Acids and Alkalis

• Solutions can be acidic, alkaline or neutral.
• Pure water is neutral.
• Vinegar and lemon juice are acids found at home.
• Hydrochloric acid, sulfuric acid and nitric acid are acids found in the lab.
• Baking soda, bleach and indigestion tablets are alkalis found at home.
• Sodium hydroxide and calcium hydroxide are alkalis found in the lab.
• If a substance has the word hydroxide in its name it is an alkali, for example, potassium hydroxide.
• Universal indicator can be used to find out whether a solution is acidic, alkaline or neutral by the colour they turn.
• Other indicators can also be used.
• Plant extracts can be used as indicators, for example, red cabbage is a different colour in different solutions.
• Universal indicator and pH paper are indicators that turn: red in acidic solutions, green in neutral solutions, blue in alkaline solutions.
• Universal indicator/pH paper can be used to find the pH of a solution.
• The pH scale measures how acidic or alkaline a solution is, with acidic solutions having pH values less than 7, neutral solutions having pH = 7, and alkali solutions having pH values greater than 7.
• Very acidic solutions have pH values less than about 2, less acidic solutions have pH values below 7 and above 2, and very alkaline solutions have a high pH above about 12.
• Burning non-metal oxides produces Carbon Dioxide (and often sulfur dioxide), which when dissolved in water, makes an acidic solution.
• Carbon dioxide causes global warming.
• Neutralisation is the process where an acid and alkali react with each other in correct proportions, forming a solution with pH = 7.
• When hydrochloric acid is neutralised using sodium hydroxide, sodium chloride (table salt) is made.
• Solid salt can be obtained in this reaction by evaporating the salt solution.
• Neutralisation has many uses, for example, indigestion (too much stomach acid) can be neutralised using indigestion tablets (an alkali like magnesium hydroxide), wasp stings are alkaline and can be neutralised by using vinegar (an acid), and bee stings are acidic and can be neutralised by using toothpaste (an alkali).
• The neutralisation reaction between an acid and alkali can be represented by a word equation, for example, Hydrochloric acid + sodium hydroxide → sodium chloride + water.
• The above word equation can be represented in a symbol equation, HCl + NaOH → NaCl + H2O.
• There are many different salts, the metal part of the salt comes from the alkali, the non-metal part of the salt comes from the acid.
• Hydrochloric acid make salts called chlorides, Sulfuric acid makes salts called sulfates, Nitric acid makes salts called nitrates.