lab inorganic 8

ITEM	CONTENT	MARKS
Objective	The purpose of this experiment is to determine the concentration of an unknown  copper(II) solution by spectrophometric analysis.
Introduction	The intensity of the colour is proportional to the concentration of the species in the solution . We can see the colour as a complement of the visible wavelength being absorbed by a sample . Substances that appear red and absorbed blue visible light and reflect other visible colours to our eyes vice versa to the substances that absorbed red appear as blue light.Absorption of light is more related to available energy levels in the molecule or an ion.The amount of energy and therefore the wavelength of radiation involved in this transition is a function of the electronic structure of molecule or an ion.            The spectronic 20 colourimeter is an versatile instrument that is useful for spectrophotometric or colourimetric determinations of solutions.Spectrometric is difficult because concentrations is very low. If the ions do not produce an intensely coloured complex ,Cu(NH3)42- , by the addition of of concentrated aqueous ammonia .The absorbance at various concentrations is used to plot graph for the determination of the concentration of copper(II) ions in an unknown solutions.
Results	Test tube number Concentration (M) Absorbance 1 0.000 0.055 2 0.060 0.251 3 0.140 0.397 4 0.200 0.582 5 0.00153 0.060 6 0.00092 0.058
Discussion	Spectrochometry has very wide range of application .Absorbance has the value that obtained by determining the amount of light of certain wavelength that absorbed by samples . 1)graph paper at the back shown the line grah of concentration versus absorbance graph. 2)Given 0.2 M Cu2+ solution  mv = mv ( 4/1000) x 0.2 = 0.01 M M = 0.08 M mv=mv (7/1000) x 0.2 = 0.01 M M = 0.14 M 3)Y = mx + c At point (0.000,0.055) 0.055 = (0.000 x m) + c C = 0.055 At point (0.060 , 0.251) 0.251 = (0.060 x m) + 0.055 M = 3.267 Y = 3.267x + 0.055 4)Beer’s Law : Concentration unknown = absorbance – intercept                                                  slope concentration unknown = 0.060 -0.055                                           3.267                                       = 0.0015 Concentration unknown = 0.058-0.055                                              3.267                                        =0.00092 5) As we know that the Beer’s Law state that the absorbance is directly proportional to the concentration , the resulting graph yields a straight line . The equation line which is Y = 3.267x + 0.055 can be used to determine the the concentration of an unknown solution .
Conclusion	The concentration of an unknown copper(II) solution by spectrophotometric analysis was determined. The concentration is 0.00153 M and 0.00092 M .
References	1)    http://www.utc.edu/Faculty/Gretchen-Potts/chemistryhelp/beers.htm 2)    http://biomed.engr.sc.edu/bme_lab/lab%20reports/58)%20Determination%20of%20Protein%20Concentration%20using%20Spectrophotometry.pdf