C21 qualitative analysis

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  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • Chemistry Expression 01/28/13 SNP Panpac Pte Ltd.
  • C21 qualitative analysis

    1. 1. Chapter 21Qualitative Analysis LEARNING OUTCOMES  Identify gases – H2, O2, CO2, NH3, SO2, Cl2 and H2O  Identify cations – Pb2+, Al3+, Ca2+, Zn2+, Fe3+, Fe2+, NH4+, Cu2+  Identify anions – CO32-, SO42-, SO32-, NO3-, Br-, I-, Cl-
    2. 2. Chapter 21Qualitative AnalysisWhat 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.
    3. 3. Chapter 21Qualitative Analysis The QA ProcessFive important steps1. Make preliminary observations about the unknown substance.2. Carry out tests in the order given.3. Make observations and record them in a suitable format.4. Draw conclusions from the observations5. Identify the unknown substance.
    4. 4. Chapter 21 Qualitative Analysis Preliminary ObservationsWhat is the nature of the What is the colour of thesubstance? substance?- Is it crystalline, metallic - Is it white, colourless,or in powder form? blue, yellow or some other colour? The colour tells us about the possible cations present in the substance.
    5. 5. Chapter 21Qualitative AnalysisPreliminary ObservationsColour Possible identity of substanceWhite (colourless) Sodium (Na+), potassium(K+), ammonium (NH4+)Black Copper(II) oxide (CuO), Iron(II) oxide (FeO)Blue/green Copper(II), Cu2+ or Iron(II), Fe2+Yellowish/brown Iron(III), Fe3+Greyish, metallic Metals: Zinc, Iron, Magnesium, Aluminium
    6. 6. Chapter 21Qualitative Analysis Preliminary ObservationsIs it soluble in water? The solubility tells us about the Soluble possible anions present in the substance. Insoluble
    7. 7. Chapter 21Qualitative AnalysisPreliminary Observations Table of Solubility 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. 8. Chapter 21Qualitative AnalysisQuantity of Substance  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 use a dropper and drop it slowly into the test tube.
    9. 9. Chapter 21Qualitative AnalysisUsing a Bunsen burnerHeating 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.
    10. 10. Chapter 21Qualitative AnalysisRecording Results Record all your observations immediately or you may forget. Record the change in colour Before After before and after the test. Record the formation of a precipitate - its colour and whether it is soluble in excess (extra amount) of White ppt. Ppt. is the reagent. formed soluble
    11. 11. Chapter 21Qualitative AnalysisRecording Results Record the liberation of a gas by noting if any bubbles(effervescence) are seen. State the test you carried out toidentify the gas, and the result you obtained. You may use phrases and short forms: formulae for names of chemicals ppt. for precipitate aq. for aqueous solution
    12. 12. Chapter 21Qualitative AnalysisQuick Check 1 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
    13. 13. Chapter 21Qualitative AnalysisQuick Check 1 (cont’d)2. 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
    14. 14. Chapter 21Qualitative AnalysisSolution to Quick Check 11. 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
    15. 15. Chapter 21Qualitative AnalysisSolution to Quick Check 1(cont’d)whether the following substances are soluble or2. State 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: insoluble (g) Lead(II) nitrate: soluble Return
    16. 16. Chapter 21Qualitative AnalysisDetection 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.
    17. 17. Chapter 21Qualitative AnalysisTesting for gases  Note the colour of the gas by looking through the side of the Look here test tube above the substance Not here or solution. Note the smell of the gas byholding the mouth of the tube afew cm from the nose and fanningthe gas towards you.
    18. 18. Chapter 21Qualitative AnalysisTesting for gasesTesting with litmus paperWet the litmus papers (one piece ofblue and one piece of red) withdistilled water, then hold it near themouth of the test tube.Do not allow the litmus paper totouch the sides of the test tube ordrop it into the reagent, as it will reactwith the reagent and give a falseresult.
