E4 - ADVANCE CHEmestrty LAB PDF

Preview

Summary

ADVANCE CHEmestrty LAB...

Description

DEPT. OF CHEMISTRY CHE 343

EXPERIMENT NO: 4

EXPERIMENT TITLE: ELECTROLYTIC CONDUCTANCE SURNAME: FIRST NAME: ID NUMBER:

NGOMA BOYCE 201701647

DAY:

TUESDAY

DATE OF THE EXPERIMENT:

21 OCTOBER 2020

PARTNER’S NAME AND ID:

MAGAPA T. 201701224

ABSTRACT The molar conductivity of ethanoic acid was determined based on different concentration of three solution (CH3COONa, HCl, NaCl).The value obtained from the experiment was found to be 311334µs/cm /M.

AIM The aim of the experiment is to determine the constant of acetic acid using conductance measurements.

INTRODUCTION

Conductivity also known as the specific conductance of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is Siemens per meter (S/m) Mustafa, A. M. (2012). Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive, and reliable way of measuring the ionic content in a solution. For example, the measurement of product conductivity is a typical way to monitor and continuously trend the performance of water purification systems (Mendham, J. (1989). The conductance of solutions and solid materials in the metal finishing industry plays an important role in determining the overall po\\er efficiency of electroplating and anodising processes. Poorly conducting busbars, electrodes and even electrolytes (i.e., plating solutions) can lead to high cell voltages which. in turn. lead to energy inefficiencies via power dissipated as heat. Electrolytic conductivity of ultra-high purity water as a function of temperature. In many cases, conductivity is linked directly to the total dissolved solids (T.D.S.). High quality deionized water has a conductivity of about 0.5 μS/cm at 25 °C. Resistance, R, is proportional to the distance, l, between the electrodes and is inversely proportional to the cross-sectional area of the sample. i.e. R = ρ

l A

The specific conductance (conductivity), κ (kappa) is the reciprocal of the specific resistance. i.e. κ

=

1 p

The specific conductance of a solution containing one electrolyte depends on the concentration of the electrolyte. Therefore, it is convenient to divide the specific

conductance by concentration. This quotient, termed molar conductivity, is denoted by Λm

i.e. Λm =

κ c

Λºm(CH3COOH) = ν(H+)λ(H+) + ν(CH3COO-)λ(CH3COO-) Since ν(H+) and ν(CH3COO-) = 1, then; Λºm(CH3COOH) = λ(H+) + λ(CH3COO-) In addition Λºm(NaCl) =λ(H+) + λ(Cl-) (1) Λºm(HCl) =λ(H+) + λ(Cl-) (2) Λºm(CH3COONa) =λ(Na+) + λ(CH3COO-) (3) (2) + (3) – (1) ; Λºm(HCl) + Λºm(CH3COONa) - Λºm(NaCl) = λ(H+) + λ(CH3COO-)

Factors Affecting the Electrolytic Conductance The conductance of an electrolyte depends upon the following factors: (I) Nature of electrolyte: Electrolytic conduction is greatly affected by the nature of electrolytes. The degree of dissociation of electrolytes determines the concentration of ions in the solution and hence the conductivity of electrolytes. Substances such as CH3COOH, with low degree of dissociation will have a smaller number of ions in the solution and hence their conductivity will also be low, and these are called weak electrolytes. Strong electrolytes such as KNO3 have high degree of dissociation and hence their solutions have high concentration of ions and so they are good electrolytic conductance. Concentration of the solution: The molar conductance of electrolytic solution varies with the concentration of the electrolyte. In general, the molar conductance of an electrolyte increases with decrease in concentration or increase in dilution.

EXPERIMENTAL PROCEDURE 0.01M each stock solutions of HCl, NaOH and CH3OONa were prepared. Each solution was diluted into 0.005M, 0.002M, 0.001M and 0.0001M respectively into 100mL volumetric flask which there after were filled to mark with distilled water. The conductivity meter was standardized with a reference solution followed by the measuring of the specific conductivity of each solution of various molarity.

RESULTS

TABLE 4.1 SHOWING SPECIFIC CONDUCTIVITY OF SODIUM ACETATE

SPECIFIC CONDUCTIVITIES (µs/cm)

MOLAR CONDUCTIVITIES (µs/cm M -1)

SQUARE ROOT OF CONCENTRATION (√M)

8.785

87 850

0.01

66.415

66 415

0.03

135.13

67 565

324.535

64 907

0.04 0.07

647.2

64 720

0.1

TABLE 4.2 SHOWING SPECIFIC CONDUCTIVITY OF HCL

SPECIFIC CONDUCTIVITIES (µs/cm)

MOLAR CONDUCTIVITIES (µs/cm M -1)

SQUARE ROOT OF CONCENTRATION (√M)

