Learning Objectives By the end of the lesson, you should be able to: a)Give the definition of a strong and weak acid, and the properties of it. b)Identify the products of reactions between Acid and metals, carbonates, bases. c)Give the definition of a strong and weak Alkali, and the properties of it. d)Identify the products of reactions between Bases and Ammonia salts e)State the reactivity series and colour changes of each indicators.

Acids An acid is a substance which produces hydrogen ions as the only positive ions when it is dissolved in water. E.g. HCl molecules dissolve in water to give hydrogen ion and chloride ion. [Examples] Strong Acids Common NameChemical NameChemical Formula Hydrochloric Acid Hydrogen Chloride HCl Nitric AcidHydrogen Nitrate HNO 3 Sulfuric AcidHydrogen SulfateH 2 SO 4

Strength of an Acid The strength of an acid depends on its degree of dissociation/ ionization in water to form hydrogen ions (H + ). A strong acid is one that ionizes completely in water to produce hydrogen ions (H + ). There are no molecules left. The solution contains a high concentration of ions : Good electrical conductor. HCl (aq) → H + (aq) + Cl – (aq) A weak acid is one that ionizes partially in water to produce few hydrogen ions (H + ). Most of the acid molecules remain as molecules. The solution contains a low concentration of ions : Poor electrical conductor.

Properties of Acids An acid, when dissolved in water, forms a colourless solution. Solution of acids have the following properties: a)Sour taste b)Change the colour of indicators (E.g. Turns blue litmus paper red) c)Contains hydrogen ions and conduct electricity d)Reacts with metals, carbonates and bases. *Note: Acids only behave as acids when they are dissolved in water.

Reaction with metals Acids react with metals to produce a salt and hydrogen E.g. 2HCl (aq) + Zn (s) → ZnCl 2 (aq) + H 2 (g) Observations: a)Effervescence observed. Colourless, odourless gas evolved which extinguished a light wooden splint with a “pop” sound. b)Grey solid reduced in size (when in excess). Grey solid dissolves to form a colourless solution. c)Heat is liberated.

Reaction with carbonates Acids react with carbonates to produce a salt, carbon dioxide and water E.g. Na 2 CO 3 (s) + H 2 SO 4 (aq) → Na 2 SO 4 (aq)+ CO 2 (g)+ H 2 O (l) Observations: a)Effervescence observed. Colourless, odourless gas evolved which reacts with calcium hydroxide to form a white precipitate. b)White solid dissolves to form a colourless solution.

Reaction with bases Acids react with bases (metal oxides and hydroxides) to produce a salt and water E.g. MgO (s) + H 2 SO 4 (aq) → MgSO 4 (aq)+ H 2 O (l) Observations: a)White solid dissolves to form a colourless solution. b)Heat is evolved. No visible change.

Uses of acids Sulfuric Acid:Ethanoic Acid: To make Detergents and Fertilizers To preserve food In car batteries as battery acid treatment of the sting of box jellyfish Oil refining, wastewater processing, and chemical synthesis. Used in photographic films

Indicators Observations Litmus paperAn acid turns blue litmus paper red Methyl OrangeUsed to identify strong acids Colour change at pH 4 Strong acids turn methyl orange red Alkalis turn methyl orange yellow PhenolphthaleinUsed to identify strong alkalis Colour change at pH 9 Strong alkali turn phenolphthalein pink Phenolphthalein remains colourless in acid. Universal Indicator In neutral solutions (pH 7), universal indicator remains green. Strong acid: red Strong alkali: violet

Bases and Alkalis Definition of base: Bases are the oxides or hydroxides of metal that reacts with an acid to form salt and water only. Definition of alkali: An alkali is a metal hydroxide which is soluble in water and produces hydroxide ions (OH – ) in water. All alkalis are bases but not all bases are alkalis. Insoluble base: Copper (II) oxide, aluminium oxide, zinc oxide, zinc hydroxide. Soluble base/alkali: Sodium oxide, Potassium oxide, Sodium hydroxide, Potassium hydroxide, Ammonium Hydroxide

The strength of an alkali depends on its degree of dissociation/ ionization in water to form hydroxide ions (OH – ). The properties are due to hydroxide ions. A strong alkali is one that ionizes completely in water to produce hydroxide ions (OH – ). There are no molecules left. The common strong alkalis are sodium hydroxide and potassium hydroxide. KOH(aq) → K + (aq) + OH – (aq) A weak alkali is one that ionizes partially in water to produce few hydroxide ions (OH – ). Most of the alkali molecules remain as molecules. Strength of an alkali

Properties of bases a)Alkalis have a soapy feel and bitter taste b)Alkalis can change the colour of indicators (e.g. turn red litmus paper blue) c)Bases can react with acids to form salt and water only- Neutralization Example: NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O (l)

Reaction with Ammonium Salts Bases react with ammonium salts to produce a salt, ammonia and water. E.g. NaOH (aq) + NH 4 Cl (s) → NaCl (aq) + NH 3 (g) + H 2 O (l) Observations: a) A colourless, pungent gas is evolved, that turns damp red litmus paper blue.

Uses of bases and alkalis Magnesium Hydroxide: -In toothpaste to neutralize the acids on our teeth produced by bacteria Ammonia Solution: - Used for cleaning glass windows