Acids and bases (alkalis) - PowerPoint PPT Presentation

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Acids and bases (alkalis)

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  1. Acids and bases (alkalis)

  2. Hazard signs to learn… h i flammable Corrosive Harmful Irritant

  3. Acids and bases • Acid- A substance that produces hydrogen ions when it dissolves in water. • Bases- Compounds which react with acids to neutralise them • Alkali- A soluble base • Ion – a charged atom (+ or -), gains or loses an electron

  4. pH scale • Indicators can be used to find out whether a solution is acid, alkaline or neutral • Universal Indicator can be used to find the pH of a solution • Acid – red, pH less than 7 • Neutral – green, pH = 7 • Alkali – blue, pH greater than 7 pH scale

  5. Universal Indicator and the pH scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Strong acid Strong alkali Neutral Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is: 0-14 Stomach acid Lemon juice Water Soap Baking powder Oven cleaner

  6. pH scale pH scale

  7. pH scale pH scale

  8. pH scale pH scale

  9. Neutralisation • Acids react with alkaline solutions to form a salt and water • Hydrochloric acid produces chlorides • Nitric acid produces nitrates • Sulphuric acid produces sulphates • Ammonia can dissolve in water to produce an alkaline solution. This can be neutralised with acids to produce ammonium salts • Indicators can monitor neutralisation reactions Neutralisation

  10. Neutralisation Acid + alkali Salt + water E.g. hydrochloric acid + sodium hydroxide sodium chloride + water An acid and alkali will neutralise each other (if the correct amounts are used:

  11. Neutralisation – Hydrochloric acid Neutralisation

  12. Neutralisation – Sulphuric acid Neutralisation

  13. Neutralisation – Nitric acid Neutralisation

  14. Neutralisation – Fertiliser Neutralisation

  15. Neutralisation • Acids and bases neutralise each other. • Acids form H+ (aq) ions in water • Alkalis form OH- (aq) ions in water • Acid + alkali  salt + water • H+ + OH-  H2O

  16. Useful acid-alkali reactions 1) Hydrochloric acid is used in the stomach to help _______. If we eat too many “rich” foods our stomachs create too much ____ – this is called ______. This acid needs to be neutralised by taking indigestion tablets. 2) Soil is naturally acidic, mainly due to acid ____. This can have bad effects on ____ and vegetable growth, so the excess acid may need to be neutralised with an _____ . Words – plant, digestion, indigestion, alkali, rain, acid

  17. Quiz on acids and alkalis Acid, alkali or both??? • This a pH of less than 7 • This would turn Universal indicator green • This is often used in cleaners or soap • This would turn Universal Indicator red • Sodium hydroxide is a common ____________ • This would feel soapy on your skin • This could be a corrosive • This will turn universal indicator purple • This would taste sour • Lemon juice and vinegar are examples of weak _____

  18. Copy this diagram Label the stomach Write down a sentence to explain that antacids neutralise excess stomach acid.

  19. Reaction of Metals and Acid Reaction of Metals and Acid

  20. Metal Oxides & Hydroxides • Transition metal oxides and hydroxides do not dissolve in water. They are called bases • They react with acids to produce salts that are soluble • The excess metal oxide can be filtered off Metal Oxides & Hydroxides

  21. Quiz Quiz