    19. 19. Chapter 21 Qualitative Analysis Table: Testing for gases Gas Colour Odour Litmus paper (moist)Oxygen Colourless Odourless No effectHydrogen Colourless Odourless No effectCarbon dioxide Colourless Odourless Blue to redAmmonia Colourless Pungent (like urine) Red to blueChlorine Light greenish- Pungent Blue to red then yellow (Like swimming pool water) whiteSulphur Colourless Pungent Blue to reddioxide (like burning match)
    20. 20. Chapter 21Qualitative AnalysisTest for gases with lighted splintPlace a lighted (burning)splint near the mouth of the POPtest tube. (A) If the lighted splintextinguishes with a “pop”sound, then the gas ishydrogen.
    21. 21. Chapter 21 Qualitative AnalysisTest 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.(C) Insert a glowing splint (no fire) into the mouth of the test tube. If the glowing splint is relighted (rekindled) and burns flame brightly, then the gas is oxygen. extinguished(D) If the burning splint is extinguished, then the gas may be carbon dioxide, water vapour, or some other gases.
    22. 22. Chapter 21Qualitative AnalysisTesting for carbon dioxide• Pour limewater (calcium hydroxide solution) into a test tube until itreaches a depth of 2 cm from the bottom of the test tube.• Stopper the reacting test tube with a delivery tube and pass thegas into the limewater.• If a white ppt. is formed, the gas is carbon dioxide.NoteThe carbon dioxide should not be passed for too long, as thelimewater will turn clear again (due to the formation of solublecalcium hydrogen carbonate), giving a false impression of anegative test.
    23. 23. Chapter 21 Qualitative Analysis Quick Check 2 Complete the table below. Test Observation Inference1. Heat a little of solid X Gas evolved extinguishes a burningstrongly in a test tube. splint. It turns limewater chalky.2. Heat the solution P gently A pungent gas was given off. It turnedand test for any gas evolved. moist red litmus to blue.3. Heat solid Q strongly in a A colourless and odourless gas is giventest tube. Test for any gas off. The gas relights a glowing splint.evolved.4. Add solid X to the solution Bubbles of gas were given off. TheZ and warm. burning splint is extinguished with aTest for any gas evolved. “pop” sound. Solution
    24. 24. Chapter 21 Qualitative Analysis Solution to Quick Check 2 Test Observation Inference1. Heat a little of solid X Gas evolved extinguished a Gas produced is carbonstrongly in a test tube. burning splint. It turned limewater dioxide. chalky. CO32- may be present.2. Heat the solution P A pungent gas was given off. It Gas evolved is NH3.gently and test for any turned moist red litmus to blue. NH4+ may be present.gas evolved.3. Heat solid Q strongly A colourless and odourless gas Gas evolved is oxygen.in a test tube. Test for is given off. The gas relighted aany gas evolved. glowing splint.4. Add solid X to the Bubbles of gas were given off. Gas evolved is hydrogen.solution Z and warm. Gas extinguished a lighted splint Solid X may be a metalTest for any gas with a ‘pop’ sound. and solution Z may be anevolved. acid. Return
    25. 25. Chapter 21 Qualitative Analysis Identification of cations Aluminium, Al 3+ Iron(II), Fe2+ Calcium, Ca2+ Iron(III), Fe3+ Zinc, Zn2+ Ammonium, NH4+ Copper(II), Cu2+ Lead(II), Pb2+ The cations can be identified using sodium hydroxide solution andaqueous ammonia (ammonium hydroxide).The cations react with the hydroxide ions in the alkali to forminsoluble 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. 26. Chapter 21 Qualitative Analysis 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: Ppt. (a) Add sodium hydroxide solution drop formed 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 precipitatedissolves in excess sodium hydroxide solution. Colourless/ soluble
    27. 27. Chapter 21Qualitative AnalysisIdentification 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 (NH4+) in the unknown.
