MIDTERM LABORATORY

• Expt. No. 10 Preparation and Standardization of Silver nitrate solution Preparation of silver nitrate solution 1. Weigh accurately 17 to 18 g of silver nitrate crystals 2. Dissolve the crystals in a sufficient amount of distilled water to make one (1) L solution 3. Pour the solution into a 1 L amber stock bottle 4. Label properly
• Standardization of SILVER NITRATE solution

  1. Measure 40 mL of silver nitrate solution

  2. Dilute with 100 mL of distilled water

  3. Heat the solution

  4. Add standard hydrochloric acid solution slowly with continuous stirring until complete precipitation of silver chloride

  5. Boil the mixture for 5 minutes

  6. Allow to stand in the dark until supernatant is clear and precipitate has settled

  7. Transfer precipitate into tared crucible

  8. Wash precipitate with distilled water acidified with nitric acid

  9. Dry precipitate at 110°C to constant weight

  10. Determine weight of silver chloride

  11. Calculate molarity and normality of silver nitrate solution
• METHOD OF ANALYSIS EMPLOYED IN STANDARDIZATION AND PREPARATION OF SILVER NITRATE

  Precipitation - Gravimetric
• 
  

  EQUATION/S INVOLVED in AgNO3EQUATION/S INVOLVED in AgNO3
• 99.8% -100.5%


  USP STANDARD OF AGNO3
• The slow addition of precipitant, HCl, with continuous stirring of the heated solution aids in the formation of a precipitate with large particles. The mixture is allowed to stand in the dark to minimize the reducing effect of the light on the AgCl, free Ag is produced.

  The purplish color which the precipitate acquires on exposure to light is due to the free metal (Ag) being formed in the precipitate.
• The titrant used in the AgNO3 is Standard HCl, without indicator in order to obtained the end point: Formation of precipitate (AgCl)
• Silver Nitrate other names:


  Nitric acid silver(1+) salt;

  Lunar caustic; Nitrate d'argent;

  Nitric acid silver(I) salt; Silver mononitrate;

  Silver(I) nitrate
• Sodium chloride content experiment

  1. Weigh 15 g of salt-preserved food sample

  2. Macerate the sample for one hour, using 150 mL of hot distilled water

  3. Filter and then collect the filtrate

  4. Transfer the filtrate into a 250 mL volumetric flask

  5. Rinse the Erlenmeyer flask with 100 mL of hot distilled water

  6. Filter through the same filter paper and transfer the filtrate through the same 250 mL volumetric flask

  7. Dilute with distilled water to the mark

  8. Take an aliquot portion of 100 mL then transfer it to an Erlenmeyer flask

  9. Run down 50 mL of standard silver nitrate solution to the Erlenmeyer flask

  10. Add three (3) mL of concentrated nitric acid, 5 mL of nitrobenzene and 2 mL of ferric ammonium sulfate TS

  11. Shake thoroughly and Titrate it with standard ammonium thiocyanate to a flesh color endpoint
• Volhard Method - Indirect (residual) os the method of analysis used in the experiment 11 - NaCl content
• EQUATION/S INVOLVED EXP. 11 NaCl: NaCl + AgNO3 → AgCl + NaNO3 AgCl + NH4SCN → AgSCN + NH4Cl
• Nitric acid is added to prevent the precipitation of silver as carbonate, phosphate, etc. and to prevent hydrolysis of the ferric alum. Addition of nitrobenzene shields the precipitate from aqueous medium
• EXPERIMENT 11 ASSAY OF SALT-PRESERVED FOODS FOR SODIUM CHLORIDE CONTENT
• Determination of sodium chloride content in salt-preserved food sample

  1. Weigh accurately 15 g of sample in a tared Erlenmeyer flask

  2. Macerate the sample for one hour, using 150 mL of hot distilled water

  3. Filter and then collect the filtrate

  4. Transfer the filtrate into a 250 mL volumetric flask

  5. Rinse the Erlenmeyer flask with 100 mL of hot distilled water

  6. Filter through the same filter paper and transfer the filtrate through the same 250 mL volumetric flask

  7. Dilute with distilled water to the mark

  8. Take an aliquot portion of 100 mL then transfer it to an Erlenmeyer flask

  9. Run down 50 mL of standard silver nitrate solution to the Erlenmeyer flask

  10. Add three (3) mL of concentrated nitric acid, 5 mL of nitrobenzene and 2 mL of ferric ammonium sulfate TS

  11. Shake thoroughly

  12. Titrate it with standard ammonium thiocyanate to a flesh color endpoint

  13. Calculate the % sodium chloride content
• Sodium chloride content method of analysis is Volhard Method - Indirect (residual)
• EQUATIONS INVOLVED in Sodium Chloride content are

