CHM421- Experiment 5 Distillation AND Hardness OF Water PDF

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nullLABORATORY REPORTCHM 421( ANALYTICAL CHEMISTRY )NAME:STUDENT NO.:GROUP: AS2464AEXPERIMENT NO: 5EXPERIMENT TITLE : DISTILLATION AND HARDNESS OF WATERAbstractThe purpose of this experiment is to purify the water samples by distillation, to standardise EDTA solution and to analyse hardness of water...

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LABORATORY REPORT CHM421

(ANALYTICAL CHEMISTRY)

NAME: STUDENT NO.: GROUP: AS2464A1 EXPERIMENT NO: 5 EXPERIMENT TITLE: DISTILLATION AND HARDNESS OF WATER

Abstract The purpose of this experiment is to purify the water samples by distillation, to standardise EDTA solution and to analyse hardness of water samples by titration with EDTA. Distillation can produce a clean and pure water that is free from impurities. Three are six water samples that were used in this experiment. From the experiment conducted, deionized water had the highest hardness of all the water samples, with 114.50 ppm, according to the water hardness analysis. The water sample with the lowest hardness was 3.95 ppm, which was distilled home tap water. Lab tap water had the same hardness as lab distilled water, which was 37.53 ppm. The concentrations of 32.59 ppm in home tap water and 16.79 ppm in 0.1 M NaOH were found to be 32.59 ppm and 16.79 ppm, respectively.

Introduction Distillation of water can produce a pure water which is free from impurities and contaminants. During the distillation process, the water sample was heated to form a steam. The presence of ions such as calcium and magnesium in the water samples causes hard water to form. Hardness is primarily caused by the ions calcium (Ca+2) and magnesium (Mg+2), although it can also be caused by other metals. The accumulate calcium and magnesium content in water was calculated in this experiment by titrating with a regular ethylenediamine tetraacetic acid (EDTA) solution, and because of the low concentration value of these ions, hardness is usually expressed in ppm units rather than molarity (complexometric titration).

Objective To purify water samples by distillation, to standardise EDTA solution and to analyse hardness of water samples by titration with EDTA.

Methodology A. Distillation of home tap water 150 ml of round bottom flasks was used for distilling flask and a 250ml of conical flask for receiver to collect the distillate. The distilling flask was filled to about two thirds with home tap water. A couple of boiling chips was added to the flask to prevent bumping. The tap water was turned on and the water flowing uphill was checked in the condenser. The mercury bulb of the thermometer was also checked to slightly lower than the junction of the condenser with the distillation column. The distillation flask was heated with a Bunsen flame. Start collect the liquid when the water boils followed by the condensation. While waiting for the distillation process, the titration for standardizing the EDTA had been set up. The first 20 drops or the distilled water collected was discarded as they might contain volatile impurities from the distillation glassware. The temperature of the distillation flask was recorded as soon as 1 ml of distillate was collected. The distillate was collected until there are about 5 ml of the liquid left in the distillation flask. The temperature of distilling flask was recorded at the point of distillation was stopped and turned off the burner.

B. Standardisation of the EDTA solution

A 50 mL burette was rinsed inside with distilled water. The stopcock was opened and it was completely drained into a waste beaker. The burette was thoroughly cleaned and had no reagent spot. The burette was rinsed with EDTA solution before discarded. The EDTA solution was poured into the burette beyond the zero mark and it was made sure to close the burette valve earlier. The burette was attached to the burette stand. The tip of the burette was checked to see if there is any air bubble trapped. The initial reading was adjusted after the bubble was removed. 25.0 mL aliquots of the prepared standard Ca2+ was pipetted and transferred to a 250 mL conical flask. The concentration of the CaCO 3 prepared was recorded. 8ml of pH 10 ammonia ammonium chloride buffer, 15 ml of distilled water and 3 drops of Eriochrome Black T indicator was added into the flask. The sample was titrated immediately with the EDTA solution against a white background until the light pink solution turns to light sky blue. The volume of the burette at the end point was recorded. The whole process was repeated at least with two more samples. The reaction mixture will

evaporate NH3 to some degree and the pH of the solution changes. A rough titration was performed to determine the approximate endpoint and to observe the colour change. After the titration of the rough one, about 2 or 3 mL of the endpoint was added rapidly then ½ drop or drop by drop at a time was titrated to the endpoint. The side of the flask and the burette tip was washed to ensure all the titrant had gotten into the solution in the flask.

