Determining the Concentration of a Solution – Application of Beer’s LawCandice JosephApril 10, 20071. PurposeThe purpose of this experiment was to produce a calibration curve of absorbance vs. concentration for NiSO4 and then to use this standard curve for determining concentration of an unknown solution of NiSO4.
2. IntroductionMany transition compounds exhibit colors due to d-d transition. The electrons from the partially filled d-subshells absorb a particular wavelength from the white light (which is a mixture of the seven colors in rainbow) and consequently appear as the complementary color of the wavelength absorbed.
If a material absorbs none of the wavelength it appears colorless and in case it absorbs all it appears black.
The list of complementary colors is typed below:Complementary colorsRed – Green, Blue – Orange, Violet – YellowAbsorbance is a measure of the amount of light absorbed. This is determined by using Colorimeter, a type of spectrometer, which measures the quantity of light (in visible spectrum) that passes through a sample. The absorbance increases with increasing concentration of the solution, since more the number of transition metal ions, more light is absorbed.
There exists a linear relationship between absorbance and concentration of the solution.
In this experiment we have used five standard NiSO4 solution i.e. solutions with known concentration, to make a calibration curve between absorbance and concentration of NiSO4 solution.3.
Materials:IBM compatible computer, Serial box interface, Logger pro, Vernier Colorimeter, Cuvette, five large test tube (20×150 mm), Chemwipes, glass stirring rod, 30 mL of 0.40 M NiSO4, two 10 mL pipettes, pipet bulb, distilled water, test tube rack, two 100 mL beakers, 5 mL of unknown NiSO4 solution.4. Procedure:1.
Lab coat, gloves and safety glasses were used as safety measure during the experiment as the experiment involved handling of hazards chemicals.2. Approximately 30 mL of 0.40M NiSO4 stock solution was added to a 100 mL beaker.
Another 30 mL of distilled water was added to another 100 mL beaker.3. Five clean and dry large test tubes were marked numbers 1 – 5. 2, 4, 6, 8 and 10 mL of 0.
4 M NiSO4 stock solution was pipetted into test tubes numbered 1 to 5, respectively. Also with another pipette 8, 6, 4, 2 and 0 mL of distilled water was pipetted into the test tubes marked 1 to 5, respectively. Thus NiSO4 standard solution measuring 10 mL with concentrations 0.08M, 0.
16M, 0.24M, 0.32M and 0.40M was obtained in test tubes numbered 1, 2, 3, 4 and 5 respectively.
4. Computer was prepared for acquiring the data during the experiment. The vertical axis had absorbance scaled from 0 to 0.6 and the horizontal axis had concentration scaled from 0 to 0.
5M.Calibration of the Colorimeter5. The outside of the cuvette was cleaned and dried using a chemwipe and the cuvette was filled 3/4th with distilled water in a manner to avoid bubbles in the solution. The cuvette was placed in the colorimer’s cuvette slot with the reference mark facing the white reference mark at the right of the colorimeter and the opaque side perpendicular to the direction of the light source.
6. From the experimental menu calibration was performed. The blank cuvette was inserted into the colorimeter and the lid was closed. The wavelength nob of the colorimeter was turned to the 0%T position, 0 was typed in the %edit box and keep was clicked.
7. For 2nd reading the wavelength knob of the colorimeter was turned to Red position, 100 was typed in % edit box and keep was clicked.Preparing the Calibration Curve8. The cuvette was emptied and rinsed with the 0.
08M NiSO4 standard solution. This solution was then filled into the cuvette upto 3/4th full. The solution was discarded and again filled with the same solution. The cuvette was filled thrice, discarding the solution filled twice.
The cuvette was placed inside the colorimeter. When the reading stabilized keep was clicked. 0.08 was typed in the % edit box and the entry was stored.
9. Step 8 was repeated for the remaining standard NiSO4 solutions 0.16M, 0.24M, 0.
32M and 0.40M.10. The graph was plotted and printed.
11. In the similar manner absorbance of the unknown NiSO4 solution.12. A line plot between absorbance and concentration of the NiSO4 solution was plotted in Excel and a linear trend line passing through origin was also plotted and the equation of the linear trendline was obtained.
5. Results and Analysis:The absorbance data for different standard solutions and the unknown NiSO4 solution is presented in table 1, below:Table 1: Absorbance data for standard NiSO4 solutions and unknown NiSO4 solutionTest Tube #mL of 0.40 M NiSO4mL of waterM of NiSO4Absorbance from the expt1010002280.080.
5377unknown sample0unknown0.268The plot between absorbance and concentration for standard solutions and the linear trend line is presented in figure 1, below:The linear trendline equation between absorbance and concentration is y = 1.3266x; R2 = 0.9814Because nickel sulfate solution is green, therefore, it absorbs the Red light as red is the complementary color of green.
