What I know about Acids and Alkalis… Starter: Complete this spider diagram in your books writing absolutely everything you think you know about the topic… What I know about Acids and Alkalis…

Be able to give some real life examples of indicators. Acids and Alkalis Learning objectives Be able to explain that an indicator shows the pH of a substance when added to it and that there are different types. Be able to explain the difference between an acid and an alkali and base with examples. Be able to give some real life examples of indicators.

Think, pair, share: match up the definitions. These are soluble. Have a pH of more than 7. Turn red litmus paper blue. They turn universal indicator dark blue or purple if they are strong, and blue-green if they are weak. Sodium hydroxide is an example. Acid Base They are usually metal oxides or metal hydroxides. For example, copper oxide and sodium hydroxide. Substances with a pH of less than 7. Turn blue litmus paper red. They turn universal indicator red if they are strong, and orange or yellow if they are weak. Alkali

weak bitter corrosive digest hydrochloric strong stomach hydroxides litmus Less than soapy sour More than vinegar An acid is a substance with a pH of __________ ________7. It will turn universal indicator red if they are ___________, and orange or yellow if it is weak. Acids often taste _________ and many acids can be _________________ if you touch them. Lemon juice and _________________ are examples and _________________ acid is a very strong acid found in your ___________. You can use blue_________________ paper to determine if something is acid or not because the acid will turn the paper red. Bases are usually metal oxides or metal __________ . For example, copper oxide and sodium hydroxide. Bases feel _________________ when you touch them and taste _________________. Many household cleaners are bases. Some bases can even dissolve hair and food, which makes them ideal for clearing clogged drains. Alkalis: are soluble ________. Have a pH of __________ _________7. They turn red litmus paper blue and turn universal indicator dark blue or purple if they are strong, and blue-green if they are _________. Sodium hydroxide is an example. less than strong sour corrosive vinegar hydrochloric stomach litmus hydroxides soapy bitter bases more than weak

Detecting Acids and Alkalis What is an indicator? We use special chemicals called indicators to determine if a substance is acidic, alkaline or neutral. These turn different colours in acids, alkalis and neutral solutions.

Nature’s indicators

Colour in red cabbage indicator Acid/ Alkali/Neutral Stong/Weak? Solution Colour in red cabbage indicator Acid/ Alkali/Neutral Stong/Weak? Label? A B C D E Strong Acid Weak Acid Neutral Weak alkali Strong alkali

‘Pound with the pestle’ In pairs, take one pestle and mortar with 1-2 slices red cabbage ‘Pound with the pestle’ ‘Mix with the mortar’

‘Pound with the pestle’ Cut up the cabbage into small pieces with scissors and add a small splash of warm water ‘Pound with the pestle’ ‘Mix with the mortar’

Grind the red cabbage Start Timer 1 1 Min 15 Secs

Now add another splash of warm water and mix gently Now add another splash of warm water and mix gently. Pipette out the purple liquid into a clean beaker. You have just made an indicator!

Well plate

Safety! Safety glasses – protect your eyes! Hair tied back Stand up at all times Bags, coats and chairs under desks Move around the classroom and handle equipment sensibly. DO NOT MIX PIPPETES WITH LIQUIDS!!!!

Testing for acids and alkalis. Use your pipette to add about 0.5mls of the sample you want to test to the well plate. Add a few drops of your cabbage indicator. Record the colour the indicator changes to. Use your observations to predict whether each substance is acid, alkali and neutral. Try and match the labels to the unknown liquids.

Red cabbage indicator

Well plate

Once you have completed testing your samples… 1. Write up your experiment i) describing how you made your red cabbage indicator and ii) explaining how it can be used to detect acidic, alkaline and neutral substances. 2. Make a list of safety rules for a new Year 7 class who have never handled acids or alkalis before. What are the hazards, what should they wear, what if they spill it on themselves? 3. A lorry carrying concentrated sulfuric acid spills it all over a section of motorway. Advise the police on how they could deal with this dangerous chemical and make the motorway safe again. Write down what you would say to them.

Plenary – true or false pH 8 is a strong alkali. TRUE FALSE

Plenary – true or false A weak acid would be red. TRUE FALSE

A strong alkali would be purple. Plenary – true or false A strong alkali would be purple. TRUE FALSE

Plenary – true or false Light green would be pH 5. TRUE FALSE

An acid is a soluble base. Plenary – true or false An acid is a soluble base. TRUE FALSE

The acid in your stomach is hydrochloric. Plenary – true or false The acid in your stomach is hydrochloric. TRUE FALSE

Sodium hydroxide is an example of an alkali. Plenary – true or false Sodium hydroxide is an example of an alkali. TRUE FALSE

A strong acid would be pH 1-4. Plenary – true or false A strong acid would be pH 1-4. TRUE FALSE

If you mixed an acid with an alkali they would cancel each other out? Plenary – true or false If you mixed an acid with an alkali they would cancel each other out? TRUE FALSE