Chm421 Experiment 5

EXPERIMENT 5:

Title: Distillation and Hardness of water Objectives: 1. To purify water sample by distillation. distillation . 2. To standardize EDTA solution. 3. To analyze hardness of water water samples by titration with EDTA.

INTRODUCTION: Complexometric titrations are titrations that can be used to discover the hardness of water or to discover metal ions in a solution. Ethylenediaminetetraacetic acid, also known as EDTA, is commonly used in complex metric titrations. This is because it makes six bonds with metal ions to form one to one complex (“Complex Titrations”). In a complex metric titration, an ion is transformed into a complex ion. The equivalence point is determined by a metal indicator. Erichrome black T is an indicator that can be used to determine calcium content in a solution. The complex that is initially formed is red. After all the calcium ions have reacted, the complex then turns blue. This indicates the endpoint of the titration. In the experiment, EDTA will first be made and then standardized. This will be done by preparing a calcium chloride solution. In the reaction with the EDTA, calcium carbonate is converted to calcium chloride. Ammonia-ammonium chloride will also be prepared to be used as a buffer in the solution. The professor prepared the Erichrome black T to be used as an indicator. This indicator will be cause the solution to be red at the before the titration and then at the endpoint, the solution will turn blue. Make sure it is blue and not purple. After the standardization of EDTA, the calcium content in an unknown water sample will be found. This will be done with same way as the first titration occurred. The hardness will then be calculated in parts per million. Water hardness is reported as the concentration of carbonates in parts per million (ppm), using calcium carbonate as a generalized concentration that encompasses all divalent cations in the sample. Table 1 shows how CaCO3 concentrations affect the overall hardness of a water source. Magnesium and calcium concentrations (the most abundant in water) are used to calculate water hardness by the formula: [CaCO3] total = 2.5[Ca] + 4.1[Mg] 3

PROCEDURE:  A. Distillation of the home tap water 1. Set up distillation apparatus. 2. 150 mL round bottom flasks used for the distilling flask and a 250 mL conical flask for the receiver to collect the distillate. 3. Every apparatus was clamp adequately. 4. Two third home tap water was filled in the distilling flask. A couple of boiling chips was added. 5. Water was flows uphill in the condenser and the mercury bulb of the thermometer was checked. 6. First 20 drops of the distilled water collected was discarded. 7. Temperature start and stop was recorded. B. STANDARDISATION OF THE EDTA SOLUTION 1. 50 mL burette was clean with distilled water then EDTA solution. 2. The EDTA solution was pour in the burette beyond the zero mark. 3. 25.0 mL of the prepared standard CaCO 3 was pipette to 250 mL conical flask and the concentration of the CaCO 3 was recorded. 4. 8 mL of pH ammonia-ammonium chloride, 15 mL of distilled water and 3 drops of Eriochrome Black T indicator was added to the flask. 5. The volume of the burette at the endpoint was recorded and the whole process was repeated for two more samples. C. Hardness of water 1. Burette filled with EDTA solution 2. 25 mL pipette was rinsed and 25.0 mL of lab tap water was pipette into a 250 mL conical flask. 3. 8 mL of the ammonia-ammonium chloride and 3 drops of Eriochrome Black T was added to the flask. The initial burette reading was recorded. 4. The solution turned blue and the final reading was recorded 5. The titration was repeat with another water samples which is lab distilled water, home tap water and distilled home top water.

RESULT: EXPERIMENT 5: DISTILLATION AND HARDNESS OF WATER  A. Distillation of home tap water 1. Temperature at the start of collecting the distillate = 100  oC 2. Temperature at the end of collecting the distillate = 99 oC 3. Experimental boiling range for collected sample = 100 oC B. Standardization of the EDTA solution Concentration of standard Ca 2+ solution = 0.1 M Volume of the standard Ca 2+ solution

= 25.0 mL

Rough

1

2

3

Final reading of EDTA solution

6.5

17.0

25.0

39.5

Initial reading of EDTA solution

0

10.5

17.0

25.0

Volume of EDTA solution (mL)

50

50

50

50

C. Hardness of water Concentration of EDTA = 1 M Water samples

Lab tap water

Lab distilled water

Home tap water

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)

0.2

1.1

1.2

Distilled home tap water 1.4

0

0.2

1.1

1.2

50

50

50

50

25

25

25

25

Hardness (ppm)

