Experiment 2.docx - Experiment#2 Synthesis and Analysis of...

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Experiment #2 Synthesis and Analysis of a Chromium Salt Student Name: Gabriella Selestiyanta Student Number: 1004627914 Lab Partner: Section Number: 132 Date the experiment was performed: 2 February 2018 Date the lab report was submitted: 9 February 2018 Submitted to George Li Pre-lab Questions Pre-lab Quiz Introduction Experimental Method Results and Calculations Accuracy Discussion Learning Objectives Summary References Experimental Technique Report Presentation Introduction The purpose of this experiment was to synthesize and analyze potassium dioxalatodiaquochromate (III) dehydrate (K[Cr(C 2 O 4 ) 2 (H 2 O) 2 ]*2H 2 O) in order to determine the concentration of Cr 3+ in the solution and the percent by weight of Cr in the complex that had
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been synthesized . The process of synthesizing the chromium salt was done through crystallization that involved both physical (mixing and grinding the two reactants) and chemical (boiling) reactions. Whilst the process of analyzing the chromium was done by carrying out a list of process that involved heating, washing (to get rid of contaminants), dissolving, and diluting in order to measure its absorbance at the same wavelength as the calibration curve by using the Spectronic 20 spectrophotometer. In real life, synthesizing chromium is important due to the fact that it can be used to produce pigment for paints since the 19 th century 6 . At that time, chromium(III) oxide (Cr 2 O 3 ) was used as a pigment for deep green paint 6 . Experimental Method The calibration curve process in which we were supposed to measure the absorbance of the 0.050M solution over the wavelength range of 400nm to 600nm using the Ultraspec 3100 Pro UV/Visible spectrophotometer was not done during the experiment due to limited amount of time. Next, since there were no vials present, the product of the reaction was measured by putting it in the electronic balance and carefully transferring the crystallized product into the test tube until the reading was around 0.5g. The complete method of this experiment can be found in the “CHM 120H5S Chemical Principles 2 2018 Course Manual” on page 31-33. Results Graphs 1 Figure 1 The Absorbance of 0.05M Cr(NO 3 ) 3
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0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.04 0.05 0.05 0.06 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 f(x) = 12.58x - 0.02 Absorbance vs Concentration Concentration Absorbance Figure 2 Graph of Absorbance vs. Concentration of Cr(NO 3 ) 3 Calculations K 2 Cr 2 O 4(s) + 7 H 2 C 2 O 4 *2H 2 O 2K[Cr(C 2 O 4 ) 2 (H 2 O) 2 ]*2H 2 O (s) + 6CO 2(g) + 13H 2 O (l) i 0.0034mol 0.0238mol r 0.0034mol 0.0238mol 0.068mol 0.0204mol 0.0442mol f - - 0.068mol 0.0204mol 0.0442mol A. Moles of Cr(NO 3 ) 3 Absorption of Cr(NO 3 ) 3 = 0.338 Finding Concentration of Cr(NO 3 ) 3 using Beer-Lambert Law o Beer-Lambert Law: A = lc o (slope) = 12.58 o C = A/ l = 0.338/(12.58) x (1cm) = 0.027M Moles of Cr(NO 3 ) 3 = 0.027M x 0.05 L = 0.0013 moles 2
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B. % Yield of the Reaction % yield = (moles of the product)/(theoretical moles of product) x 100% (0.0013 moles)/(0.0068 moles) x 100% = 19.76% C. Experimental Mass ratio of Cr 3+ Mass of Cr 3+ found = 0.0013 moles x 52 g/moles = 0.0676 g (mass of Cr 3+ found)/(mass of complex) = 0.0676g/2g = 0.0338 % by weight = 3.38% D. Theoretical mass ratio of Cr 3+ (molar mass of Cr 3+ )/(molar mass of complex) (52g/mol)/(339,1935g/mol) = 0.1533
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