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Acids and Alkalis

Acids and Alkalis. Grade 10. Acids. Sour Turn litmus red pH less than 7 Dissolve carbonate rocks Corrode metals Conduct electricity. Acids. Acids are substances that give H + ions when added to water. Alkalis. Bitter Turn litmus blue pH greater than 7 Slippery caustic. Alkalis.

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Acids and Alkalis

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  1. Acids and Alkalis Grade 10

  2. Acids • Sour • Turn litmus red • pH less than 7 • Dissolve carbonate rocks • Corrode metals • Conduct electricity

  3. Acids • Acids are substances that give H+ ions when added to water.

  4. Alkalis • Bitter • Turn litmus blue • pH greater than 7 • Slippery • caustic

  5. Alkalis • An alkali is a substance that gives OH- ions when added to water

  6. Neutralizations reactions • Acids and alkalis neutralize each other to form a salt • Example: HCl + NaOHNaCl + H2O • Reactions of acids and alkalis are called neutralization reactions

  7. Neutralization examples • Indigestion is caused by too much amounts of hydrochloric acid in the stomach. • It is cured by indigestion tablets. • Indigestion tablets contain magnesium oxide that neutralises the excess HCl.

  8. Neutralization examples • Fields with acidic soil can be improved by adding lime. • The lime contains calcium hydroxide Ca(OH)2 which is an alkali

  9. Neutralization examples • Lakes affected by acid rain can be neutralized by adding lime.

  10. Strong vs. weak • Strong = complete dissociation • Example, when HCl is dissolved in water, all of it becomes H+ + Cl-HCl, H2SO4, HNO3 HCl H+ + Cl- H2SO4  2H+ + SO4 2- • Weak = incomplete dissociation • Acetic acid (vinegar) is a weak acid • CH3COOH, small amounts dissociate into H+ and CH3COO-CH3-COOH, H2CO3, HF • CH3COOH CH3COO- + H+ • More dissociation = stronger acid

  11. Strong bases dissociate completely • NaOH, KOH, Ca(OH)2 NaOH Na+ + OH- • Weak bases dissociate partially • Mg(OH)2, Fe2O3, NH4OH NH4OH NH4+ + OH- • If a base is soluble in water, it is called an alkali. NaOH, KOH

  12. Strong and weak bases • Strong bases ionises completely • NaOH Na+ + OH- • NaOH, KOH, Ba(OH)2, Ca(OH)2 • Weak bases ionises partially • Mg(OH)2, CuO, Al2O3, NH4OH • Strong acids have a small pH • strong bases have large pH • Neutral solutions have pH 7 • Smaller the pH, stronger the acid • Larger the pH, stronger the base

  13. Indicators • Indicators are substances that change colourwhen placed in an acid or an alkali. • There are four important indicators: • Methyl orange • Phenolphthalein • Litmus paper • Universal indicator.

  14. Procedure: put 3 cm3 of HCl in a test tube. Add few drops of methyl orange. record your observation.

  15. REACTIONS OF ACIDS • Neutralisation Acid reacts with a base to form salt and water. Base can be a metal oxide or metal hydroxide. Ammonium hydroxide is also a base. • Calcium oxide + Nitric acid  Calcium nitrate + water CaO + HNO3  Ca(NO3)2 + H2O • Copper(II) oxide + Hydrochloric acid  Copper(II)chloride + water CuO + HCl  CuCl2 + H2O • Sodium hydroxide + Sulphuric acid  Sodium sulphate + water 2NaOH + H2SO4  Na2SO4 + 2H2O • Ammonium hydroxide + hydrochloric acid  Ammonium chloride + water NH4OH + HCl  NH4Cl + H2O

