*****************ANALYTICAL CHEMISTRY LAB REPORT*********************** YOU ONLY
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Question
*****************ANALYTICAL CHEMISTRY LAB REPORT***********************
YOU ONLY NEED TO HELP ME WRITE THE "DISCUSSION" SECTION USING THE INFORMATION BELOW.
Percent Chloride in Sample Using Precipitation Titration
Experimental
A range of 0.0280 to 0.0443grams of unknown sample was weighed on the analytical balance. The unknown sample was added into a 250ml flask and 10ml of DI water was added to dissolve the unknown sample. Few drops of indicator for both methods (Mohr’s and Fajan’s) were added to the solution inside the 250ml flask. 50ml of 0.05M AgNO3 was added into a clean burette and titration was performed. Color change for both methods (Mohr’s and Fajan’s) was noted as the titration progresses. Mohr’s method was done first using dilute potassium chromate as the indicator for the four trials that was done and the change is expected to go from yellow to reddish-orange depending on the amount of indicator that was added to the solution. Fajan’s method make use of dichlorofluoresceine indicator with 1ml of dextrin and the color is expected to go from yellow to pink. The process was repeated for all the 4 trials that was performed in this experiment. The initial volume of AgNO3 was recorded and the final volume which stands as the end at which the solution changes color was also recorded. The process was repeated for all the 4 trials that were made.
Results
Table 1: Total volume of AgNO3 used with the percent of Cl- for Mohr’s method
Trial
Mass of Unknown Sample (g)
Initial Volume of Silver Nitrate AgNO3 (In Burette) [ml]
Fina Volume of Silver Nitrate AgNO3 (ln Burette) [ml]
Total Volume of Silver Nitrate AgNO3 Used (ml)
Percent of Cl- (%)
1
0.0370
11.30
23.9
12.6
65.1
2
0.0371
23.9
36.9
13.0
67.0
3
0.0380
36.9
47.6
10.7
53.9
4
0.0382
25.5
36.1
10.6
53.1
Trial
Mass of Unknown Sample (g)
Initial Volume of Silver Nitrate AgNO3 (In Burette) [ml]
Fina Volume of Silver Nitrate AgNO3 (ln Burette) [ml]
Total Volume of Silver Nitrate AgNO3 Used (ml)
Percent of Cl- (%)
1
0.0368
8.50
21.0
12.5
66.6
2
0.0372
21.0
31.4
10.4
54.5
3
0.0364
31.4
41.5
10.1
54.1
4
0.0284
20.1
30.5
10.4
71.4
Table 2: Total volume of AgNO3 used with the percent of Cl- for Fajan’s method
Calculations
Percent of Cl- (%) for Mohr’s Method
Molarity of AgNO3 standardization experiment = 0.054M
Mole of AgNO3 Used = AgNO3 Molarity × Volume of AgNO3 in trial 1
= 0.054mol × 0.0126L = 0.00068moles
Molar mass of Cl- = 35.45g/mol
1:1 ratio between AgNO3 and Cl
Moles of Cl- Used = 0.00068 mols
Mass of Cl- in unknown sample = 0.00068mol × = 0.0241g
Percent Cl- = × 100% = 65.1%
Percent of Cl- (%) for Fajan’s Method
Molarity of AgNO3 standardization experiment = 0.054M
Mole of AgNO3 Used = AgNO3 Molarity × Volume of AgNO3 in trial 1
= 0.054mol × 0.0125L = 0.00069moles
Molar mass of Cl-= 35.45g/mol
1:1 ratio between AgNO3 and Cl
Moles of Cl- Used = 0.00069mols
Mass of Cl- in unknown sample = 0.00069mol × = 0.0245g
Percent Cl- = × 100% = 66.6%
Average percent Cl- in my sample for Mohr’s method was calculated to be 59.8 ± 7.3 and for Fajan’s method was 61.7 ± 8.7 . The average percent suggests that my sample for both method is higher than expected 40% but closer to the 85%. The explanation is presented below.
Discussion
The Mohr’s method in which alkaline earth chlorides react with silver nitrate in the presence of a few drops of potassium chromate
Trial
Mass of Unknown Sample (g)
Initial Volume of Silver Nitrate AgNO3 (In Burette) [ml]
Fina Volume of Silver Nitrate AgNO3 (ln Burette) [ml]
Total Volume of Silver Nitrate AgNO3 Used (ml)
Percent of Cl- (%)
1
0.0370
11.30
23.9
12.6
65.1
2
0.0371
23.9
36.9
13.0
67.0
3
0.0380
36.9
47.6
10.7
53.9
4
0.0382
25.5
36.1
10.6
53.1
Explanation / Answer
Discussion
The Mohr’s method in which alkaline earth chlorides react with silver nitrate in the presence of a few drops of potassium chromate as indicator. In this method, amount of sample is weighed in a conicla flask and then dissolved in distilled water. Two drops of indicator were added to the solution. The solution was then titrated with standerd AgNO3 till the color changes from yellow to reddish orange. AgNO3 reacts with the Cl^- present in the smaple :
Cl^- + AgNO3 ----> AgCl (white) + NO3^-
when all the Cl^- present in the solution has depleted, AgNo3 reacts to Potassium Dichromate to convert it to Silver dichromate.
AgNO3 + K2CrO4 ----> Ag2CrO4 (color changes) + NO3^-
Fajan’s method make use of dichlorofluoresceine indicator with 1ml of dextrin and the color is expected to go from yellow to pink. The process was repeated for all the 4 trials that was performed in this experiment. The initial volume of AgNO3 was recorded and the final volume which stands as the end at which the solution changes color was also recorded. Experimental redults are reported and compared in Result section
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