MOHR's SALT AIM – (a) To prepare 250ml of M/20 solution of Mohr’s salt. (b) Using this calculate the molarity and strength of the given KMnO4 solution. PPARATUS AND CHEMICALS REQUIRED- Mohr’s salt, weighing bottle, weight box, volumetric flask, funnel, distilled water, chemical balance, dilute H2SO4, beakers, conical flask, funnel, burette, pipette, clamp stand, tile, KMnO4 solution. THEORY- (a) Mohr’s salt having the formula FeSO4.(NH4)2SO4.6H2O has molar mass 392gmol-1. It is a primary standard. Its equivalent mass is 392/1 = 392 as its n factor is 1 as per the following reaction: Fe2+ → Fe3+ + ePROCEDURE: 1. Weigh a clean dry bottle using a chemical balance. 2. Add 4.9g more weights to the pan containing the weights for the weighing bottle. 3. Add Mohr’s salt in small amounts to the weighing bottle, so that the pans are 4. 5. 6. 7. 8. balanced. Remove the weighing bottle from the pan. Using a funnel, transfer the Mohr’s salt to the volumetric flask. Add about 5ml. of dilute H2SO4 to the flask followed by distilled water and dissolve the Mohr’s salt. Make up the volume to the required level using distilled water. The standard solution is prepared. (b) THEORY1. The reaction between KMnO4 and Mohr’s salt is a redox reaction and the titration is therefore called a redox titration. 2. Mohr’s salt is the reducing agent and KMnO4 is the oxidizing agent. 3. KMnO4 acts as an oxidizing agent in all the mediums; i.e. acidic, basic and neutral medium. 4. KMnO4 acts as the strongest oxidizing agent in the acidic medium and therefore dil. H2SO4 is added to the conical flask before starting the titration. IONIC EQUATIONS INVOLVED: SUDIP BHATTACHARYYA (9830843517) Reduction Half: MnO4- + 8H+ + 5e- → Mn2+ + 4H2O 5Fe2+ → 5Fe3+ + 5e- Oxidation Half: Overall Equation: MnO4- + 8H+ + 5Fe2+ → Mn2+ + 5Fe3+ + 4H2O INDICATOR- KMnO4 acts as a self indicator. END POINT- Colourless to light pink (KMnO4 in the burette) PROCEDURE1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Fill the burette with KMnO4 solution. Pipette out 10ml. of Mohr’s salt solution into the conical flask. Add half a test tube of dil. H2SO4. Keep a glazed tile under the burette and place the conical flask on it. Note down the initial reading of the burette. Run down the KMnO4 solution into the conical flask drop wise with shaking. Stop the titration when a permanent pink colour is obtained in the solution. This is the end point. Note down the final burette reading. Repeat the experiment until three concordant values are obtained. OBSERVATION TABLE: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL) Volume of Mohr’s salt solution taken = S.No BURETTE INITIAL 1 2 3 10 18.8 27.7 READINGS VOLUME OF KMnO4 FINAL USED (ml) 18.8 8.8 27.7 8.9 36.5 8.8 Concordant Value = 8.8mL SUDIP BHATTACHARYYA (9830843517) CALCULATIONS: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL) Calculation of amount of Mohr’s Salt to be weighed to prepare 100ml M/20 solution: Molecular Mass of Mohr’s Salt = 392g/mole 1000 cm3 of 1M KMnO4 require 392g Mohr’s Salt. 250 cm3 of M/40 KMnO4 require =392/40g = 4.9g Using formula: N1M1V1 = N2M2V2 Where N1=5 (for KMnO4), V1=8.8mL , M1 =? N2 =1 (for Mohr’s salt), V2 = 10ml, M2 = 1/20M M1 = [1*(1/20)*10]/[5*8.8] = 1/88M = 0.01M Strength = M X Molar Mass = 158 *( 1/88) = 1.79g/L RESULT- (ON RULED SIDE)- The Molarity of KMnO4 = And the strength of KMnO4 = 0.01M 1.79g/L SUDIP BHATTACHARYYA (9830843517) OXALIC ACID AIM: – (a) To prepare 100ml of M/40 solution of oxalic acid. (b)Using this calculate the molarity and strength of