Acids and Alkalis Grade 10

Acids Sour Turn litmus red pH less than 7 Dissolve carbonate rocks Corrode metals Conduct electricity

Acids Acids are substances that give H + ions when added to water.

Alkalis Bitter Turn litmus blue pH greater than 7 Slippery caustic

Alkalis An alkali is a substance that gives OH - ions when added to water

Neutralizations reactions Acids and alkalis neutralize each other to form a salt Example: HCl + NaOH  NaCl + H 2 O Reactions of acids and alkalis are called neutralization reactions

Neutralization examples Indigestion is caused by too much amounts of hydrochloric acid in the stomach. It is cured by indigestion tablets. Indigestion tablets contain magnesium oxide that neutralises the excess HCl.

Neutralization examples Fields with acidic soil can be improved by adding lime. The lime contains calcium hydroxide Ca(OH) 2 which is an alkali

Neutralization examples Lakes affected by acid rain can be neutralized by adding lime.

Strong vs. weak Strong = complete dissociation Example, when HCl is dissolved in water, all of it becomes H + + Cl - Weak = incomplete dissociation Acetic acid (vinegar) is a weak acid CH 3 COOH, small amounts dissociate into H + and CH 3 COO - ) More dissociation = stronger acid

Indicators Indicators are substances that change col our when placed in an acid or an alkali. There are four important indicators: Methyl orange Phenolphthalein Litmus paper Universal indicator.

Indicators Practical Aim:find the colour change for different indicators when placed in acids or alkali. Materials: HCl, NaOH, phenolphtnalein, litmus paper, universal indicator and methyl orange.

Procedure:put 3 cm 3 of HCl in a test tube. Add few drops of methyl orange. record your observation. Methyl orangePhenolphthaleinLitmus paperUniversal indicator HCl NaOH