Here’s my lab report:
Che 121 – Preparation of Solutions: The Briggs-Rauscher Reaction lab report
06 October 2017
Solution 1: To find the amount of solute needed to create 50mL of 0.15M malonic acid (CH2(COOH)2) and 0.020 M Manganese sulfate monohydrate (MnSO4H2O) was calculated by using the formula:
G = (V (in liters) x molV) x gmol.
The calculation for the malonic acid: (0.05 L x0.15 M1 L)x104 g1 mol= 0.78 g CH2(COOH)2.
The calculation for the MnSO4H2O: (0.05 L x 0.020 M1 L) x 169 g1 mol= 0.169 g MnSO4H2O.
0.785 g of malonic acid, and 0.169 g of Manganese sulfate monohydrate were weighed, and both powders were transferred into a 50 mL volumetric flask filled halfway with distilled water. The flask was sealed and the solution was inverted about 8 times (to dissolve the solids) and labeled.
Solution 2: The amount of 0.20 M potassium iodate (KIO3) needed to prepare a 50.0 mL solution was calculated using the formula:
G = (V (in liters) x molV) x gmol.
The calculation for KIO3: (0.05 L x 0.20 mol1 L)x 214 g1 mol= 2.14 g KIO3
The dilution of 1.0 M H2SO4 to create 50.0 mL of 0.080 M H2SO4 was calculated using the formula:
(concentration 1)(volume 1 in liters) = (concentration 2)(volume 2 in liters)
The calculation for H2SO4: (1.0 M H2SO4)(x) = (0.080 M H2SO4)(0.05 L)
1.0(x)1.0 = 0.0041.0= 0.004 L = 4 mL of H2SO4
2.140 g of KIO3 was weighed, and 30 ml of distilled water was added into a 250 mL beaker along with the potassium iodate. Since potassium iodate is not very soluble at room temperature, the beaker was heated and stirred with a magnetic stirrer on a hot plate on a low medium setting. Once the KIO3 was dissolved in the solution, the beaker was allowed to cool down and transferred into a 50 mL volumetric flask. 4 ml of H2SO4 was also added to the flask which was covered with a lid, and inverted about 7 times and labeled.
To create solution 3: The volume of 30.0% Hydrogen Peroxide (H2O2) needed to prepare 50.0 mL of 3.6 M H2O2 was calculated using the formula :
M = nv (L), the result was in grams, so to calculate the final volume, the density of H2O2 (1.11 g/ml) was then plugged into D=mv
Calculations for H2O2 : 3.6 M =34 g H2O20.05 L= 6.12 g of H2O2
6.12 g x 100 g30 g= 20.4 g H2O2
1.11 g/mL =20.4 gv= 18. 4 mL ≊18 mL H2O2
20 ml of distilled water was added to a 50.0 mL volumetric flask. Because of the unstable nature of H2O2, the 18 mL solution was pre measured and dispensed into the volumetric flask. Distilled water was then added until the water level reached the etched mark on the flask. The flask was then closed and inverted about 6 times and labeled.
The Briggs-Rauscher reaction was demonstrated by adding 4 drops of 3% starch solution in a 150 mL beaker.10 mL of solution 1, 2, and 3 were measured in 3 individual graduated cylinders. Solution 1 was added first, then solutions 2 and 3 were added simultaneously and swirled. The clear solution began turning an amber color, and moments later turned a dark blue color, there was a flash of an indigo/purple color before it oscillated back to the previous amber color. The first cycle observed went from blue to blue in 11:56 seconds. What appeared to be tiny gas bubbles were observed in the liquid.
The possible reactions taking place simultaneously in the Briggs-Rauscher reactions are as follows:
H2O2 (aq)+ I2 (s)⇾ 2H+1 (aq)+ 2I -1 (aq) + O2 (g)
2IO3-1(aq) + 12H+1 (aq) + 5 Mn+2 (aq) ⇾ I2 + 6H2O+ + 5Mn+4
The equation 5H2O2 (aq) + 2IO3- (aq) + 2H+ (aq) + starch ⇾ 5O2(g) + starch-I2 + 6H2O(aq) explains how the amber color appears from the colorless solution. The equation
I2 (aq) + I- (aq) ⇾ I3- explains how the dark blue solution is produced and becomes colorless from the dark blue color. The equation 5H2O2 (aq) + 2IO3- (aq) + 2H+ (aq) + starch ⇾ 5O2(g) + starch-I2 + 6H2O(aq) explains the bubbles that were observed. The equations H2O2 (aq)+ I2 (s)⇾ 2H+1 (aq)+ 2I -1 (aq) + O2 (g) and Starch-I2 (aq) + CH2(COOH)2 (aq) ⇾ ICH(COOH)2 (aq) + I- (aq) + Starch explains why the reaction does not last forever.
The second trial was timed in 7 cycles, from blue to blue. The cycle times were 13.56 seconds, 14.79 seconds, 14.94 seconds, 16.86 seconds, 17.49 seconds, 18.97 seconds, and 20.20 seconds respectively. The length of the cycles changed over time as the cycles went from blue to blue at a slower rate. Once the cycle was placed on a magnetic stirring bar, the cycle times went from 21.52 seconds, 21.06 seconds, 20.87 seconds, 29.23 seconds, 27.20 seconds, 22.82 seconds, 27.20 seconds, and 22.82 seconds respectively. It seemed that the cycle happened a little slower on the magnetic stirrer. I believe that this happened because the chemicals, I2 in particular, is being consumed at a faster rate than it is being created while on the magnetic stirrer, making the color change happen at a much slower rate making the solution clear up.