alkalis

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?


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.


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?


Contents


Neutralization

Summary activities



Hazard symbols


How can you tell which chemicals are safe and which are dangerous?

Special symbols are used on bottles and vehicles that contain dangerous chemicals.

What are hazard symbols?

corrosiveharmfulirritanttoxic

These hazard symbols show why the chemical is dangerous.

Why is it important that these symbols can be recognised by

i h

highly flammable

people from other countries?


What do hazard symbols mean?


Contents


Neutralization

Summary activities



Hazard symbols


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.

What is an indicator?

Litmus paper and litmus solution are examples of indicators.

Litmus is red in acid.

Litmus is blue in alkali.


Litmus test experiment


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 alkalistronger acid

What is the colour for a weak acid? What is the colour for a strong alkali?

weak alkali

weakacid

strongalkalineutral

strongacid


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?

weak alkali

weakacid

strongalkali

strongacid

stronger alkalistronger acid

neutral

1 2 3 4 5 6 7 8 9 10 11 12 13 14


What is the pH?


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?


Contents


Neutralization

Summary activities



Hazard symbols


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?

?


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.


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 saltacid alkali water


Neutralization and indigestion


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?


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?


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?


Contents


Neutralization

Summary activities



Hazard symbols


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.


Anagrams


Word search


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


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


Multiple-choice quiz

© boardworks ltd 2004 1 of 20 © boardworks ltd 2004 1 of 34 ks3 chemistry 7e acids and alkalis

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