  NaCl + AgNO3 → AgCl + NaNO3

  AgCl + NH4SCN → AgSCN + NH4Cl

  USP standard: Sodium Chloride contains NLT 99.0% and NMT 100.5%
• Name of Sample: NaCl – sodium chloride

  Other Names: Table salt/sea salt

  Molecular Weight: 58.45 g/mole

  Factor: 1

  Standard solution: AgNO3 & NH4SCN

  Indicator: Ferric Ammonium sulfate

  End Point: Bloodred to flesh

  Chemical Reaction Involved:

  NaCl + AgNO3 → AgCl + NaNO3

  AgCl + NH4SCN → AgSCN + NH4Cl
• Sodium chloride Reason for special step:

  Nitric acid is added to prevent the precipitation of silver as carbonate, phosphate, etc. and to prevent hydrolysis of the ferric alum.

  Addition of nitrobenzene shields the precipitate from aqueous medium.
• Expt. No. 12 Assay of Iodine content in Povidone-iodine

  Procedure:

  1 Place about 5g of povidone-iodine in 400mL E-flask, and add 200mL distilled water.

  2. Cover the E. flask, stir by mechanical means at room temperature for not more than 1 hour to dissolve as completely as possible.

  3. Titrate immediately with 0.1N sodium thiosulfate VS, adding 3mL starch TS as the endpoint is approached.

  4. Perform a blank determination, and make any necessary corrections.

  5. Each mL of 0.1N sodium thiosulfate is equivalent to 12.69mg of I.
• Experiment 12 Iodine content method of analysis is Oxidation-Reduction - Iodometry
• EQUATION/S INVOLVED in Iodine content:

  Usually Sodium thiosulfate (Na2S2O3) is used as a reducing agent in redox titration involving iodine. The reaction between iodine and thiosulfate is as follows;

  I2 + 2 S2O3^2- → 2 I- + S4O6^2-

  Iodine + thiosulfate → iodide + tetra-thionate

  Since I2 is present as the tri-iodide in aqueous solutions containing iodide , hence reaction can be written as ;

  I^3- + 2S2O3^2- → 3 I- + S4O6^ 2-

  tri-iodide + thiosulfate tri-iodide + tetra-thionate

  USP standard: Povidone-iodine contains nlt 9.0% and nmt 12% iodine ion calculated on a dry basis.
• Name of Sample Povidone-Iodine

  IUPAC name: (C6H9NO)n·xI

  Other Name/s 2-Pyrrolidinone, 1-ethenyl-Homopolymer Iodopovidone

  Trade name: Betadine

  Molecular Weight: 126.90445 g/mole for 1 molecule of Iodine

  Factor: 1

  Standard solution: 0.1N sodium thiosulfate VS

  Indicator: Starch TS

  End Point: Disappearance of Blue or violet color
• Povidone-Iodine Reason for special step

  All the iodine in the compound must be in the form of reduced iodide ion. The Na2S2O3 accomplishes this. When the typical brown color of iodine disappears, all the iodine has been reduced.
• Expt. No. 13 Preparation and standardization of disodium ethylenediaminetetracetate (EDTA)

  
  

  Preparation

  1 Take about 100 ml of water in a volumetric flask.

  2. Add about 37.2 gm of Disodium Edetate with continues stirring.

  3. Add more about 700 ml of water mix.

  4. Make up the volume 1000 ml with water.

  5. Mix the solution thoroughly.

  6. Keep the solution for at least one hour and then carry out the standardization.
• EDTA Standardization Experiment

  1. Weigh accurately about 200 mg of Calcium Carbonate

  2. Transfer it in a cleaned and dried 500 ml conical flask

  3. Add about 10 ml of water with gentle stirring to form the slurry

  4. Dissolve the carbonate in 2 ml of dilute Hydrochloric acid and shake well until dissolves

  5. Add 100 ml water through the inner surface of the flask with the stirring of the solution

  6. Add 30 ml of 0.1 M Disodium Edetate (prepared) from the burette with constant stirring

  7. Add 15 ml of Sodium Hydroxide solution with constant stirring

  8. Add 300 mg of Hydroxy Naphthol Blue solution as an indicator to a blue endpoint

  9. Add 0.1 M Disodium Edetate (prepared) with constant stirring and titrate it until the solution gives a blue color
• Calcium Carbonate


