In: Chemistry
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?
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