    28. 28. Chapter 21 Qualitative Analysis Test for cations (Table 1)Cation Add a little NaOH (aq) Add excess NaOH (aq) Al 3+ White ppt ppt. dissolves to form colourless solutionCa 2+ White ppt ppt. remains insolubleZn 2+ White ppt ppt. dissolves to form colourless solutionPb 2+ White ppt ppt. dissolves to form colourless solutionCu 2+ Blue ppt ppt. remains insolubleFe 2+ Dirty-green ppt ppt. remains insoluble (turns brown on standing)Fe 3+ Reddish-brown ppt ppt. remains insolubleNH4 + No ppt. When warmed, No change NH3 gas given off.
    29. 29. Chapter 21Qualitative AnalysisIdentification of cations (using aq. NH3)Test using aqueous ammonia:(a) Add ammonia solution drop by drop to the unknown solution.(b) Observe the precipitate formed and note its colour. Ppt. formed(c) Add more ammonia solution (excess). Shake the test tube and examine whether the precipitate dissolves in excess ammonia solution. Colourless/ soluble
    30. 30. Chapter 21Qualitative AnalysisTest for cations (Table 2)Cation Add a little NH3 (aq) Add excess NH3(aq)Al3+ White ppt. Ppt. remains insolubleCa2+ No ppt (or very slight ppt.) No changeZn2+ White ppt. Ppt. dissolves to form colourless solution Pb2+ White ppt. Ppt. remains insolubleCu2+ Blue ppt. Ppt. dissolves to form dark blue solution.Fe2+ Dirty-green ppt. Ppt. remains insoluble (turns brown on standing)Fe3+ Reddish-brown ppt. Ppt. remains insolubleNH4+ No ppt. No change
    31. 31. Chapter 21 Qualitative Analysis Quick Check 31. What are some of the preliminary observations that you can make on an unknown sample, before carrying out any test?2. When a solid is insoluble in water, what acid is used? Why?3. Which cations will produce a white precipitate with sodium hydroxide solution and aqueous ammonia?4. Which cation will produce a white precipitate which is soluble in both aqueous ammonia and sodium hydroxide?5. Which cations will produce a white precipitate which is soluble in excess sodium hydroxide, but not in excess aqueous ammonia?6. Which cation will produce a white precipitate with sodium hydroxide solution but not with aqueous ammonia?7. Which cation will produce a blue precipitate with sodium hydroxide? Solution8. Which cation will produce a deep blue solution with aqueous ammonia?
    32. 32. Chapter 21 Qualitative AnalysisSolution to Quick Check 31. Observe the colour and texture of the unknown sample, and determine if it is soluble in water.2. Dilute nitric acid is used to dissolve the solid because nitrates of all metals are soluble in water.3. Aluminium, lead and zinc ions4. Zinc ions5. Aluminium and lead ions6. Calcium ion7. Copper(II) ion Return8. Copper(II) ion
    33. 33. Chapter 21 Qualitative Analysis Identification of Anions Carbonate, CO32- Chloride, Cl- Iodide, I- Sulphate, SO42 - Nitrate, NO3- 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 distilledwater only.*If you use dilute nitric acid to dissolve it, you are introducing the nitrate ionsinto the unknown.
    34. 34. Chapter 21Qualitative AnalysisTest for carbonate Test Observation Inference Add some dilute  Bubbles of gas are The gas is CO2 .hydrochloric acid (or given off. Therefore, CO32-nitric acid) to the  The gas turns is present in theunknown. limewater chalky. unknown. Pass the gas intolimewater.
    35. 35. Chapter 21Qualitative AnalysisTest for chloride Test Observation Inference Add a little silver  A white ppt is White ppt is AgCl.nitrate solution to formed.the unknown.  White ppt is Therefore, Cl- is Add dilute nitric insoluble in nitric acid. present.acid to the above,then shake.
    36. 36. Chapter 21Qualitative AnalysisTest for iodide Test Observation Inference Add a little lead(II)  A yellow ppt is Yellow ppt is PbI2.nitrate solution to the formed. Therefore, I- isunknown.  Yellow ppt is insoluble present in the Add dilute nitric in nitric acid. unknown.acid to the above,then shake.
