[B
4
O
5
(OH)
4
2-
]
K sp ln(K sp)
T (K)
1/T(1/K)
Delta G from K
Delta G from H/S
Ken McFarland, “Thermodynamics and K sp
of Borax”, CHEM 1130, Nastaran Marzijarani, Section 108,
Room 1871, Will Bruhacher
Title: Thermodynamics and K sp
of Borax
Purpose: To determine the Ksp of Borax at different temperatures through titrating it with HCl, and use the resulting data to determine the ∆H⁰, ∆S⁰, and ∆G⁰
Materials:

50 mL buret

10 mL graduated cylinders

10 Erlenmeyer flasks

5 saturated borax solutions (5C, 15C, 25C, 35C, 50C)

Standardized HCl

Thermometer

Indicator solution
Procedure:
First prepare all of the samples of the different borax solutions. To do this, first obtain 5 mL of the first solution in a graduated cylinder, making sure to record the exact temperature of the solution that the sample came from. Then, pour it into an Erlenmeyer flask, rinsing the graduated cylinder with DI water repeatedly to insure all of the solution is in the flask. Continue adding DI water to the flask, so that the borax will stay dissolved as the solution cools to room temperature. Add three drops of indicator solution to each of the flasks. Repeat these steps, until you have two samples for each of the 5 borax solutions.
Rinse, and then fill, your buret, with the standardized HCl solution. Use this to titrate the solution in each of your flasks. The solution will turn from blue to yellow. Record the amount of HCl that must be added to each flask for this to happen. Each lab partner should do this once for each of the 5 borax solutions.
Observations / Results:
Data Collected in the lab is on attached sheets, calculated values are below:
0.07442
0.0732
0.10126
0.10248
0.11834
0.11834
0.16714
0.16836
0.30134
0.2989
0.001649 0.001569 0.004153 0.004305 0.006629 0.006629 0.018677 0.019089 0.109454 0.106816
-6.4078
-6.45739
-5.4839
-5.44797
-5.01629
-5.01629
-3.98048
-3.95866
-2.21225
-2.23664
279.4
279.4
288.8
288.8
294.3
294.3
306 306.2
321.7
321.6
0.003579 0.003579 0.003463 0.003463 0.003398 0.003398 0.003268 0.003266 0.003108 0.003109
14884.87 15000.06 13167.29 13081.03
12273.9
12273.9 10126.67 10077.74 5916.925
5980.3
15169.81 15169.81 13209.53 13209.53 12062.56 12062.56
9622.64 9580.932 6348.561 6369.415

Questions:
1.
a.
Nothing would happen b.
Solid borax would crystallize out of the solution
2.
Our ∆H was positive, so that means that the reaction would be endothermic. I could not find any equation 9-8 in the lab manual, so I am not sure what this part of the question refers to. I just used prior knowledge from the lecture.
3.
The K sp
increases as the temperature increases, because as the temperature of the solution is increased, more of the borax can dissolve in it.
4.
At 25C we got a K sp
of 0.006629. This means that our percent error was 96.23%. This means that we were quite far off in our calculated values for K sp
.