Experiment 4: Chloride Analysis
Purpose:
The purpose of this experiment is to compare two different “wet” chemical techniques. One method is
volumetric chloride determination and the second is gravimetric determination. These two techniques
will help with the analysis of an unknown chloride sample.
Reaction:
𝐴𝑔𝑁𝑂3 + 𝐶𝑙 − → 𝐴𝑔𝐶𝑙(𝑠) + 𝑁𝑂3−
𝐴𝑔𝐶𝑙(𝑠) → 𝐴𝑔+ + 𝐶𝑙 −
Procedure:
Volumetric Chloride Determination
1) Accurately weigh about 4g of AgNO3 and dissolve in 100mL of distilled water. Quantitatively
transfer the solution to a 200mL volumetric flask and dilute followed by thorough mixing.
2) Into 125mL Erlenmeyers accurately weigh about 0.1g of the unknown chloride. Dissolve each of
your three samples in 50mL of water. Add 0.03g dextrin and 5 drops of dichlorofluorescein
indicator. Titrate with silver nitrate solution to a pink endpoint.
3) Calculate the percent chloride in your sample
Gravimetric Chloride Determination
1) Prepare 3 Gooch crucibles by cleaning with an acid solution (approx 0.1M HNO3) and then a
basic solution (approx 0.1M NH3). Follow these washes with distilled water, and then drying for
at least one hour in a 120°C oven. Fit each crucible with a glass fiber filter.
2) Dissolve each of three samples (0.2g) in a 400mL beaker with 150mL distilled water, then add
1mL of 6M HNO3
3) Add enough silver nitrate solution to completely precipitate the unknown chloride. Heat the
solution on a hot plate without boiling and frequent stirring until the supernatant is clear.
4) Filter the samples through the weighed Gooch crucibles with mild suction. Use warm approx
0.1M HNO3 to wash the precipitate, five washes are suggested. Finally rinse the precipitate with
distilled water.
5) Dry the crucibles and precipitate in a 120°C oven for at least two hours before final weighing.
Data:
Mass of AgNO3: 4.0032g
Mass of dextrin: 0.0307g, 0.0300g, 0.0308g
Volumetric Chloride Determination
Grams of
Unknown, initial
0.1007
0.1007
0.1009
Flask
1
2
3
mL of AgNO3
Grams of Cl- final
%Cl in unknown
13.30
13.50
13.10
0.0556
0.0564
0.0547
55.21
56.01
54.21
Gravimetric Chloride Determination
1
2
3
Initial
Crucible Mass
+ filter paper
(g)
34.2758
32.9591
33.4165
Grams
Unknown
Final
Crucible
Mass
Grams AgCl
Grams Cl-
%of Cl-
0.2031
0.2008
0.2000
34.3837
33.1033
33.5396
0.1079
0.1442
0.1231
0.02669
0.03567
0.003045
13.14
17.76
15.22
Volumetric %
55.21
56.01
54.21
̅ )2
∑(di −d
S=√
n−1
Gravimetric %
13.14
17.76
15.22
Mean
Std. Dev
t(calc)
t calc =
Difference
-42.07
-38.25
-38.99
-39.77
2.0259
34.00
|𝑑̅ |
√n
𝑠
ttable = 2.776 for 95% confidence interval
Since ttable < tcalc , the results are considered to not be the same
Calculations:
Volumetric Determination
Grams of Cl13.3 mL AgNO3 ×
4.0032 g 1 mol AgNO3
1 mol Cl35.453 g Cl×
×
×
= 0.0556g Cl200 mL
169.872 g 1 mol AgNO3
1 mol Cl-
Percent Cl- in unknown
0.0556
× 100 = 55.21%
0.1007
Gravimetric Calculation of ClmL of AgNO3
.2031 g unknown Cl × .5541(average %)×
1 mol Cl1 mol AgNO3
200 mL
169.872 g AgNO3
×
=26.94 mL
-×
- ×
35.453 g Cl
1 mol Cl
4.0032 g AgNO3
1 mol AgNO3
Mass of AgCl= Crucibleafter-(Cruciblebefore+Filter paper)
34.3837𝑔 − 34.2758𝑔 = 0.1079𝑔
Finding Grams of Cl1 mol AgCl
1 mol Cl- 35.453 g Cl0.1079 g AgCl×
×
×
=0.02669 g Cl143.32 g AgCl 1 mol AgCl 1 mol Cl-
Percent Cl- in unknown
0.02669
×100%= 13.14%
0.2031
Conclusion:
The purpose of this experiment was to compare two different types of techniques volumetric
determination and gravimetric determination. The source of error that was in this experiment was with
titration because you could have gone past the endpoint of titration. The error that was in our
experiment was the gravimetric determination. The mass of the AgCl was less than it was supposed to
be therefore the percent of the gravimetric result was what caused the tcalc results to be even more off,
and it led to the tcalc and ttable not being close to the same result.