resources

7ea1
7Ea/1 Taste tests 1

7Ea/1 Taste tests 1

Name _____________________________ Class ____________

Apparatus

- Blindfold

- Substances to test

- Straw

Make sure that you keep all the apparatus clean.

Method

1 Work with a partner.

2 One person puts on the blindfold and puts their tongue out.

3 The second person takes a few drops of one of the liquids in a straw.

4 Drop the liquid on to the tongue of the blindfolded person.

5 Describe the taste. Can you guess what the liquid is?

6 Do the test again with the other liquids.

Recording your results

Liquid	Words to describe the taste	I think that this liquid is�
A

B

C

D

E

F

Considering your results/conclusions

Write the names of all the acids that you used

________________________________________________________________________________

What sort of taste do all the acids have? _______________________________________________

[ observing, considering ]

7Ea/2 Taste tests 2

Apparatus

- Blindfold

- Substances to test

- Straw

Make sure that you keep all the apparatus clean.

Method

1 Work with a partner.

2 One person puts on the blindfold and puts their tongue out.

3 The second person takes a few drops of one of the liquids in a straw.

4 Drop the liquid on to the tongue of the blindfolded person.

5 Describe the taste and see if you can guess what the liquid is.

6 Do the test again with the other liquids.

Recording your results

1 Design a table to record your results. The table could show:

- the letter of the liquid

- some words to describe the taste of the liquid

- what you think the liquid might be

- whether you think the liquid is an acid or not.

Considering your results

2 What sort of taste do all the acids have in common?

Optional extra

3 Were some parts of your tongue better at detecting the different types of taste? Find out, or plan an experiment to investigate which part of the tongue is best at detecting the taste of acids.

[ observing, presenting, considering ]

7Ea/3 Acids in the home 1

Name _____________________________ Class ____________

Activity 1

The chart shows the names of some substances you find in the home.

Five of them are acids, five are not. Write 'acid' or 'not an acid' in each blank box. One has been done for you.


vinegar	toothpaste	picked onions	orange juice	washing powder


soap	lemonade	bleach	milk of magnesia	hair perming lotion
		acid

Activity 2

Make a display showing the examples of acids that you use in your home.

You could:

- cut out the pictures from the table

- use labels from cans, jars and bottles

- cut out pictures from magazine adverts

- use computer graphics.

[ knowledge, research ]

7Ea/4 Acids in the home 2

Many things you use in your home are acids. Make a display showing examples of food and household products. Group all the acids together on one page of your book or one side of the poster. Put all the other substances in another section of the display.

You could:

- draw pictures showing the different uses

- use labels from cans, jars and bottles

- cut out pictures from magazine adverts

- use computer graphics.

Some examples of products containing acids that you could include in your display are:

fruit juices, lemonade, cola, vinegar, pickles, tomato ketchup.

[ knowledge ]

7Ea/5 Acids in the home 3

Activity 1

Make a display showing examples of acids that you use in your home.

You could:

- draw pictures showing the different uses

- use labels from cans, jars and bottles

- cut out pictures from magazine adverts

- use computer graphics.

Some examples of products that you could include in your display are:

fruit juices, lemonade, cola, vinegar, pickles, tomato ketchup.

You will need to look at the labels on these products to help you decide if they are acids or not. Group the acids together on your display.

Activity 2: acids in the environment

Find examples of situations where acids cause pollution in the environment. Write a brief account in your books, or produce a second poster to illustrate what you have found out.

[ knowledge, research ]

7Eb/1 Spot the hazard 1

Name _____________________________ Class ____________

In this experiment you will be comparing three different acids. You will find out which is the most hazardous.

Apparatus

- Test tube rack

- Test tubes

- Acids A, B and C

- 3 pieces of magnesium

- 3 marble chips

- Thermometer

- Eye protection

Eye protection should be worn.

