The document provides information about qualitative analysis (QA), which is a process chemists use to identify unknown substances. It describes the five main steps of QA: making preliminary observations, carrying out tests in a given order, recording observations, drawing conclusions, and identifying the unknown. It also provides details on identifying common gases, cations, and anions through a series of chemical tests and observations of color changes, precipitate formation, gas evolution and more.

1. Identify gases – H 2 , O 2 , CO 2 , NH 3 , SO 2 , C l 2 and H 2 O Identify cations – Pb 2+ , A l 3+ , Ca 2+ , Zn 2+ , Fe 3+ , Fe 2+ , NH 4 +, Cu 2+ Identify anions – CO 3 2- , SO 4 2- , SO 3 2- , NO 3 - , Br - , I - , C l - Qualitative Analysis Chapter 21 L EARNING O UTCOMES

2. What is QA? QA stands for Qualitative Analysis. It is a process that a chemist carries out to identify an unknown substance. The analysis will identify the cation(s) and anion(s) present in the unknown sample. Qualitative Analysis Chapter 21

3. The QA Process Make preliminary observations about the unknown substance. Carry out tests in the order given. Make observations and record them in a suitable format. Draw conclusions from the observations Identify the unknown substance. Five important steps Qualitative Analysis Chapter 21

4. Preliminary Observations The colour tells us about the possible cations present in the substance. What is the colour of the substance? - Is it white, colourless, blue, yellow or some other colour? What is the nature of the substance? - Is it crystalline, metallic or in powder form? Qualitative Analysis Chapter 21

5. Qualitative Analysis Chapter 21 Preliminary Observations Colour Possible identity of substance White (colourless) Sodium (Na + ), potassium(K + ), ammonium (NH 4 + ) Black Copper(II) oxide (CuO), Iron(II) oxide (FeO) Blue/green Copper(II), Cu 2+ or Iron(II), Fe 2+ Yellowish/brown Iron(III), Fe 3+ Greyish, metallic Metals: Zinc, Iron, Magnesium, Aluminium

6. Is it soluble in water? The solubility tells us about the possible anions present in the substance. Insoluble Soluble Qualitative Analysis Chapter 21 Preliminary Observations

7. Table of Solubility Qualitative Analysis Chapter 21 Preliminary Observations Salt Solubility in water Carbonates Insoluble except those of sodium, potassium and ammonium Chlorides Soluble except those of lead(II) and silver. Nitrates All are soluble. Sulphates Soluble except those of lead(II) and Barium

8. Solid : 1 small spatula, just enough to cover the bottom of a test tube. Liquid : About 2 cm-depth in a test tube. Reagent : Pour slowly and carefully down the side of the test tube. Or Quantity of Substance use a dropper and drop it slowly into the test tube. Qualitative Analysis Chapter 21

9. Using a Bunsen burner Heating Liquids Use a gentle non-luminous flame (air-hole half open) for heating a liquid in a test tube. Move the test tube up and down the flame and stop the heating as soon as the liquid starts to boil. Heating Solids When heating a solid, place it in a dry, clean test tube. Heat gently at first, then strongly. For your own safety, wear protective goggles and point the test tube away from yourself and others when heating. Qualitative Analysis Chapter 21

10. Recording Results Record all your observations immediately or you may forget. Record the change in colour before and after the test. Record the formation of a precipitate - its colour and whether it is soluble in excess (extra amount) of the reagent. Before After Ppt. is soluble White ppt. formed Qualitative Analysis Chapter 21

11. Recording Results formulae for names of chemicals ppt. for precipitate aq. for aqueous solution You may use phrases and short forms: Record the liberation of a gas by noting if any bubbles (effervescence) are seen. State the test you carried out to identify the gas, and the result you obtained. Qualitative Analysis Chapter 21

12. Quick Check 1 State the colour of the following substances: (a) Sodium carbonate: __________ (b) Potassium sulphate: _________ (c) Calcium chloride: ___________ (d) Iron(II) sulphate: ___________ (e) Iron(III) sulphate: ___________ (f) Copper(II) sulphate: _________ (g) Copper(II) carbonate: ________ (h) Copper(II) oxide: ___________ Solution Qualitative Analysis Chapter 21

13. Quick Check 1 (cont’d) State whether the following substances are soluble or insoluble in water: (a) Sodium carbonate: ________________ (b) Magnesium carbonate: _____________ (c) Calcium chloride: _________________ (d) Zinc sulphate: ____________________ (e) Calcium carbonate: ________________ (f) Lead(II) chloride (g) Lead(II) nitrate: ___________________ Solution Qualitative Analysis Chapter 21

