pH indicators

1. pH scale

1.1. has a set of numbers 1-14

1.2. used to indicate whether solution is acidic, alkaline or neutral

1.3. acids have pH values less than 7

1.3.1. eg

1.3.1.1. HCl pH 1

1.3.1.2. Sulfuric Acid pH 1

1.3.2. acids with smaller pH values have higher concentration of Hydrogen ions

1.4. alkalis have pH values more than 7

1.4.1. eg

1.4.1.1. NaOH pH 13

1.4.2. alkaline solns with larger pH value have higher concentration of hydroxide ions

1.5. a neutral soln (eg a salt soln or water) has a pH value of 7

1.5.1. has equal number if hydrogen and hydroxide ions

1.6. pH is used to compare strength of acid and alkali

2. indicators

2.1. are substances that change colour when acidic or alkaline soln added to them

2.2. Universal indicator

2.2.1. Very acidic-red

2.2.2. acidic-orange,yellow

2.2.3. neutral-green

2.2.4. basic/base/alkali-blue

2.2.5. very basic/base/alkali -purple

2.3. Methyl Orange

2.3.1. Turns red in acidic soln

2.3.2. Turns Yellow in alkaline soln

2.3.3. Changes colour at pH 3 - 5 range

2.4. Litmus paper

2.4.1. Blue litmus turns red when in acidic soln

2.4.2. red litmus turns ble when in alkaline soln

2.5. phenolphthalein

2.5.1. colourless in acidic soln

2.5.2. yellow in alkaline soln

2.5.3. changes colour at pH 8 - 10 range