Reference no: EM132366876

Colorimetric analysis of Phenols

AIM

Colorimetric analysis of ‘Total Phenols' in Waste Waters.

SAFETY

Take particular care in regard to the hazards below. Wear protective gloves during this experiment.
• Phenol solution. Toxic in contact with skin and if swallowed. Wear gloves to avoid ingestion and as skin contact causes severe burns. Wear safety glasses to protect eyes. Harmful to aquatic organisms. Dispose of waste in an appropriately labelled separate container.
• Ammonia, concentrated (33%): Wear gloves to avoid ingestion and as skin contact causes severe burns. Wear safety glasses to protect eyes. Use only in fumehood as fumes are hazardous. Dilute carefully in fumehood.
• Electrical equipment represents an electrocution risk and should be visually checked before use. Do not use a faulty power point or electrical equipment with damaged cable or plug. Make sure that electrical equipment is safely connected to power supply and away from errant sources of water.
• Distillation apparatus must be continually monitored during use. Make sure that the initial amount of liquid in the distillation flask is between one-third and one-half the flask capacity. Add anti-bumping granules to cold liquid in the distillation flask and gradually adjust heat to maintain a gentle distillation. Do not allow distillation flask to become dry as an explosion could result.

INTRODUCTION

Phenol (or hydroxybenzene, C6H5OH) and its derivatives may be encountered in natural and waste waters originating from industrial and domestic sources. Phenols are encountered widely either as the raw materials in the production of plastics, pharmaceuticals, pesticides and disinfectants or as the final products in certain manufacturing processes. They also appear as by-products from petroleum refining, paper pulping and water purification. These compounds are classified as toxic substances by environmental protection agencies and it is important to be able to determine their concentrations in sediments, soils and aqueous samples.

One of the approved methods is the 4-aminoantipyrine (4-AAP) colorimetric procedure that determines phenol, ortho- and meta-substituted phenols, and only some para-substituted phenols. The parent phenol, C6H5OH, has been chosen as the standard for this colorimetric method. Any reaction of 4-AAP with this or other phenols in natural and waste waters is expressed as "total phenols". Because substituted phenols often give reduced responses, the value for "total phenols" is regarded as the minimum concentration of phenolic compounds in the sample.

EXPERIMENTAL INSTRUCTIONS

PART 1. Distillation of Phenols

As the waste waters may be contaminated by other impurities, the Standard Method involves distillation of the phenols from any involatile impurities.

Apparatus:
The distillation apparatus consists of a 250 mL round-bottom flask, a suitable heating mantle, a stillhead, a condenser and an adapter to collect the distillate in a 100 mL graduated measuring cylinder (or similar graduated vessel).

Solutions supplied:
a. Waste water sample, preserved by addition of CuSO4 and sulfuric acid (to pH < 2).
b. 0.5M NaOH solution.

Experimental Procedure:

1. Calibrate pH meter using 4.00 and 6.88 pH buffers

2. Measure 100 mL of the waste water sample (dilute if the sample is too concentrated) into a beaker and adjust the pH to approximately

4.0 ± 0.20 by dropwise addition of the 0.5 M NaOH solution supplied. You may use a pH meter to do this or methyl orange indicator.

3. Pour the entire contents of the beaker into the round-bottomed flask, add anti-bumping granules and assemble the distillation apparatus. Make sure that all joints are secure and tight to maintain a "closed" distillation system (note that a fully closed system would lead to pressure building up and an explosion. The only opening in your setup should be the receiver end. Don't forget to put thermometer at the top and cover the flask with aluminium foil.

4. Distil 90 mL of the sample, stop the distillation and when boiling ceases, add 10 mL of distilled water to the round-bottomed flask.

5. Start the distillation again and collect a further 10 mL of distillate in the graduated measuring cylinder. Watch this last step very carefully to avoid the distillation flask drying out! The collected distillate should be clear.

PART 2. Spectrophotometric Method

Theoretical background:
"Phenols" react with 4-aminoantipyrine (4-AAP) at pH 7.9 in the presence of potassium ferricyanide as oxidant to produce a red dye that absorbs strongly at 510 nm. Interferences are reduced to a minimum by prior distillation of the waste water. The method is then capable of detecting 50 µg of phenol in 100 mL of distillate using a 1 cm spectrophotometric cell.

4-A AP DYE

Solutions supplied:
a. Stock phenol solution (1000 mg/L).
b. Concentrated ammonia (33% w/v).
c. Phosphate buffer solution.
d. Potassium ferricyanide solution (8% w/v).

Experimental Procedure:

Solutions to be made up fresh: (Only one set of solutions need to be prepared per session)

1. Prepare 0.5 M ammonium hydroxide (NH4OH) by diluting 3.5 mL of conc. ammonia to 100 mL with distilled water (CAUTION: do this dilution in a fume hood. Wear gloves).

2. Prepare a 2% 4-AAP solution by dissolving 0.5 g of 4-aminoantipyrine in 25 mL water in a 50 mL conical flask.
Sample preparation and measurement:
1. From the supplied stock phenol solution (1000 mg/L), pipette 10 mL into a 100 mL volumetric flask, make up to the mark with distilled water and mix well (wear gloves!).
From the above freshly prepared 100 mg/L phenol solution, pipette the appropriate volumes into 100 mL volumetric flasks and make up to the mark with distilled water to prepare a series of phenol standards of concentration 1.0, 2.0, 3.0, 4.0 and 5.0 mg/L. Mix the standards well.
2. Place 100 mL of the distillate in a 250-mL beaker. Pour 100 mL of each of the above five standards into five separate 250 mL beakers. In another 250-mL beaker, place 100 mL of distilled water as a blank. Seven beakers all together.
3. Calibrate pH meter using 6.88 and 9.0 buffers.
4. Treat the sample, blank and standards as follows: add 2.5 mL of freshly prepared 0.5 M NH4OH solution (do NOT use conc. ammonia here), followed immediately by dropwise addition of the phosphate buffer to adjust the pH to 7.9 ? 0.1. Add 1.0 mL of 4-AAP solution and 1.0 mL of the potassium ferricyanide solution, mixing well after each addition.
5. Allow all solutions to stand for 15 min for colour development. Measure the absorbance of the sample and standards against the blank at 510 nm using GENESYSTM 20 Visible Spectrophotometer. Construct a calibration plot for the phenol standards and determine the "total phenol" content of the sample from the calibration plot.

REPORT

AIM
State in one or two sentences what you aim to achieve in this experiment.
INTRODUCTION
Discuss about total phenol presence in water and possible methods of measuring it.

METHOD
In passive voice concisely explain the experimental procedure and also include a diagram of the distillation apparatus.

RESULTS:
Present your results in a clear and intuitive manner.
Include table, calibration graphs and sample calculations for standards Calculate standard deviation and correlation coefficient

DISCUSSION:

1. Discuss the reliability of your measurements (use standard deviations, correlation coefficients and any relevant observations for your arguments)
2. Compare your results with accepted limits of phenols in water
3. How can Phenols be removed from waste water?
4. Explain the distillation process.
5. Are there any limitations of "colorimetric analysis method of phenols" in waste water? Explain

CONCLUSION:
Quote your results in the conclusion to show you have achieved your aim. No discussion or explanation should be given here.

Attachment:- Colorimetric analysis of Phenols.rar