TAILIEUCHUNG - Ebook Complete chemistry for cambridge IGCSE (2nd edition): Part 2
(BQ) Part 2 book "Complete chemistry for cambridge IGCSE" has contents: Acids and bases, the periodic table, the behaviour of metals, making use of metals, some non metals and their compounds, organic chemistry, in the lab,.and other contents. | Acids and bases Acids and alkalis Acids One important group of chemicals is called acids: You have probably seen these acids in the lab. They are all solutions of pure compounds in water. They can be dilute, like these, or concentrated. They must be handled carefully, especially the concentrated solutions, because they are corrosive. They can eat away metals, skin, and cloth. You can tell if something is an acid, by its effect on litmus. Litmus is a purple dye. It can be used as a solution, or on paper. Acids turn litmus red. But some acids are not so corrosive, even when concentrated. These are called weak acids. Ethanoic acid is one example. It is found in vinegar. ! Remember: acid turns litmus red Some common acids The main acids you will meet in chemistry are: hydrochloric acid sulfuric acid nitric acid ethanoic acid HCl (aq) H2SO4 (aq) HNO3 (aq) CH3COOH (aq) But there are many others. For example, lemon and lime juice contain citric acid, ant stings contain methanoic acid, and fizzy drinks contain carbonic acid, formed when carbon dioxide dissolves in water. blue litmus paper goes red in an acid solution pink litmus paper goes blue in an alkaline solution Testing with litmus paper. Alkalis There is another group of chemicals that also affect litmus, but in a different way. They are the alkalis. Alkalis turn litmus blue. Like acids, they must be handled carefully. They too can burn skin. Some common alkalis The pure alkalis are solids – except for ammonia, which is a gas. They are used in the lab as aqueous solutions. The main ones you will meet are: sodium hydroxide potassium hydroxide calcium hydroxide ammonia 148 NaOH (aq) KOH (aq) Ca(OH)2 (aq) NH3 (aq) Common laboratory alkalis. The solution of calcium hydroxide is called limewater. Acids and bases Indicators Indicator Litmus is called an indicator, because it indicates whether something is an acid or an alkali. This table shows two others. All show a .
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