Jennifer Lindsay
Experiment Four:
Comparisons of Two Chloride Determinations
Objective:
To compare two different “wet” chemical techniques for the analysis of an
unknown chloride sample. The two analyses done during this lab are a volumetric
chloride and a gravimetric determination.
Procedure:
Volumetric Chloride Determination:
1. Accurately weight 4.5 grams of AgNO3 and dissolve it in 100mL of distilled
water. Transfer the solution into a 250mL volumetric flask by using three
10mL aliquots of distilled water, and dilute while mixing.
2. Standardize the AgNO3 using the oven-dried sodium chloride. Weigh enough
sodium chloride for a 25mL titration. Add 0.03 grams of dextrin and 5 drops
of dicholorflourescien indicator. Titrate until a pink endpoint.
3. Into a 125mL Erlenmeyer flask, weigh 0.1 grams of the unknown chloride.
Dissolve (three samples) in 50mL of water. Add 0.03 grams of dextrin and 5
drops of dicholorflourescien indicator. Titrate with silver nitrate solution to
pink endpoint.
Gravimetric Chloride Determination:
1. Prepare three Gooch crucibles by cleaning with acid solution (0.1 M
HNO3) and then a basic solution (0.1M NH3). Follow the washes with
distilled water, dry for at least one hour in a 120-degree oven. Let the
crucibles cool and fit each crucible with a glass fiber filter.
2. Weigh 0.2 grams of the unknown chloride. Dissolve each in a 400mL
beaker with 150mL-distilled water. 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. Vacuum filter the samples through the weighed Gooch crucibles. Use
warm 0.1M HNO3 to wash the precipitate (5 washes). Finally rinse the
precipitate with distilled water.
5. Dry the crucibles and precipitate in a 120-degree oven for a least two
hours before the final weighing.
Reactions:
AgNO3 + Cl- AgCl (s) + NO3AgCl (s)  Ag+ + ClData:
Mass of AgNO3 = 4.5006 grams
Standardize AgNO3:
Mass of NaCl (g)
Dextrin Mass (g)
Trial
1
2
3
0.1568
0.1515
0.1550
Volumetric Determination
Unknown Chloride
Dextrin Mass (g)
Mass (g)
0.1041
0.0328
0.1002
0.0336
0.1078
0.0390
Trial
1
2
3
Trial
Unknown
Chloride
Mass (g)
1
2
3
0.2016
0.2028
0.2014
Calculation Data:
Trial
1
2
3
Trial
1
2
3
Trial
1
2
0.0301
0.0326
0.0309
Gravimetric Determination
AgNO3
Crucibles
added (mL)
(g)
21.1403
22.3275
22.6890
mL of AgNO3 used
for Titration
23.5
24.4
25
mL of AgNO3 used
for titration
16
14.6
15
Crucible,
Product,
and Filter
Paper (g)
21.3759
22.6776
22.9440
Volumetric Determination Calculated Data
Molarity
Moles AgNO3
Mass Cl- in
AgNO3
and Cl
Precipitate (g)
0.106
0.0017
0.0601
0.106
0.0015
0.0532
0.106
0.00159
0.0564
Product
AgCl (g)
0.2356
0.3501
0.255
Mass % Cl- in
Unknown
57.7
53.1
52.1
Gravimetric Determination Calculated Data
Mass Cl- in precip (g)
Mass % Cl- in unknown
0.0583
28.9
0.0866
42.7
0.0631
31.3
Theoretical
AgNO3
needed
(mL)
30.4
30.4
Corrected Gravimetric Data
Fraction
Total mass
Total Mass
AgCl
AgCl (g)
Cl- (g)
obtained
0.2401
0.3125
0.9813
1.203
0.2427
0.2771
Mass % ClUnknown
(corrected)
120.4
136.6
3
30.4
0.2763
Calculations:
0.2283
113.4
Volumetric
Molarity of AgNO3
Molarity of AgNO3
𝑀 = 𝑚𝑎𝑠𝑠𝐴𝑔𝑁𝑂3 ×
0.9229
1 𝑚𝑜𝑙 𝐴𝑔𝑁𝑂3
÷𝑉
169.873𝑔𝐴𝑔𝑁𝑂3
Moles of AgNO3 & Cl𝑀 𝐴𝑔𝑁𝑂3 × ∆𝑉 𝐴𝑔𝑁𝑂3
= 𝑚𝑜𝑙 𝐴𝑔𝑁𝑂3 & 𝐶𝑙 −
