Question
A SOLUTION IS MADE BY MIXING 5.00 mL .00300 MFE(NO3) WITH 4.00mL 0.00300 M KSCN AND 3.00 mL 1.0 M HNO3. AFTER EQUILIBRIUM ISESTABLISHED, THE CONCENTRATION OF Fe(SCN)+2 WAS DETERMINED TO BE2.72*10E-4 M. CALCULATE THE EQUILIBRIUM CONSTANT FOR THISREACTION. Fe=3 (aq) + SCN- (aq) <-----> Fe(SCN)+2 (aq) A SOLUTION IS MADE BY MIXING 5.00 mL .00300 MFE(NO3) WITH 4.00mL 0.00300 M KSCN AND 3.00 mL 1.0 M HNO3. AFTER EQUILIBRIUM ISESTABLISHED, THE CONCENTRATION OF Fe(SCN)+2 WAS DETERMINED TO BE2.72*10E-4 M. CALCULATE THE EQUILIBRIUM CONSTANT FOR THISREACTION. Fe=3 (aq) + SCN- (aq) <-----> Fe(SCN)+2 (aq)
Explanation / Answer
Total initial volume 5 + 4 + 3 = 12 mL = 0.012 L . Moles of Fe3+ = molarity * volume (L) =0.003 M * 0.005 L =0.000015 moles . Initial concentration = moles / volume = 0.000015 moles/ 0.012 L =0.00125 M . Moles of SCN- = 0.003 M * 0.004 L =0.000012 moles . Initial concentration = 0.000012 moles / 0.012 L =0.001 M . Fe+3(aq) + SCN- (aq) <-----> Fe(SCN)+2(aq) . The equilibrium concentration of Fe(SCN)2+ wasfound to be 2.72 * 10^-4 M Since the initial concentration of this species in zero, thereduction in concentration of reactents is equal to the increase inconcentration of this species i.e. 2.72 * 10^-4 M . Hence equilibrium concentration of Fe3+ = 0.00125 M - (2.72 *10^-4 M) =0.000978 M . Equilibrium concentration of SCN- = 0.001 M - (2.72 * 10^-4M) =0.000728 M . Equilibrium constant, Kc = [Fe(SCN)+2] / {[ Fe+3] [ SCN-] } =(2.72 * 10^-4 M) / { 0.000978 M * 0.000728 M } =318.82 Fe+3(aq) + SCN- (aq) <-----> Fe(SCN)+2(aq) . The equilibrium concentration of Fe(SCN)2+ wasfound to be 2.72 * 10^-4 M Since the initial concentration of this species in zero, thereduction in concentration of reactents is equal to the increase inconcentration of this species i.e. 2.72 * 10^-4 M . Hence equilibrium concentration of Fe3+ = 0.00125 M - (2.72 *10^-4 M) =0.000978 M . Equilibrium concentration of SCN- = 0.001 M - (2.72 * 10^-4M) =0.000728 M . Equilibrium constant, Kc = [Fe(SCN)+2] / {[ Fe+3] [ SCN-] } =(2.72 * 10^-4 M) / { 0.000978 M * 0.000728 M } =318.82