Question

A. Determine the quantity of unknown protein that has an absorbance of 0.297 when a blank has an absorbance of 0.062. The previously determined calibration curve has the form of a straight line with the equation A = 0.0182 × x 0.007, where A is the corrected absorbance and x is quantity of protein in units of μg.

B. You have carried out five separate titrations to determine the concentration of a sodium hydroxide solution, and obtained the following values: 0.0525, 0.0530, 0.0522, 0.0548, 0.0528 M. Calculate the Q value for the highest and lowest values in this set of measurements.

C. A least-squares curve fit of the data in the table to the right led to a best straight line with the equation y = 0.615x 1.35.

(a) If the y value of a new measurement is 3.20, what are the corresponding x value and the uncertainty in the x value? [The uncertainty in y (sy) is 0.196.]

(b) Suppose y was measured five times and average of these five measurements was 3.20. What is the uncertainty in x based on these five measurements?​

Answer 1

Corrected absorbance A = measured absorbance - blank absorbance

                                        = 0.297 - 0.062 = 0.235

A = 0.0182m + 0.007

0.235 = 0.0182 m + 0.007

Quantity of protein m = (0.235 - 0.007)/0.0182

                                  = 12.53 micrograms

B)

increasing order of concentration as follows :

0.0522, 0.0525, 0.0528 M, 0.0530, 0.0548, .

Range = highest - lowest

            = 0.0548 - 0.0522

            = 0.0026

Gap = last two values difference

        = 0.0548 - 0.0530

         = 0.0018

Q calculated = Gap / range

               = 0.0018 / 0.0026

               = 0.69