1. Write the equilibrium constant expression for the FeSCN2 equilibrium inm 2. W

Question

1. Write the equilibrium constant expression for the FeSCN2 equilibrium inm 2. Which of the chemicals in the equilibrium is measured with the spectrophotometer? 3. Solutions 1 thru 4 are used to create a standard curve. Why is this necessary? 000M in part B?.00U 4. What is the concentration of iron(III) nitrate used in part A? . What color is iron(III) nitrate when it is dissolved in water? Which solution (1-4) should have the more intense color? 5. What is the dilution formula (you learned it in Chem 1411)? LMzV2 Use the dilution formula to calculate the concentrations of iron(III) ions and SCN ions when 5.00 mL of 0.002M iron(III) nitrate is mixed with 4.00 mL of 0.002 M NaSCN and dilute nitric acid is added to bring the total volume of the solution to 20.0 mL [M SCN-)- Put these calculated values into the table below as the initial concentrations of the reactants. When these reactants come to equilibrium, the concentration of FeSCN2+ in the mixture is 1.5 x 10 M With that information, complete the equilibrium table Fe3* + SCN FeSCN2 0 Initial Change Equilibrium Calculate the equilibrium constant using the equilibrium concentrations calculated in the table above.

Explanation / Answer

Q1.

FeSCN+2 is formed from

Fe+3 + SCN- --> [Fe(SCN)]+2

then

First, let us define the equilibrium constant for any species:

The equilibrium constant will relate product and reactants distribution. It is similar to a ratio

The equilibrium is given by

rReactants -> pProducts

Keq = [products]^p / [reactants]^r

For a specific case:

aA + bB = cC + dD

Keq = [C]^c * [D]^d / ([A]^a * [B]^b)

Kc = [Fe(SCN)+2] / ([Fe+3][SCN-])

Q2

we measure[Fe(SCN)]+2 complex since it has a colour i.e. initially --> invisible since not present and eventually turns to red couloured solution

we use colorimetery to approximate the vlaues via Beer's law

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