An Introduction to Acids & Bases VCE Chemistry Unit 2: Environmental Chemistry Area of Study 1 – Water

Acids & Bases – An Introduction

Acids are commonly used in our homes. Many foods contain acids to enhance flavour or as a preservative: vinegar is a solution of ethanoic acid; orange and lemon juices contain citric acid; soft drinks contain carbonic acid in solution. The sour taste of these substances is due to their acid content. The word ‘acid’ is derived from the Latin word acidus, meaning sour. In industry, solutions of acids are used extensively to produce a wide range of products, such as fertilisers, drugs, explosives and plastics. Acids are also used to clean metal surfaces before use. Acids

In general, acids have the following properties in common. They: Change the colour of some indicators. They turn litmus red! Tend to be corrosive Taste sour React with bases Have a relatively low pH Acids

Bases also have characteristic properties. In solution, they can sometimes taste bitter and have a slippery feel. They react with some plant extracts to counteract the effect of acids. If a base is continually added to a solution of an acid, the characteristic properties of the acid eventually disappear. The acid and base are said to neutralise each other. Many cleaning agents used in the home, such as washing powders and oven cleaners, contain bases. Solutions of ammonia are used as floor cleaners, and sodium hydroxide is the major active ingredient in oven cleaner. Bases are effective cleaners because they react with fats or oils to produce water-soluble soaps. Bases

In general, bases have the following properties in common. They: Turn litmus blue Have a slippery feel Are caustic React with acids Have a relatively high pH Bases

Acids and bases should be treated with caution and you should avoid these solutions coming in contact with your skin or eyes. As well as wearing protective clothing, you should also show respect when handling these materials by acting in a safe manner that will not cause an accident or spill. 1.Wear safety glasses. 2.Wear a laboratory coat. 3.Label bottles and containers. 4.When diluting acids, add the acid to the water (not the water to the acid). Safety with Acids & Bases

One of the characteristic properties of acids and bases is their ability to change the colour of certain plant extracts. Litmus is a dye obtained from lichen and turns red in the presence of acids. Such plant extracts are called indicators. They are often extracted from plant dyes, and are themselves acids or bases. Indicators change from one colour in acid to another in basic solution. Common indicators include methyl orange, phenolphthalein and litmus. Acid – Base Indicators

Acid-Base & Neutralisation Reactions When an acid reacts with a base to form a salt and water, a neutralisation reaction occurs: Acid + Base  Salt + Water Hydrochloric acid reacts with the base sodium hydroxide to form sodium chloride and water: HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)

Other Common Acid-Base Reactions 1.Acid + Metal  Salt + Hydrogen 2HCl (aq) + Mg (s)  MgCl 2 (aq) + H 2 (g) 2.Acid + Metal Carbonate  Salt + Carbon Dioxide + Water 2HCl (aq) + Na 2 CO 3 (aq)  2NaCl (aq) + CO 2 (g) + H 2 O (l) 3.Acid + Metal Hydrogen Carbonate  Salt + Carbon Dioxide + Water HCl (aq) + NaHCO 3 (aq)  NaCl (aq) + CO 2 (g) + H 2 O (l) 4.Acid + Metal Oxide  Salt + Water 2HCl (aq) + CuO (s)  CuCl 2 (aq) + H 2 O (l) 5.Acid + Metal Hydroxide  Salt + Water H 2 SO 4 (aq) + 2NaOH (aq)  Na 2 SO 4 (aq) + H 2 O (l)