(a) Interpretation: A standard-addition plot should be created using the data given. Concept introduction: A commonform of standard-addition method involves adding known amounts of a standard solution to sample aliquots containing a fixed volume. Measurements taken for each solution can be used to plot a standard-addition plot.

Question

Exactly 10.00-mL aliquots of a solution containing phenobarbital were measured into 50.00-mL volumetric flasks and made basic with KOH. The following volumes of a standard solution of phenobarbital containing 2.000μg/mL of phenobarbital were then introduced into each flask and the mixture was diluted to volume: 0.000, 0.500, 1.00, 1.50, 2.00 mL. The fluorescence of each of these solutions was measured with a fluorimeter, which gave values of 3.26, 4.80, 6.41, 8.02, 9.56, respectively. a. plot the data. b. derive a least squares equation for the data plotted in (a). c. find the concentration of phenobarbital from the equation in (b). d. calculate a standard deviation for the concentration obtained in (c).

Answer 1

Question

Chapter 1, Problem 1.11QAP

Interpretation Introduction

(a)

Interpretation:

A standard-addition plot should be created using the data given.

Concept introduction:

A commonform of standard-addition method involves adding known amounts of a standard solution to sample aliquots containing a fixed volume. Measurements taken for each solution can be used to plot a standard-addition plot.

Interpretation Introduction

(b)

Interpretation:

Using the standard-addition plot constructed, the concentration of the unknown phenobarbital sample should be determined.

Concept introduction:

In a standard-addition plot, the graph can be extrapolated to obtain thevolume of standard reagentequivalent to the amount of analyte in the sample ( (Vs)0 ). This value can be used in the following equation to calculate the concentration ( Cx ) of the unknown sample.

Cx=−(Vs)0CsVx

Where,

Cs = concentration of the standard

Vx = constant volume of the unknown added to each sample solution.

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