Introduction: The goal of this lab was for students to learn how to use a spectrophotometer to find the absorbance of four known copper (II) sulfate solutions, four copper (II) sulfate solutions that were created by dilution, and one unknown copper (II) sulfate solution. The purpose of this experiment was to help students learn how to use the Spec-20, which is a machine that measures the transmittance and absorbance of a solution, learn about the linear relationship between absorbance and concentration known as the Beer- Lambert law and use the equation involving moles, volume and molarity. Molarity is a unit used in chemistry to measure the concentration of a solution and moles are a specific amount of matter. The serial dilution technique
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The Beer-Lambert law was then used to calculate the absorbance value. The law states there is a linear relationship between the absorbance and concentration of colored substances. Equation 2: A= -log(T) and equation 3: A=2-log(%T) were used to find absorbance where A is absorbance, T is transmittance and %T is percent transmittance. To find the correct mass of solid CuSO4 · 5H2O, equation 4: M= mol/L was rearranged to solve for moles. In the equation, M stands for molarity, mol is the moles of solute and L is liters of solution. The moles of solute was converted to grams of solute by dividing by the molar mass of solid CuSO4 · 5H2O. To find the desired volume of each made solution to create the diluted solution, equation 5: M_C V_C=M_D V_D was used where M is molarity, V is volume, c is concentrated solution and d is diluted solution. Finally, the percent error of concentration and absorption was calculated using equation …show more content…
After letting the Spec-20 warm up for fifteen minutes, the wavelength was set to 600 nm because it is the maximum absorbance for Cu2+ solutions. Ten test tubes were labeled with small vertical lines so they could be aligned with the spectrophotometer. The Spec-20 was set to 0% transmittance using the left knob without a test tube sample in the holder. Then a test tube filled three-fourths of the way full with distilled water was placed into the Spec-20’s test tube well and the pointer was set to 100% transmittance using the right hand
The Beer-Lambert law was then used to calculate the absorbance value. The law states there is a linear relationship between the absorbance and concentration of colored substances. Equation 2: A= -log(T) and equation 3: A=2-log(%T) were used to find absorbance where A is absorbance, T is transmittance and %T is percent transmittance. To find the correct mass of solid CuSO4 · 5H2O, equation 4: M= mol/L was rearranged to solve for moles. In the equation, M stands for molarity, mol is the moles of solute and L is liters of solution. The moles of solute was converted to grams of solute by dividing by the molar mass of solid CuSO4 · 5H2O. To find the desired volume of each made solution to create the diluted solution, equation 5: M_C V_C=M_D V_D was used where M is molarity, V is volume, c is concentrated solution and d is diluted solution. Finally, the percent error of concentration and absorption was calculated using equation …show more content…
After letting the Spec-20 warm up for fifteen minutes, the wavelength was set to 600 nm because it is the maximum absorbance for Cu2+ solutions. Ten test tubes were labeled with small vertical lines so they could be aligned with the spectrophotometer. The Spec-20 was set to 0% transmittance using the left knob without a test tube sample in the holder. Then a test tube filled three-fourths of the way full with distilled water was placed into the Spec-20’s test tube well and the pointer was set to 100% transmittance using the right hand