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Experimental Errors Kesalahan dalam pengukuran Sumber kesalahan

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Presentation on theme: "Experimental Errors Kesalahan dalam pengukuran Sumber kesalahan"— Presentation transcript:

1 Experimental Errors Kesalahan dalam pengukuran Sumber kesalahan
Rambatan kesalahan Errors → noise in measured values


3 Can you hit the bull's-eye?
Three shooters with three arrows each to shoot. How do they compare? Both accurate and precise Precise but not accurate Neither accurate nor precise

4 Measure the diameter of the ball
Using a metric stick, determine the diameter of the ball provided. Compare your results with another group. Any problems with your measurement?

5 Can all errors be controlled?
What are some possible things that can be done to minimize errors?

6 Types of (experimental) Errors
Systematic Error  Result of an experimental “mistake” Sometimes called bias due to error in one direction- high or low Penyebabnya diketahui (known cause) Operator Calibration of glassware, sensor, or instrument, etc.

7 Types of (experimental) Errors
Systematic Error This error can be corrected/ controlled when causes of error are determined, i.e : (a) calibrating all experimental tools and/ or instruments (b) controlling skill of experimenter, operator etc. (c) Cleaning all glassware, bottles, etc before doing experiments (d) etc… ?????

8 Types of (experimental) Errors
Systematic Error Typically produce constant or proportional nature (slowly varying bias) y = ax + b Proportional error influences the slope. Constant error influences the intercept.

9 Types of (experimental) Errors
Random error Unpredictable, non-deterministic Unbiased → equal probability of increasing or decreasing measured value Result of Limitations of measuring tool Random processes within system Environmental effect (?), etc Typically cannot be controlled Use statistical tools to characterize and quantify Multiple trials help to minimize

10 Example: Sources of Error sampling preparation analysis Representative
sample homogeneous vs. heterogeneous preparation Loss Contamination (unwanted addition) analysis Measurement of Analyte Calibration of Instrument or Standard solutions

11 Example: Quantization → Random error
1 13 1 14

12 Quantization error Timer resolution → quantization error
Repeated measurements X ± Δ Completely unpredictable

13 A Model of Errors Error Measured value Probability -E x – E +E x + E

14 A Model of Errors Error 1 Error 2 Measured value Probability -E x – 2E
+E x x + 2E

15 A Model of Errors

16 Systematic errors → accuracy
How close mean of measured values is to true value Random errors → precision Repeatability/reproducibility of measurements Characteristics of tools → resolution Smallest increment between measured values

17 Most accurate and precise
Graphical methods Scatter plots Most accurate and precise Systematic error? Worst precision

18 Two students analyzing two different CaCO3 antacid tablets
True value Student 1 Student 2 Label value 500 mg 750 mg Mean 463 mg 761 mg Std. dev. 20 mg 28 mg Which student has the more accurate results? Which student has the greater precision?

19 How are we going to address these questions?
quantity Student 1 Student 2 % Relative standard deviation  asses the precision %Error  asses the accuracy

20 calibration marks + one more place
Always remember to… Make all measurements carefully and check your results or readings a second time. Read all devices to as many places as possible (significant figures): calibration marks + one more place A buret, which is calibrated to 0.1 mL, can be read to 0.01 mL. A thermometer marked every degree can be read to 0.1 degree

21 Kandungan rhodamin dalam sampel Metode Spektrofotometri
Metode ESI Metode Spektrofotometri Ulangan 1 2 3 Saos A 0.11 0.25 0.15 0.10 0.17 Saos B 0.22 0.34 0.32 0.38 Berapakah konsentrasi rhodamin pada saos A dan B yang terukur dengan metode ESI dan spektrofotometri? Berapakah ketelitian dan ketepatan pengukuran rhodamin dengan kedua metode jika konsentrasi rhodamin sebenarnya dalam saos A 0.18 ppm dan saos B 0.24 ppm? Apa saja sumber systematic dan random errors dalam pengukuran tersebut?

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