Chm 113 Lab Report Solubility of Copper Iodate Ryan Busch PDF

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Ryan Busch CHM 113 Wei Zhang 30 October 2019 Determination of the Solubility Product of Copper(II) Iodate Intro: In the experiment performed in lab, the concentration of Cu 2+ was determined by three different saturated solutions by a spectrophotometric method. The concentration of IO 3- was also determined using two additional saturated solutions. The absorbance of a solution at a certain wavelength relates to the degree of absorption of light of that wavelength by the species in solution. The absorbance is measured using a spectrophotometer. In order to determine the concentration from the measured absorbance, a series of standards were prepared for comparison. By graphing the standards along with the measured absorbances (a calibration curve), one is able to determine the unknown concentrations of the elements. In the experiment we will calculate and find 5 different Ksp values from 5 different samples, and see how their average compares to the literature value of Ksp as 1.4x10^-7. Procedure: 1. 30 mL of 0.200 M solution of CuSO4 and 30 mL of 0.300 M KIO3 solution were obtained from the stock bottles in the laboratory hood. 2. Each sample was capped and the contents were mixed thoroughly. 3. The tubes were set aside on a test tube rack to rest undisturbed for at least one hour.

4. In cuvettes labeled 2-5, 1.0 mL of copper(II) sulfate were added with the concentrations 0.160 M, 0.080 M, 0.040 M, 0.016 M 5. Using a Mohr pipet, 3.5 mL of 0.5 M aqueous NH3 and 2.25 mL of distilled water were added to each of the cuvettes. An extra 1.0 mL of distilled water was added to the cuvette labeled #1. 6. The absorbances of each copper-containing solution were measured at 610 nm. 7. Each tube was centrifuged, using an empty tube filled with water to counterbalance properly. 8. A pipet was used to transfer 0.90 mL from each of the centrifuge tubes into separate labeled (1-5) cuvettes. 9. 3.00 mL of 0.5 M NH3 solution was added to each of the cuvettes and 2.40 mL of water was added to each of the cuvettes. 10. Each of the tubes' absorbances were measured at 610 nm. Equations: The first of the equations we use is the equation for the adjusted molarities due to dilution for our calibration curve. In this we will take the original molarity(.160,.08,.04,.016, or blank) and multiply it by 1 mL(the amount of CuSO4 used in each) over 6.75mL (the total liquid in the sample). Moving away from these values we will find, we need to find the initial Cu2+ concentrations for samples 1-5. To find this value we will take the amount of mL of CuSO4 in each sample and multiply it by .2(the concentration of CuSO4) divided by 8mL, which Is the total amount of liquid in each sample. When finding the initial IO3- concentration we use a similar equation, but replace the .2 with .3 because that is the molarity of KIO3- used in the samples. Next, since the absorbances were given to us in the experiment, we can plug these into our absorbance-concentration equation which we found, In order to find the molarities of each

sample. Once we find this value, we can plug it into an equation to find our final Cu2+ values. So we plug in these found values and multiply them by 6.75mL/.9mL. This is the ratio of our total liquid in the samples to the amount of liquid taken from each centrifuged sample. Now that we have this value, we can solve for all the parts we are looking for in each sample. Since we have the initial and final values for Cu2+ concentration, we can find the change in concentration of Cu2+ by subtracting the final value from the initial value. With this we can also find the change in the IO3- concentration, as it is simply 2x the concentration of delta Cu2+. In order to find IO3- final concentration, we subtract the the delta IO3- value we just found from the initial IO3- value. Finally since we have all of our values for Cu2+ and IO3-, we can find our Ksp for each sample. This value is represented by our IO3- value being cubed and divided by 2. Observations: While observing the numbers resulting from the experiment, it is important to note how for the calibration curve, the higher the original molarity of the sample, the higher the adjusted molarity was due to dilution. Of course, this is just because of how the equation is set up, but it is important to note this, as this translated across many values in the experiment, where the lower initial concentration led to a lower final concentration. This trend can be seen even with the final Ksp values of each sample, as the samples with lower concentrations led to a negative or smaller number than the bigger values in samples 4 and 5. Something very important to note is the average Ksp value reached in this experiment, which was .000672. This is very different than the literature value for Ksp we were given, which is 1.4x 10^-7. Based on this our results show a higher Ksp value than if our experiment worked out to be completely perfect. Even with having negative Ksp values in samples 1 and 2, and having an extremely small value of 5.0x10^-10 in sample 3, our average was still high and this is partly due to experimental error. Lastly it is important to touch on the equation of the calibration curve. This value of 11.5x+.27 ended up

yielding a negative molarity for a Cu2+ concentration. However this does not mean it had a negative concentration, rather there is just variability in the readings near zero. This equation yielded very small values for x, leading to low concentrations which was very common in this experiment due to the fact everything used had a concentration significantly less than 1.0.