Method

1 Fill a test tube about one third full of acid A, as shown in the diagram.

2 Put one of the pieces of magnesium into the tube.

3 Watch what happens. Write the results in the table.

4 When the fizzing stops, measure the temperature of the liquid.

5 Put acid B into a second tube.

6 Put another piece of magnesium into this tube.

7 Now put acid C into a third tube.

8 Do the experiment again using acid C. Record your results.

9 When the tests are finished, pour all the liquid away.

10 Refill the three tubes with fresh acid: A, B and C.

11 Do the tests again, using a marble chip instead of the magnesium.

Recording your results

Acid	Solid	What happened?	Temperature at the end of the experiment (°C)
A	magnesium
B	magnesium
C	magnesium
A	marble chip
B	marble chip
C	marble chip

Considering your results

I think the most hazardous acid was __________________________________________________

The least hazardous acid was ________________________________________________________

I could tell this because ____________________________________________________________

________________________________________________________________________________

[ observing, considering ]

7Eb/2 Spot the hazard 2

In this experiment you will be comparing different acids. You will carry out some tests to find out which is the most hazardous.

Apparatus

- Test tube rack

- Samples of different acids

- Test tubes

- Pieces of magnesium

- Marble chips

- Sodium hydroxide solution

- Thermometer

- Eye protection

Eye protection should be worn.

Method

1 Fill a test tube about one third full of acid A, as shown in the diagram.

2 Put one of the pieces of magnesium into the tube and watch what happens.

3 Measure the temperature of the liquid when the reaction stops.

4 Repeat the tests with magnesium using the other acids. Compare the reaction.

5 Pour the liquid away, and refill the tubes with fresh acid.

6 Repeat the tests again, using a marble chip instead of the magnesium.

7 Carry out a third test by mixing a third of a tube of acid with a third of a tube of sodium hydroxide solution. In this test the temperature change will be the most important observation.

Recording your results

1 Design a table to display your results. This should show:

- the letter of the acid that you used

- the results of the tests with magnesium, marble chips, and sodium hydroxide

- any temperature changes that took place.

Considering your results

2 Put the acids in order, from the most hazardous to the least hazardous.

3 Explain how you arrived at your decision.

[ observing, presenting, considering ]

7Eb/3 What hazard?

Cut out the boxes on the sheet.

Match the warning symbol to the hazard, and find the correct example.

Stick the correct sets into your book.

[ knowledge ]

	Hazard: flammable	Example: concentrated sulphuric acid

	Example: dilute sulphuric acid	Hazard: irritant

Hazard: toxic		Example: petrol

Example: mercury	Hazard: corrosive

7Eb/4 Cracking the Hazchem Code 1

A B C D

1 Which of these hazard warnings means that a chemical is:

a flammable b poisonous c corrosive d an irritant?

2 The Hazchem Code tells the police and fire services about the hazards of a chemical in a tanker. Look at the Hazchem symbol. Collect a copy of Worksheet 7Eb/6. Use this sheet to help you answer the questions.

Hazchem code on a tanker.

a What chemical is being carried in the tanker?

b What is the number on the Hazchem warning sign?

c What word matches this number on the code chart?

d How should the fire brigade put out a fire on this tanker? Choose from:

A use jets of water

B use a fine spray mist of water

C use a dry powder.

e What is the letter on the Hazchem warning sign?

f The 'V' means that there could be a violent reaction with the chemical. Is this a problem with the sulphuric acid?

g The fire brigade will either have to wear breathing apparatus and gloves (BA) or a FULL protective suit. Which should they wear in this case?

h A spillage of the chemical may be able to be washed away (DILUTE). Some chemicals need to be collected up (CONTAIN). Which should the fire brigade do in this case?

i Does the warning sign have an 'E' in the code?

j Should the police clear the area, or is it safe for people to stay where they are?

k How do you know?

[ knowledge ]

7Eb/5 Cracking the Hazchem Code 2

The Hazchem Code tells the police and fire services about the hazards of a chemical in a tanker. Look at the Hazchem symbol. Collect a copy of Worksheet 7Eb/6. Use the sheet to help you answer the questions.

1 a Look at the number on the Hazchem warning sign. Use the code chart to decide how the fire brigade should put out a fire on this tanker. Choose from:

A use jets of water

B use a fine spray mist of water

C use a special foam

D use dry powder or carbon dioxide gas.

b What is the letter on the Hazchem warning sign?

