Solubility Equilibrium And The Effect Of Temperature

Introduction

For this experiment, we are going to determine the effect of temperature on solubility, to be done in a chemical by dissolving a solute in a definite amount of solution which is saturated. Specifically, the goal of this experiment is to prepare a saturated solution of Na2C2O4 in water at different temperatures, determine the effect of temperature in solubility, and to apply Le Chatelier's Principle. We can do all this by simply titrating a certain amount of standard KMnO4, and measuring how much KMnO4 was needed to help Na2C2O4 reach chemical equilibrium at certain temperatures. In doing this, we will have fulfilled all the goals of our experiment, as well as being able to determine the Solubility of Na2C2O3 at both 20 and 100 C, in addition to determining both experimental and theoretical ∆H for the reactions.

Procedure

A. Preparation and Standardization of KMnO4 Solution:

I weighed out about 2.8 grams of potassium permanganate and dissolved it in about 200 ml of distilled water. I made sure to make all of the permanganate dissolve, of course, by stirring it thoroughly. I then weighed about 2 samples of sodium oxalate (.47 and .50 g) then placed them in some 200-ml Erlenmeyer flasks, then and added about 50 ml of distilled water to them as well. I then titrated the potassium permanganate solution after adding about 15 ml of 3 M sulfuric acid to the oxalate and heating the whole solution to about 60-90 C, using a magnetic stirring bar to help stir. I kept on slowly titrating at the same temperature until the solution turns very light pink. I then stopped, recorded the amount of KmnO4 used, then went on.

B. Preparation and Analysis of Samples:

I weighed out about 12 g of sodium oxalate and then put it into a 250-ml Erlenmeyer flask, along with 150 ml of distilled water. I then stirred it around, to make sure that the solution dissolved completely. After stirring, I measured its current temperature then allowed it to settle for a while. When it is done, I used a pipette to remove about 5 ml of the clear saturated solution at room temperature from the Erlenmeyer flask, calling it B1, then I heated the solution to 40 C then removed another 5 ml sample, called it C1, and then got a cool 5 ml sample of 3 C solution, called it A1, then heated the solution to 80 C and got one last sample, called it D1. I then added 50 ml of distilled to the test tubes A1, B1, C1 and D1, then titrated them with the potassium permanganate solution (making sure to add 15 ml 3M sulfuric acid in each), then recorded the amount it took for them to turn pink.

Data

A. Standardization of KMnO4 solution:

Sample g Na2C2O4 moles Na2C2O4 (x 10^-3) moles KMnO4 (x 10^-3) ml KMnO4 used M KMnO4

#1 .47 3.51 1.4 15.5 .090

#2 .50 3.73 1.5 16 .093

Average M = .091

B. Solubility of Na2C2O4 at different temperatures: in M and g/ L.

Sample and temp (C): ml of KMnO4 titrated moles KMnO4 (x 10^-4) moles NaC2O4 dissolved (x 10^-3) M (moles/L) Na2C2O4 g Na2C2O4 dissolved in sample g / L Na2C2O4

A1 - 3 5.0 4.55 1.14 .228 .152 30.5

B1 - 31.1 6.0 5.46 1.37 .274 .183 36.6

C1 - 45 8.8 8.01 2.00 .400 .268 53.7

D1 - 80 9.5 8.65 2.16 .432 .290 57.9

Solubility of Na2C2O4 in g / L Experimental Value in g / L Handbook Value in g / L

At 20 C 36 37

At 100 C 73 63.3

C. Relationship of K and ∆H

Sample Average M of Na2C2O4 K=[Na^+]^2[C2O4] ln K T K 1 / T K (x 10^-3)

A1 .228 .047 -3.05 276 3.62

B1 .274 .082 -2.50 304.1 3.29

C1 .400 .256 -1.36 318 3.14

D1 .432 .322 -1.13 353 2.83

At 20 C .276 .084 -2.48 293 3.41

At 100 C .472 .421 -0.87 373 2.68

Experimental