Calculations: For calibration curve, adjusted molarities due to dilution: 1. 0.160 M x 1.0 mL / 6.75 mL = 0.0237 M 2. 0.080 M x 1.0 mL / 6.75 mL = 0.01185 M 3. 0.040 M x 1.0 mL / 6.75 mL = 0.005936 M 4. 0.016 M x 1.0 mL / 6.75 mL = 0.00237 M

Initial Cu2+ Concentration: 1. 3.5 mL x 0.200 M / 8 mL = 0.0875 M

2. 4.0 mL x 0.200 M / 8 mL = 0.1 M 3. 4.3 mL x 0.200 M / 8 mL = 0.1075 M 4. 4.6 mL x 0.200 M / 8 mL = 0.115 M 5. 5.0 mL x 0.200 M / 8 mL = 1.25 M Initial IO3- Concentration: 1. 4.5 mL x 0.300 M / 8 mL = 0.169 M 2. 4.0 mL x 0.300 M / 8 mL = 0.15 M 3. 3.7 mL x 0.300 M / 8 mL = 0.139 M 4. 3.4 mL x 0.300 M / 8 mL = 0.128 M 5. 3.0 mL x 0.300 M / 8 mL = 0.113 M Absorbances: Test tube # Absorbance

1 .155

2 .300

Calculated concentrations (y=11.5x+ 0.27) 1. .155 = 11.5x+.27 X= -0.01 M 2. .300 = 11.5x+.27 X= .00261 M 3. .329=11.5x+.27 X= .00513 M

3 .329

4 .412

5 .540

4. .412=11.5x+.27 X= 0.0123 M 5. .540=11.5x+.27 X= .0235 M

Final Calculated Final Cu 2+ Concentration Values Adjusted for Dilution: 1. -.01 x 6.75mL / 0.9mL= -0.075 M 2. .00261 x 6.75mL / 0.9mL= 0.0196 M 3. .00513 x 6.75mL / 0.9mL= 0.0385 M 4. .0123 x 6.75mL / 0.9mL= 0.0923 M 5. .0235 x 6.75mL / 0.9mL= 0.176 M

Sample 1: [Cu2+] Initial: 0.0875 M [IO3-] Initial: 0.169 M [Cu2+] Final: -0.075 M Δ[Cu2+]: 0.1625 M Δ[IO3-]: 2 x Δ[Cu2+] = 0.325 M Final [IO3- ] = Initial [IO3-] - Δ[IO 3-] = -.156 Ksp = ½(-0.156)3 = -0.00189 Sample 2: [Cu2+] Initial: 0.1 M [IO3-] Initial: 0.15 M [Cu2+] Final: 0.0196 M

Δ[Cu2+]: 0.0804 Δ[IO3-]: 2 x Δ[Cu2+] = 0.1608 Final [IO3- ] = Initial [IO3-] - Δ[IO 3-] = -0.0108 Ksp = ½(-0.0108)3 = -6.3E-7 Sample 3: [Cu2+] Initial: 0.1075 M [IO3-] Initial: 0.139 M [Cu2+] Final: 0.0385 M Δ[Cu2+]: .069 Δ[IO3-]: 2 x Δ[Cu2+] = 0.138 Final [IO3- ] = Initial [IO3-] - Δ[IO 3-] = 0.001 Ksp = ½(0.001)3 = 5.0E-10 Sample 4: [Cu2+] Initial: 0.115 M [IO3-] Initial: 0.128 M [Cu2+] Final: 0.0923 M Δ[Cu2+]: 0.0227 Δ[IO3-]: 2 x Δ[Cu2+] = 0.0454 Final [IO3- ] = Initial [IO3-] - Δ[IO 3-] = 0.0826 Ksp = ½(0.0826)3 = 2.81E-4 Sample 5: [Cu2+] Initial: .125 M [IO3-] Initial: 0.113 M [Cu2+] Final: 0.176 M Δ[Cu2+]: -.051 Δ[IO3-]: 2 x Δ[Cu2+] = -0.102 Final [IO3- ] = Initial [IO3-] - Δ[IO 3-] = 0.215 Ksp = ½(0.215)3 = 0.00497(4.97E-3) Average Ksp Value: 0.000672

Conclusion: The importance and end goal of this experiment was to be able to calculate the 5 different Ksp values for each of the five different samples. This goal was reached through a long and specific calculation process, where it yielded an average value not too similar to the literature value we were given. This is alright, it just shows how error occurred in the process of this experiment. Error can absolutely be introduced in simply reusing the same pipette or even not following the rule of going from lowest concentration to highest concentration when pipetting liquid into sample tubes. This can always be prevented if careful measures are taken to ensure this basic rule is being followed, as well as washing the pipette before every new use of it. In addition to this, there are many small and accurate measurements in this experiment. Adding a slight amount more or less of any element would affect all the values for concentration and eventually the Ksp values. It is important that all measurements be taken carefully, and if possible a second set of eyes could be a good aid to ensure all measurements are exact. Lastly if in the experiment the lab worker did not wait long enough for the precipitate to form, this could have affected absorbance values, throwing off the rest of the values in the experiment. Though these errors and many other small things led to skewed results, the purpose of the experiment was achieved above all things....