The protein bovine serum albumin can bind several molecules of the dye methyl orange. To measure the binding constant K for one dye molecule, solutions were prepared with a fixed concentration of dye and a larger, variable concentration of protein (P). The equilibrium is Reaction 19-18, with X 5 methyl
orange.
Experimental data are shown in cells A16-D20 in the spreadsheet on the next page. The authors report the increase in absorbanceat 490 nm as P is added to X. X and PX absorb visible light, but P does not. Equilibrium expression 19-20 applies and [PX] is given by Equation 19-21. Before P is added, the absorbance is. The increase in absorbance when P is added is
The spreadsheet uses Solver to vary K and in cells B10:B11 to minimize the sum of squares of differences between observed and calculatedin solutions with different amounts of P. Cell E16 computes [PX] from Equation 19-21, which is Equation A on line 6 of the spreadsheet. Cells F16 and G16 find [X] and [P] from mass balances. Cell H16 computes which is Equation B on line 7.
To estimate a value of K in cell B10, suppose that 50% of X has reacted in row 20 of the spreadsheet. The total concentration of X is. If half is reacted, thenThe binding
constant is which we enter as our guess for K in cell B10. We estimatein cell B11 by supposing that 50% of X has reacted in row 20. In Equation B on line 7, .The measured
value ofin row 20 is 0.0291 and we just estimated that. Therefore, our guess for localid="1668328314124" in cell B11 is
Your assignment is to write formulas in columns E through J of the spreadsheet to reproduce what is shown and to find values in cells E17:J20. Then use Solver to find K andin cells B10:B11 to minimizein cell I21.
