In This Section We Will Be Studying The Following Topics: ACIDS AND ALKALIS In This Section We Will Be Studying The Following Topics: What are acids and alkalis? How to work safely with acids and alkalis and their hazard symbols. What an indicator is and what it does. What is in a name? The pH scale. The strength of acids and alkalis. Neutralisation. Using acids and alkalis. Wasp and bee stings. Upset tummy.

ACIDS What is an acid? It is a substance that is opposite in action to an alkali. If it is a food it will have a sour, sharp taste. Our skin is acidic so we often use alkaline substances to clean it. Lemons are strong enough to clean things with, they have a sharp taste too. We use acids to flavour food. It would be strange to have only plain crisps! Vinegar is used to flavour chips too. Strong acids can wear away or corrode metals quickly. Car batteries are in plastic containers.

We use alkalis as cleaners. We often see bottles and containers with warnings on them or instructions to keep these substances AWAY FROM CHILDREN. Alkalis are described as CAUSTIC as they can damage living tissue. People think that they do not sound as dangerous as acids but they can be just as strong and damaging. They often feel slippery. But what are these things? They are substances that are all around you, it is what they do that makes them special. We use alkalis as cleaners. If something is described as alkaline it means that it works as an alkali.

SAFETY WITH ACIDS AND ALKALIS We need to have some way of recognising that substances are dangerous. But it would be silly to have lemons with big notices on them. Look at these things and decide which ones are acids and alkalis. Wash up Alkalis. Acids. Aspirin.

Harmful Irritant Corrosive HAZARD SYMBOLS Do we need some sort of code to recognise the dangerous acids and alkalis? There are special symbols that give us information about acids and alkalis. These are Hazard Symbols. For example: Harmful Irritant Corrosive Can make you ill if you swallow it or get it on your skin. If it is a gas, breathing it in will be harmful. May cause reddening or blisters on skin. This can attack and destroy living tissue. If it got into your eyes it would make you blind. So that is why we wear goggles when we use them. :

HOW CAN WE TELL THE DIFFERENCE BETWEEN ACIDS AND ALKALIS? Acids and alkalis can be gases, liquids and solids. They can often be colourless. It is very hard to tell by looking so we have to have a way of finding out. We use substances called INDICATORS to help us. Most indicators come from plants. You can make an indicator using red cabbage, beetroot or flower petals. When the liquid from these is added to a substance it changes colour. There are four main indicators that scientists use to tell the difference between acids and alkalis. Indicator. Litmus. Universal Indicator. Phenolphthalein. Methyl Orange. Colour in acid. Pink Red/orange Clear Orange Colour in alkali. Purple Purple/blue Yellow

CAN YOU GUESS WHAT IT MIGHT BE FROM A NAME? The strength of acids and alkalis is measured by how many hydrogen ions they have in them. Scientists call this measurement the pH scale. The names we give to the chemicals give us a clue. Here are two groups of names - can you guess which ones are acids and which ones are alkalis? Ammonium hydroxide Calcium hydroxide Sodium hydroxide Nitric Citric Acetic Hydrochloric Phosphoric Sulphuric Acids. Alkalis. The endings of the words often tells us what the chemical is.

pH SCALE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Strong acids Weak acids This is a scale between 1 and 14, it tells us how acidic or alkaline something is. The mid point is when a solution is not an acid or an alkali and this is at pH 7. Universal indicator. This indicator is used because it changes colour from a very strong ‘pinky red’ for a strong acid to a ‘deep purple’ for a strong alkali. The colour changes can be seen if you mix acids and alkalis very slowly. A number is given to each colour and it is a way of describing acids and alkalis. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Strong acids Weak acids Neutral Weak alkalis Strong alkalis

Strong acids and alkalis are more powerful than weak ones. STRONG OR WEAK? Strong acids and alkalis are more powerful than weak ones. Some alkalis are described as strong and they can be corrosive. This means we have to take extra care when we are using them. We can use a strong acid to etch glass . We cover up the parts we do not want to get acid on and then leave the parts to be ‘eaten away’ by the acid. This makes the surface of the glass go cloudy. Some acids are very weak. Milk is a weak acid. It does not corrode or ‘eat away’ our digestive system. Rain water is a weak acid called carbonic acid and it is responsible for wearing away stone buildings. This takes a long time, but the stronger the acid rain gets the faster the erosion of the stone. The older a headstone is, the more the rain water has eroded it and it becomes harder to read.

BEING NEUTRAL The things around us that are not acid or alkali are called neutral. This means that they have a pH scale number of 7. Water is neutral and has a pH of 7. When we add an acid to an alkali we can make the solution neutral. We can get as close to pH 7 as possible by titration (adding small amounts together). How much you need depends on how concentrated the acid and alkali are. Weak alkali pH8. Strong acid pH3. Neutral solution pH7.

USING ACIDS AND ALKALIS We bleach cloth or hair using hydrogen peroxide solution We often use the properties of acids to store food. We pickle vegetables such as cucumbers and onions in vinegar to store them. Different types of vegetables and crops need the soil to be acidic or alkaline. Farmers add lime to the soil. This is powdered calcium oxide and it makes the soil more alkaline.

WASP AND BEE STINGS acid + alkali → neutral The sting from an insect can really hurt. When ants bite us they put formic acid under our skin. Bees and wasps use different solutions and we can treat them in different ways to neutralise the sting. acid + alkali → neutral Wasp Bees The sting from a wasp is alkaline. It can be treated with vinegar or lemon juice. This neutralises the alkali and the same thing happens, the sting stops hurting. The sting from a bee is acidic. It can be treated with calamine lotion or baking soda. This neutralises the acid so it stops hurting.

UPSET TUMMY Sometimes we get excess acid in our stomachs and it makes us feel ill. We can neutralise this acid with an alkali. We buy this alkali in the form of medicine. It can be as a tablet or liquid. What kind of solution do you think the medicine contains? Alkali. Why would a child need a smaller dose than an adult? They have a smaller stomach and less acid to neutralise.

What have we learned? ACID DCAI ALKALI LALIKA pH SCALE SLACE Hp Look at the following words. See if you can work out what they are. ACID ALKALI pH SCALE NEUTRALISE WEAK STRONG DCAI LALIKA SLACE Hp TRENSLIEUA WEKA GROSNT Click for the answers

I WISH I HAD WORKED SAFELY! Think about Check that you have remembered these facts. Acids and alkalis are substances with different pH . How to work safely with acids and alkalis and their hazard symbols. What an indicator is and what it does. The pH scale is a way of measuring how acidic or alkaline a solution is. Neutralisation means getting to pH 7. Using acids and alkalis in every day life. Wasp and bee stings can be treated differently with acids and alkalis. Medicines to treat stomach acid are alkaline. I WISH I HAD WORKED SAFELY!