Natural Sciences4th YearTerm 2

Acids & Bases

Purifying water Weather & Materials

Name and Surname: ________________________________________Year group: ____________________

Introduction: Acids & BasesDate:___________________

You don’t need to go to a chemistry lab to find acids and bases. These chemicals

are part of your everyday life! Have you ever bitten into a lemon? That sour

sensation is citric acid reacting with the taste buds on your tongue.

Have you ever dropped a bar of soap and found that it was

hard to pick up? That’s because bases are often slippery to the

touch.

When most people hear the word ‘acid’ they think of something very dangerous that

can dissolve metal and burn skin. In fact, many acids are not dangerous at all.

Some are even found in the foods we eat! Any food that tastes sour is acidic.

Bases are also found in common household products. Bases can be very strong

and dangerous, or weak and safer for use around the house. Weaker bases

are often used as cleaning products. We don’t find many bases in our foods

because they taste bitter – think about the taste of soap…

There are many strong acids and bases found in nature. Some of them are

dangerous and are used as poisons for insects and animals. Some are helpful.

Many plants have acids and bases hidden in their parts like leaves, thorns, seeds or

sap.

Scientists keep track of acids and bases using the pH scale. pH stands for “potential

of hydrogen” (substance found in water) and the scale assigns values from zero to

fourteen. Substances with a pH less than seven are acidic and a pH greater than

seven are basic. A pH of zero is virtually pure acid. In the middle of the pH scale is

distilled water (neutral). With a pH of seven, it’s considered neutral, which means it’s

not an acid or a base. At the top of the scale, a pH of fourteen is virtually a pure

base. Sometimes bases are also called alkaline (al-KUH-line).

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pH Values ACID BASIC

Pure acid NEUTRAL Pure base

Let’s look at a few concepts:

AcidsA sour, corrosive (making something weaker) substance.

BasesA bitter soapy substance.

SaltwaterIf an acid and a base are mixed in equal amounts they react together to make

saltwater.

IndicatorsA chemical compound that changes colour and structure when exposed to certain

conditions. It is useful for chemical tests.

Universal indicatorA solution which undergoes several colour changes over a wide range of pH’s. The

colour is used to “indicate” pH directly. Universal indicators are usually mixtures of

several indicators.

NeutralA substance with a pH-value of seven.

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NeutraliseTo cause an acidic solution to become neutral by adding a base to it or to cause a

basic solution to become neutral by adding an acid to it.

Activity 1

1.1 A lemon is an example of an (acid / base).

1.2 A bar of soap is an example of a (acid / base).

1.3 Bases are often __________________ to the touch.

1.4 Acids are found in our food. YES / NO

1.5 Bases are mainly found in ____________________________.

1.6 Where do we find acids and bases in nature?

______________________________ _____________________________

______________________________ _____________________________

1.7 Scientists keep track of acids and bases using the _______ scale.

1.8 What does a pH scale measure?

________________________________________________________________

1.9 Substances with a pH less than seven are __________________.

1.10 Substances with a pH greater than seven are _________________.

1.11 Bases are also known as ___________________.

1.12 Define the term ‘acid’.

________________________________________________________________

1.13 Define the term ‘base’.

________________________________________________________________

1.14 Define the term ‘saltwater’.

________________________________________________________________

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1.15 Define the term ‘neutral’.

________________________________________________________________

1.16 Complete the following labels:

pH Values __________________ ___________________

__________________ _________________ ___________________

Acids & BasesDate:___________________

Which drink do you prefer – lemonade or sweet tea? Did you know that the one is a

weak acid and the other one is a weak base? Do you think you can guess which

one is which? Remember we said the previous period that an acid has a sour taste

and a base has a bitter taste…

Any substance that can be dissolved in water is an acid, a neutral or a base. Can

you still remember the pH value of a neutral substance?

