Chem 1212l Borax Experiment

Topics: Thermodynamics, Temperature, Solubility Pages: 6 (1437 words) Published: April 20, 2011
Chem 1212L-345
Lab report
Experiment #20: Temperature Change and equilibrium

Woochul Jin
Jeeyoon Kong, Alla
Asmerom Hagos

Woochul Jin
Chem 1212L-345

Experiment #20 Lab Report
Temperature change and equilibrium
In this experiment, we will find out how the variation of the value of an equilibrium constant with temperature can be used to determine the enthalpy (heat), entropy (randomness), and free energy (G) changes associated with the system in question. Materials: 125mL flasks (5), 100mL beaker (1), hotplate, graduated cylinder, stir rod, borax, water, thermometer, pipet, bromcresol green, distilled water, 0.5M HCL solution, titrating kit (stand and buret) Procedures:

1) Five clean 125mL flasks were labeled from 30*C to 50*C in increments of 5*C. 2) 5mL water was added to each flask.
3) 30-32g of borax was weighed and placed in a 100mL flask and 50mL of water was added to it. 4) Mixture of borax was then heated on a hotplate stirred occasionally. 5) Mixture was carefully observed until 65*C to check whether borax was dissolved completely. a. If the mixture still contained un-dissolved borax, mixture was taken off the hotplate. b. If the mixture of borax was completely dissolved, more borax was required to be added to the mixture until some borax remained un-dissolved at 65*C. 6) After allowing the borax mixture to heat to 65*C, the mixture was removed from heat and set aside to cool. 7) As the mixture was cooling, mixture was stirred and the temperature was carefully monitored. 8) After the mixture reached 50*C, 5mL of solution was pipetted from the mixture (less any solid/borax crystals) and pipetted into the 125mL flask containing 5mL of water. 9) Then 20mL of distilled water and 3-4 drops of bromcresol green was added into the flask containing 5mL water and 5mL borax solution. 10) Titration kit consisting of the stand and buret was assembled. 11) Buret was filled to 0mL mark with 0.5M HCL solution.

12) Solution in 125mL flask was then titrated with the 0.5M HCL solution (while being stirred) until the solution turned a pale yellow. 13) Final buret readings were then recorded.
14) Repeat step 8-13 for 45*C, 40*C, 35*C, and 30*C.

|Flask label |  |50*C |45*C |40*C |35*C |30*C | |  |  |  |  |  |  |  | |Temperature *C |  |50 |45 |40 |35 |30 | |Temperature K |  |323 |318 |313 |308 |303 | |1/T (K-1) |  |0.00309 |0.0031 |0.0032 |0.00325 |0.0033 | |Actual concentration of HCL solution |  |0.5M HCL | |Final buret reading |  |25.4mL |23.6mL |38.7mL |13.3mL |19.3mL | |Initial buret reading |  |0mL |2.9mL |23.6mL |2.1mL |13.3mL | |Volume HCL used |  |25.4mL |20.7mL |15.1mL |11.2mL |6.0mL | |Moles of H+ used |  |0.0127mol |0.01035mol |0.00755mol |0.0056mol |0.003mol | |Moles of B4O5(OH)42- reacted |  |0.00635 mol |0.005175 mol |0.003775 mol |0.0028 mol |0.0015 mol | |M,...
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