C. Hardness of Water

The burette was filled up again by using the EDTA solution. A 25 mL pipette was rinsed with tap water 25.0 mL of lab tap water was pipetted into a 250 mL conical flask. 8 ml of ammonia ammonium chloride buffer, 3 drops of Eriochrome black T indicator was added into water sample flask. The initial burette was recorded to the nearest 0.01 mL. The standard EDTA solution in the burette was added to the water sample in the flask. Slow down the addition of titrant when the blue colour started to form. The red colour will replace the blue colour once all the calcium and magnesium are exhausted. Once the colour changed, the titration was stopped, the final burette reading was recorded. The titration was repeated with another two more lab tap water samples. A little bit of lab distilled water was obtained using the rubber filler. The filler was removed, the pipette was tilted and rotated to rinse the inside of the pipette with the distilled water. The tained distilled water was thrown away. 25.0 mL of fresh distilled water was pipetted into a clean but not necessarily dry flask. Buffer and indicator were added and titrated with the standardised EDTA solution. The same step was repeated. The pipette was rinsed with home tap water or an unknown supply. 25.0 mL of the unknown was pipetted into a clean flask. Buffer and indicator were added and titrated with the standardised EDTA solution. The method for the rest of the sample was repeated and data was recorded.

Results

A. Distillation of home tap water 1. Temperature at the start of collecting the distillate = 96.0 °C 2. Temperature at the end of collecting the distillate = 99.0 °C 3. Experimental boiling range for collected sample = 3.0 °C

B. Standardisation of the EDTA solution Concentration of standard Ca2+ solution = 0.007M Volume of the standard Ca2+ solution = 25.0 ml

Final reading of EDTA solution Initial reading of EDTA solution Volume of EDTA solution (mL)

Rough 37.50

1 35.75

2 35.55

0.10

0.15

0.20

37.40

35.60

35.35

Average volume

C. Hardness of Water

Concentration of EDTA = 0.004933M M1V1=M2V2 (0.007)(25) = M2 (35.475) M2 = 0.004933M

Water sample

Lab tap water

Lab distilled water

Home tap water

Distilled home tap water

Deionized water

0.1 M NaOH

Final reading of standard EDTA Initial reading of standard EDTA Volume of standard EDTA used (ml) Volume of water sample (ml) [Ca2+ + Mg2+] (mol/L) Hardness (ppm)

2.00

4.00

1.85

0.30

9.90

10.85

0.10

2.10

0.20

0.10

4.10

10.00

1.9

1.9

1.65

0.20

5.8

0.85

25.0

25.0

25.0

25.0

25.0

25.0

3.749×10-4

3.749×10-4

3.256×10-4

3.946×10-5

1.144×10-3

1.677×10-4

37.53

37.53

32.59

3.95

114.50

16.79

*Hardness is usually expressed as ppm CaCO3

Lab tap water M1V1 (EDTA)

= M2V2 (lab water)

(0.004933) (1.9)

= M2 (25)

