Zach Bensley
Experiment 8: Separation of Cations
Purpose:
The purpose of this lab was to experiment with two different techniques: masking and ion
exchange resin conversions. With these two methods, it helped determine the unknown liquid.
Procedure:
In the standardization of NaOH, 500 mL of 0.01 M NaOH was made. KHP was massed
appropriately and was dissolved in 50.0 mL of water for a 25.0 mL titration. The solution was then
titrated and three trials were obtained. From these results, the molarity of NaOH was obtained.
In order to determine the H+ concentration, approximately 5.0 mL of unknown was diluted
to 100 mL with the use of distilled water. With this solution, 20.0 mL was decanted into an
Erlenmeyer flask and was titrated with NaOH. During this titration, the pH was being recorded
along with the titration. Three trials were obtained.
The unknown sample ran through a cation exchange resin. Once that was completed, it was
then titrated by 20.0 mL increments of standardized NaOH.
In order to standardize EDTA, calcium carbonate was dissolved in HCl. During calcium
carbonate being dissolved, 0.1 M EDTA was prepared. In a flask, calcium carbonate, buffer and
calmagite indicator were added into the flask. The solution was titrated with 0.1 M EDTA and three
trials were obtained. The endpoint was determined by the solution turning a dark blue color.
Within an Erlenmeyer flask, 5.0 mL of unknown and buffer were added in a flask. The
solution was required to have a pH of 10 or higher because there was an addition of KCN. Once the
solution had a pH of 10, it was titrated with EDTA and three trials were obtained.
Data:
Standardization of NaOH:
Trial
KHP (g)
NaOH (mL)
1
2
3
Average
0.0446
0.0470
0.0452
0.0456
27.59
26.82
22.21
25.54
Titration of Unknown with NaOH:
Molarity of
NaOH
0.007915
0.008581
0.009965
0.00874
Trial
1
2
3
Average
Volume of Unknown (mL)
20.00
20.00
20.00
20.00
[H+]
0.000839
0.000879
0.000853
0.000857
Unknown Titrated with NaOH:
Trial
Aliquots (mL)
[H+]
20.00
20.00
20.00
20.00
Volume of NaOH
(mL)
18.50
17.50
17.50
17.83
1
2
3
Average
Volume of CaCO3
(mL)
5.00
5.00
5.00
5.00
Volume of EDTA
(mL)
6.90
6.70
7.30
6.96
[EDTA]
Volume of Unknown
(mL)
5.50
5.40
5.60
5.50
[Zn2+], [Mg2+]
Volume of EDTA
(mL)
4.25
4.05
4.29
4.20
[Mg2+]
0.00808
0.00764
0.00764
0.00779
EDTA Standardization:
Trial
1
2
3
Average
0.02890
0.02979
0.02795
0.02869
EDTA Titration with Unknown:
Trial
1
2
3
Average
Volume of EDTA
(mL)
5.00
5.00
5.00
5.00
0.0158
0.0155
0.0161
0.0158
EDTA Titration of Unknown and KCN:
Trial
1
2
3
Average
Calculations:
Volume of Unknown
(mL)
25
25
25
25
0.00487
0.00465
0.00492
0.00481
Mass of KHP needed for titration:
0.025L * 0.01M _ NaOH *
1molKHP 204.23gKHP
*
 0.05106gKHP
1molNaOH
1molKHP
Molarity of NaOH of NaOH:

0.0456gKHP *
1molKHP
1molNaOH
1
*
*
 0.00874 M
204.23gKHP 1molKHP 0.02554L
Concentration of H+ titrated with NaOH:

0.01783LNaOH * 0.00874 M _ NaOH *
1molH 
1
*
 0.00779M
1molNaOH 0.020L
[Mg+2] and [Zn+2]

0.0055L _ EDTA * 0.02869M *
1
 0.0158M
0.01Lunknown
[Mg2+]

0.00420L * 0.02869M *
1
 0.00481M
.025L
Conclusion:

Since this was a group experiment, there may have been many sources of error. At first, there
was a great amount of confusion and the results may have been skewed. But in the end, we obtained
the concentrations of magnesium and zinc in this experiment.