2 Match the letter on the warning sign to the information on the code chart to answer these questions.

a Is there a problem of a violent reaction of other chemicals with the sulphuric acid?

b Should the fire brigade wear breathing apparatus and gloves only (BA) or a FULL protective suit?

c Could a spillage of the chemical be washed away down the drains (DILUTE), or collected up for safe disposal elsewhere (CONTAIN)?

d Should the police and fire brigade evacuate the area, or is it safe for people to stay where they are?

3 Use the Hazchem code to recommend the appropriate safety precautions for the following chemicals:

a methanol: code 2PE

b phosphorus: code 2WE.

[ knowledge ]

7Eb/6 Hazchem code information sheet

The number code: 1 Jets 3 Foam 2 Fog 4 Dry agent
P	V	FULL
R			DILUTE
S	V	BA
T
W	V	FULL
X			CONTAIN
Y	V	BA
Z
E consider evacuation

What the numbers mean:

1 Jets means that the fire can be put out using jets of water from a hose.

2 Fog means that the fire brigade can still use water. It has to be a fine mist or spray rather than full power jets.

3 Foam means that the tanker needs to be sprayed with a layer of thick foam to smother the flames.

4 Dry agent means that water must NOT be used on this fire. It has to be kept dry. Examples of dry agents are sand, powders, or carbon dioxide gas.

[ knowledge ]

7Ec/1 Red cabbage indicator 1

Part 1: Making the indicator

Apparatus

- Pestle and mortar

- Filter paper and a filter funnel

- Red cabbage leaves

- Boiling tube or conical flask

- Hot water

Method

1 Put some red cabbage leaves into the mortar.

2 Add a little hot water.

3 Grind up the leaves so that you get as much of the colour out as possible.

4 Filter the mixture and collect the liquid in a tube or flask.

Part 2: Using your indicator

Apparatus

- Red cabbage juice

- Dropping pipette

- Spotting tile

- Substances to test

Method

1 Put one of the substances into a circle on the spotting tile. Write the name of the substance in a table.

2 Add a few drops of your cabbage juice.

3 Write the colour in your table.

4 Do this again with another substance.

7Ec/2 Red cabbage indicator 2

Name _____________________________ Class ____________

1 Label diagram 1 with the words:

pestle water red cabbage leaves mortar

2 Label diagram 2 with the words:

filter funnel conical flask cabbage leaves cabbage juice

3 Fill in the missing words, using the words in the box.

dissolves filtering insoluble water

a In this experiment the _________________________ is the solvent.

b Some of the red colour _________________________ in the water.

c The rest of the cabbage leaves do not dissolve. They are ________________________ .

d The cabbage juice is separated from the leaves by _________________________ .

Recording your results

Draw a results table in your book like this. Leave room for at least ten different substances to go into the table.

5 Now use your indicator to test different substances.

Considering your results/conclusions

6 Write a list of all the things which made the cabbage juice turn red.

7 Make a list of all the things which made the cabbage juice turn blue or green.

[ observing, knowledge ]

7Ec/3 Red cabbage indicator 3

Make your red cabbage indicator and then answer these questions.

1 Draw and label a diagram of the apparatus you used to grind up the red cabbage.

2 Describe how you made you indicator. Explain why:

- you use hot water rather than cold water

- you grind the cabbage up rather than just stirring it.

3 Draw and label a diagram to show how you separated the cabbage juice from the bits of cabbage.

4 Explain how the filtering method works. Why do you need filter paper rather than ordinary paper?

Recording your results

5 Draw a results table in your book like this. Leave room for at least ten different substances to go into the table.

Now use your indicator to test different substances.

Considering your results/conclusions

6 Write a list of all the things which made the cabbage juice turn red.

7 Make a list of all the things which made the cabbage juice turn blue or green.

8 Which of these lists contains all the acids?

[ knowledge, observing, considering ]

7Ec/4 Indicators at home 1

Name _____________________________ Class ____________

In this experiment you will be looking to see if there are any things that you can find around your home that could be used as indicators.

blackcurrant or blackberry juices
cold tea
beetroot juice
crushed berries
food colourings

Remember that an indicator will:

- be coloured

- change colour when mixed with acid or alkali.

Here are some suggestions. Put a tick by the things that you have in your home that you could try.