M2

= 3.749×10-4 mol/L

Molar mass of CaCO3 (40.1) + (12.0) + (16 x 3) =100.1 g/mol

Mass concentration of CaCO3 3.749×10-4 mol/L × 100.1 g/mol = 0.03753 g/mol

ppm(w/v) CaCO3 0.03753 × 1000 = 37.53 ppm

Discussion

In this experiment, for the first part the distillation of home tap water was done to purify the water sample. The function of distillation was to separate the impurities such as mineral, magnesium and calcium from the water. The experimental boiling range for collected samples in the distillation process was 3.0˚C. For the standardisation of the EDTA solution, the concentration of standard Ca2+ was 0.007M and the volume of standard Ca 2+ was 25.0 ml. The average EDTA solution used was 35.75 ml. The concentration of EDTA used calculated was 0.004933 M. For the hardness of water, the water sample was titrated with the same concentration of EDTA solution. There are six water samples used in this titration which are lab tap water, lab distilled water, home tap water, distilled home tap water, deionized water and 0.1 M NaOH. In the water sample, ammonia ammonium chloride buffer and Eriochrome black T indicator was added. By adding the buffer and indicator, the water sample will change from blue to red which indicates all the calcium and magnesium was exhausted. From the experiment, all six samples had different volumes of standard EDTA titrant. From the calculation done, the hardness water for deionized water was the highest with 114.50 ppm which classified as medium hard. For the rest of the sample, all water samples were categorized as soft water with the range of ppm being between 0 - 60 ppm. Lab tap water and lab distilled water has the same hardness, 37.53 ppm. The lowest hardness was distilled home tap water which is 3.95 ppm. For the home tap water and 0.1 M NaOH was 32.59 ppm and 16.79 ppm respectively. From the experiment, deionized water which has the highest hardness among the other water samples contains more Ca2+ ions.

There are a few precautions that can be done in this experiment. Firstly make sure all the apparatus used was free from impurities before use to prevent any contaminant. Next, remove any bubble in the burette nozzle before taking the initial reading. Other than that, always read any reading in the meniscus.

Conclusion In conclusion, all the three objectives stated were achieved. The average concentration of EDTA solution was 0.004933 M. Through the analyse hardness of the water sample, deionized water was the highest hardness among all the water samples with 114.50 ppm. The lowest hardness of the water sample was 3.95 ppm which is distilled home tap water. The hardness of lab tap water was the same as lab distilled water which is 37.53 ppm. For the home tap water and 0.1 M NaOH was 32.59 ppm and 16.79 ppm respectively.

References 1. Verma, K. C., & Kushwaha, A. S. (2014). Demineralization of drinking water: Is it prudent?. Medical Journal Armed Forces India, 70(4), 377-379. 2. Saidur, R., Elcevvadi, E. T., Mekhilef, S., Safari, A., & Mohammed, H. A. (2011). An overview of different distillation methods for small scale applications. Renewable and sustainable energy reviews, 15(9), 4756-4764. Questions 1. Why should the water in the condenser flow uphill during distillation? By forcing the water uphill, the condenser will be entirely filled. 2. Compare the hardness between i) lab tap water and lab distilled water ii) home tap water and home distilled tap water. Did the distillation have a significant effect on the water hardness? Explain your answer. i. The hardness of lab tap water is more than lab distilled water. This is because lab tap water contains impurities such as calcium and magnesium.

ii.

The hardness of home tap water is higher and home distilled tap water. This is because home distilled tap water had removed the impurities by distillation process.

3. Water with hardness in the range 0-60 ppm is termed soft, 60-120 ppm is medium hard, 120180 ppm is hard and above 180 ppm is very hard. Classify the water samples that you analysed in the experiment.4. Do you think there should be a correlation between conductance and hardness results? Explain your answer.  Lab tap water- soft  Lab distilled water- soft

   

Home tap water- soft Distilled home tap water- soft Deionized water- medium hard 0.1 M NaOH- soft

4. Suggest any ways you can think of to improve any parts in this experiment. The experiment should be repeated at least once to ensure that the value of the titre that was obtained was accurate. Hardness of water can be defined as the amount of impurities such as calcium and magnesium that dissolved in water. The presence of inorganic dissolved solids, such as cation and anion, affects water conductivity. Higher concentrations of these impurities will result in increased conductivity. 5. Suggest any ways you can think of to improve any parts in this experiment. The experiment should be repeated at least once to ensure that the value of the titre that was obtained was accurate. Make the burette must be observed at eye level straight to the bottom of the meniscus and all the apparatus must be free from any impurities....