Chemistry - Acids and Alkalis


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This presentation was tailored to meet the GCE 'O' Level Chemistry (Pure) syllabus.

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Chemistry - Acids and Alkalis

  1. 1. This presentation was produced by the Sciencedepartment of Temasek Secondary School.Redistribution or reproduction of this resource isprohibited by copyright regulations.
  2. 2. Acids and AlkalisPhysical and Chemical Properties
  3. 3. Today’s LessonWhat is an acid?Examples of acidsWhat is an alkali?Examples of alkalis
  4. 4. Acids around usLactic acidCarbonic acidFormic acidEthanoicacid
  5. 5. Acids around usMalic acid Tartaric acidCitric acidWhat is commonamong all these acids?
  6. 6. Properties of Acids1. Acids have sour taste.2. Acids are corrosive.3. Acids dissolve in water to form solutionswhich conduct electricity.
  7. 7. Acids in the LaboratoryHydrochloricacid, HClSulfuric acid,H2SO4Nitric acid, HNO3STRONG acidsNEVER EVER TASTEACIDS IN THE LAB!
  8. 8. Acids in Foodo Citric acid (in lemons)o Ethanoic acid (in vinegar)o Carbonic acid (in soft drinks)o Tartaric acid (in grapes)o Malic acid (in apples)o Lactic acid (in yoghurt)Weakorganic acidsfound in foodThese acids are safe to consume! 
  9. 9. An acid is a substance which produceshydrogen ions when it is dissolved in water.The hydrogen ions give an acid its acidicproperties.Acids only behave as acids when they aredissolved in water.What is an Acid?
  10. 10. What is an Acid?Video showing dissociation of hydrogen chloride, HCl in water: (play until about 26s)
  11. 11. How is an Acid Formed?Molecules of hydrogen chloride gasBefore dissolving in water…H Cl
  12. 12. How is an Acid Formed?Ions of dilute hydrochloric acidAfter dissolving in water…This process is called ionisation.
  13. 13. Examples of IonisationH2SO4 (aq) 2H+(aq) + SO42-(aq)Sulfuric acid Hydrogen ions Sulfate ionsHCl (aq) H+(aq) + Cl-(aq)Hydrochloric acid Hydrogen ions Chloride ionsHNO3(aq) H+(aq) + NO3-(aq)Nitric acid Hydrogen ions Nitrate ionsDo you notice a difference between the ionisationof hydrochloric acid and sulfuric acid?
  14. 14. Examples of IonisationH2SO4 (aq) 2H+(aq) + SO42-(aq)HCl (aq) H+(aq) + Cl-(aq)HNO3(aq) H+(aq) + NO3-(aq)The properties and reactions of acids are due tothe presence of these hydrogen ions, H+(aq).
  15. 15. TAKE NOTENOT all substances that containhydrogen are acids.For example,•NH3 (ammonia) contains hydrogen but it is notan acid.•H2 (hydrogen) is also not an acid.
  16. 16. Alkalis around usAlkalis around usDetergentShampoo SoapAntacid ToothpasteWhat is commonamong all thesealkalis?
  17. 17. Properties of Alkalis1. Alkalis have bitter taste.2. Alkalis have soapy feel.3. Alkalis dissolve in water to form solutionswhich conduct electricity.
  18. 18. Alkalis in the LaboratorySodiumhydroxide, NaOHPotassiumhydroxide, KOH
  19. 19. Alkalis in the LaboratoryAqueous ammonia,NH3 (aq)Calcium hydroxide,Ca(OH)2NEVER EVER TASTEALKALIS IN THE LAB!
  20. 20. • An alkali is a substancewhich produceshydroxide ions when it isdissolved in water.• The hydroxide ions,OH-(aq) give an alkali itsalkaline properties.• Alkalis only behave asalkalis when they aredissolved in water.What is an Alkali?
  21. 21. An acid is a substance which produces hydrogenions when it is dissolved in water.SummaryWhat is an acid?Hydrochloric acid, sulfuric acid, nitric acid,ethanoic acid, citric acid …Examples of acids?
