Using this booklet
When you see this symbol it means you have some reading to do.
When you see this symbol it means you have an activity or an experiment to do.
When you see this symbol it means you have a writing task to do.
When you see this symbol you will have an internet research task.
You will be using many chemicals in this topic. Read this page before you start and refer to it when these symbols appear on the bottles of chemicals you are using. Handle all chemicals with great care. Always wash your hands after using chemicals.
Hazard warning symbols
This shows that the chemical is corrosive.
These chemicals can cause burns to the skin, as well as holes in some metal objects. Acids are corrosive chemicals
This shows that the chemical is flammable (this means the same as inflammable).Flammable chemicals catch fire and burn very easily.
This shows that the chemical is harmful oran irritant. Chemicals with this warning symbol can make you feel very unwell by affecting your skin or organs. In many cases your lungs or breathing system can be damaged by these chemicals.
This shows that a chemical is an oxidizer. This means it could cause irritation if in contact with skin.
1. Acids and Alkalis – The pH Scale
im
In this part of the topic you will learn about acids, alkalis and neutral substances and how they can be identified using the pH scale.
Think/Discuss
Have you heard of acids and alkalis before?
Do you know any examples of acids and alkalis?
Ask your teacher to show the DVD(3) on Acids and Alkalis
2.1Acids and Alkalis
There are many different chemicals in the world – so many that it is impossible to study them all. To make things easier scientists have put chemicals into different groups. Acids and alkalis are two of theses chemical groups. Acids and alkalis are chemical opposites.
The pH Scale
The pH scale is a numerical scale which goes from1 to 14 and tells us whether a substance is an acid, an alkali or neutral. You will find acids, alkalis and neutral solutions in a laboratory but we also come across them in our everyday lives.
You will also notice that the numbers have an associated colour.
The pH scale
The rules for using the pH scale are:
Using the pH scale handout make your own pH scale and stick it in the space below.
Make sure you have a heading and complete the following paragraph:
The numbers on the pH scale range from ___ to ____. The pH of a substance tells us how ac_ _ _ _ or al ______.
A substance with a pH 9 is an a _ _ _ _ _. A substance with a pH of 7 is n______. A substance with a pH of 14 is an a _ _ _.
Teachers checkpoint2. Making an indicator from beetroot
im: In this section you will use cabbage to make an indicator.
Read: Chemists use indicators to tell if a substance is acidic, alkaline or neutral. Usually a chemical called Universal Indicator is used but we can also use everyday items like cabbage and beetroot.
Follow these instructions to make your own indicator:
Wear gloves when preparing the indicator
solution to avoid staining your hands.
This method uses about ¼ of a beetroo
- Chop the piece of beetroot into 1-inch pieces and place in a beaker.
- Add 50cm3 hot distilled water from a kettle until the dye is removed from the beetroot.
- Decant into a clean container. Keep the liquid, discard the beetroot.
- Allow the indicator solution to cool before using.
Now we can add the indicator to different substances and observe the colour change. In the table below fill in the result as you complete the experiments.
Solution / Starting Colour / Finishing ColourStep 1: Collect three test-tubes and a test-tube rack.
Step 2: To each test-tube add approximately 10cm3of
solution A, B and C.
Step 3: Using a dropper add in 4 drops of your beetroot
indicator and note down the colour change.
im
Our aim at this point is to learn through experiment how we can test different substances to see if they are acid, alkali or neutral.We will be using the pH scale and chemicals called indicators.
3.1 pH Indicators
To measure pH we must use a chemical called a pH indicator. When the indicator comes into contact with an acid, alkali or neutral substance it will change colour. This colour can then be matched to the pH chart to work out the pH number of the substance.
There are several types of indicators:
● Special paper called pH paper
●A chemical called universal indicator
● An electronic pH meter
Note: To measure the pH of a solid we must dissolve it in water first!
Experiment 2: Measuring the pH of different substances
Your teacher will demonstrate how to use universal indicator/ pH paper and a colour chart to measure the pH of some liquids and some solid substances.
While your teacher is setting up write the heading ‘Testing the pH of Household Items’ and copy the following results table into your jotter.
Substance / pH / Acid/Alkali/NeutralVinegar
Lemonade
Soda water
Household cleaner
Table salt
Indigestion tablets
Sugar
Washing powder
Orange juice
Distilled water
Mouth wash
Follow the instructions given by the teacher.
Teacher checkpointOnce you have had your work checked by your teacher, complete the following paragraph
pH paper, a pH meter or U______I______can all be used to measure pH. If we had to measure the pH of a solid we would have to d______it in water first.
- Collect your own pH colour chart and some colouring in pencils. Colour it in and paste it into your jotter.
- Louise measured the pH of several solutions using universal indicator and wrote down her results in a table.
