Lu Le Laboratory: 2013

Monday, October 7, 2013

UV-Visible Spectrophotometric Determination of Phenol in Wastewater-Experiment of Instrumental Analysis

Propose

1. Learn to use UV-2100 UV-Visible Spectrometer.

2. Become familiar with the determination of phenol in wastewater.

Principle

Phenol is a chemical substance which is toxic, harmful and unfriendly for the environment. But it is still used in food and drug, so wastewater containing phenol is produced during manufacturing. The most important thing is controlling the concentration of phenol in the wastewater.

Neutral phenol wastewater has a strong absorption at λ_max= 270 nm. We can utilize the characteristic to determine the concentration of phenol in the wastewater according to Lambert-Beer law.

Equipment

1. Shimadzu UV-2100 uv-Visible Spectrometer

UV-Visible spectrometer

Deuterium lamp

Tungsten lamp

2. Volumetric flask 100mL x1, 50mL x6

3. Quartz cuvettes

Chemicals

1. Standard phenol solution, 1.000 L, 0.3170 g/L

2. Wastewater

Procedure

1. Turn on the spectrometer and allow about 30 minutes for warm up.

2. Fill the blank cuvette with pure water (reference solution). Polish to clean, insert into the cuvette chamber, aligning mark to front. Close chamber cover. Click the blank icon.

3. Determine the full spectrum of the standard phenol sample.

4. Set the wavelength at 270 nm. Dilute following samples into 50.00mL with volumetric flasks.

Label	Volume of Standard Phenol Solution
0	0.00 mL
1	2.00 mL
2	4.00 mL
3	6.00 mL
4	8.00 mL
5	10.00 mL

Label	Volume of Unknown
Unknown	2.00 mL

5. Measure absorption of samples and make a calibration curve with sample 1 to sample 5.

6. Determine the concentration of phenol of the unknown with the calibration curve.

Results

1. The full UV spectrum of standard phenol solution (solvent: water).

2. Calibration Curve of Phenol Solution

Label	Absorption (270.00 nm)	Concentration (mg/L)
0	0.000	0.000
1	0.197	12.680
2	0.387	25.360
3	0.571	38.040
4	0.756	50.720
5	0.948	63.400

Equation	*y = a + bx**
Adj. R-Square	0.99986
		Value	Standard Error
Absorption	Intercept	0.005	0.00305
Absorption	Slope	0.01487	7.95E-05

y = 0.005 + 0.01487*x

3. Determination of the Unknown

Label	Absorption (270.00 nm)
Unknown	0.416

0.416 = 0.005 + 0.01487*x

=> x = 27.640 mg/L

Concentration of Phenol of the Unknown Sample

27.640 mg/L

So we can get the molar absorptivity

(0.416 / ((27.640 mg/L) /1000 / (94.11g/mol))) / (1.00 cm)

= 1416.42 L mol⁻¹ cm⁻¹

Molar absorptivity of Neutral Phenol solution (270.00 nm)

27.640 mg/L

Friday, September 20, 2013

Isoteniscope-The Determination of the Saturated Vapor Pressure of Liquid-Experiments in Physical Chemistry

Purposes

1. Use the Clausius-Clapeyron equation to figure out the average molar enthalpy of vaporization of a liquid inside the measured temperatures.
2. To master measuring saturated vapor pressure of liquid.

Principle

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of particles to escape from the liquid.

The vapor pressure of any substance increases non-linearly with temperature according to the Clausius–Clapeyron relation:

Where R is gas constant, T is the temperature, p Is the pressure, Δvap Hm is the enthalpy of vaporization.
When the change of the temperature is small, we can assume the enthalpy of vaporization is independent of temperature, this equation can be integrated as follows:

then

where A is Δvap Hm/R , B is a integral constant.

According to the equation, we can get a line if we make (ln p)-(1/T) figure, and the slope “m” should be –A = -Δvap Hm/R. And then we get:

And the boiling point can be figured out by the figure.

Apparatus

1. An isoteniscope

2. A vacuum pump

Vacuum pump (right) and desiccators (middle)

3. A barometer

Chemicals

1. Absolute Ethanol (A.R.)

Procedure

1. Stet up the apparatus as below:

2. Leak detection:
Turn off the H valve, and open the I, F, G valves. Turn on the vacuum pump until the pressure reaches 25~30 kPa and then turn off the I, F, G valves, and then turn off the pump. Wait for a minutes and check the value of the barometer.

3. Heating:
Open the stirrer and adjust the voltage of the heater to about 160V.

An autotransformer

4. Degas:
When the temperature of the hot water bath is over 50℃, the ethanol inside the isoteniscope starts bubbling. Keep the temperature at about 52℃ for 5 minutes by adjusting the voltage of the heater.

5. The measurement of vapor pressure:
Open the H valve slowly let air defuse through the capillary, until the BC phase is matched and is stable at least 1 minute. Record the temperature of the hot water bath and the pressure of the barometer. Keep heating the water bath and do the same things 6~10 times after raise about 2 degrees every times.

6. Finish:
Turn on all the valves, turn off all the electronics, and clean up the table.

Report Sheet

Data Processing

Fitting with an exponential function, y = a*b^x , on the P-T figure.

Figure 1

Linear fitting on the ln(Pa)-1/T figure

Figure 2

From this fitting curve, we can get the enthalpy of vaporization by using the equation as follow:

Δvap Hm = - (8.3144621 J / (K mol) ) x (-5172.43 K)
= 43.0 kJ/mol
We can also get the normal boiling point from the fitting curve.
y = 26.29912 - 5172.43*x
ln(101325 Pa) = 26.29912 – 5172.43x
x = 1/T
=> T = 1/(((ln 101325) – 26.29912) /(.5172.43))
= 350.12 K = 76.97 ℃

To compare with the literature datas