the given KMnO 4 solution. APPARATUS AND CHEMICALS REQUIRED- Oxalic acid, weighing bottle, weight box, volumetric flask, funnel, distilled water, chemical balance, beakers, conical flask, funnel, burette, pipette, clamp stand, tile, dilute H2SO4, KMnO4 solution. THEORY- (a) Oxalic acid is a dicarboxylic acid having molar mass 126gmol-1. It is a primary standard and has the molecular formula COOH-COOH.2H2O. Its equivalent mass is 126/2 = 63 as its n factor is 2 as per the following reaction: COOH-COOH → 2CO2 + 2H+ + 2e-. PROCEDURE: 1. 2. 3. 4. 5. 6. 7. 8. Weigh a clean dry bottle using a chemical balance. Add 3.15g more weights to the pan containing the weights for the weighing bottle. Add oxalic acid in small amounts to the weighing bottle, so that the pans are balanced. Remove the weighing bottle from the pan. Using a funnel, transfer the oxalic acid to the volumetric flask. Add a few drops of distilled water to dissolve the oxalic acid. Make up the volume to the required level using distilled water. The standard solution is prepared. (b) THEORY1. The reaction between KMnO4 and oxalic acid is a redox reaction and the titration is 2. 3. 4. 5. therefore called a redox titration. Oxalic acid is the reducing agent and KMnO4 is the oxidizing agent. KMnO4 acts as an oxidizing agent in all the mediums; i.e. acidic, basic and neutral medium. KMnO4 acts as the strongest oxidizing agent in the acidic medium and therefore dil. H2SO4 is added to the conical flask before starting the titration. The titration between oxalic acid and KMnO4 is a slow reaction, therefore heat the oxalic acid solution to about 600C to increase the rate of the reaction. SUDIP BHATTACHARYYA (9830843517) IONIC EQUATIONS INVOLVED: Reduction Half: MnO4- + 8H+ + 5e- → Mn2+ + 4H2O] X 2 Oxidation Half: C2O42- → 2CO2 + 2e- ] X 5 Overall Equation: 2MnO4- + 16H+ + 5C2O42- → 2Mn2+ + 10CO2 + 8H2O INDICATOR- KMnO4 acts as a self indicator. END POINT- Colourless to light pink (KMnO4 in the burette) PROCEDURE1. Fill the burette with KMnO4 solution. 2. Pipette out 10ml. of oxalic acid solution into the conical flask. 3. Add half a test tube of dil. H2SO4 and heat the solution to about 600C to increase the rate of the reaction. 4. Keep a glazed tile under the burette and place the conical flask on it. 5. Note down the initial reading of the burette. 6. Run down the KMnO4 solution into the conical flask drop wise with shaking. 7. Stop the titration when a permanent pink colour is obtained in the solution. 8. This is the end point. Note down the final burette reading. 9. Repeat the experiment until three concordant values are obtained. OBSERVATION TABLE: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL) Volume of Oxalic Acid solution taken = 10mL SUDIP BHATTACHARYYA (9830843517) S.No BURETTE INITIAL 1 2 3 16 26.5 36.9 READINGS VOLUME OF KMnO4 FINAL USED (ml) 26.5 10.5 36.9 10.4 47.4 10.5 Concordant Value = 10.5mL CALCULATIONS: (TO BE PUT UP ON THE BLANK SIDE USING A PENCIL) Calculation of amount of oxalic acid to be weighed to prepare 100ml M/20 solution: Molecular Mass of Oxalic Acid = 126g/mole 1000 cm3 of 1M oxalic acid require 126g oxalic acid. 1000 cm3 of M/40 oxalic acid require =126/40g = 3.15g Using formula: N1M1V1 = N2M2V2 Where N1=5 (for KMnO4), V1= 10.5 , M1 = ? N2=2 (for oxalic acid), V2 = 10ml, M2 = 1/40 M1 = [2*(1/40)*10]/[5*10.5] = 1/105M = 0.0095M Strength = M X Molar Mass = 158 *( 1/105) = 1.504g/L RESULT- (ON RULED SIDE)- The Molarity of KMnO4 = 0.0095M And the strength of KMnO4 = 1.504g/L SUDIP BHATTACHARYYA (9830843517)
