PERMANGANIMETRIC SMK Negeri 13 Bandung

In The Name of Allah, The Precious, The Merciful  Rabbi zidnaa ilmaan Warzuqnaa fahmaan  Look at us, God, we are gathering here in this silent morning. Ask Ye with all our hearts, beg Ye by all our souls. Would Ye mind open our hearts and give us Thee lights. Give us a drop of knowledge of Thee ocean of knowledge, Give us knowledge o Allah bless us wisdom o Allah. Amien

PERMANGANIMETRI  The system of oxidimetric titration with potassium permanganate standard solution  Use no indicator because of potasium permanganate is auto indicator Teknologi dan Rekayasa

After this chapter you are expected to be able to :  Explain the characteristic of KMnO 4  Explain the reaction of KMnO 4 in acid, neutral or basic solution and in strongly alkaline solution  Explain the end point in permanganimetric  Explain the conditioning the titration  Doing standardisation of KMnO 4, determining of errous ion, peroksides and calcium

You should be familiar with:  Oxidation-reduction  Equivalent weights  Normal concentration  Theory of oxidation- reduction

KMnO 4  Blackish purple solid  Mr = 158,3  Dissolve in water easily  Strong Oxidizing agent (E 0 = 1,51 V)  Decomposed by light  Reduced in acid, neutral or basic and strongly alkaline solution

With these all characters mentioned above KMnO 4 used as secondary standard substance.

Reaction of KMnO4 Acid MnO H + + 5e -  Mn H 2 O Neutral/basic: MnO H 2 O + 3e -  Mn OH - Strongly alkaline MnO e -  MnO 4 =

Preparation of KMnO 4 solution  Weigh out 3,16 grams of KMnO 4  Dissolve in 1 liter of water in a beaker glass or Erlenmeyer flask. Cover it with a watch glass or short stem funnel. Put some granule glass as boiling stones.  Heat until boil. Boil gently for 30 minutes.  Allow to stand at least 1 night.  Filter the solution through a sintered glass funnel (G4).  Keep the solution in an amber glass bottle

Watch up!  If you use Erlenmeyer flask and short stem funnel, make sure that the surface is about 2 cm below the edge of the stem  Fill only ¾ height of the apparatus  Make some boiled water with a few drops of KMnO 4 solution as diluting water. Make sure the color of the solution still pink at the end of heating.

Keeping the solution  Keep in a dark brown glass bottle  Keep away from heat and light  Make sure the bottle is clean and organics free by wash and rinse the bottle with chromic acid solution  Repeat the standardization every month

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Preparation of KMnO 4 Filtering Saving the solution Teknologi dan Rekayasa

Why should we do all these steps?  KMnO 4 is a strong oxidizing agent, it oxidize any organics compounds but very slowly. If water contain some organics compounds, they react slowly so KMnO 4 concentration will reduced during storage  To avoid this, we boil KMnO 4 solution for 30 minutes to faster the reaction so the organics completely react and will not consume KMnO 4 anymore  The reaction results are MnO 2, water and CO 2

Why sintered glass?  Remember that KMnO 4 reacts easily with organics compound to form Mno 2. If we filter it through filter paper, automatically they react and MnO 2 is formed because filter paper is organic compound. If it happens, the goal of filtering isn’t gained.  Beside sintered glass we also can use Gooch crushible or Buchner with glass wool

Other reasons  KMnO 4 is unstable substance, it will be decomposed by light to MnO 2.  Decomposition faster by heat, any impurities and MnO 2 formed before. (MnO 2 ) is auto catalyst in this way  When we allow the boiled solution 1 night the MnO 2 will precipitated at the bottom of solution. It’s make removing MnO 2 by filtering is easier.

Standardization of KMnO 4  Primary substance available: Na 2 C 2 O 4, H 2 C 2 O 4.2H 2 O, As 2 O 3, Iron powder or Ferro ammonium sulfate  Reaction took place in acid condition  KMnO 4 reduced into Mn 2+  Equivalent weight of KMnO 4 is Mr/5  The end point of titration is colorless to faint pink/rose

.What happen when the end point appear?  The end point (colorless to pink/rose) visually objected because the equivalent point has been reached. A drop of KMnO 4 then will not reduced anymore because the reducing agent not exist anymore. This small excess of KMnO 4 makes the color change to pink.

Permanganimetric titration always took place in acid condition, because  Only in this condition the reaction occurs fast and quantitatively  Mn 2+ formed is almost colorless, the end point is clear and sharp

Standardization of KMnO 4 with H 2 C 2 O 4. 2 H 2 O or Na 2 C 2 O 4  Weigh out 1,6 grams of H 2 C 2 O 4. 2 H 2 O orNa 2 C 2 O 4’ dissolve in volumetric flask of 250 mL. Use aq-DM as solvent.  Transfer 25 mL of the solution into an Erlenmeyer flask. Add 25 mL of 4N H 2 SO 4 and heat the solution until about 70 0 C  Titrate with KMnO 4 solution until the color change from colorless to faint pink/pale rose  Calculate the Normality of KMnO 4

Reaction  H 2 C 2 O 4. 2 H 2 O or Na 2 C 2 O 4 is written as C 2 O 4 =  C 2 O 4 =  2CO e - X 5  MnO H + + 5e -  Mn H 2 O X2  5C 2 O 4 = + 2MnO H +  10CO 2 + 2Mn H 2 O

Discussion  H 2 SO 4 is added as acidifier as the titration should be took place in acid condition  Heating the titran before titration is needed to make the reaction occur faster, because at room temperature reaction of C 2 O 4 = and 2MnO 4 - is too slow. Heating only until 70 0 C because overheating will make oxalic decomposed.

. Thank you & Good luck