    37. 37. Chapter 21Qualitative AnalysisTest for sulphate Test Observation Inference To the unknown  A white ppt is White ppt issolution, add a little formed. BaSO4.barium chloride (or  White ppt is Therefore, SO42-barium nitrate) insoluble in is present in thesolution. hydrochloric acid unknown. Then add some (or nitric acid).dilute hydrochloric acid(or nitric acid) andshake.
    38. 38. Chapter 21Qualitative AnalysisTest for nitrate Test Observation Inference To the unknown, add alittle sodium hydroxidesolution.  A pungent gas is NH3 gas isThen add a few pieces of given out. produced.aluminium foil (or a  The gas turns moistspatula of aluminium NO3- is present in red litmus paper blue. the unknown.powder). Warm the mixturegently. Test for ammonia gasevolved.
    39. 39. Chapter 21 Qualitative Analysis Summary of Tests for Anions (Table 3) Anion Test ObservationCarbonate, Add dilute HCl. Test for gas Effervescence. Gas evolved CO32- evolved. turned limewater chalky.Chloride, Add AgNO3 solution, White ppt. insoluble in HNO3 Cl- followed by dilute HNO3Iodide, Add Pb(NO3)2 solution, Yellow ppt. insoluble in HNO3 I- followed by dilute HNO3Sulphate, Add BaCl2 solution, White ppt. insoluble in HCl SO42- followed by dilute HCl.Nitrate, Add NaOH solution, then Al foil. NH3 gas evolved turned red NO3- Warm gently. litmus blue
    40. 40. Chapter 21 Qualitative Analysis Quick Check 41. When we add aqueous silver nitrate to an unknown, what anion(s) are we looking for?2. When we add aqueous barium chloride or barium nitrate to an unknown, what anion(s) are we looking for?3. When we are told to add dilute hydrochloric acid to an unknown, what anion are we testing for and what should we get ready?4. 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?5. When we add silver nitrate or barium chloride solution to an unknown, what reagent should we also add? What is the reason for this? Solution
    41. 41. Chapter 21Qualitative AnalysisSolution to Quick Check 41. Chloride, Cl- or iodide, I-2. Sulphate, SO42-3. Carbonate, CO32-. We should get a delivery tube and test tube containing some limewater ready.4. Nitrate, NO3-. 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. Return
    42. 42. Chapter 21 Qualitative Analysis Quick Check 5 Complete the table below and identify the substance S1.Test Observation Inference1. Dissolve a sample of S1 in distilled S1 dissolved to form a pale bluewater and divide it into 3 portions. solution.2. To the first portion, add aqueous A blue ppt was formed.sodium hydroxide slowly until in excess. Ppt was insoluble in excess NaOH.3. To the second portion, add aqueous A blue ppt was formed.ammonia slowly until in excess. Ppt dissolved to form a deep blue solution.4. To the third portion, add barium chloride A white ppt was formed.solution, then dilute HCl. Ppt was insoluble in HCl. Conclusion: S1 is _________ . Solution
    43. 43. Chapter 21 Qualitative Analysis Solution to Quick Check 5 Complete the table below and identify the substance S1.Test Observation Inference1. Dissolve a sample of S1 in distilled S1 dissolved to form a pale blue Cu2+ may be presentwater and divide it into 3 portions. solution.2. To the first portion, add aqueous A blue ppt was formed. Cu2+ is present.sodium hydroxide slowly until in excess. Ppt was insoluble in excess NaOH.3. To the second portion, add aqueous A blue ppt was formed. Cu2+ is confirmed.ammonia slowly until in excess. Ppt dissolved to form a deep blue solution.4. To the third portion, add barium A white ppt was formed. SO42- ischloride solution, then dilute HCl. present. Ppt was insoluble in HCl. Conclusion: S1 is copper(II) sulphate. Solution

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