dr. reem m. alghanmi [email protected] 2017-1 … · analytical chemistry. gary d. christian....
TRANSCRIPT
Topics:
1-Classification of Analytical Methods
2- Sample preparation
3- Statistical Treatment of Data
4-Thermal Analysis
Learning Resources
ANALYTICAL CHEMISTRY.
Gary D. Christian. 6th ed.
JOHN WILEY & SONS, INC. 2003
QUANTITIVE CHEMICAL ANALYSIS
D. Harris 8th ed.
presentations (ppt)
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Schedule of Assessment Tasks for Students During the Semester
Assessment task (e.g. essay, test, group project,
examination, speech, oral presentation, etc.)
Week Due Proportion of Total
Assessment 1
Class Activities (home work, case study and other
assignments)
Weekly
10
2
First Exam
Week 6
15
3
Second Exam
Week 13
15
4
Excel Exam
---
15
5
Project
Week 5
5
6
Final Examination
Week
15 or 16
40
Total
100
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5
6
7
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10
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Statistical Treatment of Data
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Why do we need statistics in
analytical chemistry?
Scientists need a standard format to communicate
significance of experimental numerical data.
Objective mathematical data analysis methods
needed to get the most information from finite data
sets
To provide a basis for optimal experimental design.
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What Does Statistics Involve?
Defining properties of probability distributions
for infinite populations
Application of these properties to treatment of
finite (real-world) data sets
Probabilistic approaches to:
Reporting data
Data treatment
Finite sampling
Experimental design
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Ways to detect the systematic error
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Ways to
detect
the
systemat
ic error:
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Accuracy and Precision:
Is There a Difference?
Accuracy: degree of agreement between measured
value and the true value.
Absolute true value is seldom known
Realistic Definition: degree of agreement between
measured value and accepted true value.
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Accuracy
Precision
Precision: degree of agreement between replicate
measurements of same quantity.
Repeatability of a result
Standard Deviation
Coefficient of Variation
Range of Data
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Fig. 3.1. Accuracy and precision.
You can’t have accuracy without good precision.
But a precise result can have a determinate or systematic error.
©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)
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Ways of Expressing Accuracy
Absolute Errors: difference between true value and measured value
Mean Errors: difference between true value and mean value
Relative Error: Absolute or Mean Errors expressed as a percentage of
the true value
((m-x)/m)*100 = % Relative Error
Relative Accuracy: measured or mean value expressed as a percentage
of true value
((x/m)*100 = % Relative Accuracy
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Example 3.6:
The results of an analysis are 36.97 g. compared with the accepted value
of 37.06 g. What is the relative error in part per thousand?