1. Indicators 1.Indicators are dyes which change colour when acidic or alkaline solutions are added to them. 2.Some common indicators are litmus, methyl orange, phenolphthalein and universal indicator.

2. Indicators universal indicator Best indicator- universal indicator, why? Universal indicator acidic (yellow, orange or red)alkalineblue, indigoor violetstrong acid or a weakacidstrong alkali or a weak alkali. Universal indicator - a mixture of many indicators - shows not only whether a substance is acidic (yellow, orange or red) or alkaline ( blue, indigo or violet ) but also if it is a strong acid or a weak acid, a strong alkali or a weak alkali.

3. Indicators colours of the universal indicator is associated with different pH numbers 1.The different colours of the universal indicator is associated with different pH numbers 2.Used in the form of paper or liquid Universal Indicator / pH indicator - Dip universal indicator paper into solution - Observe colour change - Compare colour with colour chart => pH of solution - Dip universal indicator paper into solution - Observe colour change - Compare colour with colour chart => pH of solution

4. pH scale The pH scale is a range of numbers from 0 to 14, which indicates the strength of an acid or alkali (how acidic or alkaline a substance is).

5. pH scale Strong acidic solution Weak acidic solution Strong alkaline solution Weak alkaline solution 1-21-2 4 - 6 8-108-1012-1412-14 Generally Acid Rain - pH 2 to 5 Normal Rain - pH 5 to 6 Why is rain water slightly acidic? pH range Type of Solution

6. pH meter an electronic device used to measure the acidity or the alkalinity of solutions very effectively, more accurate than indicators pH electrode is placed into the solution and the reading is given on the digital displaypH electrode is placed into the solution and the reading is given on the digital display

7. pH meter A pH meter is an electronic device that can be used to measure the acidity or the alkalinity of solutions very effectively. (a) pH meter is used to measure the pH of water in swimming pool (b) pH meter is used to measure pH of the soil

8. pH and Agriculture plants grow well in soil about pH 6.5 (about neutral) plants grow well in soil about pH 6.5 (about neutral) soil becomes acidic from soil becomes acidic from To reduce acidity of soil -> acid rain -> extensive use of chemical fertilisers such as ammonium sulphate - add calcium hydroxide (slaked lime), a cheap alkali - spread calcium hydroxide powder over fields => liming the soil