DISCUSSION: From the first purpose of this experiment is the purification of the water sample by distillation, which is to separate the substances and as such can be used for water purification. The experimental boiling range for collected sample is about 100 ˚C and the water sample was kept for the other procedure. For the second objectives is to standardize EDTA solution. We are using 0.1 M of concentration of standard Ca2+ solution and the volume of it is 25 mL. The volume of EDTA solution that we are used which is 50 mL. Meanwhile, the average concentration of EDTA solution as we have been calculated is 0.05M. To analyse the hardness of water samples by titration with EDTA is the last purpose of this experiment. As you can see at the table data, about four water sample than six we are doing when conduct the experiment which is lab tap water, home tap water, lab distilled water and distilled tap water. We do not have the water sample of home tap water and also distilled home tap water because we are conducting the experiment in the laboratory room. The total amount of Calcium ion and Magnesium ion that react with the EDTA solution in lab tap water is mol/L and their hardness is 403.6 ppm. The water hardness is very hard because the theoretical value for very hard water is more than or equal to 450 ppm. Next, for the lab distilled water, the amount of concentration of Calcium ion and Magnesium ion is about mol/L. The hardness of water is also very hard, which is ppm. About mol/L of concentration of Ca2+ and Mg2+ and the amount of their hardness is ppm for water samples of home tap water. Lastly, distilled home tap water was done by calculate its concentration of Ca2+ and Mg2+, mol/L, hence their hardness of water is very hardness which is about ppm. As a student, I have found that some errors while doing the experiment by us which is when reading the scale of the liquid inside the pipette. After that, maybe we are put an extra drops of titrant to the solution which is to prevent the overshoot of the endpoint, frequently wash the sides of the flask and the burette tip to ensure all the titrant has gotten into the solution in the flask. Not even that, the EDTA solution that we are used must be not exposed to the air and it was made sure that the solution is always closed. The EDTA solution also must be in a fresh solution, not the old solution one.

CONCLUSION:  As a conclusion, the purification water sample by distillation was achieved. Next, the average value of standardize the EDTA solution is 0.05 M. Lastly, the analyze hardness of water samples by titration with EDTA is hardness (soft) include home tap water, lab distilled water, distilled home tap water and the hardness (medium) is lab tap water, which is their hardness is around 403.6 ppm, 240.2 ppm, 220.2 ppm and 280.25 ppm.

REFERENCES: 1. Adams, C., Wang, Y., Loftin, K., & Meyer, M. (2002). Removal of antibiotics from surface and distilled water in conventional water treatment processes. Journal of environmental engineering, 128(3), 253-260. 2. Hardness in Drinking-water. (2003). Retrieved October 7, 2009, from http://www.who.int/water_sanitation_health/dwq/chemicals/en/hardness.pdf 3. Dean, Norman, Cathrine Reck, Todd Stone, and Jill Robinson. Chemistry C117: Principles of Chemistry and Biochemistry: Laboratory Manual. 8th ed. Plymouth: Hayden-McNeil, 2009.

QUESTIONS: 1. Why should the water in the condenser flow uphill during distillation? - The flowing of cool water should be uphill to prevent the condenser from becoming too hot on it inner surface. If the condenser became too hot, the distillate will escape as a vapor from the system 2. Compare the hardness between: i. Lab tap water and lab distilled water ii. Home tap water and home distilled water - Lab tap water is more hardness than lab distilled water. Home tape water is more hardness than home distilled tap water. Distillations have significant effect on the water hardness. Distillation process will remove the impurities in the water, so distilled water and home distilled tap water is clean because it does not contain impurities. 3. Water with hardness in the range 0-60 ppm is termed soft, 60-120 ppm medium hard, and 120-180 ppm hard and above 180 ppm very hard. Classify the water samples that you analyzed in this experiment. Hardness (soft): - lab tap water - lab distilled water - home tap water - distilled home tap water 4. Do you think there should be a correlation between conductance and hardness results? Explain your answer. - Conductivity will have a large concentration to the water hardness because concentration of calcium is easier to measure than the calcium ion

concentration. The conductivity contribution due to the sodium can be subtracted from the total observed electrolyte conductivity 5. Suggest any ways you can think of to improve any part of this experiment. - For part C of the experiment, at least 3 readings should have been taken to obtain a more precise reading for the hardness of water samples.