Mass of Cl- in Precipitate
35.453𝑔𝐶𝑙 −
𝑚𝑜𝑙 𝐶𝑙 − ×
= 𝑚 𝐶𝑙 −
1 𝑚𝑜𝑙 𝐶𝑙 −
Mass Percent of Cl- in Unknown
𝑚 𝐶𝑙 −
× 100% = 𝑚𝑎𝑠𝑠 % 𝐶𝑙 −
𝑚 𝑖𝑛𝑖𝑡. 𝑠𝑎𝑚𝑝𝑙𝑒
1 𝑚𝑜𝑙
169.873𝑔
÷ 0.250𝐿
Moles of AgNO3 & Cl- Trial 1
0.106𝑀 × 0.01600𝐿 = 0.0017 𝑚𝑜𝑙
0.106𝑀 = 4.5006𝑔 ×
Mass of Cl- in Precipitate Trial 1
35.453𝑔𝐶𝑙 −
0.0017𝑚𝑜𝑙𝐶𝑙 − ×
1 𝑚𝑜𝑙 𝐶𝑙 −
= 0.0601𝑔𝐶𝑙 −
Mass Percent of Cl- in Unknown Trial
1
0.0601𝑔 𝐶𝑙 −
× 100% = 57.7% 𝐶𝑙 −
0.1041𝑔 𝑈𝐾
Gravimetric
Mass of AgCl (precipitate)
Mass of AgCl (precipitate) Trial 1
𝑚𝑓𝑖𝑛𝑎𝑙 − 𝑚𝑐𝑟𝑢𝑐. − 𝑚𝑓 𝑝𝑎𝑝𝑒𝑟 = 𝑚 𝐴𝑔𝐶𝑙
21.3759𝑔 − 21.1403𝑔 = 0.2356𝑔 𝐴𝑔𝐶𝑙
Mass of Cl in precipitate
Mass of Cl- in precipitate Trial 1
−
1 𝑚𝑜𝑙
1 𝑚𝑜𝑙 𝐶𝑙
1 𝑚𝑜𝑙
1 𝑚𝑜𝑙 𝐶𝑙 −
𝑚 𝐴𝑔𝐶𝑙 ×
×
0.2356𝑔 ×
×
143.321𝑔 1 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙
143.321𝑔 1 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙
35.453𝑔
35.453𝑔
×
= 𝑚 𝐶𝑙 −
×
= 0.0583𝑔 𝐶𝑙 −
1 𝑚𝑜𝑙
1 𝑚𝑜𝑙
Mass Percent of Cl- in Unknown
Mass Percent of Cl- in Unknown Trial
1
0.0583𝑔 𝐶𝑙 −
𝑚 𝐶𝑙 −
× 100% = 28.91% 𝐶𝑙 −
× 100% = 𝑚𝑎𝑠𝑠 % 𝐶𝑙 −
0.2016𝑔 𝑈𝐾
𝑚 𝑖𝑛𝑖𝑡. 𝑠𝑎𝑚𝑝𝑙𝑒
Correction Gravimetric Determination Data
Theoretical amount of AgNO3 needed
Theoretical amount of AgNO3 needed
Trial 1
̅̅̅̅ AgNO3 × 2 ≅ 𝑉 𝐴𝑔𝑁𝑂3 𝑛𝑒𝑒𝑑𝑒𝑑
15.20mL AgNO3 × 2 ≅ 30.40𝑚𝐿 𝐴𝑔𝑁𝑂3
∆V
Fraction of AgCl obtained
Fraction of AgCl obtained Trial 1
𝑉 𝐴𝑔𝑁𝑂3 𝑢𝑠𝑒𝑑
0.0073𝐿 𝐴𝑔𝑁𝑂3 𝑢𝑠𝑒𝑑
𝑉 𝐴𝑔𝑁𝑂3 𝑛𝑒𝑒𝑑𝑒𝑑
0.03040𝐿 𝐴𝑔𝑁𝑂3 𝑛𝑒𝑒𝑑𝑒𝑑
= 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐴𝑔𝐶𝑙 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑
= .2401 𝐴𝑔𝐶𝑙 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑
Total mass of AgCl
Total mass of AgCl Trial 1
𝑚 𝐴𝑔𝐶𝑙 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑
𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝐴𝑔𝐶𝑙 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑
= 𝑡𝑜𝑡𝑎𝑙 𝑚 𝐴𝑔𝐶𝑙
Total mass of Cl
1 𝑚𝑜𝑙
1 𝑚𝑜𝑙 𝐶𝑙 −
𝑚𝑡𝑜𝑡 𝐴𝑔𝐶𝑙 ×
×
143.321𝑔 1 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙
35.453𝑔
×
= 𝑚 𝐶𝑙 −
1 𝑚𝑜𝑙
Mass Percent of Cl- in Unknown
𝑚 𝐶𝑙 −
× 100% = 𝑚𝑎𝑠𝑠 % 𝐶𝑙 −
𝑚 𝑖𝑛𝑖𝑡. 𝑠𝑎𝑚𝑝𝑙𝑒
0.2356𝑔 𝐴𝑔𝐶𝑙 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑
= .9813𝑔 𝐴𝑔𝐶𝑙
0.2401 𝐴𝑔𝐶𝑙 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑
Total mass of Cl- Trial 1
1 𝑚𝑜𝑙
0.9813𝑔 𝐴𝑔𝐶𝑙 ×
143.321𝑔
1 𝑚𝑜𝑙 𝐶𝑙 −
35.453𝑔
×
×
1 𝑚𝑜𝑙 𝐴𝑔𝐶𝑙
1 𝑚𝑜𝑙
= 0.2427𝑔 𝐶𝑙 −
Mass Percent of Cl- in Unknown Trial
1
0.2427𝑔 𝐶𝑙 −
× 100% = 120.4% 𝐶𝑙 −
0.2016𝑔
Student’s T Test
|𝑑̅ |
t calc =
√n
𝑠
Volumetric
Gravimetric
%
%
57.7
28.9
28.8
53.1
42.7
10.4
52.3
31.3
21.0
Difference
20.07
× √6 = 10.47
1.444
ttable for at 95% confidence interval is = 2.776
10.47 > 2.776, the results are considered significantly different from each other
Discussion Questions:
1. The gravimetric data seems to be more precise rather than the volumetric
data. Due to some errors in our lab the mass percent of Cl- is well over 100%,
more trials should be done in order to test the unknown.
2. We preformed a direct gravimetric analysis.
3. We preformed an indirect titration.
Conclusion Questions:
1. To improve the experiment we could of measured all the crucibles at the
same temperature during the final weighing. Another thing we could of done
to make sure the experiment was better was to use a better indicator that
showed a more distinctive color change.