  22. 22. An alkali is a substance which produceshydroxide ions when it is dissolved in water.SummaryWhat is an alkali?Sodium hydroxide, potassium hydroxide,calcium hydroxide, aqueous ammoniaExamples of alkalis?
  23. 23. Today’s LessonEffect of acids and alkalis on litmuspaperReactions of acids and alkalis usingword equations
  24. 24. Indicatorso An indicator is a substance which changes colourdepending on whether the solution tested is acidic oralkaline.o There are many types of indicators, including theuniversal indicator and litmus indicator.
  25. 25. Litmus Indicatoro Litmus paper exists in two colours, red and blue.
  26. 26. Litmus IndicatorAcids turn blue litmus paper red.Red litmus paper remains red.What about red litmus paper in acid?
  27. 27. Litmus IndicatorAlkalis turn red litmus paper blue.Blue litmus paper remains blue.What about blue litmus paper in alkali?
  28. 28. Litmus IndicatorA solution is tested with apiece of red litmus paperand the paper stays red.Sue says that the solution isacidic.Marcus says he is not sureand that the solution shouldalso be tested with a pieceof blue litmus paper.Who is correct? Marcus!
  29. 29. Reactions of Acids and Alkalis3 important reactions1.ACIDS + METALS (SOME)2.ACIDS + CARBONATES3.ACIDS + ALKALIS
  30. 30. Acids + MetalsAcids react with some metals to form a salt andhydrogen gas.hydrochloricacid magnesiummagnesiumchloridehydrogengas+  +sulfuric acid magnesiummagnesiumsulfatehydrogengas+  +1Acid + Metal  Salt + Hydrogen gas
  31. 31. Acids + Metals The type and name of salt depends on the acid used.Reaction with• Hydrochloric acid • Sulfuric acid • Nitric acid Chloride saltsSulfate saltsNitrate salts
  32. 32. Acids + MetalsAcids react with some metals to form a salt andhydrogen gas.Some metals which can react with acids are magnesium,aluminium, zinc and iron.Explosive reactions occur when using reactive metals likelithium, sodium and potassium.Exception:Unreactive metals such as copper and silver do not reactwith dilute acids.
  33. 33. Acids + MetalsHow to test for hydrogen gas? Place a lighted splint in the presence of the gas. If hydrogen is present, the lighted splint will beextinguished with a ‘pop’ sound.
  34. 34. Acids + MetalsVideo:
  35. 35. Acids + CarbonatesAcids react with carbonates to form a salt, carbondioxide gas and water.2hydrochloricacidsodiumcarbonatesodiumchloridecarbondioxidegas+  +nitric acid calciumcarbonatecalciumnitrate+ water+carbondioxidegas+ water+Acid + Carbonate  Salt + Carbon dioxide gas + Water
  36. 36. Acids + CarbonatesHow to test for carbon dioxide gas? Bubble the gas through limewater. Carbon dioxide forms a white precipitate withlimewater.
  37. 37. Acids + CarbonatesHow to test for carbon dioxide gas? Bubble the gas through limewater. Carbon dioxide forms a white precipitate withlimewater.LimewaterBubble carbondioxide gas Whiteprecipitateformed
  38. 38. Acids + AlkalisAcids react with alkalis to form a salt and water only.The reaction between acids and alkalis is calledneutralisation.3Acid + Alkali  Salt + Water
  39. 39. Acids + AlkalisExamples:hydrochloricacidsodiumhydroxidesodiumchlorideWater+  +sulfuric acidpotassiumhydroxidepotassiumsulfateWater+  +
  40. 40. Summary3 important reactions1. Acid + Metal2.Acid + Carbonate3.Acid + Alkali Salt + Hydrogen gas Salt + Water + Carbon dioxide gas Salt + Water