Laboratory Report on Water Salinity PDF

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University of the Philippines Visayas Tacloban College Division of Natural Sciences and Mathematics Analytical Chemistry LaboratoryName:Reynaldo P. Peja Jr. Date Performed: November 25, 2014 Laboratory Schedule: TF 8:30-11:30 Date Submitted: December 12, 2014 Group No. 3 “LON-LON” Rating:SALINITY DE...

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University of the Philippines Visayas Tacloban College Division of Natural Sciences and Mathematics Analytical Chemistry Laboratory Name:Reynaldo P. Peja Jr. Laboratory Schedule: TF 8:30-11:30 Group No. 3 “LON-LON”

Date Performed: November 25, 2014 Date Submitted: December 12, 2014 Rating:

SALINITY DETERMINATION IN WATER BY MOHR METHOD Experiment No. 13 Objective: 1. To determine the salinity of a natural water using the Mohr method. Results and Discussion: Salinity is the measure of the amount of salt in a solution (Merriam Webster). In this experiment, the salinity of natural water as sample were determined by Mohr method. This method is an example of argentometric titration method that uses chromate ion as indicator in the titration of chloride ions with silver nitrate. Since the chloride ions can be easily precipitated by silver nitrate, and the quantity of chloride ion is directly proportional to the salinity of the water, the experimentation measure the amount of the ions. At the start of the experiment solutions were prepared by the groups. These solutions were Silver nitrate of approximately 0.0141 M, Sodium chloride of same concentration, Potassium chromate indicator (5%) and sulfuric acid. The silver nitrate was standardized by titrating a proper amount of NaCl, and distilled water with potassium chromate indicator into it. As an end point indicator, the solution turns from yellow to pinkish. The results are shown below for the three trials. Table 1. Pertinent data for Standardization of Silver Nitrate solution

Trial No.

1 2 3

First Reading of Silver nitrate Volume 1.1 mL 13.2 mL 25.6 mL

Final Reading of Silver nitrate volume 13.2 mL 25.4 mL 38.2 mL

Volume of Silver Molar nitrate Concentration Delivered of Silver Nitrate 12.1 mL 0.0116 M 12.2 mL 0.0115 M 12.6 mL 0.01119 M Average: 0.01143 M

For the computation of M of Silver nitrate, the group used the formula:

M Silver Nitrate =

mL where the mL of NaCL used was 10 mL and ( mL NaCl)( M NaCl ) nitrate ¿ ¿ its concentration was 0.0141 M.

After standardizing the Silver nitrate solution, the group determine the salinity of the water sample collected at Mangonbangon River in Tacloban City. Three proper amounts of this sample were transferred to corresponding Erlenmeyer flasks and were added with potassium chromate indicator and sulfuric acid to adjust the pH to 7-10.Distilled water as blank titration with the indicator was also prepared. These were titrated with standardized Silver nitrate. Shown below were the results of the titration for the trials made. Table 2. Pertinent data for the Determination of Chloride ions (mg) per liter in the water sample

Trial

1

First Reading of Silver nitrate Volume 0.6 mL

Final Reading of Silver nitrate volume 10 mL

Volume of Silver nitrate Delivered 9.4 mL

2

10 mL

18.7 mL

8.7 mL

3

18.7 mL

28.3 mL

9.6 mL

Blank titration

11.4

12.4 mL

0.7 mL Average: 346.253 Cl- mg per liter

mg per liter of Chlorine ion 353.016 mg per liter 324.612 mg per liter 361.131 mg per liter

For the calculation of the amount of Chlorine ion (mg per liter) in the water sample, the group use the formula:

mg/L Cl+ =

[ mL titrant ( sample ) −mL titrant ( blank ) ] x [ M tirant x 35500 ] mL sample

where the M titrant was 0.01143 M Silver nitrate and the mL of the water sample used was 10 mL.

Conclusion: The experiment focuses on the determination of the salinity of the water sample collected from Mangonbangon River in Tacloban City. The method used was the Mohr method wherein the silver nitrate was titrated to react with the salt (with Cl-) in the water sample. And for easy determination of the endpoint, indicating that all the Chlorine ions have reacted with the silver ions (yellow to pinkish color), 5% potassium chromate indicator was used. After the titration

process and calculations the group was able to conclude that the salinity of the water sample collected was 340.253 mg per liter....