Question

Name Equilibrium Constant Lab Prelab assignment 1. Determine the initial concentrations (in molarity) of Fe and SCN" after mixing in each of the 5 beakers in Part I. Then, calculate the [FeSCN2 1 assuming that the reaction goes to completion and that all of the SCN ions react. Show a sample calculation then put your answers in the box below. [FESCN2 Jeg Beaker number [Fe") [SCN' 2 3 4 5 2. In preparing the standard solutions for Part 1, the equilibrium [FeSCN2] is assumed equal to the initial [SCN'] because the reaction is assumed to go to completion. Explain why this assumption is valid. 3. Consider the following reaction: X+3Y 2N +4Z The absorbance (A) due to the presence of Z was found for each of four solutions as shown below. [Z] 2.00 x 104 M 0.100 5.00 x 104 M 0.240 8.00 x 104 M 0.390 1.80 x 103 M 0.880 was found to have an absorbance of 0.662, what is the [Z] in If a solution with an unknown [Z] that solution? Attach a graph of A vs. [Z] with appropriate labels and a figure caption.

Answer 1

Answer 3:

1.0 у 3а + b*x No Weighting Equation Weight Residual 2.42206E-5 Sum of 0.8 0.99999 Pearson's r 0.99997 Adj. R-Squar Standard Err Value Intercept Slope 0.0488 1.20502E-4 0.6 0.4 0.2 0.0 2 6 8 10 12 14 16 18 20 Concentration (x10 M) Absorbance

Figure 1: Plot of Absorbance vs [Z].

The values fit into the linear equation, y= a+bx, where

y is the absorbance, x is [Z] and slope, b=0.0488, intercept, a=0.

By rearranging the equation, we have x=y/b

After the substitution of values, we have x= 0.662/0.4889, x= 13.56.

Since the units are in (x 10^-4 M), the concentration of Z, [Z]= 13.56 x 10^-4 M or 1.356 x 10^-4 M.