© Boardworks Ltd 20081 of 31 Behaviour Focus: Get your own work done! That’s the only way to help others then. Copy and leave LOTS of space to write answers

© Boardworks Ltd 20081 of 31

Behaviour Focus: Get your own work done! That’s the only way to help others then.

• Copy and leave LOTS of space to write answers/ responses to the learning objectives

The Big Question: How do we know what’s acidic?

L.O.1: What are Acids and Alkalis?

L.O.2: How can we test if for Acidity and Alkalinity?

L.O.3: Compare the properties of acids and alkalis, and then list the colours of 5 indicators in acids?.

Acids, Alkalis and IndicatorsThursday 20 April 2023

6 marks question


What is an acid?

Acids are a group of soluble chemicals.

What do you know about acids?

Are all acids dangerous?


Acid or alkali?

Aim: To investigate how to Use Universal Indicator

• Equipment:

• Methods:

1.Put 3 drops of each solution on a spot on the spotting tile

2.Put 3 drops of universal indicator in each spotting tile

3.Record observation


What is universal indicator?

Universal indicator has a range of colours that show how weak or strong the acid or alkali is.

What is the colour for a strong alkali?

What is the colour for a weak acid?

Universal indicator is made from a mixture of indicators.Why do you think it is more useful than litmus?

weak alkaliweak acidstrong acid neutral strong alkali


What is the pH?


The litmus test

The litmus test – starter, write 1 – 5 and then if they are acidic, alkaline or neutral


Behaviour Focus: READ EACH WORD CAREFULLY! That is the most helpful hint to exams.


The Big Question: Which indigestion remedy is the best?

L.O.1: What if we mix acids and alkalis?

L.O.2: How can we tell if we have the equal mixture?

L.O.3: What do we need to do to determine which

indigestion tablets work the best?

NeutralisationThursday 20 April 2023

6 marks question


Testing the pH of soils


Changing soil pH

If soil is too acidic to grow certain crops, lime can be added.

Lime is an alkali called calcium oxide.

What effect does lime have on the pH of soil?


What is the pH?


L.O.1: How can we tell if we have the equal mixture?

When a pH indicator tells us that the solution is neutral, the mixture is balanced. E.g. when the universal indicator turns green.

Aim: To investigate which indigestion tablet works best.

• Equipment: Beakers, Pipettes, dilute Hydrochloric acid, Indigestion tablet solutions, Universal indicator

• Methods:

1.Put 3 drops of universal indicator and 20 mL of indigestion tablet solution in each beaker

2.Drop-by-drop put hydrochloric acid in each beaker

3.Record the number of drops before universal indicator change to green

Aim: To investigate which indigestion tablet works best.

Indigestion tablet solution

Number of drops of hydrochloric acid

Qu 1. What was the independent variable (that we change)?

Qu 2. What is the dependent variable (that we measured)?

Qu 3. Which indigestion tablet solution is the strongest? Why?

Qu 4. Complete the wordequation (it’s a neutralisation reaction).

___________ Acid + ______________ ________ + ________


Behaviour Focus: Get your own work done! That’s the only way to help others then.


L.O.1: What are natural indicators?

L.O.2: How can we use cabbages to make

indicators?

L.O.3: How do we name salts from neutralisation?

Making Natural IndicatorsThursday 20 April 2023


What is an indicator?

An indicator is a chemical that turns a different colour depending on whether it is added to an acid or an alkali.

Litmus is a commonly used indicator. It can be added to filter paper, or used as a liquid. Litmus is made from lichen, which grows on stone and rock.

Litmus can be blue or red. Blue litmus turns red under acidic conditions (< pH 4.5), and red litmus turns blue under alkaline conditions (> pH 8.3).

What colour do you think litmus is under neutral conditions?

acid

alka

li

neu

tral


What is the pH scale?

The strength of an acid or alkali is measured by the pH scale.

Each universal indicator colour is given a pH value.

Universal indicator can tell you the pH of a solution.

What is the pH of a strong alkali?

