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Acids, Alkalis and Indicators

Acids, Alkalis and Indicators. Prepared by Mdm RY Leow The Chinese High School. Acids. What causes the sour taste in these beverages?. The presence of citric acid. Some Common Acids. Organic acids are found in living things. Which of the acids listed above are organic acids?

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Acids, Alkalis and Indicators

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  1. Acids, Alkalis and Indicators Prepared by Mdm RY Leow The Chinese High School

  2. Acids • What causes the sour taste in these beverages? The presence of citric acid.

  3. Some Common Acids • Organic acids are found in living things. • Which of the acids listed above are organic acids? • Hydrochloric acid is an mineral acid (inorganic acid) and is commonly found in science laboratories.

  4. Acids 1 All solutions of acids contain hydrogen ions,H+ 2 Examples of acids commonly found in the laboratories. • Hydrochloric acid (HCl) • Sulphuric acid (H2SO4) • Nitric acid (HNO3) • Ethanoic acid (CH3COOH)

  5. Physical properties of acidic solutions Note: All acids only show acidic properties in the presence of water! Concentrated acids are corrosive.

  6. Physical properties of acidic solutions • Acids taste sour. • Acids turn blue litmus paper red but have noeffect on red litmus paper. • They have pH less than 7. • They are good electrical conductors. *All acids can only show their acidic properties in the presence of water.

  7. metal + acid salt + hydrogen eg Mg + 2HCl MgCl2 + H2 Mg + H2SO4 MgSO4 + H2 Chemical properties of acids 1. Dilute acids react with some metals (K, Na, Ca,Mg, Zn, Fe) to produce hydrogen gas. *Dilute acids do not react with copper, silver, gold

  8. acid + carbonate carbon dioxide gas +salt + water White precipitate is formed 2HCl + CaCO3 CO2 + CaCl2 + H2O Chemical properties of acids a salt, water and carbon dioxide. 2. An acid reacts with a carbonate to produce Carbon dioxide gas is bubbled into limewater

  9. acid + base salt + water HCl + NaOH NaCl + H2O HNO3 + KOH KNO3 + H2O H2SO4 + Ca(OH)2 CaSO4 + 2H2O H2SO4 + CuO CuSO4 + H2O Chemical properties of acids 3. An acid reacts with a baseto form a salt and water only. The reaction between an acid and a base to form a salt and water only is called neutralisation

  10. Hydrochloric acid Sulphuric acid Nitric acid Ethanoic acid Citric acid Cleaning metallic surfaces before they are painted or coated with other metals Used as an electrolyte in car batteries making fertilisers, and plastics Making fertilisers and explosives Preserving food and cooking Making health salts Some Uses of Acids

  11. Alkalis • Many household products such as toothpaste, soap and detergents contain alkalis. Click the picture for uses of alkalis.

  12. Alkalis 1All solutions of alkalis contain hydroxide ions, OH - 2 Examples of common alkalis found in the laboratories are Sodium hydroxide solution NaOH Potassium hydroxide solution KOH Calcium hydroxide solution Ca(OH)2 Ammonia solution NH3.H2O

  13. Physical Properties of Alkaline solutions *All alkalis can only show their alkaline properties in the presence of water. • Strong alkalis are corrosive liquids.

  14. Physical Properties of alkaline solution • Alkalis taste bitter. • They feel soapy. • They turn red litmus paper blue but have no effect on blue litmus paper. • 4. Alkalis are good electrical conductors. • 5. They have pH greater than 7.

  15. ammonia gas, salt and water. alkali + ammonium salt salt + water + ammonia gas NaCl + H2O + NH3 a salt and water. alkali + acid salt + water KCl + H2O Chemical Properties of Alkalis 1. An alkali reacts with an ammonium salt to produce e.g. NaOH + NH4Cl • An alkali neutralises an acid to form e.g. KOH + HCl

  16. Alkalis Alkalis Common names Uses Sodium hydroxide caustic soda Making soap, washing powder, drain cleaner Potassium hydroxide caustic potash Making dyes for fabric and paint removers Calcium hydroxide slaked lime Reducing acidity of soil and making mortar Aqueous ammonia Making fertilisers and (Ammonia solution) household cleaning liquids

  17. Indicators • Indicators are dyes which change colour with the acidity or alkalinity of a solution. • Some common indicators are (litmus, methyl orange, phenolphthalein, universal indicator)

  18. pH scale The pH scale is a range of numbers from 0 to 14, which indicates how acidic or alkaline a substance is.

  19. pH scale Other indicator such as pH paper can be used A pH meter is an electronic device that can be use to measure the acidity or the alkalinity of solutions very effectively. (a) pH meter being used to measure the pH of water in swimming pool (b) pH meter is used to measure pH of the soil

  20. Neutralisation 1 Neutralisation occurs when an acid neutralises a base or an alkali to form salt and water. (An indicator can be use to find the pH 7 of the solution) *acid + base salt + water H2SO4 + MgO MgSO4 + H2O *acid + alkali salt + water HNO3 + KOH KNO3 + H2O • Acid and alkali are reactants. • salt and water are products.

  21. Neutralisation 2 Example of everyday uses of neutralisation • Shampoo (a mild alkali) and conditioner (a mild acid) • Toothpaste (alkaline) neutralises acids produced by bacteria • wasp sting (alkaline) is treated with vinegar to relieve pain • Excess acid in the soil is neutralised by adding slaked lime (calcium hydroxide)

  22. Salts • Salts are metal compounds that can be made from acids. * All acids contain hydrogen. *When the hydrogen in an acid is replaced by a metal, we get a salt. nitric acid nitrates hydrochloric acid chlorides sulphuric acid sulphates

  23. Preparation of Salts 1 The four methods of preparing salts are: (a) precipitation of an insoluble salt (mixing) HCl + AgNO3 AgCl + HNO3 (b) neutralisation of an acid with a base (excess insoluble oxide or hydroxide) CuO + H2SO4CuSO4 + H2O (c) neutralisation of an acid with an alkali (soluble hydroxide) HCl + KOH KCl + H2O (d) reaction of an acid with excess insoluble carbonate CuCO3 + 2HClCuCl2+ H2O + CO2

  24. Flowchart to decide which method to use Start No (a) PRECIPITATION METHOD Mix solutions of two soluble salts to precipitate an insoluble salt. eg NaCl + AgNO3 AgCl + NaNO3 Is the salt soluble? Yes React (b) acid with metal oxide or (c) acid with alkali or(d) acid with metal carbonate Are all reactants soluble in water? Yes (c) Mix acid with alkali to produce salt and water eg HCl + NaOH NaCl + H2O No (b)Mix acid and excess metal oxide or (d) excess metal carbonate to produce salt? eg CuO + H2SO4 CuSO4 + H2O MgCO3 + H2SO4 MgSO4 +H2O+CO2

  25. Salts Soluble Insoluble All sodium, potassium and ammonium salts All nitrates All chlorides except lead(II) chloride and silver chloride. All sulphates except lead(II) sulphate, barium sulphate and calcium sulphate sodium carbonate, All other carbonates potassium carbonate and ammonium carbonate

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