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 was also used to dilute solutions to a lower concentration. The main goal of this lab was to teach the practical skill of creating solutions at a specific molarities by diluting with water to help see the relationship between concentration and absorption. After collecting the percent transmittance values of the known copper (II) sulfate solutions, the made copper (II) solutions and the unknown copper (II) solution, the percentages were converted into transmittance using equation 1: T= (%T)/100 where T is transmittance and %T is percent transmittance.
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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 6: %error= |made value-standard value|/(standard value)×100%. Procedure: The first step in this lab was to calibrate the Spec-20 spectrophotometer. …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 knob. The next step in the lab is to find the absorbance of the standard solutions of copper (II) sulfate. To find the absorbance, the percent transmittance of the 0.500 M, 0.200 M, 0.100 M and the 0.050 M CuSO4 was recorded by placing each sample into the calibrated Spec-20 spectrophotometer. Transmittance was found by dividing percent transmittance by one hundred. The absorbance value was calculated using the equation A=-log(T) and was graphed to create a calibration curve. The purpose of the third section of the lab was to prepare four solutions of copper (II) sulfate with concentrations of 0.500 M, 0.200
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 6: %error= |made value-standard value|/(standard value)×100%. Procedure: The first step in this lab was to calibrate the Spec-20 spectrophotometer. …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 knob. The next step in the lab is to find the absorbance of the standard solutions of copper (II) sulfate. To find the absorbance, the percent transmittance of the 0.500 M, 0.200 M, 0.100 M and the 0.050 M CuSO4 was recorded by placing each sample into the calibrated Spec-20 spectrophotometer. Transmittance was found by dividing percent transmittance by one hundred. The absorbance value was calculated using the equation A=-log(T) and was graphed to create a calibration curve. The purpose of the third section of the lab was to prepare four solutions of copper (II) sulfate with concentrations of 0.500 M, 0.200