Y7 Acids and Alkalis C7.2

Lesson 1 – An Introduction to acids and Alkalis

What are acids and alkalis? What if something is neither an acid nor an alkali? What substances are acids and alkalis? Are acids and alkalis dangerous? What is the difference between an acid and an alkali?

Some acids are safe enough to eat….. …they all taste sour!

This is used to make your cola taste ‘tangy’

These are all citrus fruits. They contain citric acid. Like many other foods they also contain ascorbic acid = vitamin C

A lack of vitamin c causes scurvy, a disease which used to be fatal. Your joints and muscles ache, your gums start bleeding and your skin and hair become very dry. British sailors had lemons and limes in their rations to stop them getting scurvy, so the Americans called them ‘limeys’. Ascorbic means ‘no scurvy’ and vitamin c is also known as ascorbic acid. James Lind – he discovered that citrus fruits were the best prevention for scurvy

We pickle foods in vinegar. Vinegar is an acid….. …..it’s old name is acetic acid. ….it’s scientific name is ethanoic acid Why do you think we pickle foods?

Vinegar is also used as a flavouring. It is made using alcohol

These sweets contain Citric acid Tartaric acid Ascorbic acid to make them tangy!

Why do you think acid foods are bad for your teeth?

What do these symbols mean? Why do you think you don’t see them on food labels?

Other useful acids that we don’t eat…. the mass of elephants a day! 165 million tonnes of sulphuric acid was produced in 2001 ….. that’s kg or to put it another way….

Other useful acids that we don’t eat…. Sulphuric acid is used for Car batteries Metal processing Making fertilisers

Other useful acids that we don’t eat…. Sulphuric acid is found naturally in lakes in volcanic regions and in the atmosphere of venus Sulphuric Acid’s formula is H 2 SO 4

This is deoxyribonucleic acid or DNA It is the genetic instructions for a living thing What is this?

This is 2-acetoxybenzoic acid

Alkalis In ancient times, Arabic scientists took ashes from fires and mixed them with water. The ashes were called ‘al qali’ القلي, القالي

Alkalis They mixed the ashes with water and boiled them with animal fat to make soap القلي, القالي

Alkalis Alkalis all feel soapy because they react with the oils in your skin. Some are too dangerous to touch. Which hazard symbol do you think they should have on them? القلي, القالي

Common alkalis…..

Do we now know the answers to these questions? What are acids and alkalis? What if something is neither an acid nor an alkali? What substances are acids and alkalis? Are acids and alkalis dangerous? What is the difference between an acid and an alkali?

Lesson 2 – Indicators

How do I know if a substance is an acid or an alkali?

The ‘magic’ flask

What was special about the substance that was in the flask?

Indicators An indicator is a substance which could help a scientist tell whether a solution is acidic, alkaline or neutral

Do indicators work for acids and alkalis? What if the solution is neutral?

Let’s find out!

You should now be able to answer these questions based on what you found out today… 1.What is an indicator? 2.Do all indicators work for acids, alkalis and neutral solutions? 3.Why are indicators useful? *Bring in flowers for next lesson*

Lesson 3 – Making Indicators

Can you make indicators from plants? How?!?

Making indicators There is a chemical in the red cabbage that can act as an indicator – we can’t just put cabbage in our solutions so we need to get it out.

Making Indicators What is the purpose of these processes?

There are loads of other plants that make useful indicators – you can use the petals from many flowers as indicators Try and make your own!

Could anyone manage this?

Write about the experiment you did today. Use the following headings: Aim Method – also mention why you carried out these steps Results Conclusion

Lesson 4 – Measuring pH

Is one acid ‘stronger’ than another?

Universal indicator can help us decide whether one acid is stronger than another… But what does stronger mean?

‘Acid particles’ We can think of acidity as being something to do with how many acid particles are present in the solution. We measure this on a scale from 1 to 14 This is called the pH scale

pH pH 3-4 pH 1

Why is hydrochloric acid ‘stronger’ than vinegar?

This is because hydrochloric acid releases more acid particles into the solution than vinegar

Will hydrochloric acid always be pH 1?

Let’s find out! What happens when you add water?

If you dilute and acid (add water) there are fewer acid particles in the same volume and so the acid is weaker It’s like this ribena – the more concentrated one has more ‘ribena molecules’ in it than the diluted one

The pH scale Strong acid Weak acid Weak alkali Strong Alkali Using the universal indicator colours we can see how acidic or alkaline household substances are…

Lesson 5 – Neutralisation

What happens when you add an acid and an alkali together?

Acids and alkalis react together to make water and a salt which are neutral. This is called a neutralisation reaction

What happens if you add more acid than alkali or more alkali than acid?

It’s like a war between acid and alkali particles! One acid particle will ‘kill’ one alkali particle and one alkali particle will kill one acid particle! Vs. 100 acid particle soldiers 100 alkali particles soldiers Result: no acid or alkali particles so you get a neutral solution

When one side has more particles than the other, there will be acid or alkali particles left over.. Vs. 500 acid particle soldiers 100 alkali particles soldiers Result: 400 acid particles left over – acid solution

What happens if you have more alkali particles than acid particles?

Some substances can neutralise an acid but they don’t use alkali particles – we call these substances bases – they don’t dissolve in water

What is the difference between a base and an alkali?

A base and an alkali can both neutralise an acid An alkali is a soluble base

All alkalis are bases but not all bases are alkalis

Lesson 6 – Using Neutralisation

Insect stings contain acids or alkalis

People use ‘old fashioned remedies’ on wasp and bee stings. How can you test these substances to find out if they would neutralise a bee or wasp sting? Which is the best substance for bee stings? One is alkali and one is acid… Ant stings contain formic acid. What type of substance would you suggest putting on an ant sting and why?

Investigation: Finding the best remedy for the sting You will be given some samples of bee and wasp stings – you have to try and find the best cure. You must plan and carry this out yourselves!

If you are stung by a box jellyfish you should put vinegar on it. What does this tell you about the box jellyfish sting?

What is this?

Chewing gum manufacturers claim that chewing gum after meals helps reduce acid erosion of teeth. How?

Clues: Tooth decay is caused by acid erosion Bacterial plaque produce the acid These bacteria live on food in the mouth Saliva neutralises the acid produced by the bacteria So how does chewing gum reduce gum disease? Can you think of any drawbacks?

From the Orbit website

Do you still need to brush your teeth?

Lesson 7 – Neutralisation Assignment

You are a senior scientist at a chemical plant – one afternoon a researcher bursts into your office and tells you there has been a massive chemical spill – some sulphuric acid has been spilled from a barrel and it is leaking everywhere You have called in to advise the lab manager When you arrive in the lab two researchers are already arguing about whether to use a sodium hydroxide solution (alkali) or use solid sodium carbonate (a base).

You have to write a report which will address the following: 1.How will you test the spill to see how acidic it is 2.How will you make sure the spill is treated to make it a neutral solution 3.A full explanation as to whose advice was better and why (should you use sodium carbonate or sodium hydroxide)

Level 4Level 5Level 6 Name what is used to tell if a substance is alkali or acid Describe how you would use this Explain why using this is important Describe how you would know if the treatment of the spill was successful Explain what is going on with the particles in the treatment Choose which advice to take and give a reason Describe the differences between the two pieces of advice Explain correctly why you have chosen that piece of advice

Which key words will I have to use?

Lesson 9 – Having fun with neutralisation reactions

Do acids and alkalis react without water?

Making a bath bomb!