QUALITATIVE ANALYSIS (CONFIRMATORY TEST FOR CATIONS)

CHAPTER 6 ACID, BASE AND SALT
6.11 Qualitative Analysis for Salts
Confirmatory test for cations (Ammonium ion, NH4+; iron(II) ion, Fe2+, iron(III) ion, Fe3+ and lead(II) ion, Pb2+) using
1. Nessler's Reagent (for ammonium ion, NH4+)
2. Potassium hexacyanoferrate(III) and potassium thiocyanate (for iron(II) ion, Fe2+ and iron(III) ion, Fe3+)
3. Potassium iodide (for lead(II) ion, Pb2+)

1. CHAPTER 6 ACID, BASE AND SALT PREPARED BY : ESTHER ANNE ANAK RANDI

2. Chapter 6 Acid, Base and Salt 6.1 Role of water in showing acidic and alkaline properties. 6.2 pH value 6.3 Strength of acids and alkalis 6.4 Chemical properties of acids and alkalis 6.5 Concentration of aqueous solutions 6.6 Standard solution 6.7 Neutralisation 6.8 Salts, crystals and their uses in daily life 6.9 Preparation of salts 6.10 Effect of heat on salts 6.11 Qualitative analysis

3. Both Al 3+ ion and Pb 2+ ion give the same observations when tested with sodium hydroxide solution, NaOH and ammonia solution, NH 3 . Thus, a confirmatory test is required to differentiate between Pb 2+ ion and Al 3+ ion. Other than that, ions such as Fe 2+ , Fe 3+ and NH 4 + too can be confirmed using specific reagents .

4. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Aim : To confirm the presence of cations ( NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) in aqueous solution. Problem statement : How to confirm the presence of cations ( NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) in aqueous solutions? Hypothesis : Presence of cations (NH4 + , Fe2+, Fe3+, Pb2+) can be confirmed using : Nessler’s reagent for ammonium ions, NH 4 + Potassium hexacyanoferate (II), K 4 Fe(CN) 6 and potassium thiocyanate solution, KSCN for iron (II) ions, Fe 2+ and iron(III) ions, Fe 3+ Potassium iodide, KI for lead(II) ions, Pb 2+ Variables : Manipulated : Types of reagent used for confirmatory test b) Responding : Presence of cations c) Fixed : Volume of aqueous solution

5. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Procedures :

6. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) M Procedures : Based on Figure 6.58, list the apparatus and reagents that are needed for this experiment. Discuss the experimental procedure for the experiment with your group members. Make sure you repeat Method III by using potassium thiocyanate solution, KSCN instead of potassium hexacyanoferate (II), K 4 Fe(CN) 6 . Carry out the experiment with your teacher̕s permission. Record your observations in Table 6.18.

7. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) M Procedures : Based on Figure 6.58, list the apparatus and reagents that are needed for this experiment. Discuss the experimental procedure for the experiment with your group members. Make sure you repeat Method III by using potassium thiocyanate solution, KSCN instead of potassium hexacyanoferate (II), K 4 Fe(CN) 6 . Carry out the experiment with your teacher̕s permission. Record your observations in Table 6.18.

8. EXPERIMENT 6.11 CONFIRMATORY TEST FOR CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Apparatus : Dropper, text tube, test tube holder, Bunsen burner Reagent : 1.0 mol dm -3 ammonium chloride solution, NH 4 Cl, Nessler reagent, 50 g dm -3 potassium hexacyanoferrate solution, K 2 Fe(CN) 6 , 1.0 mol dm -3 iron(II) sulphate solution, FeSO 4 , 50 g dm -3 potassium thiocyanate solution, KSCN, 1.0 mol dm -3 iron(III) chloride solution, FeCl 3 , 1.0 mol dm -3 lead(II) nitrate solution, Pb(NO 3 ) 2 , 0.5 mol dm -3 potassium iodide solution, KI, distilled water.

9. EXPERIMENT 6.11 CONFIRMATORY TEST FOR CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Method I : Confirmation of ammonium ion, NH 4 + Pour 2 cm 3 of ammonium chloride, NH 4 Cl solution into a test tube. Add a few drops of Nessler’s reagent to the test tube using a dropper. Shake well. Record your observation. What is a Nessler’s reagent? an alkaline solution of potassium mercuric iodide used in chemical analysis especially in a test for ammonia in aqueous solution (as when obtained from water, blood, or urine) with which it forms a yellowish brown color or precipitate. The intensity of the color is in direct proportion to the ammonia concentration .

10. EXPERIMENT 6.11 CONFIRMATORY TEST FOR CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Method II : Confirmation of iron(II) ion, Fe 2+ Method III : Confirmation of iron( IIi ) ion, Fe 2+ Pour 2 cm 3 of iron(II) sulphate, FeSO 4 solution and 2 cm 3 of iron(III) chloride, FeCl 3 solution respectively into two separate test tubes. Using a dropper, add a few drops of potassium hexacyanoferrate(II), K 4 Fe(CN) 6 solution into each of the test tubes and shake well. Record your observations. Repeat steps 1 to 3 using potassium thiocyanate, KSCN solution to replace potassium hexacyanoferrate(II), K 4 Fe(CN) 6 solution.