Not all acids and bases are safe to consume. There are many sorts of acid. Fizzy

lemonade contains carbonic acid and the hydrochloric acid in your stomach helps to

digest your food. This strong acid also kills bacteria and helps to keep us from

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getting sick. Car batteries are filled with sulphuric acid. Although these are all acids,

they are not all the same strength. Carbonic acid is very weak and sulphuric acid is

very strong. If you fill a car battery with lemonade, it certainly won’t

make enough electricity to start the engine! Acids have a sour taste,

can be sticky and are able to dissolve many materials.

There are also strong and weak bases. Bicarbonate of soda is a weak base used

when cooking. Sodium hydroxide is a strong base that can clean baked-on grease

from inside ovens. Strong bases have a bitter taste and tend to be slippery and

slimy.

Balancing acids with basesWhen you add an acid to a base, the base substance becomes more acidic. When

the two balance each other out scientist say they neutralise each other. People can

get indigestion pains when there is too much acid in their stomach. Look at the

packet of indigestion tablets. You will see they contain bicarbonate of soda. Why do

you think this helps?

ExperimentLitmus paper reveals whether a substance is an acid or a base. It turns red for acids

and blue for bases.

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Did you know…? Strong acids are pH1, becoming weaker as the number rises to

pH6. Neutral substances are pH7 – neither acidic nor basic. Weak bases are pH8, becoming stronger as the number

rises to pH14.

Dip the litmus paper in vinegar. It should turn red to show acidity.

Dip the litmus paper in a solution of baking soda and water. It should turn

blue to show that the solution is a base.

(Your teacher will show you a video on experiments with Litmus Paper.)

Remember everything around us is made up of elements, atoms and molecules.

Let’s take water as an example:

The symbol for water is H2O. The “H” stands for hydrogen; the “O” stands for

oxygen. Therefore H2O indicates that there are two hydrogen atoms and one

oxygen atom bound together.

If a substance produces more hydroxide (OH), it is a base; if it produces more

hydrogen (H), it is an acid.

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Activity 2

1. What value on the pH scale would be considered a ‘weak acid’? _________

2. What value on the pH scale would be considered a ‘weak base’? _________

3. Bases have a ________________ taste.

4. Acids have a _________________ taste.

5. What is the value on the pH scale of a ‘neutral substance’? ___________

6. What type of acid does ‘soda water’ contain?

___________________________________

7. What type of acid is found in your stomach?

___________________________________

8. Name two functions of the acid that you identified in the previous question.

______________________________________________________________

______________________________________________________________

9. Car batteries are filled with _______________ acid.

10.Describe what a base feels like.

______________________________________________________________

11.Litmus paper turns ________________ to show acidity.

12.Litmus paper turns ________________ to show a base.

13.What is the symbol for ‘water’? ________________________

Examples of Acids & Bases

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Date:___________________

Activity 3Find the following examples of acids and bases in the word search below.

U K F B T K S B X C Q F E U A Y Q KE T Q O L H B E A A L O C A C O C VM I L K A A D A V K N I R I P S A MV S H M D N C I T C I O B L M Q Q EU M P V I T O K C T L N O Z E J C SE O B W U M Z O C O E L G M F I M IO G R W C J K Q E O G R R S U H E DT O O T H P A S T E F A Y J O C T HM X J W U E J T W A S F O A I D I RO R A N G E J U I C E T E U C O A AA E N I R U W Q D K A Y J E S I G GM K S W Z Z C W T M K N T A G B D EM M P P O T A Z O N O J M S G E K NO A P K B X J T T M L B J P E J A IN B L E A C H Q E S O M U C K V M VI B O H N D Z L M O Y B V C X D Y AA P Q B H H N S P A R P B V J T E CW J K S N D C V X P D Q Q L B O V C

Acids BasesLemon juice Bleach

Orange juice Soap

Tomato juice Baking soda

Black coffee Windex

Vinegar Milk

Aspirin Toothpaste

Coca Cola Shampoo

Battery acid Eggs

Urine Ammonia

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