Quantitative Chemical Analysis
Quantitative Chemical Analysis
9th Edition
ISBN: 9781464135385
Author: Daniel C. Harris
Publisher: W. H. Freeman
Question
Book Icon
Chapter 4, Problem 4.33P

(a)

Interpretation Introduction

Interpretation:

For measurement giving y value of 2.58, the corresponding x value and its standard uncertainty has to be found out.

Concept Introduction:

Uncertainty with a Calibration Curve:

Propagation for the equation y=mx+b (but not y=mx) gives,

The standard uncertainty in x is given as:

ux=sy|m|1k+1n+(yˉy)2m2(xiˉx)2

Where,

ux is standard uncertainty for x

y is the corrected absorbance of unknown

xi is the mass of sample in standards

ˉy is the average of y values

ˉx is the average of x values

k is the number of replicate measurements

(a)

Expert Solution
Check Mark

Answer to Problem 4.33P

The corresponding x and its standard uncertainty value for y value of 2.58 is 2.0±0.3

Explanation of Solution

Given data:

Consider least-squares in Figure 4-11

A new single measurement gives a y value of 2.58

Finding of x value and its standard uncertainty:

The equation of straight line from figure 4-11 is y=mx+by=0.61538x+1.34615

On rearranging, we get,

x=ybm   =2.581.350.615   =2.00

The value of ˉy and ˉx is calculated as follows,

ˉy=(2+3+4+5)/4   =3.5ˉx=(1+3+4+6)/4   =3.5

The (xiˉx)2 is found as follows,

(xiˉx)2=(13.52)+(33.52)+(43.52)+(63.52)      =13.0

The standard uncertainty in x is given as,

ux=sy|m|1k+1n+(yˉy)2m2(xiˉx)2    =0.19612|0.61538|11+14+(2.583.5)2(0.61538)2(13.0)    =0.38    =0.3(rounded off)

Therefore, the value for x is 2.0±0.3

Conclusion

The corresponding x and its standard uncertainty value for y value of 2.58 is found out as 2.0±0.3

(b)

Interpretation Introduction

Interpretation:

The four times measurement of y gives an average value of 2.58, the corresponding x value and its standard uncertainty based on four measurements has to be found out.

Concept Introduction:

Uncertainty with a Calibration Curve:

Propagation for the equation y=mx+b (but not y=mx) gives,

The standard uncertainty in x is given as:

ux=sy|m|1k+1n+(yˉy)2m2(xiˉx)2

Where,

ux is standard uncertainty for x

y is the corrected absorbance of unknown

xi is the mass of sample in standards

ˉy is the average of y values

ˉx is the average of x values

k is the number of replicate measurements

(b)

Expert Solution
Check Mark

Answer to Problem 4.33P

The corresponding x and its standard uncertainty value based on four measurements is   2.0±0.2

Explanation of Solution

Given data:

Consider least-squares in Figure 4-11

The y is measured four times and its average value is 2.58

The numbers in subscript denotes insignificant figures.

Finding of x value and its standard uncertainty:

The equation of straight line from figure 4-11 is y=mx+by=0.61538x+1.34615

On rearranging, we get,

x=ybm   =2.581.350.615   =2.00

The value of ˉy and ˉx is calculated as follows,

ˉy=(2+3+4+5)/4   =3.5ˉx=(1+3+4+6)/4   =3.5

The (xiˉx)2 is found as follows,

(xiˉx)2=(13.52)+(33.52)+(43.52)+(63.52)      =13.0

Here, the number of replicate measurement is four. Hence, k=4

The standard uncertainty in x is given as,

ux=sy|m|1k+1n+(yˉy)2m2(xiˉx)2    =0.19612|0.61538|14+14+(2.583.5)2(0.61538)2(13.0)    =0.26   =0.2(rounded off)

Therefore, the value for x is 2.0±0.2

Conclusion

The corresponding x and its standard uncertainty value based on four measurements is found out as 2.0±0.2

(c)

Interpretation Introduction

Interpretation:

The 95% confidence intervals for (a) and (b) has to be found out.

