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Uncertainty of Measurement in Calibration
A topic from the subject of Calibration in Chemistry.
Uncertainty of Measurement in Calibration
Key Points:
- Uncertainty is an estimate of the range of values within which the true value is likely to be found.
- Calibration is the process of determining the relationship between a measurement instrument and a known reference standard.
- Uncertainty in calibration can arise from a variety of sources, including instrument error, environmental conditions, and operator error.
- It is important to consider the uncertainty of measurement when interpreting calibration results.
Main Concepts:
Uncertainty of measurement is a fundamental concept in chemistry that must be considered when interpreting any measurement result. Calibration is a process that helps to minimize uncertainty by establishing a relationship between a measurement instrument and a known reference standard. However, even after calibration, there will always be some degree of uncertainty associated with any measurement.
The sources of uncertainty in calibration can be classified into three main categories:
- Instrument error: This refers to the inherent accuracy and precision of the measurement instrument itself.
- Environmental conditions: These can affect the accuracy of the measurement, such as temperature, humidity, and vibration.
- Operator error: This refers to mistakes that can be made by the person operating the measurement instrument.
It is important to consider the uncertainty of measurement when interpreting calibration results. The uncertainty should be reported along with the measurement result, and it should be taken into account when making decisions based on the data.
Uncertainty of Measurement in Calibration Experiment
Objective
To determine the uncertainty of measurement in the calibration of a volumetric flask.
Materials
- Volumetric flask (100 mL)
- Analytical balance
- Pipette (10 mL)
- Distilled water
Procedure
- Clean and dry the volumetric flask.
- Weigh the empty flask on the analytical balance and record the mass (m1).
- Fill the flask with distilled water to the calibration mark.
- Weigh the flask and water and record the mass (m2).
- Calculate the mass of the water (m3) by subtracting m1 from m2.
- Repeat steps 2-5 several times (n).
- Calculate the average mass of water (m̄) by summing up all the masses of water and dividing by n.
- Calculate the standard deviation (σ) of the masses of water using the formula:
σ = √( Σ(m3i - m̄)² / (n-1) ) - Calculate the relative uncertainty (u) of the measurement using the formula:
u = σ / m̄
Results
The following table shows the results of the experiment:
| Trial # | Mass of empty flask (m1) | Mass of flask and water (m2) | Mass of water (m3) |
|---|---|---|---|
| 1 | 100.000 g | 200.005 g | 100.005 g |
| 2 | 100.001 g | 200.006 g | 100.005 g |
| 3 | 100.002 g | 200.007 g | 100.005 g |
| 4 | 100.003 g | 200.008 g | 100.005 g |
| 5 | 100.004 g | 200.009 g | 100.005 g |
The average mass of water is:
m̄ = 100.005 g
The standard deviation of the masses of water is:
σ = 0.0005 g
The relative uncertainty of the measurement is:
u = 0.0005 g / 100.005 g = 0.0005%
Significance
The uncertainty of measurement is a critical factor in the calibration of laboratory equipment. It is important to be aware of the uncertainty of measurement when using calibrated equipment in order to ensure accurate and reliable results.