Determining Concentration of a solution Lab BY satntG22 Determining the Concentration of a Solution: Beer’s Law Purpose: The purpose of the experiment is to determine the concentration and formula of an unknown cobalt nitrate solution by measuring absorbance. Introduction: A Colorimeter will be used to determine the concentration and formula of an unknown cobalt nitrate solution. The colorimeter sends blue light from the LED light source to pass through the solution and hit a photocell. A solution with a higher oncentration will absorb more light and transmits less than s solution of lower concentration.
Five solutions with a known concentration of cobalt chloride hexahydrate will be used. Each solution will be put into a small cuvette which will ultimately be placed inside the colorimeter to find the amount of light that strikes the photocell; calculating the absorbance. When the absorbance to concentration information is graph it should be a direct relationship resulting in a linear relationship. Three samples of unknown cobalt chloride hexahydrate will be btained. The samples contain the same compound but different concentrations.
By entering the absorbance on the relationship graph from part one, the concentration can be obtained. Observations: All solutions were a pinkish color liquid. As the concentration increased, the concentration increased as well. Data: Data Table 1: Standard Solutions- Co Trial Concentration (mg/mL) Concentration, calc. (mol/L) Absorbance 8 0. 034 0. 106 2 16 0. 068 0. 231 3 24 0. 10 0. 339 4 32 0. 14 0. 454 5 0. 17 0. 597 Data Table 2: Unknown Solutions- Concentration, exp. (mol/L) 20 0. 078 0. 254 26 0. 0879 0. 276 0. 088 0. 0 Graph 1 : Concentration and Absorbance Relationship of Standard Solutions Graph 2: Concentration and Absorbance Relationship of Unknown Solutions Calculations: 1 . To start the experiment the given concentration of (mg/mL) must be converted to (mol/L). To do so, set up a molar ration using the molar mass and given concentration. For trial 1 the given concentration is 8 mg/mL. The molar mass of the compound was determined to be 238 g. Set up the formula: Insert the provided concentration into the given value part of the formula and solve accordingly for all trials. . In part two of the experiment, the experimental concentration must be determined by using the provided information from part one of the experiment. In part one the linear trend was calculated to be EO. 0344x-O. 0008. By using the obtained absorbance and entering it into to equation the experimental concentration will remain. For trial 1 the absorbance value was obtained to be 0. 254. The absorbance represents the x part of the equation so it should be set up as: By using algebraic techniques, the y value is solved to be 0. 78. Perform the same method substituting the absorbance values in for x. 3. Formula of the Unknown: Solve by using molar mass ratios: Average: Discussion/Conclusion: The concentrations, absorbance and formula of the unknown were all obtained by performing the experiment. The results confirmed Beer’s Law which states that absorbance and concentration have a direct relationship and show a linear regression. This makes sense because as the concentration increases, there are more articles in the solution to be absorbed.
The linear regression line of our graph was determined to be EO. 0344x-O. 0008. The determined concentration values are shown in table 2 above. Some things that may have caused our concentration of solutions to be off may have been contamination of other concentrations, or water on the outside of the cuvette when it was placed in the Colorimeter. The formula of the unknown was calculated to be . Our determined values were a little off indicating an error. This may be due to the same reasons listed above.