Solution / Colour / pH
A / Purple / 13
B / red / 2
C / blue / 10
D / Orange / 4
E / green / 7
(a)Which solutions are acids?
(b)Which solutions are alkalis?
(c)Which solution is neutral?
(d)Which solution is most acidic?
(e)Which solution is most alkaline?
- Copy and complete the following:
Acids often turn universal indicator R_____ or O______and have a pH number of 1 to __. Alkalis often turn universal indicator P______or B______and have a pH number of 14 to ___. Neutral solutions like pure water will turn universal indicator ______and have a pH number of _
Teacher checkpointim
In this section we will look at what happens to the pH of strong acids and strong alkalis as they are successively diluted.
3.1 Dilution of Solutions
In first year, during the Model of Matter course, you learned how to change a concentrated solution into a dilute solution. Can you remember what you had to add to do this?
Experiment 3: Dilution of a Strong Acid and a Strong Alkali
Write a heading in your notes and copy the following results tables into your jotter.
Acids / Colour of pH paper / pH of SolutionAcid Solution A
Acid Solution B
Acid Solution C
Alkalis / Colour of pH paper / pH of Solution
Alkali Solution A
Alkali Solution B
Alkali Solution C
Apparatus: Acid solution A
Alkali solution A
Two Large glass beakers
pH paper
Large measuring cylinder
Small measuring cylinder
Stirring rod
Safety glasses
Instructions:
- Measure out 5ml of Acid solution ‘A’ and measure the pH off the solution using some pH paper. Record you results in your table.
- You will now make solution B. Pour the 5ml of acidsolution A into the large beaker. Add 200ml of water to the beaker and mix the solution. Measure the pH of acid solution B again using pH paper. Keep solution B. Record your results.
- You will now make acid solution C.This time pour the 5ml of acidsolution B into the large beaker. Add 200ml of water to the beaker and mix the solution. Measure the pH of solution B again using pH paper. Record your results.
Teacher checkpoint
- Wash out all your equipment with water when you have finished.
- To find out the results for diluting an alkali repeat the above instruction only this time start with Alkali Solution A. Again record all your results in your table.
- Once you have completed the experiment tidy up, wash all your apparatus and put it away.
Teacher checkpoint
Complete the following paragraph by filling in the blanks:
Acids with a pH of _ are the most acidic. Alkalis with a pH of _ _ are the most alkaline. When w_ _ _ _ is added to an acid the pH will i ______towards 7. When w_ _ _ _ is added to an alkali the pH will d ______towards 7.
Draw a diagram to show how an acid is diluted, remember to show the colours of the universal indicator as the acid changes.
Teacher checkpointim
In this section we will look at what happens when we mix acids and alkalis together. The reaction that occurs is called Neutralisation.
Read
Look back to the pH chart. Find the pH number of a solution which is neither acidic nor alkaline. What colour would this go in universal indicator? What is the pH number of this solution?
Remember, solutions which are neither acids nor alkalis are called neutral solutions.
You can make a neutral solution by adding an acid to an alkali together.
Copy and complete the equation above and collect a copy of the diagram below. Use coloured pencils to colour the solutions in the beaker. Use the pH chart to guide you.
Teacher checkpointIn every neutralisation reaction between an acid an alkali the neutral substances made are a salt and water. When Hydrochloric acid reacts with the alkali sodium hydroxide the products are water and a salt called sodium chloride.
Questions:
N______substances are formed by a neutralisation reaction. The pH of these substances is _.
Teacher checkpoint6. Everyday Neutralisation Reactions
im: In this section you will learn why neutralisation reactions are useful in everyday life.
Read
Neutralisation reactions are used to neutralise acids in many everyday life situations.
Many gardeners will have bags of a powder called lime in their garden sheds. If the soil in their garden is too acidic, they will sprinkle the lime onto the soil. Lime is an alkali so it will neutralise the acid in the soil. This will
help the plants grow.
Due to acid rain, many lakes in Sweden are turning acidic. This is killing the fish. Lime powder is sprinkled from aeroplanes onto these lakes to neutralise the acid and help save the fish.
You will probably have heard people complaining of having indigestion. This is often caused because there is too much acid in the stomach. To neutralise the acid people take indigestion remedies. An example of an indigestion remedy is milk of magnesia. Milk of magnesia is an alkali so it neutralises the acid in the stomach and stops the pain.
Have you ever been stung by a bee or a wasp? If you do get stung it pays to remember some neutralisation chemistry! A bee has an acidic sting. If you want to help stop the pain you should neutralise the sting by putting an alkali onto it. Many people put the household alkali called baking soda onto bee stings because baking soda is an alkali and it neutralises the acid in the bee sting.
Wasp stings are different from bee stings. Wasp stings are made from an alkalinesubstance so to neutralise a wasp sting we need to add an acid. Many people put vinegar onto a wasp sting. Vinegar is an acid and so it will neutralise the alkali in the wasp sting and help stop the pain.
Complete the following sentences by filling in the blanks.
L _ _ _ _ will neutralise acid in soil. Sweden uses thousands of tonnes of lime every year in order to stop the a_ _ _ r _ _ _ _ from killing the fish.
Indigestion is caused by too much a _ _ _ _ in the stomach. Milk of magnesia is used to neutralise this acid.
B _ _ _ _ _ S _ _ _ is used on a bee sting to neutralise the acid in the sting.
V______is used to stop the pain of a wasp sting. This works because the v______neutralises the alkali in the wasps’ sting.
Teachers checkpointInternet Research
ACID RAIN
You have just read a section which mentioned one of the problems of Acid Rain. Your next task is to research the problem of Acid Rain and prepare a power point presentation or an information leaflet or a scientific poster on this problem. You can use the internet as a resource, or any books the Science Department may have.
Your presentation must include:
●The causes of Acid Rain
● The effects on animals, plants and buildings
● How we can solve the problem of Acid Rain.
Teacher checkpoint7. Neutralisation Investigation
im: In this section you will carry out an investigation to find out which fast food shop has diluted their vinegar.
In your group, discuss how you could use the apparatus to do the experiment (see list below). At the end you must be able to say if any of the bottles of vinegar have been watered down.
What volume of vinegar will you start with?
If you decide to use an indicator, which one will you use? How can you find out what colour change you will see?
Think about how you are going to record your results.
Good chemists will repeat their experiments. Why?
We need to know when all the vinegar we have started the experiment with has been neutralised. This is where we can use special dyes called indicators. They change colour when the neutralisation is complete.
How will you know what the colour change of the indicator will be? How will you be able to tell if any of the bottles of vinegar has been watered down?
Apparatus:
Measuring cylinders
- Small beakers
- Plastic dropping pipettes and syringes
- Two test tubes in a test tube rack
- Stirring rods
- Bottles of indicator solutions
- Bottles of dilute sodium hydroxide solution
- White tiles
You also have:
A bottle of vinegar from the supermarket
Bottles of vinegar from each of the three Fast Food shops
Record your ideas (you can use diagrams too) on the Experiment 1 Notes Sheet and then get it checked.
Once your teacher has checked your plan you should carry out your investigations in groups.
You should then complete the report sheet with the help of your group.
8.Fertilisers and Neutralisation Reactions
im: In this section you will learn why fertilisers are important and about some of their properties.
Read
Plants take in the elements that they need for growth from the soil, without these elements they would are not able to grow properly. When plants are harvested some of the elements that the plants need are removed. In order to replace these nutrients fertilisers are added. Fertilisers are made by neutralisation reactions.
You have already learned that adding an acid to an alkali produces a salt and water:
Acid + Alkali →Salt + Water
Depending on the type of acid and alkali used the salt produced can be used as a fertiliser.
Here are some examples:
Nitric + Potassium → Potassium + water
acid Hydroxide Nitrate
ammonia + nitric acid→ ammonium nitrate + water
phosphoric acid + ammonia → ammonium phosphate + water
9Essential Elements
im: In this section you will learn the names of the three elements that are always used in fertilisers.
Read
You already know that we can help keep plants healthy by using chemicals to kill pests, diseases and weeds but unless plants get the correct food they will still not be able to grow healthily.
You will already know that some things are essential for animals to stay alive. It is the same for plants. There are three elements in the periodic table that plants must have to survive. These elements are called essential elements because the plant would die without them.
Sarah carried out an experiment to find out the names of these three essential elements and wrote a conclusion in her jotter.
Use a periodic table and the picture of Sarah’s jotter above to copy and complete the following sentence.
10. What is a fertiliser?
im
In this lesson, we will learn about fertilisers and why they are important in the production of food.
Think about where you have heard about fertilisers before, share your ideas with your partner. Your teacher will then ask for your ideas.
Watch as your teacher shows you a power point presentation / video on the importance of fertilisers.
- Write down three key facts on why fertilisers are important.
Read
The population of the world is steadily getting bigger. This means that we need to make more food to feed more people. To make more food, farmers need to make their crops grow bigger and faster. They give their crops extra help by giving them plant food. The scientific word for a plant food is fertiliser. The chemical industry has found ways to manufacture fertilisers for farmers tomeet the world demand for more food.
There are two main kinds of fertilisers. The ones that are made by the chemical industry are called artificial fertilisers. There are four major types of articicial fertilisers: ammonium, nitrate, phosphate and potassium.
Ferlisers that are made from living things are called natural fertlisers. Manure and compost are examples of natural fertilisers.