Concept Introduction:

Confidence Intervals:

The confidence interval is given by the equation:

Confidence interval = ˉx±tsn      =ˉx±tux(since standard uncertainty(ux)=s/n

Where,

ˉx is mean

s is standard deviation

t is Student’s t

n is number of measurements

ux is standard uncertainty

To Find: The 95% confidence intervals for (a) and (b)

(c)

Expert Solution
Check Mark

Answer to Problem 4.33P

The 95% confidence intervals for (a) is 2.0±0.8

The 95% confidence intervals for (b) is 2.0±0.6

Explanation of Solution

Given data:

The results of the measurement in part (a) is 2.00±0.38

The results of the measurement in part (b) is 2.00±0.26

The numbers in the subscript denotes insignificant figures.

Calculation of Confidence intervals:

The t value corresponding to 90% confidence level for three degrees of freedom is t90%=2.353

The 90% confidence interval for part (a) is calculated as follows,

     confidence interval    = ˉx±tux90% confidence interval =2.00(±2.353×0.38)   =2.00(±0.89)   =2.0(±0.8)(rounded off)

The 90% confidence interval for part (b) is calculated as follows,

     confidence interval    = ˉx±tux90% confidence interval =2.00(±2.353×0.26)   =2.00(±0.61)   =2.0(±0.6)(rounded off)

Conclusion

The 95% confidence intervals for (a) is calculated as 2.0±0.8

The 95% confidence intervals for (b) is calculated as 2.0±0.6

Want to see more full solutions like this?

Subscribe now to access step-by-step solutions to millions of textbook problems written by subject matter experts!
Students have asked these similar questions
Indicate the processes in the dismutation of Cu2O.
1. Consider these three reactions as the elementary steps in the mechanism for a chemical reaction. 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 Potential Energy (kJ) 600 400 200 0 -200- -400 -600- -800 (i) Cl₂ (g) + Pt(s) → 2Cl (g) + Pt(s) (ii) Cl (g)+ CO (g) + Pt (s) → CICO (g) + Pt (s) Ea = 1550 kJ Ea = 2240 kJ (iii) Cl (g) + CICO (g) → Cl₂CO (g) Ea = 2350 kJ AH=-950 kJ ΔΗ = 575 ΚΙ AH=-825 kJ a. Draw the potential energy diagram for the reaction. Label the data points for clarity. The potential energy of the reactants is 600 kJ Reaction Progress b. What is the overall chemical equation? c. What is the overall change in enthalpy for the above chemical reaction? d. What is the overall amount of activation energy for the above chemical reaction? e. Which reaction intermediate would be considered a catalyst (if any) and why? f. If you were to add 2700kJ of energy to the reaction (e.g. 2700 kl of heat or electricity), would you be able to make the reaction reverse itself (i.e. have…
draw the enolate anion and the carbonyl that would be needed to make this product through an aldol addition reaction.
Knowledge Booster
Background pattern image
Similar questions
SEE MORE QUESTIONS
Recommended textbooks for you
Text book image
Chemistry
Chemistry
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Cengage Learning
Text book image
Chemistry
Chemistry
ISBN:9781259911156
Author:Raymond Chang Dr., Jason Overby Professor
Publisher:McGraw-Hill Education
Text book image
Principles of Instrumental Analysis
Chemistry
ISBN:9781305577213
Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher:Cengage Learning
Text book image
Organic Chemistry
Chemistry
ISBN:9780078021558
Author:Janice Gorzynski Smith Dr.
Publisher:McGraw-Hill Education
Text book image
Chemistry: Principles and Reactions
Chemistry
ISBN:9781305079373
Author:William L. Masterton, Cecile N. Hurley
Publisher:Cengage Learning
Text book image
Elementary Principles of Chemical Processes, Bind...
Chemistry
ISBN:9781118431221
Author:Richard M. Felder, Ronald W. Rousseau, Lisa G. Bullard
Publisher:WILEY