You will need an acid to test your indicator - choose from vinegar or lemon juice.

I will use ________________________________________________________ as my acid.

You will also need an alkali - you might use bicarbonate of soda, or toothpaste.

I will use ________________________________________________________ as my alkali.

Method

1 Write in the name of the coloured substance that you are going to test in the table.

2 Write down its normal colour.

3 Mix a little of your substance with the acid. Write the colour in the table.

4 Now mix the indicator with the alkali. Write down the colour.

5 In the last column of the table, say whether you think the substance that you've chosen is a good indicator.

6 Repeat the test with other substances.

Substance	Natural colour	Colour in acid	Colour in alkali	Is it a good indicator?

[ observing, considering ]

7Ec/5 Indicators at home 2

In this experiment you will be looking to see if there are any things that you might find around your home that could be used as indicators.

Remember that an indicator will:

- be coloured

- change colour when mixed with acid or alkali.

Here are some suggestions for things that you might try out:

- fruit juices (especially darker colours like blackcurrant)

- beetroot juice

- cold tea

- crushed berries

- food colourings.

You will need to choose a suitable acid to test your indicator - you could use vinegar or lemon juice.

You will also need an alkali - you might use bicarbonate of soda, or toothpaste. Most soaps are also alkaline.

Method

1 Draw a table like this for your results.

2 Write in the name of the coloured substance that you are going to test, and write down its colour.

3 Mix a little of your substance with your chosen acid. Write the colour in the table.

4 Now mix the indicator with the alkali. Write down the colour.

5 In the last column of the table, say whether you think the substance that you have chosen is a good indicator, and explain why.

6 Repeat the test with other coloured substances.

[ observing, considering ]

7Ec/6 Indicators at home 3

In this experiment you will be looking to see if there are any things that you can find around your home that could be used as indicators.

Remember that an indicator will:

- be coloured

- change colour when mixed with acid or alkali.

Planning

1 Suggest some coloured substances that you have in your home that you could test to see if they could be good indicators.

2 You will need an acid and an alkali to test your indicator. From the work you have done in class, suggest some acids and alkalis that you have at home that would be safe to use in this experiment. Will you also need to test your indicator using a neutral substance? What will you use in this case?

3 How will you carry out your test to show if each of the coloured substances that you are trying behaves as an indicator?

Recording your results

4 You should design a table or chart to show:

- the name of the substance that you are testing

- if it changes colour when you mix it with chemicals that are acidic, alkaline or neutral.

Considering your results

5 Which of the substances that you tested is the best indicator? How have you reached this decision?

6 Which other substances would also work as indicators?

7 Are there any substances that you have tested that are no good as indicators?

Why not?

[ planning, observing, considering ]

7Ec/7 Alkalis in the home

Make a display showing examples of alkalis that you use in your home.

You could:

- draw pictures showing the different uses

- use labels from cans, jars and bottles

- cut out pictures from magazine adverts

- use computer graphics.

Some examples of products containing alkalis that you could use in your display are:

toothpaste, oven cleaner, soda crystals, any products containing ammonia (e.g. kitchen cleaners or hair perming lotion), many indigestion remedies (e.g. milk of magnesia)

[ knowledge ]

7Ed/1 pH testing 1

Name _____________________________ Class ____________

Apparatus

- Universal indicator solution

- Dropping pipette

- pH colour chart

- Substances to test

- Spotting tile

- Eye protection

Wear eye protection.

Method

1 Put one of the substances into a circle on the spotting tile. Write the name of the substance in the table.

2 Add two drops of universal indicator.

3 Write the colour into the table.

4 Look up the pH number using the colour chart. Write it into the table.

5 Do this again with another substance.

Recording your results

Name of substance	Colour of universal indicator	pH number	Type of substance

Considering your results/conclusion

Check in the textbook to find out if each of the substances you have tested is:

- a strong acid - a weak acid - neutral

- a weak alkali - a strong alkali.

Write your answer in the column of the table marked 'Type of substance'.

[ knowledge, observing ]

7Ed/2 pH testing 2

Apparatus

- Universal indicator solution

- Dropping pipette

- pH colour chart

- Substances to test

- Spotting tile (or a rack of test tubes)

- Eye protection

Wear eye protection.