  16. Acid reacts with metals to form salt and hydrogen gas • Most metals react with dilute acids to form salt and hydrogen • Copper, Silver, Gold etc do not react with acids easily because these metals are not reactive. • Magnesium + sulfuric acid  Magnesium sulfate + Hydrogen Mg + H2SO4  MgSO4 + H2 • Zinc + Hydrochloric acid  Zinc chloride + Hydrogen Zn + HCl  ZnCl2 + H2 Acids react with carbonate to form salt, carbon dioxide and water • Sodium carbonate + Hydrochloric acid  Sodium chloride + Carbon dioxide + water Na2CO3 + 2HCl  NaCl + CO2 + H2O • Copper(II) carbonate + sulphuric acid  Copper(II) sulphate + Carbon dioxide + water CuCO3 + H2SO4  CuSO4 + CO2 + H2O

  17. Salts • Salts formed from an acid and a base. • First part of a salt is from the base (+) • Second part from the acid (-) • For example, Sodium chloride is a salt. • Sodium part comes from a base like sodium hydroxide. • Chloride part comes from an acid (hydrochloric acid) • Second part of the salt depends on the acid. • Hydrochloric acid HCl - chloride Cl (-) • Sulphuric acid H2SO4 - sulphate SO4 (2-) • Nitric acid HNO3 - nitrate NO3 (-) • Carbonic acid H2CO3 - carbonate CO3 (2-) • Phosphoric acd H3PO4 - phosphate PO4 (3-)

  18. How to make salts? • Acid react with metal • Example: Making Zinc sulphate. • Take sulphuric acid in a beaker. • Add excess zinc and warm the mixture. • Wait until no more bubbles come out. • Cool the mixture and filter to get rid of excess Zinc. • Take the filtrate in an evaporating dish, heat and evaporate until crystallisation point. • Cool it in room temperature to get the crystals of Zinc sulphate.

  19. Two soluble chemicals • Best example is acid and alkali reaction(neutralisation) and a salt is made. • Example: When hydrochloric acid and potassium hydroxide solution are mixed, we can make Potassium chloride salt. • KOH (aq) + HCl (aq)  KCl (aq) + H2O (l) • First conduct a titration to know what volume of acid and base exactly required for neutralisation. • Then mix acid and base in larger volume in the same ratio you found in the titration for complete neutralisation. • Heat and evaporate the resulting solution until crystallisation. • Cool it to get the crystals of potassium chloride.

  20. Double decomposition or Precipitation. • This method is useful to make a salt which is insoluble in water. • For example to make calcium carbonate salt which is insoluble. Mix solutions of sodium carbonate and calcium chloride; both soluble and the calcium carbonate precipitates. Na2CO3 (aq) + CaCl2 (aq)  CaCO3 (s) + 2NaCl (aq) • When two soluble salt solutions when mixed, the insoluble salt is precipitated out. • The mixture is then filtered and the solid salt is left for drying.

  21. Soluble and insoluble • Following statements help you to identify if a chemical can dissolve in water or not. • All compounds of SODIUM, POTASSIUM and AMMONIUM are solublein water. • All NITRATE compounds are soluble. • All CHLORIDES are solubleexceptSilver chloride and Lead(II) chloride. • All SULPHATES are solubleexceptBarium sulphate and Lead(II) sulphate. • All CARBONATES are insoluble except sodium carbonate, potassium carbonate and ammonium carbonate. • All metal oxides and metal hydroxides are insoluble in water exceptsodium, potassium and calcium oxide/hydroxide.

  22. Soluble or insoluble??? • Sodium carbonate Na2CO3 • Soluble • Copper(II) sulphate CuSO4 • Soluble • Lead(II) chloride PbCl2 • Insoluble • Silver sulphate Ag2SO4 • Soluble • Barium chloride BaCl2 • Soluble • Ammonium sulphate (NH4)2SO4 • Soluble • Iron(III) oxide Fe2O3 • Insoluble

  23. Copper(II) hydroxide Cu(OH)2 • Insoluble • Silver chloride AgCl • Insoluble • Barium sulphate BaSO4 • Insoluble • Lead(II) nitrate Pb(NO3)2 • Soluble • Sulphuric acid H2SO4 • Soluble • Potassium chloride KCl • Soluble • Calcium sulphate CaSO4 • Soluble • Magnesium carbonate MgCO3 • Insoluble

  24. THE END

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