1. ERT 207 ANALYTICAL CHEMISTRY
ALINA RAHAYU MOHAMED
School of Bioprocess Engineering

2. Lecture 3 (16th July 2007)

3. 2. HANDLING OF DATA ANALYSIS
Before learning what types of errors, you need to understand accuracy and precision.

4. 2.1 ERRORS IN QUANTITATIVE STUDY
2.1.1 ACCURACY
Q1: What is accuracy?

5. A1: Accuracy is the degree of agreement between the measured value and the accepted true value.
It is expressed as absolute error or relative error.

6. 2.1.2 PRECISION
Q2: What is precision?

7. A2: The degree of agreement between the replicate measurements of the same quantity. That is, the repeatability of the result.
It can be expressed as standard deviation, deviation from the mean, deviation from the median, and range or relative precision.

8. Consider this case:
You are at target practise. You shoot the series of bullets that land in:

9. -you are both precise and accurate
bulls-eye
-you are both precise and accurate
imprecise and inaccurate
precise but inaccurate

10. 2.2 TYPES OF ERRORS IN EXPERIMENTAL DATA
Errors in experimental data can be divided into two main categories:
(i) Determinate or systematic errors.
(ii) Indeterminate or random or accidental errors.

11. 2.2.1 DETERMINATE OR SYSTEMATIC ERRORS
Determinate errors occur because of some reasons and have specific values.
Determinate errors are determinable.
Hence, determinate errors can be avoided.
For example, change in solution volume and concentration occuring with changes in temperature.
Solution to this error: by measuring the solution temperature.
Determinate errors are errors that occur because of some reasons and have specific values.

12. Characteristics of determinate errors:
1. Cause of error is known.
2. Consistency, that is the values are almost the same.
3. One-sided, example having the same sign.
4. Will give effect to accuracy of the method.
5. Can be corrected and avoided.

13. 2.2.1.1 TYPES OF DETERMINATE ERRORS
Types of determinate or systematic errors:
1.Operative errors
2.Instrumental errors
3.Method errors
4.Error of the reagent.

14. (i) Personal errors
It is also known as observation error and is
caused by carelessness, clumsiness or not using the
right techniques by the operators.
For example, recording wrong burette reading
as mL, whereas the correct reading is mL.
To avoid this error is by reading
the volume correctly.

15. (ii) Instrumental errors
The faulty equipments, uncalibrated weight and glasswares used may cause instrumental errors. Example, using instruments that are not calibrated and this can be corrected by calibrating the instruments before using.

16. (iii) Method errors
Method errors are caused by the nature of the methods used.
This error cannot be omitted by running the experiments several times.
It can be recognized and corrected by calculations or by changing to a different methods or techniques.
This type of error is present in volumetric analysis that is caused by reagent volume.
An excess of volume used as compared to theory will result in the change of colours. Example, mistakes made in determining end point caused by coprecipitation.

17. (iv) Errors of the reagent
This error will occur if the reagents used are not pure. Correction is made by using pure reagents or by doing back-titration.

18. 2.2.2 INDETERMINATE OR RANDOM ERRORS
Also known as accidental or random error.
This represent experimental uncertainty that occurs in any measurement.
This type does not have specific values and are unpredictable.

19. Charateristics of indeterminate errors:
a) Cause of error is unknown.
b) Spreads randomly around the middle value.
c) Usually small.
d) Have effects on precision of measurement
e) cannot be corrected
Example of indeterminate errors: change in humidity and temperature in the room that cannot be controlled.

20. Attempt Tutorial 1
Submit next Monday (23rd July 2007)
Tutorial session will be conducted in Week 4 (11am-12 pm).

21. Thank you for your attention

22. SELAMAT MENGULANGKAJI