A standard solution of FeSCN^2+ is prepared by combining 6.00 mL of 0.00150 M Fe

Question

A standard solution of FeSCN^2+ is prepared by combining 6.00 mL of 0.00150 M Fe(NO_3)_3, 1.048 g KSCN, and deionized water in a 250 mL volumetric flask. The net ionic equation for the reaction is below. Fe^3+ + SCN^- Fe(SCN)^2+ What allows us to assume that the reaction goes essentially to completion? The concentration of KSCN is much higher than that of Fe(NO_3)_3. The concentration of Fe(NO_3)_3 is much higher than the concentration of KSCN. Under the conditions given above, LeChatelier's principle dictates that the reaction shifts to the left. The equilibrium reaction has a very high K_c. The reaction quotient Q is greater than K_c. Based on that assumption, what is the equilibrium concentration of Fe(SCN)^2+? For clarification see the example calculation on page 10-7 of your lab manual. Once checked, the calculated molarity will be copied to the appropriate space on Data Sheet page 10-11.

Explanation / Answer

a) the moles of Fe(NO3)3 = molarity X volume = 0.00150 X 6 millimoles = 0.009 millimoles

Moles of KSCN = Mass / Molecular weight of KSCN = 1.048 / 97.18 = 0.011 moles

The high concentration of KSCN shows that the reaction will go to completion

The equilibrium concentration = moles of Fe(SCN)+2 formed / total volume

The concentration = moles of Fe+3 taken / total volume = 0.009 millimoles / 250 = 0.000036 moloar

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