Method

1 Draw a table in your books with these headings:

2 Put one of the substances into a circle on the spotting tile.

3 Add a few drops of universal indicator.

4 Write the colour into the table.

5 Repeat with other substances.

Recording your results

6 Look up the pH number using the colour chart. Write it into the table, and complete the last column to show whether the substance is a strong acid, weak acid, neutral, weak alkali or strong alkali.

[ observing ]

7Ed/3 Making a pH chart

Use the whole of a piece of paper to draw the pH scale running from 1 to 14.

Add the colours to show how universal indicator would change colour.

Label the chart by drawing arrows from each substance to the correct pH number. You may be able to draw pictures or find photos in a magazine that you could cut out and stick onto your chart.

Substance	pH	Substance	pH
battery acid	1.0	mineral water	8.0
bee sting	3.5	oven cleaner	13.0
blood	7.5	skin	5.5
distilled water	6.0	tap water	7.0
egg white	9.0	toothpaste	9.5
fizzy drinks	4.5	vinegar	3.0
indigestion powder	8.5	washing up liquid	5.0
kitchen surface cleaner	11.0	washing powder	10.5
lemon juice	2.5	washing soda	11.5
milk	6.5	wasp sting	10.0

[ knowledge ]

7Ed/4 More about indicators 1

There are many different substances that can be used as indicators. Different indicators change colour at different pH numbers.

This table shows the pH numbers at which some indicators change colour.

Indicator	First colour (more acid)	pH number when it changes colour	Second colour (more alkaline)
Methyl violet	yellow	1	blue
Methyl orange	red	4	yellow
Methyl red	red	5	yellow
Litmus	red	7	blue
Thymol blue	yellow	9	blue
Phenolphthalein	colourless	9	red
Alizarin yellow	yellow	12	red

7Ed/5 More about indicators 2

You will need worksheet 7Ed/4 to answer the questions on this sheet.

1 State the pH number at which each of these indicators changes colour:

a phenolphthalein

b alizarin yellow

c methyl red.

2 What colour is:

a methyl red in alkali

b thymol blue in acid

c methyl violet in weak acid?

3 Copy out a pH colour chart like this:

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

a In the first row, colour in the boxes to show the colour change for methyl red.

b In the second row, colour in the boxes to show the colour change for thymol blue.

c In the third row, colour in the boxes to show what would happen if you mixed the two indicators together.

4 What colour would a mixture of thymol blue and phenolphthalein go if the following solutions were added:

a hydrochloric acid

b salt water

c sodium hydroxide?

5 a Choose three indicators from the table that would mix together to give a good universal indicator.

b How many different colours would your indicator would go? Name them.

c Draw a colour chart for your indicator, showing the colour at each pH number.

[ knowledge ]

© Pearson Education Limited 2002 - copyright acknowledged

7ed6
7Ed/6 Are pH balanced products really better for your skin

7Ed/6 Are pH balanced products really better for your skin?

This is an exercise in planning.

Many products now advertise the fact that they are 'pH balanced' or match our skin pH of 5.5. Are these products really better for us, or is it just another advertising trick to get us to spend more money when a cheaper product would do the job just as well?

This is a scientific question, because it can be investigated using an experiment.

It is not easy to plan this type of investigation because:

- it involves using people rather than test tubes or apparatus

- the results would take a long time to gather

- it is difficult to make it a fair test.

The questions on this sheet will help you to think about how you could set up a fair test. You probably won't be able to actually carry out the experiment, unless you have friends or family who are very patient!

1 Would it be fair to test the product on only one person? Why not?

2 How many people would you need to involve in your test to make sure you had a large enough sample? Would the age or gender be important? Suggest how you might choose a good scientific sample of people to be involved.

3 Would everyone in the group try the pH balanced soap, or only some people?

4 How do adverts try to show that hair treatments (e.g. dandruff shampoos) work? Could you use this method for soaps?

5 How would you tell if one soap was better than another? Would it be good enough to rely on what the people using the soap told you?

6 Would it matter if some people in the experiments thought that pH balanced products were better before they did the experiment? Explain your answer.