14. State the colour of the following substances: (a) Sodium carbonate: white (b) Potassium sulphate: white (c) Calcium chloride: white (d) Iron(II) sulphate: greenish-yellow (e) Iron(III) sulphate: reddish-brown (f) Copper(II) sulphate: blue (g) Copper(II) carbonate: green (h) Copper(II) oxide: black Return Qualitative Analysis Chapter 21 Solution to Quick Check 1

15. 2. State whether the following substances are soluble or insoluble in water: (a) Sodium carbonate: soluble (b) Magnesium carbonate: insoluble (c) Calcium chloride: soluble (d) Zinc sulphate: soluble (e) Calcium carbonate: insoluble (f) Lead(II) chloride: i nsoluble (g) Lead(II) nitrate: soluble Return Qualitative Analysis Chapter 21 Solution to Quick Check 1 (cont’d)

16. Detection of gases How do we tell if a gas is given off? (a) Effervescence - Bubbles of gas are seen in the solution. (b) Fumes - White fumes are seen when a substance is heated. Qualitative Analysis Chapter 21

17. Testing for gases Look here Not here Note the smell of the gas by holding the mouth of the tube a few cm from the nose and fanning the gas towards you. Note the colour of the gas by looking through the side of the test tube above the substance or solution . Qualitative Analysis Chapter 21

18. Testing for gases Testing with litmus paper Wet the litmus papers (one piece of blue and one piece of red) with distilled water , then hold it near the mouth of the test tube. Do not allow the litmus paper to touch the sides of the test tube or drop it into the reagent, as it will react with the reagent and give a false result. Qualitative Analysis Chapter 21

19. Table: Testing for gases Qualitative Analysis Chapter 21 Gas Colour Odour Litmus paper (moist) Oxygen Colourless Odourless No effect Hydrogen Colourless Odourless No effect Carbon dioxide Colourless Odourless Blue to red Ammonia Colourless Pungent (like urine) Red to blue Chlorine Light greenish-yellow Pungent (Like swimming pool water) Blue to red then white Sulphur dioxide Colourless Pungent (like burning match) Blue to red

20. Test for gases with lighted splint POP Place a lighted (burning) splint near the mouth of the test tube. (A) If the lighted splint extinguishes with a “pop” sound , then the gas is hydrogen . Qualitative Analysis Chapter 21

21. Test for gases with lighted splint (B) If the lighted splint burns more brightly , then the gas may be oxygen . In this case, you can confirm its identity by using a glowing splint. (D) If the burning splint is extinguished , then the gas may be carbon dioxide , water vapour, or some other gases. (C) Insert a glowing splint (no fire) into the mouth of the test tube. If the glowing splint is relighted (rekindled) and burns brightly, then the gas is oxygen. flame extinguished Qualitative Analysis Chapter 21

22. Testing for carbon dioxide Note The carbon dioxide should not be passed for too long, as the limewater will turn clear again (due to the formation of soluble calcium hydrogen carbonate), giving a false impression of a negative test. Pour limewater (calcium hydroxide solution) into a test tube until it reaches a depth of 2 cm from the bottom of the test tube. Stopper the reacting test tube with a delivery tube and pass the gas into the limewater. If a white ppt. is formed, the gas is carbon dioxide. Qualitative Analysis Chapter 21

23. Quick Check 2 Solution Complete the table below. Qualitative Analysis Chapter 21 Test Observation Inference 1. Heat a little of solid X strongly in a test tube. Gas evolved extinguishes a burning splint. It forms a white ppt. with limewater 2. Heat the solution P gently and test for any gas evolved. A pungent gas was given off. It turned moist red litmus to blue. 3. Heat solid Q strongly in a test tube. Test for any gas evolved. A colourless and odourless gas is given off. The gas relights a glowing splint. 4. Add solid X to the solution Z and warm. Test for any gas evolved. Bubbles of gas were given off. The burning splint is extinguished with a “pop” sound.

24. Return Qualitative Analysis Chapter 21 Solution to Quick Check 2 Test Observation Inference 1. Heat a little of solid X strongly in a test tube. Gas evolved extinguished a burning splint. It formed a white ppt. with limewater. Gas produced is carbon dioxide. CO 3 2- may be present. 2. Heat the solution P gently and test for any gas evolved. A pungent gas was given off. It turned moist red litmus to blue. Gas evolved is NH 3. NH 4 + may be present. 3. Heat solid Q strongly in a test tube. Test for any gas evolved. A colourless and odourless gas is given off. The gas relit a glowing splint. Gas evolved is oxygen. 4. Add solid X to the solution Z and warm. Test for any gas evolved. Bubbles of gas were given off. Gas extinguished a lighted splint with a ‘pop’ sound. Gas evolved is hydrogen. Solid X may be a metal and solution Z may be an acid.

