Data collected before the reaction included the molar mass of copper sulfate pentahydrate (CuSO4 ° 5H2O) found by the use of the values on the periodic table and the mass of copper sulfate pentahydrate (CuSO4 ° 5H2O) needed to prepare ten milliliters of a 0.140 M solution. Copper sulfate pentahydrate (CuSO4 ° 5H2O) is a light blue crystalline solid substance. The chemical reactions that took place involved hydration of copper sulfate pentahydrate (CuSO4 ° 5H2O) in deionized water and dilution of a stock solution. To calculate the volume of stock solution required, molarity of the solution is multiplied by the volume to be made and then divided by the molarity of the stock. Grams or moles of a solute are the same before and after the reaction. To calculate the mass of a substance needed to prepare a solution of target concentration and volume, a formula is used. The formula used involves multiplying the molar mass of the substance by the volume to be made by the molarity and finally by a conversion factor of one liter to 1000 milliliters. A special piece of laboratory equipment called a spectrophotometer is used to calculate the absorbance of the solution once prepared. This is to compare the molarity of the solution to the target molarity to assure accuracy.
Procedure one used the instructions outlined in the laboratory experiments manual for this course. A plastic weigh boat was tared and the required mass of copper sulfate pentahydrate (CuSO4 ° 5H2O) was added to the boat on top of the analytical balance. The small amount was transferred to a beaker and dissolved in a minimal amount of deionized water, no more than six milliliters was used. This solution was then transferred to a ten milliliter flask and combined with enough deionized water to make a ten milliliter solution and gently mixed together. Some of the solution was moved to a cuvette and the instructor verified the correctness of the prepared solution using the spectrophotometer. Upon being verified by the instructor, a new target concentration was assigned and prepared using the same method.
Procedure two used the instructions outlined in the laboratory experiments manual. The required volume of the 0.200 M stock solution that had been previously prepared was transferred to a ten milliliter flask. The flask was filled up to the ten milliliter mark with deionized water and uniformly mixed. Some of the solution was transferred to a pipette and compared to the laboratory standard and the absorbance was checked by the instructor with the use of a spectrophotometer. One solution was prepared as opposed to the two suggested in the directions in the laboratory book. All solutions were disposed of in the waste beaker under the hood and all glassware was rinsed thoroughly with deionized water.
(Absorbance .65 A)
Molar mass of (CuSO4 ° 5H2O):
Cu- 63.55 +
SO4- (32.07)+ (16 x 4=64) +
5H2 - (1.008 x 10=10.08) +
5O- (16 x 5=80) =
Mass of (CuSO4 ° 5H2O) required to prepare 10.00 mL of a 0.140 M solution:
Mass (CuSO4 ° 5H2O) = molar mass (CuSO4 ° 5H2O) x molarity solution x volume to be made x (1L/1000mL)
.349468(.3)=249.6 g/mol x 0.140 M x 10.00 mL x (1L/1000 mL)
Volume of a 0.200 M stock solution required to make each solution:
Molarity of solution x Volume to be made =Volume stock required
.06 (absorbance .65) x 10 mL = 3 mL
This experiment provided further understanding about the concentration, preparation, and dilution of solutions. Calculations were confirmed by experimental data obtained from quantitative and qualitative observations.
Pre-Lab: Calculate the volume of 0.200 M stock solution required to make each solution as follows: