CHEM 1252L-045 Elleansar Okwei Thermodynamic Analysis of Chemical Equilibria

Pierina Parraga

CHEM 1252L-045

Elleansar Okwei

04/28/16

Thermodynamic Analysis of Chemical Equilibria Introduction The intention of this lab was to identify the change in the equilibrium of the supernatant liquids once it was introduced to various temperatures. This value can be obtained once the volume of the borax utilized during this experiment is determined, which can allow us to identify the end point of the titration that is required in order for this solution to change to the desired color of green.Procedure Preparation of the Hot Water Rinse and Supersaturated Borax Mixture A 250 mL beaker was filled half way with distilled water then placed on a hot plate. This same beaker was then later utilized as a hot water rinse while the pipettes were used. By using this hot water rinse, the pipettes avoided get clogged with the element that were being transferred. During this time, a supersaturated solution of water with solid borax was created.This was carried out by placing 50 mL of distilled water into a 100 mL beaker along with 20 grams of solid borax. This same solution was then also placed on the plate and heated to 65

C.This beaker was stirred to ensure that the borax was mixed properly with the distilled water.Since the borax did not all go towards the solution, it was not required to place more borax into the beaker. Instead a layer of borax formed at the bottom, which also resulted in enough supernatant liquid to be used for the remainder of this lab. Once the temperature of the beaker had reached 65

C it was stirred once again for the duration of one minute.Obtaining Samples of the Borax Supernatant For this portion of the lab three Erlenmeyer flasks were gathered, and checked to ensure that they were both clean and dry. Next, in a timely manner, the borax solution was taken off the hot plate an allowed to cool to 50

C all the while it was being stirred. Once it had reached this temperature, the solution was no longer stirred, and allowed to settle in order to obtain the liquid above the borax. Before this step was carried out, the temperature was noted. Next, using the Mohr pipette, 5 mL of the supernatant liquid was extracted and quickly transferred into one of the Erlenmeyer flasks. After this was carried out, with the pipette, 5 mL of the hot distilled water was also transferred in the Erlenmeyer flask until a total of 20 mL were placed with the supernatant liquid. This same process was then carried out for the second Erlenmeyer flask once the temperature of the solution dropped to 40

C, and then again once it reached 30

• During this

repeated trials the pipette was rinsed with the hot water in order to ensure an accurate experiment. This study source was downloaded by 100000819946675 from CourseHero.com on 04-10-2021 03:43:56 GMT -05:00 https://www.coursehero.com/file/14477330/Thermodynamic-Analysis-of-Chemical-Equilibria/ This study resource was shared via CourseHero.com

Pierina Parraga

CHEM 1252L-045

Elleansar Okwei

04/28/16

Titration of the Borax Solution The previous three Erlenmeyer flasks were then diluted with 50 mL of distilled water, and combined with 2 drops of bromocresol green indicator. These same solutions were then lastly titrated with 0.195 M HCI.Data/ Calculations Erlenmeyer Flask Titrations Erlenmeyer flask Temperature HCI added 150

C60 mL 240

C44.5 mL 330

C25 mL Na2B4O7 (s) .10H2O (s) ↔ 2Na + (aq) + B4O7 2- (aq) + 10H2O (l) I0 0 C+2x +x E2x x Kc= [Na + ] 2 [B4O7 2- ] Kc = [2x] 2 [x] Kc= 4x 3 Erlenmeyer flask- 50

C M= mol/ L → mol= M*L (0.195 M HCl) (0.06 L) = 0.0117 mol HCl (1mol B4O7 2- / 2 mol HCl) = 0.00585 mol B4O7 2- Kc= 4x 3 → x= 0.00585 B4O7 2- → Kc= 4(0.00585 B4O7 2- ) 3 → Kc= 8.01*10 -7 This study source was downloaded by 100000819946675 from CourseHero.com on 04-10-2021 03:43:56 GMT -05:00 https://www.coursehero.com/file/14477330/Thermodynamic-Analysis-of-Chemical-Equilibria/ This study resource was shared via CourseHero.com

Pierina Parraga

CHEM 1252L-045

Elleansar Okwei

04/28/16

Erlenmeyer flask- 40

C M= mol/ L → mol= M*L (0.195 M HCl) (0.0445 L) = 0.0087 mol HCl (1mol B4O7 2- / 2 mol HCl) = 0.00434 mol B4O7 2- Kc= 4x 3 → x= 0.00434 B4O7 2- → Kc= 4(0.00434 B4O7 2- ) 3 → Kc= 3.27*10 -7 Erlenmeyer flask- 30

C M= mol/ L → mol= M*L (0.195 M HCl) (0.025 L) = 0.00488 mol HCl (1mol B4O7 2- / 2 mol HCl) = 0.00244 mol B4O7 2- Kc= 4x 3 → x= 0.00244 B4O7 2- → Kc= 4(0.00244 B4O7 2- ) 3 → Kc= 5.79*10 -8 ln(Kc)1/T (K)

-14.040.00307

-14.930.00320

-16.660.00328

0 0 0 0 0 0

-17 -16.5 -16 -15.5 -15 -14.5 -14 -13.5 -13 -12.5 f(x) = - 11933.23x + 22.78

R² = 0.9

ln (Kc) vs 1/T 1/T ln(Kc) This study source was downloaded by 100000819946675 from CourseHero.com on 04-10-2021 03:43:56 GMT -05:00 https://www.coursehero.com/file/14477330/Thermodynamic-Analysis-of-Chemical-Equilibria/ This study resource was shared via CourseHero.com

Pierina Parraga

CHEM 1252L-045

Elleansar Okwei

04/28/16

ln Kc = - ∆H

rxn (1/T) + ∆S

rxn

R R

∆H

rxn = 11933K R ↓ ∆H

rxn = (11933K) (8.314 J/ mol *K)= (99210.96 J/mol) (1KJ /1000 J) = 99.2 KJ/mol R Discussion Through this lab, the solubility of the borax increases when the temperature is raised, as the value of Kc demonstrates when it decreases while the temperature also decreases. The forward reaction for this experiment is endothermic, because the enthalpy that was obtained through the calculations was of a positive value. As it can also be observed in the previous data, the highest Kc values were obtained accordingly with higher temperatures, which relates to the solubility of the borax in references to the greater amount of moles are dissolved when the borax is in higher temperatures. In the graph above, ∆S

rxn/ R is listed as 22.78, which in turn allows ∆S

rxn to be 0.1894 kJ/mol. The sign of ∆S

rxn is positive, because the molecules in this reaction were in an aqueous state, which allows them have an overall greater entropy. Through this reaction it is also important to take into consideration that the borax is dissolving, which increases the entropy as well. It can also be noted from the graph that the value of ∆H

rxn/R is 11933 K, but this also equals positive 99.21 kJ/mol for ∆H

rxn. The values of ∆G

indicate that the following reaction is spontaneous, because its values are positive and proceed in a reverse manner. This study source was downloaded by 100000819946675 from CourseHero.com on 04-10-2021 03:43:56 GMT -05:00 https://www.coursehero.com/file/14477330/Thermodynamic-Analysis-of-Chemical-Equilibria/ This study resource was shared via CourseHero.com