gammagirl Posted March 7, 2018 Share Posted March 7, 2018 1.Consider a reaction mixture that has initial concentrations of Fe3+ = 0.0050 M and SCN– = 0.0050 M. Without doing any calculations, which of the following values do you know? a) The equilibrium concentrations of Fe3+, SCN– , and FeSCN2+ b) The sum of the equilibrium concentrations of Fe3+ , SCN– , and FeSCN2+ c) The product of the equilibrium concentrations of Fe3+ , SCN– , and FeSCN2+ d) The ratio of equilibrium concentrations of products to reactants: [FeSCN2+]/[Fe3+][SCN– ] e) The ratio of equilibrium concentrations of reactants to products: [Fe3+][SCN– ]/[FeSCN2+] Explain your answer, Earlier in the experiment, a calibration curve measuring absorbance on the y-axis and concentration on the x-axis was generated from a set of 3 standard solutions. So, I am thinking perhaps the d and e are known due to a concentration/absorbance ratio that graph? Next is this question, Consider a reaction mixture that has an initial concentration of FeSCN2+ = 0.0050 M, no Fe3+ or SCN. Without doing any measurements or calculations, which of the following two values do you know? a) The equilibrium concentrations of Fe3+, SCN– , and FeSCN2+ b) The sum of the equilibrium concentrations of Fe3+, SCN– , and FeSCN2+ c) The product of the equilibrium concentrations of Fe3+, SCN– , and FeSCN2+ d) The ratio of equilibrium concentrations of products to reactants: [FeSCN2+]/[Fe3+][SCN– ] e) The ratio of equilibrium concentrations of reactants to products: [Fe3+][SCN– ]/[FeSCN2+] Explain your answer. By the way the equation for both is , the equation is Fe3+ (aq) + HSCN (aq) <-----> FeSCN2+ (aq) and everything is 1:1. Using the ice table, Fe3+ is 0.0050M -x , SCN-, is 0.0050M- x. So, we know a and b? Link to comment Share on other sites More sharing options...
hypervalent_iodine Posted March 8, 2018 Share Posted March 8, 2018 1 hour ago, gammagirl said: Earlier in the experiment, a calibration curve measuring absorbance on the y-axis and concentration on the x-axis was generated from a set of 3 standard solutions. So, I am thinking perhaps the d and e are known due to a concentration/absorbance ratio that graph? Absorbance of what, exactly? 1 hour ago, gammagirl said: Using the ice table, Fe3+ is 0.0050M -x , SCN-, is 0.0050M- x. So, we know a and b? How do you figure that? They haven't said that the FeSCN2+ was made from those two ions, just that there was a flask that contained FeSCN2+. Besides, this is a reaction that exists in equilibrium and does not go to completion (in addition to the fact that they said that it was an initial concentration of FeSCN2+). Perhaps try writing the reaction in the other direction. You may find this useful: http://mctcteach.org/chemistry/C1152/Laboratory/Lab_Protocals/Det_of_Equil_Const_v.1.16.pdf Link to comment Share on other sites More sharing options...
gammagirl Posted March 8, 2018 Author Share Posted March 8, 2018 (edited) Absorbance of FeScn2+ And the link IS the experiment And that is the point the reaction is in equilibrium but the questions are confusing. If The Fe3+ was in excess, then Scn-=FeScn2+. But for the first question question, Fe 3+=Scn - is the same amount (as in the lab). It is something intuitive and easy. Edited March 8, 2018 by gammagirl Link to comment Share on other sites More sharing options...
hypervalent_iodine Posted March 8, 2018 Share Posted March 8, 2018 I definitely agree that the questions are confusingly written. I will think on it more and get back to you tomorrow, though you may need to contact your professor or TA. Link to comment Share on other sites More sharing options...
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