Core & Extension - Acids, Bases & Salts II Salt Preparation.pptx

Igcse notes on acid bases and salts

1. © 2004-05 Dorje Gurung Core & Ext. Acids, Bases & Salts II: Salt Preparation

2. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 2 of 46 Learning Objectives Concepts : Core Salt, filtration, crystallization, titration, indicator, Extension soluble, insoluble, solubility rules, precipitation, Skills : Core Describe the preparation, separation and purification of salts Describe the use of suitable solvent, the techniques of filtration and crystallization as it relates to salt preparation

3. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 3 of 46 Learning Objectives Skills : Extension Construct ionic equations for reactions involving reactions in solution Describe the preparation of insoluble salts by precipitation Suggest a method of making a given salt from suitable starting material, given appropriate information

4. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 4 of 46 Salts Salts are ionic compounds produced during acid reactions. All salts contain a positively charged metal ion and a negatively charged non-metal ion (and therefore are ionic compounds). The most common salts are nitrates, sulfates and chlorides: Salts can be formed from acids. They have two parts, a metal part and a part that comes from an acid. Common salts are: Nitrates from nitric acid Sulfates from sulfuric acid Chlorides from hydrochloric Copper sulfate Sodium chloride SO 4 Cu Metal part from sulfuric acid Cl Na Metal part from hydrochloric acid

5. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 5 of 46 Methods of preparing soluble salts. There are different ways of producing salt solutions. In each case the final solution must be evaporated to so that we end up with the pure dry salt. A. The Filtration method . This method is used the acid is reacted with an insoluble substance (e.g a metal , most metal oxides and carbonates)

6. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 6 of 46 Methods of preparing soluble salts.

7. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 7 of 46 Methods of preparing soluble salts. (g) When the salt has crystallized, separate it from the solvent by filtration. (h) Wash the residue with distilled water to remove any impurities in the salt. (i)Dry the salt between dry filter paper or in an oven. Not all salts can be dried in an oven however. Those that cannot/should not be dried in an oven are the ones that contain water in the crystals such as CuSO 4 • 5H 2 O. The purity of the salt can be determined by testing its melting point. A highly pure salt will melt at its melting point while one that is not very pure will melt at a lower temperature.

8. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 8 of 46 B. The titration or indicator method. This method is used when an acid is reacted with an alkaline solution such as sodium hydroxide

9. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 9 of 46 B. The titration or indicator method.

10. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 10 of 46 B. The titration or indicator method. Note on experimental method: The problem with the method outlined above is that the indicator solution colors the salt. Dry sodium chloride crystals will be green! To overcome this problem, it is common to do the experiment several times under controlled conditions, carefully measuring the amount of acid needed to just neutralize the alkali solution. These results can be used to do a final salt preparation without the indicator. Then the final salt solution can be boiled to evaporate the water and obtain the crystals or most of it boiled and evaporated and then left for the salt to crystallize, and then filter, wash and dry.

11. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 11 of 46 A method for preparing insoluble salts The only way to prepare an insoluble salt is by precipitation. Precipitation involves mixing two salt solutions to produce an insoluble salt or precipitate. When a precipitate is formed, the small solid particles produced in the solution make the solution turn cloudy or milky. For example, suppose you want to make some insoluble silver chloride , AgCl. You will need to mix a soluble silver salt with a soluble chloride salt. All nitrates are soluble so we can use silver nitrate solution. All sodium salts are soluble so we can use sodium chloride solution. The reaction is represented in diagrams on one of the later slides.

12. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 12 of 46 Will a precipitate be formed when two solutions are mixed? To work out whether a solid precipitate will be produced, you can use the following method. Let’s use barium nitrate solution and potassium sulfate solution as an example: Step 1 . Write down the two solutions in words or symbols in two rows, one underneath the other:

13. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 13 of 46 Will a precipitate will be formed when two solutions are mixed? Step 2 . Find the two possible “cross products” by drawing diagonals Step 3 . If either of these cross products is insoluble , it will be produced as a solid precipitate in the solution, and can be separated by filtration.

14. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 14 of 46 Will a precipitate be formed when two solutions are mixed? In this example, barium sulfate is insoluble. Solid barium sulfate will be produced as a precipitate in the beaker. The potassium nitrate remains in solution. Note: Often in exams you are asked to work out which two salt solutions could be mixed to produce a particular insoluble salt such as silver chloride. You can use the above method “in reverse” to solve these problems. However all these questions will depend on whether you know which salts are soluble and which salts are insoluble. You must learn the table that appears on one of the later slides.

15. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 15 of 46 Ionic Equation The equation for the reaction is Ba(NO 3 ) 2 (aq) + K 2 SO 4 (aq)  BaSO 4 (s) + 2KNO 3 (aq) Notice then that the overall reaction is between barium ions and sulfate ions that are floating around in the two solutions. Since the chemicals are in solution, they can be better represented in the following manner Ba 2+ (aq) + NO 3 - (aq) + 2K + (aq) + SO 4 2- (aq)  BaSO 4 (s) + 2K + (aq) + NO 3 - (aq) Notice that K + (aq) and NO 3 - (aq) do not undergo any change, and can be removed from the equation. The actual change that the chemicals undergo can be summarized by writing out what’s called an ionic equation . Ba 2+ (aq) + SO 4 2- (aq)  BaSO 4 (s)

16. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 16 of 46 Precipitation Reaction in Diagrams The equation for the reaction is AgNO 3 (aq) + NaCl (aq)  AgCl (s) + NaNO 3 (aq) Ionic equation is therefore. Ag + (aq) + Cl - (aq)  AgCl (s)

17. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 17 of 46 Salt preparation: Precipitation Reaction

18. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 18 of 46 Reaction of Ba(NO 3 ) 2 ( aq ) and K 2 CrO 4 ( aq ) Reactant Solutions to the left: (a) Ba(NO 3 ) 2 ( aq ) and (b) K 2 CrO 4 ( aq ) Bottom left, on mixing, (a) before reaction, (b) at the end of reaction. Bottom right, appearance of reaction mixture at the end of reaction.

19. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 19 of 46 Solubility Rules: The solubles All sodium potassium salts are soluble. ammonium All nitrates are soluble All chlorides are soluble except……. Silver chloride (white) Lead chloride (white) All iodides are soluble except……. Silver iodide (creamy yellow) Lead iodide (bright yellow) All sulfate are soluble Silver sulfate except……. Barium sulfate (white) Calcium sulfate Lead sulfate

20. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 20 of 46 Solubility Rules: The insolubles All carbonates are insoluble except……… sodium carbonate potassium carbonate ammonium carbonate (of course…duh!) All hydroxides are insoluble except…….. sodium hydroxide potassium hydroxide ammonium hydroxide (of course…duh!) and calcium hydroxide is slightly soluble All (metal) oxides are insoluble except…….. sodium oxide potassium oxide (of course…duh again!) (Ammonium oxide does not exist!)

21. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 21 of 46 Salt Preparation Flowchart Is the salt soluble? Is the base soluble? Use acid reactions Yes Use precipitation Mix solutions Filter, wash and dry No Use indicator method Add base to acid until just neutral, evaporate and crystallize Yes Use excess solid + acid Filter off excess solid, evaporate and crystallize No

22. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 22 of 46 Preparation of Salts: Summary You now know several methods of preparing salts. To summarize, they can be prepared by reacting the following pairs of chemicals: 1.A metal and an acid metal + acid  salt + hydrogen gas The salt formed depends on the metal and the acid 2.A metal oxide and an acid Metal oxide + acid  salt + water The salt formed depends on the metal oxide and the acid This method does not apply to the preparation of group 1 metal salt from their oxide. 3. A metal hydroxide and an acid metal hydroxide + acid  salt + water The salt formed depends on the hydroxide and the acid

23. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 23 of 46 Preparation of Salts: Summary 4. A metal carbonate (or hydrogen carbonate) and an acid metal carbonate + acid  salt + water + carbon dioxide The salt formed depends on the metal carbonate and the acid 5. If the salt to be prepared is insoluble in water, two solutions of soluble salts which give the insoluble salt can be used to produce it. The salt that results can be separated from the solution either by re-crystallizing the dissolved salt and filtration, after evaporating some of the water, or by simply filtering the insoluble salt obtained. To produce a chloride, hydrochloric acid needs to be used. To produce a sulfate sulfuric acid is required. To produce a nitrate nitric acid is required. After filtration, the salt is dried by pressing it between two pieces of filter paper or by placing it in the oven.

24. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 24 of 46 Practice Questions: Preparation of salt using an acid Name a suitable acid to make the following salts. 1.Calcium nitrate 2.Potassium sulfate 3.Magnesium chloride 4.Magnesium bromide A reminder: Salts from acids can be made by reacting the appropriate acid with a suitable alkali or metal. Answers: Nitric acid sulfuric acid, Hydrochloric acid, Hydrobromic acid

25. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 25 of 46 Choose your starting materials: Choose appropriate reagents to make the salts named below: 1.Sodium chloride 2.Potassium nitrate 3.Zinc chloride 4.Nickel sulfate 5.Potassium sulfate There is more than one correct answer in each case – can you work out ALL the possibilities? Answers on the next slide.

26. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 26 of 46 Answers 1.Hydrochloric acid plus sodium oxide or sodium hydroxide or sodium carbonate or sodium hydrogencarbonate. 2.Nitric acid plus potassium oxide or potassium hydroxide or potassium carbonate. 3.Hydrochloric acid plus zinc oxide or zinc hydroxide or zinc metal or zinc carbonate. 4.sulfuric acid plus nickel metal or nickel hydroxide or nickel oxide or nickel carbonate. 5.sulfuric acid plus potassium oxide or potassium hydroxide or potassium carbonate. Why should you NOT use potassium or sodium metal with an acid to make a salt?

27. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 27 of 46 Now for the difficult bits: For the salts below you need to decide on the starting materials and write a word equation to represent the reaction. 1.Potassium chloride 2.Magnesium sulfate 3.Aluminum chloride. There is more than one way to make each salt.

28. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 28 of 46 Answers: 1. Potassium oxide or potassium hydroxide with hydrochloric acid. potassium oxide + hydrochloric acid  potassium chloride + water potassium hydroxide + hydrochloric acid  potassium chloride + water 2. Magnesium metal or magnesium oxide or magnesium hydroxide with sulfuric acid. magnesium + sulfuric acid  magnesium sulfate + hydrogen magnesium oxide + sulfuric acid  magnesium sulfate + water magnesium hydroxide + sulfuric acid  magnesium sulfate + water 3. Aluminum metal or aluminum oxide or aluminum hydroxide with nitric acid. aluminum + nitric acid  aluminum nitrate + hydrogen aluminum oxide + nitric acid  aluminum nitrate + water aluminum hydroxide + nitric acid  aluminum nitrate + water

29. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 29 of 46 Practice Questions 1. N04/2/3. Read the following instructions for the preparation of hydrated nickel(II) sulphate (NiSO 4  7H 2 O), then answer the questions which follow. 1 Put 25 cm 3 of dilute sulphuric acid in a beaker. 2 Heat the sulphuric acid until it is just boiling then add a small amount of nickel(II) carbonate. 3 When the nickel(II) carbonate has dissolved, stop heating, then add a little more nickel carbonate. Continue in this way until nickel(II) carbonate is in excess. 4 Filter the hot mixture into a clean beaker. 5 Make the hydrated nickel(II) sulphate crystals from the nickel(II) sulphate solution. The equation for the reaction is NiCO 3 (s) + H 2 SO 4 (aq)  NiSO 4 (aq) + CO 2 (g) + H 2 O(l) (a) What piece of apparatus would you use to measure out 25 cm 3 of sulphuric acid? [1]

30. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 30 of 46 Practice Questions (b) Why is the nickel(II) carbonate added in excess? [1] (c) When nickel(II) carbonate is added to sulphuric acid, there is a fizzing. Explain why there is a fizzing. [1] (d) Draw a diagram to describe step 4. You must label your diagram. [3]

31. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 31 of 46 Practice Questions (e) After filtration, which one of the following describes the nickel(II) sulphate in the beaker? Put a ring around the correct answer. crystals filtrate precipitate water [1] (f) Explain how you would obtain pure dry crystals of hydrated nickel(II) sulphate from the solution of nickel(II) sulphate. [2]

32. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 32 of 46 Practice Questions 2. N99/2/6. (d)(iii) Sodium chloride can be made by adding an acid to an alkali. Name an acid and alkali you can use to make sodium chloride. acid ............................................................................................. alkali ............................................................................................ [2] (iv) Starting with this acid and alkali, describe how you can obtain sodium chloride crystals. [2]

33. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 33 of 46 Practice Questions 3. N99/6/2. Barium carbonate is insoluble in water but barium nitrate is soluble. Outline how you could obtain from a mixture of barium carbonate and barium nitrate: [6] (a) a pure dry sample of barium carbonate; (b) crystals of barium nitrate.

34. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 34 of 46 Practice Questions 4. J99/6/5. A student investigated the reaction between solutions of sodium hydroxide ( A and B ) and two different acids. Hydrochloric acid and sulphuric acid were used. Experiment 1 By using a measuring cylinder, a 25 cm 3 sample of dilute hydrochloric acid was added into a plastic cup and the temperature of the solution measured and recorded. By using another measuring cylinder, a 25 cm 3 sample of the aqueous sodium hydroxide labelled A was added to the acid. The mixture was stirred and the maximum temperature measured and recorded. Use the thermometer diagrams to read the temperatures and record the values in the table. Universal Indicator paper was used to measure the pH of the final mixture which is recorded in the table.

35. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 35 of 46 Practice Questions Experiment 2 Experiment 1 was repeated using 25 cm 3 of aqueous sodium hydroxide labelled B . Use the thermometer diagrams to read the temperatures and record the values in the table. Experiment 3 Experiment 1 was repeated using aqueous sodium hydroxide labelled A but dilute sulfuric acid instead of hydrochloric acid. Use the thermometer diagrams to read the temperatures and record the values in the table. Experiment 4 Experiment 1 was repeated but using aqueous sodium hydroxide labelled B and dilute sulphuric acid instead of hydrochloric acid. Use the thermometer diagrams to read the temperatures and record the values in the table (which appears on the next slide).

36. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 36 of 46 Table of results [4]

37. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 37 of 46 Practice Questions The equations for the reactions are given below. HCl + NaOH  NaCl + H 2 O H 2 SO 4 + 2NaOH  Na 2 SO 4 + 2H 2 O (a) Plot the results of the experiments as a bar chart on the grid below. [3] (b) (i) Compare the temperature changes in Experiments 1 and 3. [1] Temperature difference/ °C Experiment number

38. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 38 of 46 Practice Questions (ii) Explain the pH values obtained in Experiment 1, [1] in Experiment 2. [1] (c) What type of chemical reaction occurred when the acids reacted with sodium hydroxide? [1] (d) (i) Compare the temperature changes in Experiments 2 and 4. [1] (ii) Suggest an explanation for the difference in the temperature changes. [1]

39. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 39 of 46 Practice Questions (e) Predict what the temperature of the reaction mixture in Experiment 4 would have been after 1 hour. Explain your answer. [2] (f) Suggest one change that could be made to the apparatus used in the experiments to obtain more accurate results. [1] Experiment 5 Experiment 1 was repeated using 50 cm 3 of the aqueous sodium hydroxide labelled A . Use the thermometer diagrams to read the temperatures and record the values in the table (which appears on the next slide).

40. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 40 of 46 Practice Questions Explanation [2] (g) (i) In which of the two experiments, 1 or 5, was the temperature change larger? Suggest an explanation for this difference. Experiment:

41. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 41 of 46 Practice Questions (h) Predict the temperature rise expected if Experiment 3 was repeated using 50 cm 3 of the sodium hydroxide labelled A . temperature rise explanation [3]

42. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 42 of 46 Practice Questions 5. N04/3/2. The salt copper(II) sulphate can be prepared by reacting copper(II) oxide with sulphuric acid. Complete the list of instructions for making copper(II) sulphate using six of the words below. blue cool dilute filter saturated sulphate white oxide Instructions 1 Add excess copper(II) oxide to sulphuric acid in a beaker and boil it. 2 to remove the unreacted copper(II) oxide. 3 Heat the solution until it is . 4 the solution to form coloured crystals of copper (II) . [6]

43. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 43 of 46 Practice Questions 5. J04/3/4.(a) Insoluble compounds are made by precipitation. (i) Complete the word equation for the preparation of zinc carbonate. [2] (ii) Complete the following symbol equation. Pb(NO 3 ) 2 + ……. NaCl → …………………………. + …………………… [2] (iii) Write an ionic equation for the precipitation of the insoluble salt, silver(I) chloride. [2] (b) 2.0 cm 3 portions of aqueous sodium hydroxide were added to 4.0 cm3 of aqueous iron(III) chloride. Both solutions had a concentration of 1.0 mol/dm . After each addition, the mixture was stirred, centrifuged and the height of the precipitate of iron(III) hydroxide was measured. The results are shown on the following graph.

44. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 44 of 46 Practice Questions (i) Complete the ionic equation for the reaction. Fe 3+ …..OH  → ……………………………… [1]

45. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 45 of 46 Practice Questions (ii) On the same grid, sketch the graph that would have been obtained if iron(II) chloride had been used instead of iron(III) chloride? [2] (iii) If aluminium chloride had been used instead of iron(III) chloride, the shape of the graph would be different. How are the shapes of these two graphs different and why? difference in shape reason for difference [2]

46. Core & Extension Acids, Bases & Salts: Salt Preparation Slide 46 of 46 Practice Questions 6. N02/3/1b. There are three ways of making salts from sulphuric acid. titration using a burette and indicator precipitation by mixing the solutions and filtering neutralisation of sulphuric acid using an excess of an insoluble base Complete the following table of salt preparations. method Reactant 1 reactant 2 salt titration sulphuric acid sodium sulphate neutralisation sulphuric acid zinc sulphate precipitation sulphuric acid barium sulphate sulphuric acid copper(II) oxide copper(II) sulphate