What is the pH of a weak acid?

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

strong acid neutral strong alkali


Making indicators from plants

Go back to this table and fill it inName Colour in

Acidic Solutions

Colour in Alkali Solutions

Properties (what does it do?)

Dangerous or not

Hydrochloric Acid

Sodium Hydroxide

Universal Indicator

Red, orange, yellow

Purple and blue Test for acids or alkali

No

Blue Litmus Red Blue Test for acids No

Red Litmus Red blue Test for alkali No

Red Cabbage RED Yellow/green Can test for alkali or acid

NO

Hibiscus Flower Dark pink Dark green Can test for alkali or acid

NO


How are salts made and named?

When an acid reacts with a base, a neutralization reaction occurs and produces a chemical called a salt.

acid alkali salt water+ +

+ +

++

sodiumhydroxide

NaOH (aq)

sodiumchloride

NaCl (aq)

water

H2O (aq)

hydrochloricacid

HCl (aq)

hydrochloricacid

2HCl (aq)

+

+

+

+

zinc

Zn (aq)

zincchloride

ZnCl2 (aq)

hydrogen

H2 (aq)


What is the name of the salt?


Acid or alkali: true or false?


Acid or alkali: summary




What is a weak acid?

Some acids are found in everyday items such as food and drink, and skincare products.

It is safe to handle these acids, and in some cases even to taste them! These acids are known as weak acids.


What is a strong acid?

Some acids, like those found in the laboratory or a car battery, are too dangerous to taste or touch.

These acids are said to be corrosive as they can damage other materials by wearing them away.

What safety precautions should you take when handling a strong acid?

These are strong acids.


The Acid Bath Murderer

Concentrated acids can completely dissolve skin and bones.

In the 1940s, an Englishman called John Haigh murdered six people, and disposed of each of the bodies by dissolving them in sulfuric acid for two days.

Without the bodies as evidence Haigh thought he would get away with the crimes, but a pathologist found human fat, pieces of bone, gall stones and false teeth, which had resisted the acid.

John Haigh was found guilty of the murders and sentenced to death by hanging in 1949.


What is an alkali?

Alkalis are substances that are chemically the opposite of acids.

Weak alkalis are found in soaps and other cleaning materials. They are also used in antacids to treat indigestion.

It is safe to handle these alkalis, which often feel soapy.

These alkalis are weak alkalis.


What is a strong alkali?

Some alkalis, like those used in laboratories, or in cleaning materials such as bleach, are too dangerous to touch.

What safety precautions should you take when handling a strong alkali?

These alkalis are said to be caustic because they can burn skin, and damage other materials.

These are strong alkalis.


What effect do alkalis have on our skin?

Many people suffer from eczema, a condition which can make the skin itchy and sore.

Sometimes this is caused by an allergic reaction to soap or other cleaning materials.

Which chemicals in soap do you think might cause the allergic reaction?

How could you find out what is causing the allergic reaction?


What is a neutral substance?

Neutral substances are neither acidic nor alkaline.

Pure water is a neutral substance.

What safety precautions should you take when handling a neutral substance?

Saltwater, milk, saliva and blood may actually be slightly acidic or alkaline, but are all very close to neutral.



Acids, alkalis and plants

Some flowers change colour depending on whether they are growing in acidic or alkaline soil. Hydrangeas grow blue flowers in an acidic soil, but pink flowers in an alkaline soil.

The flowers contain compounds called anthocyanins, which act as indicators.



Using universal indicator


Soil pH

Different soils have different pH levels. This is because they are made up of different rocks, and so contain different chemicals.

The pH of soil affects the availability of nutrients, and plants prefer to grow in soils of a certain pH.

How could you check the pH of the soil in your garden?

For example, strawberries grow best in acidic soil, and plums grow best in alkaline soil.



Glossary


Anagrams


Multiple-choice quiz

Documents

© Boardworks Ltd 20081 of 31 Behaviour Focus: Get your own work done! That’s the only way to help others then. Copy and leave LOTS of space to write answers