  • Previously dried at about 110°C for about 2 hours
• Disodium Edetate


  0.1 M solution prepared
• Sodium Hydroxide solution is added
• Hydroxy Naphthol Blue solution is used as an indicator
• The solution is titrated until it gives a blue color
• Formula used to calculate EDTA molarity

  M = W / 100.90V

  w is weight of Calcium carbonate

  V is volume used of EDTA
• EDTA

  METHOD OF ANALYSIS: Complexation

  EQUATION/S INVOLVED:

  C10H14N2Na2O8.2H2O + CaCO3 ➔ C10H12CaN2NaO8 + CO3^2-

  MW = 351.28

  USP standard: Edetate Disodium contains not less than 99.0% and not more than 101.0% of EDTA
• EDTA DATA:

  Other NameS: 2,2′,2′′,2′′′-(Ethane-1,2-diyldinitrilo)tetraacetic acid

  N,N′-Ethane-1,2-diylbis[N-(carboxymethyl)glycine]

  Diaminoethane-tetraacetic acid

  Edetic acid (conjugate base edetate) (INN, USAN)

  Ethylenedinitrilo-tetraacetic acid, Versene

  Molecular Weight: 372.24 g/mole

  Factor: 4

  Standard solution: Std. EDTA Solution

  Indicator: Hydroxy Naphthol Blue

  End Point: Blue color
• EDTA Reason for special step

  The HCl solubilizes the CaCO3 by converting it to CaCl2.

  The NaOH alkalinizes the solution to a pH of about 13, so that the Ca-EDTA complex would be stable and any magnesium which might be present as contaminant would not react.

  After all the Ca+2 has been complexed with the EDTA, the colored calcium-indicator complex gives up the calcium to the EDTA, liberating the free, uncomplexed indicator, which is blue.
• Expt. No. 14 Preparation and Standardization of Potassium Permanganate Solu'n

  Preparation of KMnO4 solu'n

  1. Weigh 3 g of potassium permanganate in a tared Erlenmeyer flask

  2. Dissolve it in a sufficient amount of distilled water to make 1 L solution

  3. Cover the flask with an inverted beaker

  4. Boil the solution for about 15 minutes and allow it to stand for at least 2 days

  5. Filter through asbestos into an amber colored stock bottle
• Standardization of potassium permanganate solution

  1. Weigh accurately 0.2 to 0.3 g of sodium oxalate

  2. Dissolve it in 250 mL of distilled water

  3. Add 7 mL of sulfuric acid

  4. Heat the solution to about 70°C

  5. Titrate it with potassium permanganate solution until a light or pale pink color,which persist for 15 seconds, is produced
• KMnO4 METHOD OF ANALYSIS: REDOX – Direct Permanganate Method

  EQUATION/S INVOLVED:

  Preparation OF KMnO4:

  4KMnO4 + 2H2O ➔ 4KOH + 4MnO2 + 3O2

  Standardization:

  Na2C2O4 + 2KMnO4 + 8H2SO4 ➔ 2MnSO4 + 5Na2SO4 + K2SO4 + 10CO2 + 8H2O
• Name of Sample Potassium permanganate – KmnO4

  Other Names: Permanganate of potash; mineral Chameleon

  Molecular Weight: 158.034 g/mol

  Factor: 5

  Standard solution/ Secondary standard: KMnO4

  primary standard: sodium oxalate

  Indicator: KMnO4 (works as self-indicator)

  End Point: light or pale pink color
• Potassium permanganate solution Reason for special step

  Sodium oxalate is the best standard to be used in the standardization of KMnO4. Sufficient H2SO4 must be added to keep the H+ constant throughout the titration, thereby preventing the formation of MnO2 and supplying the H+ used up in the reduction of the permanganate ion.
• Expt. No. 15 Assay of Hydrogen peroxide

  Procedure:

  1. Pipette 1 mL of hydrogen peroxide solution into an Erlenmeyer flask

  2. Add 10 mL of distilled water into the flask

  3. Add 10 mL of diluted sulfuric acid into the flask

  4. Titrate it with standard potassium permanganate solution to a light pink color endpoint.