Answer these questions in the back of your

Answer these questions in the back of your book. l l l l What is a chemical reaction? What is a physical reaction? What is an acid? What is an alkali? What is a base? What does neutral mean? What does neutralisation mean?

Objectives l l To be able to test chemicals and decide if they are acid/alkali/basic/neutral. To be able to record chemical reactions in word and symbol equations.

Facts about acids l l l Weak acids, like lemon juice and vinegar, taste sour. Strong acids are corrosive and can “eat away” at metal, stone and flesh! Acids turns blue litmus paper red. Acids have a p. H of less than 7. Acids can be neutralized with alkalis.

Facts about alkalis l l l Alkalis feel soapy and are used in household cleaning materials. Strong alkalis are caustic. Alkalis turn red litmus paper blue. Alkalis have a p. H of more than 7. Alkalis can be neutralized with acids.

p. H scale http: //www. phschool. com/atschool/science_activity_library/images/acids_and_bases_phscale. jpg

Testing the p. H of chemicals Practical

There a wide variety of indictors Universal Indicator Litmus Phenolphthalein Methyl orange

Neutralisation l l Compounds of alkali metals called salts can be made by reacting solutions of their hydroxides, which are alkaline, with acids. The general equation is:

Names of salts l When we replace the hydrogen in an acid by a metal, we get a salt. Acid Name in salt Example Hydrochloric Sulphuric Nitric

Symbol equations l l No atoms are created or destroyed in a chemical reaction. There should be the same number of atoms of each type of element each side of the equation. Nitric acid + potassium hydroxide potassium nitrate + water

State symbols l (s) l (l) l (g) l (aq)

You try l l l Measure 20 cm 3 of hydrochloric acid into a beaker. Add a few drops of UI soln. Using a pipette, add sodium hydroxide to the acid. Observe please note that an indicator can be used to show when acidic and alkaline solutions have completely reacted to produce a neutral salt solution. Write a word and balanced symbol equation for the reaction (can you add state symbols? ).

Plenary – true or false? 1. 2. 3. 4. 5. Bases and alkalis are the same. Acids have a p. H of less than 7. Neutralisation reactions always produce water. Symbol equations must always be balanced. (aq) means liquid.

Homework – complete the following: l l l Hydrochloric acid + sodium hydroxide Sulphuric acid + potassium hydroxide Nitric acid + Lithium hydroxide Hydrochloric acid + potassium hydroxide Sulphuric acid + sodium hydroxide