Question 1 – standard solution preparation by dilution a) Beer’s Law shows that the absorbance measured for a species in solution is directly proportional to (directly related to) its concentration in that solution. If there are any large sources of error present or you are not thorough and careful whilst preparing your solutions, would you expect this to show up in your calibration plot? Explain.
b) The solution of copper ions appears to be a bright blue-green colour. What colour light must copper ions therefore be absorbing? c) What colour(s) must they be transmitting (allowing to pass through, unabsorbed)?
Question 2 – solution analysis for a calibration plot a) You must choose one of the following wavelengths to investigate your solutions at: 660nm (red), 610nm (orange), 565nm (green) or 468nm (blue). Mark these wavelengths on the spectrum of [Cu(H2O)6]2+ in your report book and use this to decide what colourimeter wavelength to use. (Hint: consider your answer to Question 1b.)
b) Why did you not use a wavelength in the blue region (430 – 480nm) to analyse your samples? Explain your answer with respect to the colour of the solutions and the spectrum of the absorbing species, [Cu(H2O)6]2+.
c) What would you expect your absorbance values would have been if you had used a wavelength in the blue region? d) With reference to Beer’s Law, does the trend of your absorbance values agree with the increasing concentrations of the sample solutions? (Remember, molar absorptivity and path length are constant for all your readings.
Question 3 – constructing a calibration plot a) Based purely on Beer’s Law (not your experimental results), what absorbance reading would you expect for the deionised water sample? Why?
b) The stock solution is five times more concentrated than the solution #1 that you prepared. Using Beer’s Law (not your experimental results), what would you expect the absorbance reading of the stock solution to be, compared to that of solution 1? Why?
c) Are your absorbance results expected given what you can predict from Beer’s Law?
d) Draw a “line of best fit” onto the graph. A line of best fit is a line that connects as many of the points as possible that fall within the trend. There are different types of lines of best fit depending on how the variables relate to each other. This one should be a straight line if the absorbing species has obeyed Beer’s Law because the law states that the absorbance is directly proportional to the concentration.
e) Does this calibration plot confirm that Beer’s Law was obeyed? Explain why or why not.
f) Are there any points that do not appear close to the line of best fit? Suggest why this is.
If you need the answers from the expirement please just make up numbers so you can do an example on how its done.
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