7 When doctors try out a new medicine, they use a 'blind test'. Some patients receive the medicine being tested and others get a similar pill or liquid without the drug in it (a 'placebo'). The patient does not know if they are taking the real medicine or the placebo. Could you use this method for the soap experiment? Explain whether or not you think it might work.

8 In a 'double blind' test, neither the doctor nor the patient knows which is the real medicine. Why do they set up a test like this? If you were doing the observations in the soap experiment, could you be trusted to be fair, or would it be better if you didn't know which soap was which until after you had collected your results?

[ knowledge, planning, considering, evaluating ]

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7ee1
7Ee/1 Rainbow fizz

7Ee/1 Rainbow fizz

In this activity you will be using your senses to make observations.

You will also need to follow instructions carefully.

If you are careful, you should be able to produce a rainbow effect in the tube.

Apparatus

- test tube rack containing four test tubes and a boiling tube, with chemicals in them

- eye protection

Method

1 The boiling tube contains sodium carbonate. Describe the appearance of the substance in the tube.

2 Test tube 1 contains water. Add the water to the boiling tube. Feel the outside of the tube. Describe what you see and what you can feel.

3 Shake the tube. Describe what you can see now.

4 Tube 2 contains universal indicator. Smell the tube carefully by wafting the smell towards you. Describe the appearance and the smell of the liquid in the tube.

5 Add the universal indicator to the boiling tube. Observe the tube without shaking. What do you see?

6 Now shake the tube. What do you see now? What type of substance is sodium carbonate?

7 Tubes 3 and 4 contain ethanoic acid. Smell each tube carefully. Describe the appearance and the smell of the liquid in the tubes.

8 Add the contents of tube 3 to the boiling tube. Do not shake the tube. Describe what happens.

9 Very carefully pour the contents of tube 4 into the boiling tube. You may find it helpful to tilt the boiling tube slightly as shown in the diagram.

Do not shake the tube. Describe what you see.

10 Explain why you get the 'rainbow' effect.

[ observing ]

7Ee/2 Rainbow fizz - results sheet

Name _____________________________ Class ____________

1 The substance in the boiling tube was a __________________________________________ .

2 When I added the water to the boiling tube I saw __________________________________

______________________________________________________________________ and

the tube felt ________________________________________________________________ .

3 When I shook the tube _______________________________________________________ .

4 The smell of the universal indicator in tube 2 was __________________________________ .

5 The colour of the liquid in tube 2 was ____________________________________________ .

6 Was the liquid in tube 2 clear or cloudy? __________________________________________

7 When I added the universal indicator to the boiling tube the colour went _________________

__________________________________________________________________________ .

8 When I shook the tube ________________________________________________________

___________________________________________________________________________

9 Is sodium carbonate acid, alkali or neutral? ________________________________________

10 The smell in tubes 3 and 4 reminded me of _______________________________________.

11 When I added the liquid in tube 3 to the boiling tube _________________________________

___________________________________________________________________________

12 When I added the liquid in tube 4 to the boiling tube I saw ___________________________

different colours. These were: ___________________________________________________

_________________ . I also saw ________________________________________________

__________________________________________________________________________ .

13 The liquid in the tube was _______________ at the top and _______________ at the bottom.

[ observing ]

7Ee/3 Indigestion

Which indigestion remedy works best?

Indigestion remedies react with acid in our stomachs and cancel it out. We can test different indigestion remedies by reacting them with some dilute acid and measuring the pH of the mixture after it stops reacting.

Apparatus

- Various indigestion remedies

- Stop-clock

- Dilute sulphuric acid

- 250 cm³ beaker

- Universal indicator paper or solution

- Eye protection

- Electronic balance

Planning

1 When you plan your experiment you should think about these things:

- What apparatus will you use?

- How many indigestion remedies will you use?

- How will you add the indigestion remedy to the acid?

- How much of the indigestion remedy will you use?

- How much acid will you use?

- How will you test the pH?

- When will you test the pH - before adding the remedy, after adding it, or both before and after?

- What will you do to make sure that this is a fair test?

- How will you stay safe while doing your experiment?

Predicting

2 What will happen to the pH when you add the indigestion remedy? Explain why you think this.

3 Which rememdy do you expect to work best? You could look for information on the side of the packet to help you. However, it may not be possible to make a prediction like this. If you do make a prediction, explain your reasoning.