25. Identification of cations Aluminium, Al 3+ Iron(II), Fe 2+ Calcium, Ca 2+ Iron(III), Fe 3+ Zinc, Zn 2+ Ammonium, NH 4 + Copper(II), Cu 2+ Lead(II), Pb 2+ Qualitative Analysis Chapter 21 The cations can be identified using sodium hydroxide solution and aqueous ammonia (ammonium hydroxide). The cations react with the hydroxide ions in the alkali to form insoluble metal hydroxides . These hydroxides appear as precipitates . The cations can be identified from: (a) the colour of the precipitate, (b) the solubility of the precipitate in excess of the reagent.

26. Identification of cations The unknown substance must be in solution form . If not, a solution must be made as follows: - soluble salt : dissolve in distilled water. - insoluble salt : dissolve in a little dilute nitric acid. Test using sodium hydroxide solution: (a) Add sodium hydroxide solution drop by drop to the unknown solution. (b) Observe the precipitate formed and note its colour . (c) Add more sodium hydroxide solution (excess). Shake the test tube and examine whether the precipitate dissolves in excess sodium hydroxide solution. Ppt. formed Colourless/ soluble Qualitative Analysis Chapter 21

27. Identification of cations d) If no precipitate is formed, warm the mixture and test for ammonia gas . Ammonia gas has a pungent smell (like urine) and turns moist red litmus paper blue. This confirms the presence of ammonium ion (NH 4 + ) in the unknown. Qualitative Analysis Chapter 21

28. Test for cations (Table 1) Qualitative Analysis Chapter 21 C ation Add a little NaOH (aq) Add excess NaOH (aq) Al 3+ White ppt ppt. dissolves to form colourless solution Ca 2+ White ppt ppt. remains insoluble Zn 2+ White ppt ppt. dissolves to form colourless solution Pb 2+ White ppt ppt. dissolves to form colourless solution Cu 2+ Blue ppt ppt. remains insoluble Fe 2+ Dirty-green ppt ppt. remains insoluble (turns brown on standing) Fe 3+ Reddish-brown ppt ppt. remains insoluble NH 4 + No ppt. When warmed, NH 3 gas given off. No change

29. Identification of cations (using aq. NH 3 ) Test using aqueous ammonia: (a) Add ammonia solution drop by drop to the unknown solution. (b) Observe the precipitate formed and note its colour . (c) Add more ammonia solution (excess). Shake the test tube and examine whether the precipitate dissolves in excess ammonia solution. Qualitative Analysis Chapter 21 Ppt. formed Colourless/ soluble

30. Test for cations (Table 2) Qualitative Analysis Chapter 21 Cation Add a little NH 3 (aq) Add excess NH 3 (aq) Al 3+ White ppt. Ppt. remains insoluble Ca 2+ No ppt (or very slight ppt.) No change Zn 2+ White ppt. Ppt. dissolves to form colourless solution Pb 2+ White ppt. Ppt. remains insoluble Cu 2+ Blue ppt. Ppt. dissolves to form dark blue solution. Fe 2+ Dirty-green ppt. Ppt. remains insoluble (turns brown on standing) Fe 3+ Reddish-brown ppt. Ppt. remains insoluble NH 4 + No ppt. No change

31. Quick Check 3 What are some of the preliminary observations that you can make on an unknown sample, before carrying out any test? When a solid is insoluble in water, what acid is used? Why? Which cations will produce a white precipitate with sodium hydroxide solution and aqueous ammonia? Which cation will produce a white precipitate which is soluble in both aqueous ammonia and sodium hydroxide ? Which cations will produce a white precipitate which is soluble in excess sodium hydroxide, but not in excess aqueous ammonia ? Which cation will produce a white precipitate with sodium hydroxide solution but not with aqueous ammonia ? Which cation will produce a blue precipitate with sodium hydroxide? Which cation will produce a deep blue solution with aqueous ammonia? Qualitative Analysis Chapter 21 Solution

32. Return Observe the colour and texture of the unknown sample, and determine if it is soluble in water. Dilute nitric acid is used to dissolve the solid because nitrates of all metals are soluble in water. Aluminium, lead and zinc ions Zinc ions Aluminium and lead ions Calcium ion Copper(II) ion Copper(II) ion Qualitative Analysis Chapter 21 Solution to Quick Check 3

33. Identification of Anions Carbonate, CO 3 2- Chloride, Cl - Iodide, I - Sulphate, SO 4 2 - Nitrate, NO 3 - Each anion has a different specific test. For carbonate , you need not make a solution to carry out the test. For other anions , you must make a solution of the unknown in distilled water only . *If you use dilute nitric acid to dissolve it, you are introducing the nitrate ions into the unknown. Qualitative Analysis Chapter 21

34. Test for carbonate Qualitative Analysis Chapter 21 Test Observation Inference Add some dilute hydrochloric acid (or nitric acid) to the unknown. Pass the gas into limewater. Bubbles of gas are given off. The gas forms a white ppt. with limewater. The gas is CO 2 . Therefore, CO 3 2 - is present in the unknown.

