Neutralisation. November 29, neutral

Transcription

1 Neutralisation November 29, 2015 neutral

2 STARTER Decide if the statements are true or false. 1. Vinegar is an example of an alkali. FALSE 2. Tea contains tannic acid. TRUE 3. Coke is an alkali. FALSE 4. Water is the only liquid that is neutral. FALSE 5. Tooth decay is caused by bacteria that release acid in the mouth. TRUE 6. Sodium hydroxide will produce a ph value between 1 and 6. FALSE 7. Hydrochloric acid is an example of a concentrated acid. TRUE 8. You can dilute an acid by adding water to it. TRUE 9. You should treat an acid spill by adding alkali. 10. Lactic acid is an acid found in yoghurt. TRUE FALSE

3 Today s Aim November 29, 2015 By the end of this lesson I will be able describe some circumstances where neutralisation is useful

4 What is neutralization? The chemical reaction between an acid and an alkali is called neutralization. What is the ph value of the mixture of salt and water? + acid alkali salt + water The mixture of salt and water is neutral, so its ph is 7. The chemical reaction between an acid and an alkali can be written as: acid alkali salt + water +

5 Neutralisation If the right amounts of an and an are added together the of the mixture changes to (ph 7). This reaction is called neutralisation. acid + alkali neutral

6 Neutralisation Practical You will need: Boiling tube Bung to fit tube UI solution 2x 100 ml beakers 2x plastic pipettes Patience What to do: 1. Pour about 50 ml of HCl into one beaker and label it. 2. Pour about 50 ml of NaOH into the other beaker and label it. 3. Put about 1cm depth of NaOH into a boiling tube and add a few drops of UI. 4. Using a pipette now add HCl to the boiling tube to make it turn neutral

7 Neutralisation reactions A neutralisation reaction occurs when an acid reacts with an alkali. H Cl Na O H Cl Na H O H ACID + ALKALI SALT + WATER

8 Neutralizing stings Bee stings are acidic. Wasp stings are alkaline. Which safe household substances could you use to treat a bee sting? Which safe household substances could you use to treat a wasp sting?

9 Stings A bee sting is acidic. A wasp sting is alkaline. So one way to treat a an acidic bee sting is to dab on a base: bicarbonate of soda more properly known as sodium hydrogen carbonate. One way to treat a basic wasp s sting is with an acid : vinegar - ethanoic acid.

10 Soil ph Plants remove compounds from the soil in a way that tends to leave the soil acidic. Many plants won t grow well in acid soil and so farmers have to regularly check the ph and adjust it by adding a base. Some flowers change colour depending on whether they are growing in acidic or alkaline soil. Hydrangeas grow blue flowers in an acidic soil, but pink flowers in an alkaline soil.

11 Soil ph Different soils have different ph levels. This is because they are made up of different rocks, and so contain different chemicals. The ph of soil affects the availability of nutrients, and plants prefer to grow in soils of a certain ph. For example, strawberries grow best in acidic soil, and plums grow best in alkaline soil. How could you check the ph of the soil in your garden?

12 Testing the ph of soils

13 Changing soil ph If soil is too acidic to grow certain crops, lime can be added. Lime is an alkali called calcium oxide. What effect does lime have on the ph of soil?

14 Poisonous gases Many power stations burn coal containing sulphur. When this burns it produces acidic sulphur oxides which can cause acid rain. The gases are scrubbed, as much as possible, of these acidic oxides by reacting them with a base before releasing them into the air. Calcium oxide or calcium hydroxide are often used for this purpose.

15 Read through the sheet and answer all questions

16 7E Neutralisation - Using neutralisation Plenary: neutralisation Neutralisation can be a very useful reaction. Acidic problem 1. Indigestion caused by too much stomach acid 2. Acid rain pollutes lakes and poisons wildlife 3. Power stations produce gas which forms acid rain 4. Jellyfish sting contains alkali which irritates skin 5. Mouth bacteria produce acid from sugary foods Neutralising treatment A. Spray with vinegar B. Regular brushing with alkaline toothpaste C. Antacid tablets D. Calcium carbonate neutralises acidic gas before it is released E. Calcium carbonate reduces acidity of water

17 Multiple-choice quiz