Recording your results

4 Design a results table to record your results.

Considering your results/conclusions

5 a What happened to the pH when the remedies reacted with the acid?

b Was this what you predicted?

6 a Which remedy worked best?

b How do you know?

Evaluation

7 Can you suggest improvements to the way the experiment was done, to make the results more precise?

[ planning, observing, considering, evaluating ]

7Ee/4 Reverseword

Here is a crossword grid with the answers already filled in. Write a clue for each word in your book.

	¹_P
	_U
	_R			²_L	_I	_T	_M	³_U	_S
	_P		⁴_P					_N			⁵_S
	_L		_H			⁶_A	_C	_I	_D		_U
⁷_N	_E	_U	_T	_R	_A	_L		_V			_L
_I			_W			_K		_E			_P
_T			_O			_A		_R			_H
_R						_L		_S			_U
_I			⁸_I	_N	_D	_I	_C	_A	_T	_O	_R
_C								_L			_I
											_C

-----------------------------------------------------------------------------------------------------------

You can fold the sheet along the dotted line and ask a friend or someone in your family to see if they can do your crossword on the blank grid below.

	¹

			²		³
		⁴				⁵
				⁶
⁷



		⁸

[ knowledge ]

7Ee/5 Making sherbet 1

Sherbet can be made from three ingredients:

- sugar (icing sugar is likely to be best)

- citric acid (the acid that is in oranges, lemons and grapefruit)

- bicarbonate of soda.

How sherbet works

When two chemicals are mixed together, they sometimes react to make a new substance. Citric acid and bicarbonate of soda react when they are mixed with water.

When you put the sherbet mixture in your mouth, the moisture from your tongue helps the acid to react with the alkali. When this happens, carbon dioxide gas is given off. This makes the fizz on your tongue. The acid also gives the sherbet its tangy flavour.

The chemical equation for this reaction is:

+ → + + water

1 Which of the ingredients in sherbet is:

a an acid b an alkali c neutral?

2 Which ingredient makes the sherbet taste:

a sweet b tangy?

3 Which two ingredients are needed to make the sherbet fizzy?

4 What is the name of the 'fizz gas' in sherbet?

5 What is the proper chemical name for bicarbonate of soda?

6 If you get the recipe for sherbet wrong, how might it affect the taste?

7 How could you plan an investigation to find the best recipe for sherbet?

8 Suggest a mixture of the ingredients that you think might give a tangy taste and a good fizz.

[ knowledge, planning ]

7Ee/6 Making sherbet 2

Sherbet can be made from three ingredients:

- sugar (icing sugar is likely to be best)

- citric acid (the acid that is in oranges, lemons and grapefruit)

- bicarbonate of soda.

You should be able to buy these ingredients at a supermarket or a pharmacy.

You can investigate the best recipe for sherbert by making up a number of different recipes for small amounts of sherbet.

For example, recipe 1 could be 2 spoons of sugar, 1 spoon of citric acid and half a spoon of 'bicarb'.

Planning

1 How many different recipes do you want to try?

2 What will you change in each one? Make a table to show the different quantities of each ingredient you will use.

3 Decide how you will score the results:

- you could ask people for marks out of 10; or

- you might ask for an order of merit, from best to worst.

Make a table to show your results.

Recording your results

4 Try a little of each of these recipes out on friends and family. Ask them to rate the mixtures for taste and 'fizz factor'.

Record your results

Considering your results

5 Which recipe was best?

What effect did changing the ingredients have on the taste or fizziness of the mixture?

Evaluation

6 If you had time, is there any way you could improve your investigation?

[ planning, observing, considering, evaluating ]

7E Summary Sheet

Acids and alkalis

Indicators are coloured dyes which often come from plants such as red cabbage and beetroot. Acids make indicators change colour. Litmus is an indicator which turns red in acids. Common acids include vinegar and lemon juice. Fizzy drinks, pickles and spicy sauces also contain acids. Stronger acids such as sulphuric and nitric acids can be more dangerous. Often they are corrosive.

Alkalis have a different effect on indicators to acids. Litmus turns blue in alkalis. Alkalis can also be corrosive. Weak alkalis include soap and toothpaste.

