yr 6 science revision acids an

8/11/2019 YR 6 Science Revision Acids An

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What is an acid?

Here are some facts about acids.

Strong acids are corrosive eating away at things like

metal, stone and flesh!

Weak acids, like lemon juice and vinegar, taste sour.

Acids turn litmus red.

Acids have a pH below 7. Acids contain hydrogen (but not all things that contain

hydrogen are acids!).

Acids can be neutralised with alkalis.


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Indicators: acid or alkali?

An indicator is a dye which changes colour according to

whether it is in an acidic or alkaline solution.

Litmus is available as a liquid that

can be added to the solution.

For example, litmus is an indicator

that is red in acid and blue in alkali.

It is also available as strips of

paper so that you can add a drop

of the solution to the paper.


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Litmus Test


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Indicators: the pH scale

This attaches a number called the pH value to eachuniversal indicator colour.

This means we can quickly say how acid or alkali asubstance is by quoting a single number.

1 2 14131211109876543

Strong acid Neutral Strong alkali

Weak acid Weak alkali

pH7 is neutral

pH 1 is strongly acid

pH14 is strongly alkali


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Will it be acidic, basic or neutral and how strong?

1 2 14131211109876543

Substance pH Description of acid / alkali

Soda water 6

Car battery acid 1

Soap 8Washing 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




Bases

Bases are substances that neutralise acids.

Bases are usually:

Metal hydroxides contain OH

Metal oxides contain O

Metal carbonates contain CO3

The following general word equation describes

neutralisations:

acid + base a salt + water

In the case of carbonates we also get carbon dioxide.



Alkalis

Bases are substances that neutralise acids.

Alkalis are soluble bases.

Although both can neutralise acids solubility is

important when it comes to the pH of

solutions. For example, adding sodium

hydroxide to water gives a solution with a pHof about 14.

When calcium carbonate is added to water it

does not dissolve and so the pH remainsclose to 7. Even so it can neutralise acid that

is added although more slowly than a soluble

base might.



Neutralisation - Indigestion

If we have too much acid in our stomachs, we

get indigestion.

Acid can move up out of our stomach creating

a burning feeling in the chest.

We neutralisethe excess acid by taking a tablet containing

a base.

This is usually a carbonate or an oxide.

Strong soluble bases (like sodium hydroxide) would create

too alkaline a solution and cannot be used.

AlkaliAcid 1 2 14131211109876543



Neutralisation - Stings

A bee sting is acidic.

One way to treat a basic wasps sting is with

an acid: vinegar - ethanoic acid.

So one way to treat a an acidic bee sting is to

dab on a base : bicarbonate of soda more

properly known as sodium hydrogen

carbonate.

A wasp sting is alkaline.



NeutralisationSoil pH

Many plants wont grow well in acid soil and so

farmers have to regularly check the pH and

adjust it by adding a base.

Plants remove compounds from the soil in a way

that tends to leave the soil acidic.

Calcium carbonate or calcium

hydroxide are cheap and so are

often used for this purpose.



NeutralisationSoil fertilisers

Ammonia is a water soluble gas high in nitrogen and in

some countries it is injected directly into moist soil.

However, because it is a gas much of it is quickly lost.

In the UK ammonia is dissolved in water to giveammonium hydroxide (an alkali) and this is neutralised

by reacting it with nitric acid to give a solid nitrogen rich

fertiliser.

Plants also remove nitrogen compounds from the soil and

this is often replaced using fertiliser.

water+ammonium

nitrate

nitric acid+ammonium

hydroxide

NH4OH + HNO3 NH4NO3 + H2O


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Steps have been taken to reduce emissions of acidic

sulfur oxides from power stations and nitrogen oxides

from cars.

Even so the atmosphere still contains enough of them to

make the rain from industrial areas quite acidic.

Acid rainliving things

Trees and lakes are badly

affected in many parts of the

world including Northern

Germany and Scandinaviawhich suffers from South-West

winds from the UK.Acid rain damaged tress

A id i l d



Acid rain increases the rate of corrosion of metals.

Acid rainmetals and stone

The metal above the

wheel arch of this caris rusting away

It also greatly accelerates the rate of chemical weathering

of certain stones used in building such as limestone and

marble. (These stones are carbonates. What gas will be

given off as they dissolve?)

CO2



Acid

Alkali

Carbonate

Chloride

HydrogenIndicator

Indigestion

Litmus

Metal

Neutralise

Nitrate

Nitrogen

SaltWater

There are sixteen

easy-find words

in the word square.

Write a clue for

each word drawing

upon what you

have studied in this

unit of work

I Q W R A C I D Q P S S W K G

N E U T R A L I S E G A R M Y

D P L X S R Q N I T R O G E N

I M S U U B K D X O C G W Y I

G S C H L O R I D E B Z S R F

E W T Y F N S C M E T A L O J

S G K D A A U A L K A L I J O

T S A R T T L T C U W A T E R

I I P O E E F O S D H I M U W

O N K G E E U R A C O W U M D

N O B E B C R C L Q K D S U J

N V J N I T T A T E A J N B B

A id d Alk li



Acids and Alkalis

Multiple-Choice Questions



A Sodium bicarbonate

B Vinegar

C LitmusD Salt

1. Which of these is an indicator?



A Potassium hydroxide

B Sodium chloride

C Sodium hydroxideD Sodium

2. Which of these is a salt?



A pH 7

B pH 1C pH 8

D pH 13

3. Which of these is a weak alkali?

A substance with:



A Water - pH 7

B Lemon - pH 3

C Oven cleaner - pH 14D Bicarbonate of SodapH 9

4. Which of these might you put on a ant

sting to neutralise the acid in the sting?



A Hydrogen

B Sulphur

C Oxygen

D Nitrogen

5. Which of these do all acids contain?


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A Silver nitrate

B Sodium hydroxide

C Calcium hydroxideD Magnesium hydroxide

6. Which of these substances would not

neutralise an acid?

yr 6 science revision acids an

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