1. A cids Bases & Salts (Bases) an e-learning series by ycs

2. Learning Objectives By the end of the lesson, pupils would be able to –Name the common bases –Define the meaning of an alkali –Explain the importance of water as solvent –Describe the physical properties of alkali –Describe the chemical reaction of bases

3. Types of Bases Metal oxides –magnesium oxide, MgO –Iron(III) oxide, Fe 2 O 3 Metal hydroxides –sodium hydroxide, NaOH –Copper(II) hydroxide, CuO

4. Definition A substance when dissolved in water produces hydroxide ions as the only negative ions NaOH (aq)  Na + (aq) + OH - (aq)

5. Releasing the OH - ions Water is needed for the release of OH - ions. –e.g. If the dry ammonia gas, NH 3 (g), is passed through a piece of red litmus, there would be no change in colour.

6. Alkalis If a base is soluble in water, it is called an alkali. –e.g. potassium oxide & sodium oxide are highly soluble in water. The resulting solution would be an alkaline solution.

7. Properties of Alkalis Bitter taste Soapy feeling Turns red litmus blue Changes the colour of indicators like universal indicator, methyl orange..etc

8. Chemical Reactions Bases/Alkalis react with acids to form a salt and water...ie. neutralisation MgO(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 O(l) NaOH(aq) + 2HNO 3 (aq)  NaNO 3 (aq) + H 2 O(l)

9. Alkalis when warmed with ammonium salt will produce a salt, water and ammonia gas. –NaOH(aq) + 2NH 4 NO 3 (aq)  NaNO 3 (aq) + H 2 O(l) + NH 3 (g) Chemical Reactions

10. Ammonium chloride is warmed with sodium hydroxide. The vapour produced turned damped red litmus blue. Why must the litmus be damped? Explain the change in colour on the litmus paper. Nutshell Activity