ACIDS, BASES & SALTS A guide for GCSE students

1. ACIDS, BASES & SALTS A guide for GCSE students 2010 SPECIFICATIONS KNOCKHARDY PUBLISHING

2. ACIDS, BASES & SALTS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards. Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at... www.knockhardy.org.uk All diagrams and animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any commercial work.

3. ACIDS, BASES & SALTS • CONTENTS • Acidity and alkalinity • Indicators • pH • Acids • General methods for making salts • Making salts from metal oxides • Making salts from metal carbonates • Making salts from metals • Making salts from alkalis – by titration • Making insoluble salts – by precipitation • Questions

4. ACIDITY AND ALKALINITY • water is a neutral substance • when substances dissolve in water, the solution may become… ACIDIC or ALKALINE or stay NEUTRAL

5. ACIDITY AND ALKALINITY • water is a neutral substance • when substances dissolve in water, the solution may become… ACIDIC or ALKALINE or stay NEUTRAL • hydrogen ions H+(aq) make solutions acidic • hydroxide ions OH¯(aq) make solutions alkaline • solutions with equal numbers of H+(aq) and OH¯(aq) are neutral

6. INDICATORS • show by a colour change if a solution is acidic, alkaline or neutral • some can even show how acidic or how alkaline a solution is

7. INDICATORS • show by a colour change if a solution is acidic, alkaline or neutral • some can even show how acidic or how alkaline a solution is • well known indicators include…

8. INDICATORS • show by a colour change if a solution is acidic, alkaline or neutral • some can even show how acidic or how alkaline a solution is • well known indicators include… LITMUS acidic RED alkaline BLUE neutral PURPLE

9. INDICATORS • show by a colour change if a solution is acidic, alkaline or neutral • some can even show how acidic or how alkaline a solution is • well known indicators include… LITMUS acidic RED alkaline BLUE neutral PURPLE

10. INDICATORS • show by a colour change if a solution is acidic, alkaline or neutral • some can even show how acidic or how alkaline a solution is • well known indicators include… LITMUS acidic RED alkaline BLUE neutral PURPLE UNIVERSAL acidic RED alkaline VIOLET neutral GREEN

11. INDICATORS • show by a colour change if a solution is acidic, alkaline or neutral • some can even show how acidic or how alkaline a solution is • well known indicators include… LITMUS acidic RED alkaline BLUE neutral PURPLE UNIVERSAL acidic RED alkaline VIOLET neutral GREEN

12. pH SCALE

13. pH SCALE Used to compare the relative acidity (and alkalinity) of solutions. The value is related to the concentration of H+ions, in solution.

14. pH SCALE Used to compare the relative acidity (and alkalinity) of solutions. The value is related to the concentration of H+ions, in solution. “The greater the concentration of hydrogen ions in solution, the lower the pH”

15. pH SCALE Used to compare the relative acidity (and alkalinity) of solutions. The value is related to the concentration of H+ions, in solution. “The greater the concentration of hydrogen ions in solution, the lower the pH” <— 0 1 23 4 5 678 9 10 1112 13 14 —> stronglyweaklyneutralweakly strongly acidicacidicalkalinealkaline

16. pH SCALE Used to compare the relative acidity (and alkalinity) of solutions. The value is related to the concentration of H+ions, in solution. “The greater the concentration of hydrogen ions in solution, the lower the pH” <— 0 1 23 4 5 678 9 10 1112 13 14 —> stronglyweaklyneutralweakly strongly acidicacidicalkalinealkaline HCl CH3COOH H2O NH3 NaOH HYDROCHLORIC ETHANOIC AMMONIA SODIUM ACID ACID HYDROXIDE

17. pH SCALE Used to compare the relative acidity (and alkalinity) of solutions. The value is related to the concentration of H+ions, in solution. “The greater the concentration of hydrogen ions in solution, the lower the pH” <— 0 1 23 4 5 678 9 10 1112 13 14 —> stronglyweaklyneutralweakly strongly acidicacidicalkalinealkaline HCl CH3COOH H2O NH3 NaOH HYDROCHLORIC ETHANOIC AMMONIA SODIUM ACID ACID HYDROXIDE Acidic solutions pH < 7 Alkaline solutions pH > 7 Neutral solutions pH = 7

18. pH SCALE Despite what some people think, the pH scale is not restricted to between 0 and 14. It extends beyond those values, but is not as relevant; e.g. the pH of the dilute HCl and H2SO4 found on the laboratory shelves is -0.3 and -0.6 respectively.

19. pH SCALE Despite what some people think, the pH scale is not restricted to between 0 and 14. It extends beyond those values, but is not as relevant; e.g. the pH of the dilute HCl and H2SO4 found on the laboratory shelves is -0.3 and -0.6 respectively. Weak acids have higher pH values than stronger ones of the same concentration. Ethanoic acid CH3COOH has a larger pH than hydrochloric acid HCl of the same concentration.

