C21 qualitative-analysis-edited

[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21 L EARNING O UTCOMES

What is QA? ,[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21

The QA Process ,[object Object],[object Object],[object Object],[object Object],[object Object],Five important steps Qualitative Analysis Chapter 21

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

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

[object Object],[object Object],[object Object],Insoluble Soluble Qualitative Analysis Chapter 21 Preliminary Observations

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

[object Object],[object Object],[object Object],[object Object],Quantity of Substance use a dropper and drop it slowly into the test tube. Qualitative Analysis Chapter 21

Using a Bunsen burner ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21

Recording Results ,[object Object],[object Object],[object Object],[object Object],[object Object],Before After Ppt. is soluble White ppt. formed Qualitative Analysis Chapter 21

Recording Results formulae for names of chemicals ppt. for precipitate aq. for aqueous solution ,[object Object],[object Object],Qualitative Analysis Chapter 21

Quick Check 1 ,[object Object],Solution Qualitative Analysis Chapter 21

Quick Check 1 (cont’d) ,[object Object],[object Object],Solution Qualitative Analysis Chapter 21

[object Object],Return Qualitative Analysis Chapter 21 Solution to Quick Check 1

[object Object],Return Qualitative Analysis Chapter 21 Solution to Quick Check 1 (cont’d)

Detection of gases ,[object Object],(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

Testing for gases Look here Not here ,[object Object],[object Object],Qualitative Analysis Chapter 21

Testing for gases ,[object Object],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

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

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

Test for gases with lighted splint ,[object Object],(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

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. ,[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21

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.

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.

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 ,[object Object],[object Object],[object Object]

Identification of cations ,[object Object],[object Object],[object Object],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

Identification of cations ,[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21

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

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

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

Quick Check 3 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21 Solution

Return ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21 Solution to Quick Check 3

Identification of Anions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21

Test for carbonate Qualitative Analysis Chapter 21 Test Observation Inference ,[object Object],[object Object],[object Object],[object Object],The gas is CO 2 . Therefore, CO 3 2 - is present in the unknown.

Test for chloride Qualitative Analysis Chapter 21 Test Observation Inference ,[object Object],[object Object],[object Object],[object Object],White ppt is AgCl. Therefore, Cl - is present.

Test for iodide Qualitative Analysis Chapter 21 Test Observation Inference ,[object Object],[object Object],[object Object],[object Object],Yellow ppt is PbI 2 . Therefore, I - is present in the unknown.

Test for sulphate Qualitative Analysis Chapter 21 Test Observation Inference ,[object Object],[object Object],[object Object],[object Object],White ppt is Ba SO 4 . Therefore, SO 4 2- is present in the unknown.

Test for nitrate Qualitative Analysis Chapter 21 Test Observation Inference ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],NH 3 gas is produced. NO 3 - is present in the unknown.

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

Quick Check 4 Solution ,[object Object],[object Object],[object Object],[object Object],[object Object],Qualitative Analysis Chapter 21

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

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.

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.

C21 qualitative-analysis-edited

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