18.705

189 750

0.01

344.235

344 235

0.03

598.933

299 466.5

1 814.635

362 927

0.04 0.07

3 659.635

365 963.5

0.1

TABLE 4.3 SHOWING SPECIFIC CONDUCTIVITY OF NaCl

SPECIFIC CONDUCTIVITIES (µs/cm)

MOLAR CONDUCTIVITIES (µs/cm M -1)

SQUARE ROOT OF CONCENTRATION (√M)

21.615

216 150

0.01

182.735

182 735

0.03

360.535

180 267.5

0.04

881.835

176 367

0.07

1 762.635

176 263.5

0.1

SAMPLE CALCUTION Conversion of ms/cm to µs/cm 1 millisecond / centimetre = 1000 microseconds / centimetre 1 ms/cm = 1000 µs/cm 3.46 ms/cm = 3460 µs/cm

Values of specific conductivity = Specific conductivity of each solution – conductivity of water (double distilled water) k HCl = k sol - k H20 = 3460 µs/cm – 11.5 µs/cm = 3448.5µs/cm

MOLAR CONDUCTIVITY CALCULATIONS Ʌ m = k = 3448.5 µs/cm c 0.01M = 344850 µs/cm M -1

SQUARE ROOT OF THE CONCENTRATION = √c = √0.01 = 0.1 M The limiting molar conductivity of Acetic acid

0 mΛ ( CH3COOH ) = ƛ ( H+ ) + ƛ ( CH3COO¯)

= Ʌ 0 m ( HCl ) + Ʌ 0 m ( CH3COONa ) - Ʌ 0 m ( NaCl ) = 403022 + 75208- 166896 = 311334µs/cm /M

MOLAR CONDUCTIVITY vs SQUARE ROOT CONCENTRATION ACETATE 100000

90000

80000 f(x) = − 196762 x + 80129.5 R² = 0.5 70000

MOLAR CONDUCTIVITY

60000

50000

40000

30000

20000

10000

0

0

0.02

0.04

0.06

0.08

SQUARE ROOT OF CONCENTRATION

0.1

0.12

MOLAR CONDUCTIVITY vs SQUARE ROOT OF CONCENTRATION NaCl 250000

200000

f(x) = − 352572 x + 203985.2 R² = 0.55

MOLAR CONDUCTIVITY

150000

100000

50000

0

0

0.02

0.04

0.06

0.08

SQUARE ROOT OF CONCENTRATION

0.1

0.12

MOLAR CONDUCTIVITY vs SQUARE ROOT AONCENTRATION NaCl 400000 f(x) = 1617470 x + 231594.9 R² = 0.6

350000

300000

MOLAR CONDUCTIVITY

250000

200000

150000

100000

50000

0

0

0.02

0.04

0.06

SQUARE ROOT FUNCTION

0.08

0.1

0.12

DISCUSSION From the experiment, the limiting molar conductivity of ethanoic acid was determined to be 311334µs/cm /M. On another similar experiment conducted by (Wang J., and Luo, D.B., 1984) the molar conductivity was found to be 415744µs/cm /M. The difference between my obtained results and theirs emphasises their disagreement towards the result from this experiment. Not only that as another literature value differs with the results, as (Smith, A.B. 1986)’s results were different as 425447 µs/cm /M, are not in parallel with the results of this experiment the accuracy of the experiment was poor. The percentage deviation from the experiment is 50% which is very high hence reflect poor results. The R2 of the graphs of molar conductivity vs function of the square root was an average of 0.5 hence this shows poor precision. The possible errors that might have affected the result is the contamination of standardizing liquid of the conductivity meter hence leading to a systematic error being occurred. One of the advantages of using spectrometers is the accuracy of the device. Even small spectrometers can give extremely accurate readings, which is crucial when you are preparing chemical solutions or recording the movement of celestial bodies. Recommendations when dealing with conductometric experiments is that, one should ensure that the probe is fully submerged in the sample. Also, the conductivity meter should be standardized.

CONCLUSION The limiting molar conductivity was determined from the experiment to be 311334µs/cm /M.

REFERENCE Basset, G., Denney, R., Jeffery, G., & Mendham, J. (1989). Vogel's textbook of chemical analysis, fifth edition. New York: John Wiley and Sons. Byers, A. J. (2003, 3 24). Phenomenex catalog. Retrieved 03 24, 2015, from www.Phenomenex.com: http://www.chemical-ecology.net/java/solvents.htm Mustafa, A. M. (2012). Advanced Gas Chromatography: Prgress in Agricultural, Biochemical and Industrial Applications. Croatia: In Tech. Riley, R., & Szecsody, J. (2005). Carbon Tetrachloride and Chloroform Partition Coefficients Derived from Aqueous Desorption of Contaminated Hanford Sediments. U.S.A: U.S Department of Energy.

Wang, J and Luo, D.B. Electroanalysis, 31. (1984) Smith, A.B. “Instrumental Chemical Analysis”; Jones Publishing Co. New York, 1986, (pp 23-30)...