20. MEASURING pH Indicator Add a few drops of universal (full-range) indicator to the solution and compare the colour against a chart. The colour you “see” depends not only on how many drops of indicator you add but also on your perception of colour.

21. MEASURING pH Indicator Add a few drops of universal (full-range) indicator to the solution and compare the colour against a chart. The colour you “see” depends not only on how many drops of indicator you add but also on your perception of colour. pH meters Electrical/electronic devices which measure the conductivity of the solution. Having calibrated the apparatus against a solution of known pH, you place the probe in any solution and read off the pH value on a scale or digital read-out.

22. ACIDS

23. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can be arranged into groups according to how many H+ ions they produce from each molecule

24. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can be arranged into groups according to how many H+ ions they produce from each molecule ACID SALTS ION EXAMPLE hydrochloric HCl chloride Cl¯ NaCl nitric HNO3 nitrate NO3¯ NaNO3 ethanoic CH3COOH ethanoate CH3COO¯ CH3COONa THE ABOVE ARE MONOPROTIC (MONOBASIC) ACIDS

25. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can be arranged into groups according to how many H+ ions they produce from each molecule ACID SALTS ION EXAMPLE hydrochloric HCl chloride Cl¯ NaCl nitric HNO3 nitrate NO3¯ NaNO3 ethanoic CH3COOH ethanoate CH3COO¯ CH3COONa THE ABOVE ARE MONOPROTIC (MONOBASIC)ACIDS sulphuric H2SO4 hydrogensulphate HSO4¯ NaHSO4 sulphate SO42- Na2SO4 “carbonic” H2CO3 hydrogencarbonate HCO3¯ NaHCO3 carbonate CO32- Na2CO3 THE ABOVE ARE DIPROTIC (DIBASIC)ACIDS

26. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can also arranged into groups according to the extent they split into ions when put in water.

27. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can also arranged into groups according to the extent they split into ions when put in water. STRONG ACIDSCOMPLETELY dissociate (split up) into ions e.g. sulphuric, hydrochloric, nitric

28. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can also arranged into groups according to the extent they split into ions when put in water. STRONG ACIDS COMPLETELY dissociate (split up) into ions e.g. sulphuric, hydrochloric, nitric WEAK ACIDS PARTIALLY dissociate (split up) into ions e.g. ethanoic, citric, carbonic

29. ACIDS Definition ACIDS ARE PROTON (H+ ion) DONORS Categories Acids can also arranged into groups according to the extent they split into ions when put in water. STRONG ACIDS COMPLETELY dissociate (split up) into ions e.g. sulphuric, hydrochloric, nitric WEAK ACIDS PARTIALLY dissociate (split up) into ions e.g. ethanoic, citric, carbonic This means that if you take similar concentrations of HCl and CH3COOH, the concentration of H+ ions in the solution of CH3COOH will be less as only a few of its molecules will have split up into ions. Its pH will consequently be higher.

30. ACIDS Reactions The hydrogen ions produced by acids can be replaced by other positive ions (metal ions or ammonium ions) to produce salts. This occurs when dilute acids react with metals, oxides of metals, hydroxides of metals, carbonates, hydrogencarbonates and ammonia.

31. ACIDS ReactionsThe hydrogen ions produced by acids can be replaced by other positive ions (metal ions or ammonium ions) to produce salts. This occurs when dilute acids react with metals, oxides of metals, hydroxides of metals, carbonates, hydrogen carbonates and ammonia. HYDROCHLORIC ACID SODIUMHYDROXIDE AMMONIA SODIUM CHLORIDE AMMONIUM CHLORIDE ZINC COPPEROXIDE MAGNESIUM CARBONATE ZINC CHLORIDE COPPER CHLORIDE MAGNESIUM CHLORIDE

32. ACIDS ReactionsThe hydrogen ions produced by acids can be replaced by other positive ions (metal ions or ammonium ions) to produce salts. This occurs when dilute acids react with metals, oxides of metals, hydroxides of metals, carbonates, hydrogen carbonates and ammonia. SULPHURIC ACID SODIUMHYDROXIDE AMMONIA SODIUM SULPHATE AMMONIUM SULPHATE ZINC COPPEROXIDE MAGNESIUM CARBONATE ZINC SULPHATE COPPER SULPHATE MAGNESIUM SULPHATE

33. MAKING SALTS - POSSIBILITIES MIX SOLUTIONS OF TWO SUITABLE SALTS TO PRECIPITATE THE INSOLUBLE SALT IS THE SALT SOLUBLE OR INSOLUBLE? FILTER OFF THE SALT INSOLUBLE SOLUBLE ADD EXCESS METAL TO THE ACID THEN FILTER OFF THE EXCESS METAL DOES THE METAL REACT WITH DILUTE ACIDS? IS IT SAFE? YES YES NO NO ADD EXCESS METAL OXIDE OR METAL CARBONATE TO ACID THEN FILTER OFF THE EXCESS SOLID CRYSTALLISE THE SALT FROM THE FILTRATE NO IS THE METAL OXIDE OR CARBONATE SOLUBLE IN WATER? YES TITRATE THE METAL HYDROXIDE WITH ACID