11. EXPERIMENT 6.11 CONFIRMATORY TEST FOR CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) What are potassium thiocyanate, KSCN solution and potassium hexacyanoferrate(II), K 4 Fe(CN) 6 ? Why do we use them to test the presence of iron(II) ion, Fe 2+ and iron(III) ion, Fe 3+ ?

12. EXPERIMENT 6.11 CONFIRMATORY TEST FOR CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Method IV : Confirmation of lead(II) ion, Pb 2+ Pour 2 cm 3 of lead(II) nitrate, Pb(NO 3 ) 2 solution into a test tube Add 2 cm 3 of potassium iodide solution, KI into the test tube and shake well. Observe any precipitate formed and if there is record its colour . Pour 3 cm 3 of distilled water in to the test tube. Heat the mixture until no further change occurs. Cool the mixture in the test tube to room temperature using running water from the tap. Record all your observations.

13. EXPERIMENT 6.11 CONFIRMATORY TEST FOR CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Why do we use potassium iodide, KI to test the presence of lead(II) ion, Pb 2+ ?

14. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Results : Confirmatory test Observation Method I : Confirmatory test for ammonium ion, NH 4 + A brown precipitate was formed. Method II : Confirmatory test for iron(II) ion, Fe 2+ Pale blue precipitate a) Using potassium hexacyanoferrate(II) solution, K 4 Fe(CN) 6 b) Using potassium thiocyanate solution, KSCN Pink colouration Method III : Confirmatory test for iron(III) ion, Fe 3+ Pale blue precipitate a) Using potassium hexacyanoferrate(II) solution, K 4 Fe(CN) 6 b) Using potassium thiocyanate solution, KSCN Blood-red colouration Method IV : Confirmatory test for lead(II) ion, Pb 2+ A yellow precipitate was formed. When heated, the yellow precipitate dissolved in hot water to form a colourless solution. When cooled to room temperature, shiny yellow crystals were formed

15. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Conclusion : Is the hypothesis accepted? What is the conclusion of this experiment? Discussion : Write an ionic equation for the reaction between potassium iodide solution, KI and lead(II) nitrate solution, Pb(NO 3 ) 2 . 2. Other than Nessler reagent, what are other reagents that can be used to confirm the presence of ammonium ion, NH 4 + ? Briefly explain how the chemical test is carried out. 3. Predict the observation obtained if potassium chloride solution, KCl is used instead of potassium iodide solution, KI in Method IV

16. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Discussion : Write an ionic equation for the reaction between potassium iodide solution, KI and lead(II) nitrate solution, Pb(NO 3 ) 2 . Pb 2+ ( aq ) + 2I – ( aq ) → PbI 2 (s)

17. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Discussion : 2. Other than Nessler reagent, what are other reagents that can be used to confirm the presence of ammonium ion, NH 4 + ? Briefly explain how the chemical test is carried out. Sodium hydroxide solution, NaOH Procedure : Pour 2 cm 3 salt solution into a test tube. Add 2 cm 3 sodium hydroxide solution, NaOH and shake. Heat the mixture. Put a moist red litmus paper at the mouth of the test tube. Observation : The moist red litmus paper turns blue. Hence, ammonium ion, NH 4 + is present.

18. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) Discussion : 3. Predict the observation obtained if potassium chloride solution, KCl is used instead of potassium iodide solution, KI in Method IV. A white precipitate is formed. When heated, the white precipitate dissolves in hot water to form a colourless solution. When cooled, the white precipitate forms again.

19. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) To summarize,

20. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ ) To summarize,

21. EXPERIMENT 6.11 CONFIRM THE PRESENCE OF CATIONS (NH 4 + , Fe 2+ , Fe 3+ , Pb 2+ )

22. PLAN QUALITATIVE ANALYSIS TO IDENTIFY SALTS ACTIVITY 6.28 ( TEXTBOOK, PAGE 213 ) Aim : To identify the cation and anion in L2 solid. Materials : L2 solid, 2.0 mol dm –3 sodium hydroxide solution, NaOH, 2.0 mol dm –3 ammonia solution, NH 3 , 2.0 mol dm –3 nitric acid, HNO 3 , 0.1 mol dm –3 silver nitrate solution, AgNO 3 , 2.0 mol dm –3 hydrochloric acid, HCl, 1.0 mol dm –3 barium chloride solution, BaCl 2 , distilled water, blue litmus paper and wooden splinter Apparatus : Test tubes, dropper, test tube rack, test tube holder, Bunsen burner, 10 cm 3 measuring cylinder, 100 cm 3 beaker, spatula and glass rod Procedure : Carry out qualitative analysis to identify the cation and anion in L2 solid. Put half a spatula of L2 solid into a test tube. Add the remaining L2 solid into a beaker. Add 25 cm 3 of distilled water into the beaker to dissolve the L2 solid. Divide the L2 solution into four portions to be used for the chemical tests below :

23. PLAN QUALITATIVE ANALYSIS TO IDENTIFY SALTS Test to identify the cation : Tests to identify the anion : 4. Record you observation for the activity.

24. PLAN QUALITATIVE ANALYSIS TO IDENTIFY SALTS Interpreting data : State the inference that corresponds to each observation. Based on the chemical test, name L2.