35. Test for chloride Qualitative Analysis Chapter 21 Test Observation Inference Add a little silver nitrate solution to the unknown. Add dilute nitric acid to the above, then shake. A white ppt is formed. White ppt is insoluble in nitric acid. White ppt is AgCl. Therefore, Cl - is present.

36. Test for iodide Qualitative Analysis Chapter 21 Test Observation Inference Add a little lead(II) nitrate solution to the unknown. Add dilute nitric acid to the above, then shake. A yellow ppt is formed. Yellow ppt is insoluble in nitric acid. Yellow ppt is PbI 2 . Therefore, I - is present in the unknown.

37. Test for sulphate Qualitative Analysis Chapter 21 Test Observation Inference To the unknown solution, add a little barium chloride (or barium nitrate) solution. Then add some dilute hydrochloric acid (or nitric acid) and shake. A white ppt is formed. White ppt is insoluble in hydrochloric acid (or nitric acid). White ppt is Ba SO 4 . Therefore, SO 4 2- is present in the unknown.

38. Test for nitrate Qualitative Analysis Chapter 21 Test Observation Inference To the unknown, add a little sodium hydroxide solution. Then add a few pieces of aluminium foil (or a spatula of aluminium powder). Warm the mixture gently. Test for ammonia gas evolved. A pungent gas is given out. The gas turns moist red litmus paper blue. NH 3 gas is produced. NO 3 - is present in the unknown.

39. Summary of Tests for Anions (Table 3) Qualitative Analysis Chapter 21 Anion Test Observation Carbonate, CO 3 2- Add dilute HCl. Test for gas evolved. Effervescence. Gas evolved formed white ppt. with limewater. Chloride, Cl - Add AgNO 3 solution, followed by dilute HNO 3 White ppt. insoluble in HNO 3 Iodide, I - Add Pb(NO 3 ) 2 solution, followed by dilute HNO 3 Yellow ppt. insoluble in HNO 3 Sulphate, SO 4 2- Add BaCl 2 solution, followed by dilute HCl. White ppt. insoluble in HCl Nitrate, NO 3 - Add NaOH solution, then Al foil. Warm gently. NH 3 gas evolved turned red litmus blue

40. Quick Check 4 Solution When we add aqueous silver nitrate to an unknown, what anion(s) are we looking for? When we add aqueous barium chloride or barium nitrate to an unknown, what anion(s) are we looking for? When we are told to add dilute hydrochloric acid to an unknown, what anion are we testing for and what should we get ready? When we are told to add sodium hydroxide and aluminium powder to an unknown solution, what anion are we testing for and what should we get ready? When we add silver nitrate or barium chloride solution to an unknown, what reagent should we also add? What is the reason for this? Qualitative Analysis Chapter 21

41. Return 1. Chloride, Cl - or iodide, I - 2. Sulphate, SO 4 2- 3. Carbonate, CO 3 2- . We should get a delivery tube and test tube containing some limewater ready. 4. Nitrate, NO 3 - . We should get a piece of moist red litmus paper ready. 5. We should add some dilute nitric acid. This is to exclude any carbonate present from forming a precipitate. Qualitative Analysis Chapter 21 Solution to Quick Check 4

42. Quick Check 5 Conclusion: S1 is _________ . Complete the table below and identify the substance S1. Solution Qualitative Analysis Chapter 21 Test Observation Inference 1. Dissolve a sample of S1 in distilled water and divide it into 3 portions. S1 dissolved to form a pale blue solution. 2. To the first portion, add aqueous sodium hydroxide slowly until in excess. A blue ppt was formed. Ppt was insoluble in excess NaOH. 3. To the second portion, add aqueous ammonia slowly until in excess. A blue ppt was formed. Ppt dissolved to form a deep blue solution. 4. To the third portion, add barium chloride solution, then dilute HCl. A white ppt was formed. Ppt was insoluble in HCl.

43. Solution to Quick Check 5 Conclusion: S1 is copper(II) sulphate . Complete the table below and identify the substance S1. Solution Qualitative Analysis Chapter 21 Test Observation Inference 1. Dissolve a sample of S1 in distilled water and divide it into 3 portions. S1 dissolved to form a pale blue solution. Cu 2+ may be present 2. To the first portion, add aqueous sodium hydroxide slowly until in excess. A blue ppt was formed. Ppt was insoluble in excess NaOH. Cu 2+ is present. 3. To the second portion, add aqueous ammonia slowly until in excess. A blue ppt was formed. Ppt dissolved to form a deep blue solution. Cu 2+ is confirmed. 4. To the third portion, add barium chloride solution, then dilute HCl. A white ppt was formed. Ppt was insoluble in HCl. SO 4 2- is present.