34. PREPARATION OF SOLUBLE SALTS Salts can be made by NEUTRALISATION of acids; • acidic solutions contain aqueous hydrogen ions H+(aq) • sulphuric acid produces a sulphate • hydrochloric acid produces a chloride • nitric acid produces a nitrate

35. PREPARATION OF SOLUBLE SALTS Salts can be made by NEUTRALISATION of acids; • acidic solutions contain aqueous hydrogen ions H+(aq) • sulphuric acid produces a sulphate • hydrochloric acid produces a chloride • nitric acid produces a nitrate Other chemicals are formed, it depends on what is neutralising the acid. OXIDES SALT + WATER HYDROXIDES SALT + WATER CARBONATES SALT + CARBON DIOXIDE + WATER METALS SALT + HYDROGEN (not all metals are suitable; some are too reactive; others are not reactive enough)

36. PREPARATION OF SALTS BY NEUTRALISATION

37. MAKING SALTS – FROM INSOLUBLE BASES MIX SOLUTIONS OF TWO SUITABLE SALTS TO PRECIPITATE THE INSOLUBLE SALT IS THE SALT SOLUBLE OR INSOLUBLE? FILTER OFF THE SALT INSOLUBLE SOLUBLE ADD EXCESS METAL TO THE ACID THEN FILTER OFF THE EXCESS METAL DOES THE METAL REACT WITH DILUTE ACIDS? IS IT SAFE? YES YES NO NO ADD EXCESS METAL OXIDE OR METAL CARBONATE TO ACID THEN FILTER OFF THE EXCESS SOLID CRYSTALLISE THE SALT FROM THE FILTRATE NO IS THE METAL OXIDE OR CARBONATE SOLUBLE IN WATER? YES TITRATE THE METAL HYDROXIDE WITH ACID

38. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide

39. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 1 Place dilute acid in a beaker and warm it gently without letting it boil (reactions are faster at higher temperatures)

40. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 1 Place dilute acid in a beaker and warm it gently without letting it boil (reactions are faster at higher temperatures) • Remove the heat

41. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 1 Place dilute acid in a beaker and warm it gently without letting it boil (reactions are faster at higher temperatures) • Remove the heat • 3. Carefully and slowly add small amounts of the solid while stirring (most reactions of this type are exothermic i.e. they give off energy - the energy released would make the solution boil over)

42. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 1 Place dilute acid in a beaker and warm it gently without letting it boil (reactions are faster at higher temperatures) • Remove the heat • 3. Carefully and slowly add small amounts of the solid while stirring (most reactions of this type are exothermic i.e. they give off energy - the energy released would make the solution boil over) • 4. Continue adding the solid until no more dissolves (this ensures all the acid has been used - it is easier to filter off excess solid than extract excess acid).

43. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide 5. Filter the solution into an evaporating dish to remove excess solid

44. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 5. Filter the solution into an evaporating dish • to remove excess solid • Transfer the dish to a tripod and carefully warm the mixture to remove some of the water. Too much heat will drive off any water of crystallisation.

45. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 5. Filter the solution into an evaporating dish • to remove excess solid • Transfer the dish to a tripod and carefully warm the mixture to remove some of the water. Too much heat will drive off any water of crystallisation. • When some of the water has been evaporated, let the solution to cool; (allows crystallisation takes place)

46. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 5. Filter the solution into an evaporating dish • to remove excess solid • Transfer the dish to a tripod and carefully warm the mixture to remove some of the water. Too much heat will drive off any water of crystallisation. • When some of the water has been evaporated, let the solution to cool; (allows crystallisation takes place) • When sufficient crystals have appeared, filter them off, wash with a little cold water and transfer them to a filter paper. Place another filter paper over the top and press gently to help remove some of the water.

47. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble oxide • 5. Filter the solution into an evaporating dish • to remove excess solid • Transfer the dish to a tripod and carefully warm the mixture to remove some of the water. Too much heat will drive off any water of crystallisation. • When some of the water has been evaporated, let the solution to cool; (allows crystallisation takes place) • When sufficient crystals have appeared, filter them off, wash with a little cold water and transfer them to a filter paper. Place another filter paper over the top and press gently to help remove some of the water. • 9. Allow the crystals to dry naturally in air. (heat can cause the crystals to decompose and lose their water of crystallisation)

48. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble carbonate

49. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble carbonate The method used is similar to that used with acids and metal oxides. The main differences is that it is not necessary to use heat and that carbon dioxide gas is given off so you have to make sure the solution doesn’t effervesce (fizz) too much.

50. PREPARATION OF SALTS BY NEUTRALISATION Acid with excess insoluble carbonate The method used is similar to that used with acids and metal oxides. The main differences is that it is not necessary to use heat and that carbon dioxide gas is given off so you have to make sure the solution doesn’t effervesce (fizz) too much. • Place dilute acid in a beaker