Bottles in the laboratory and tankers carrying chemicals on the road all have to carry hazard warning labels to show when there is a chemical hazard. Some of the common warning signs are:

toxic (poisonous) harmful (irritant) corrosive flammable

The strengths of acids and alkalis can be measured on the pH scale, which runs from 1 to 14. pH numbers 1 to 6 are acids, 7 is neutral, and 8 to 14 are alkalis. You can find out the pH number using a universal indicator, or by using a pH meter.

Alkalis can cancel out acids, making them neutral.

Neutralising reactions can be important:

- in gardening and agriculture, to make sure the soil is the correct pH

- when dealing with insect stings and bites

- to control indigestion caused by excess acid in the stomach

- to keep foods such as jam at the correct pH.

7E Target Sheet

Name _____________________________ Class ____________

Topic		Targets	Before the unit	I have learned this	I have revised this
7Ea	1	Know the main ingredients in fizzy drinks.
	2	Know the taste of acids.
	3	Know the names of some acids.
	4	Know why acids are used in pickling foods.
7Eb	1	Know why some acids are more dangerous than others.
	2	Know the meanings of some safety symbols.
	3	Know that alkalis are another type of dangerous chemical.
	4	Know how to interpret the Hazchem warning signs.
7Ec	1	Know what an indicator is.
	2	Know some examples of common laboratory acids.
	3	Know some examples of common alkalis.
	4	Know what a neutral substance is.
7Ed	1	Know what the pH scale measures.
	2	Know the pH numbers of strong and weak acids.
	3	Know the pH numbers of strong and weak alkalis.
	4	Know what a neutral substance is.
7Ee	1	Know what is meant by neutralisation.
	2	Know how to neutralise an acid or an alkali.
	3	Know some practical examples of neutralisation.
	4	Know how the pH will change if an acid or alkali is diluted.

7E Word Sheets

Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.

7Ea - Tangy tastes

Word	Pronunciation	Meaning
acetic acid	a-see-tick	The old name for ethanoic acid. It is the acid in vinegar.
acid		A substance that turns litmus red. It has a pH of less than 7.
ascorbic acid	a-score-bick	Chemical name for vitamin C.
citric acid	*sit*-rick	The acid in citrus fruits.
ethanoic acid	eth-an-know-ic	The acid in vinegar.
gas		Something made of particles that are very spread out and have no bonds between them.
sweetener		A substance that makes things taste sweeter. Sugar is a natural sweetener.

7Eb - Diamonds are for safety

Word	Pronunciation	Meaning
corrosive	cor-row-sive	Substances that attack metals, stonework and skin are called corrosive.
harmful		Another word for irritant.
hydrochloric acid		A common acid that is also found in your stomach.
irritant		Something that irritates the skin and eyes.
nitric acid		A common acid.
sulphuric acid		A common acid. Used in car batteries.

7Ec - In the red/Making an ash of it

Word	Pronunciation	Meaning
alkali	*alk*-al-lie	Substance that turns litmus blue. Has a pH of more than 7.
indicator	*ind*-ic-ay-ter	A dye that will change colour in acids and alkalis.
litmus		A simple kind of indicator. It turns red in acids and blue in alkalis.
neutral		Substance that is not an acid or an alkali. Has a pH of 7.

7Ed - Mixing a rainbow

Word	Pronunciation	Meaning
antacid	ant-ass-id	A medicine containing an alkali used to cancel out some of the acid in the stomach to treat heartburn.
pH scale		A numbered scale from 1-14 showing the strengths of acids and alkalis. Numbers below 7 are acids. Numbers above 7 are alkalis. pH 7 is neutral.
universal indicator		A mixture of indicators giving a different colour depending on how weak or strong an acid or alkali is.

7Ee - Finding the balance

Word	Pronunciation	Meaning
burette	bew-rett	A tube with a tap at the bottom and a measuring scale on its side. Used to add a measured quantity of a liquid to another one.
dilute	die-loot	We dilute a solution by adding more of the solvent to it.
neutralisation		When something is neutralised.
neutralise		When an acid is added to a base (or alkali) a neutral substance is produced.