Because the solution absorbs red colors therefore, red light was used in this experiment. If the solution was orange, then blue line would have been used.Using the linear trendline equation y = 1.3266x, concentration of the unknown solution isx = 0.
268/1.326 M = 0.21M3. Then was done because, when there is no NiSO4 solution all the light passes through thecuvette.
4 Not exactly as my R2 value for my data is 0.9814 slightly less than 0.99, but this value is also indicative of very good linear fit.5 The required absorbance value will be y = 1.
326x = 1.326*0.50 = 0.6636 The concentration of this new standard solution will be (0.
40M * 3)/(3+7) = 0.12M7 This is to ensure that no air gap or air bubble is present in the solution and also the solution in the cuvette is not contaminated by the previous solution or diluted by the distilled water. Understanding of the Chemistry of BreathalyzersCandice JosephApril 10, 20071. PurposeThe purpose of this experiment was to understand the chemistry behind breathalyzers and to study the correlation between blood alcohol content and breath alcohol level by employing Henry’s Law.
2. IntroductionDrunken driving is a major life hazard of the driver as well to others. Therefore, there are regulations prohibiting driving with blood alcohol level more than 0.08%.
For monitoring alcohol level of drivers, the regulating authorities use portable equipment known as Breathalyzer. This works by utilizing color change involved in oxidation of ethanol in acetic acid by a strong oxidant potassium dichromate in acidic medium. The reaction is8 H2SO4 + 3 C2H5OH + 2 K2Cr2O7 3 CH3COOH + 2 Cr2(SO4)3 + 11 H2O + 2 K2SO4Potassium dichromate has distinct yellow color which reacts with ethanol in presence of sulfuric acid and oxidizes it into acetic acid. The associated color change is proportional to the ethanol in the breath and allows the monitoring of alcohol level in the breath using a colorimeter.
This alcohol level in blood is then converted to alcohol level in blood by following empirical relation:2100 mL of breath alcohol level = 1 mL of Blood alcohol content (BAC)Using Henry’s law, one can compare the breath alcohol level to blood alcohol contentCg, ethanol in blood = KPethanolWhere, Cg is dissolved ethanol concentration, in mols/liter (Equivalent to blood alcohol)K is Henry’s law constant and Pethanol is partial pressure of ethanol or breath alcohol level3. Materials and equipment:IBM compatible computer, Serial box interface, Logger pro, Vernier Colorimeter, Cuvette, 50 mL graduated cylinder, Erlenmeyer flask, two 100 mL and one 50 mL beakers, Headspace sampling syringe, 10 test tubes with rubber stoppers, 10 mL graduated cylinder, disposable pipette, glass stirring rod, spatula, 25 mL of 50% by volume H2SO4(aq), distilled water, 250 mL of ethanol (95% concentration), ~ 0.265 gm potassium dichromate and 0.065 gm silver nitrate.
4. Procedure:1. Lab coat, gloves and safety glasses were used as safety measure during the experiment as the experiment involved handling of hazards chemicals.2.
25 mL of 50% by volume H2SO4(aq) was transferred in an Erlenmeyer flask and ~ 0.065 gm potassium dichromate and ~ 0.065 gm silver nitrate was added into it. The solution was mixed throughly and using a 10 mL pipette 5 mL of this solution was transferred to the five test tubes marked 1 to 5.
3. In test tubes numbered 6 to 10 respectively 0, 25, 50, 75 and 100 mL of 95% ethanol and 100, 75, 50, 25 and 0 mL distilled water was added.4. 20 cm3 of vapor from test tube number 6 was collected using handspace sampling syringe and bubbled through the potassium dichromate solution in test tube number 1 and again anther 20 cm3 was also collected and bubbled through the same solution.
This exercise was repeated for vapors of test tube numbers 7 through 10 which were bubbled through potassium dichromate solutions in test tube numbers 2 through 5 respectively.5. The colorimeter was calibrated using a blank solution as in experiment 7, above.6.
A calibration curve was prepared using solutions in test tubes 1 to 5 as was done in experiment 7 above, but this time using 440 nm light.7. Data was collected, plotted and the linear trendline equation was obtained.5.
Results and Analysis:3. The proof for this beer is 44. I am female and my weight is 52 kg.Therefore, p = 52 kg = 52000 g, r = 0.44Using the formula, %BAC = (m)(1.055)(100)/(pr)To be beyond legally allowed limit of %BAC = 0.08%, the minimum mass of ethanol consumed will be m =10 volume% alcohol 10 mL alcohol (ethanol) in 100 mL wineAssuming, the specific density of wine to be 1 (similar to that of water)This means 100 mL of wine contains 7.8 gm of ethanol as density of ethanol is 0.78 gm/mLTherefore, the minimum volume of wine needed to be legally drunk will be(17.35*100)mL/7.8 = 222.44 mL
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