LECTURE 2_Experimental Errors Flashcards
It is the minimum number of digits needed to write a given value in scientific notation without loss of precision.
significant figures
It is the closeness of results to others obtained in exactly the same way.
Precision
It is the closeness of a measured value to the true or accepted value, and is expressed by the error
Accuracy
uncertainty of a measurement is the difference between the measured value and the true value
Absolute error (absolute uncertainty)
uncertainty of a measurement is the absolute error divided by the true value
Relative error (relative uncertainty)
What are the 3 types of error
Random error
Systematic error
Gross error
What is a Random or indeterminate error?
It causes data to be scattered more or less symmetrically around a mean value
Affect measurement precision
What is Systematic (or determinate error) error
It causes the mean of a data set to differ from the accepted value
Affect the accuracy of results
What is Gross error
They usually occur only occasionally, are often serious, and may cause a result to be either high or low. They are often the product of human errors
Gross errors lead to outliers
What are the two components of precision in a measurement system
Repeatability and reproducibility
How does repeatability & reproducibility differ?
Repeatability: Focuses on the consistency of a single measurement process. “Can I get the same result every time I do it?”
Reproducibility: Focuses on the consistency of measurement processes across different conditions. “Can anyone get the same result when they do it?”
The reproducibility of a method is normally expected to be poorer (ie large random errors) than its repeatability
What are the sources of systematic error?
- Instrumental errors
- Environmental errors
- Observational errors
Ways to detect systematic errors.
- Analyze a known sample such as a certified reference material or standard reference materials.
- Analyze blank samples with no analyte being sought.
- Use different analytical methods to measure the same quantity
- Round robin experiment: Different people in several laboratories analyze identical samples by the same or different methods
Confidence intervals can be used to test for _____________________
systematic errors
Define mean.
The mean is the average of a set of numbers. It’s calculated by adding up all the values in a dataset and then dividing by the number of values.
What is a standard deviation?
The standard deviation measures the amount of variation or dispersion of a set of values.
In simpler terms, it tells you how spread out the data is around the mean.
How to avoid Enviromental errors?
- use air conditioner
- sealing certain components in the instruments
- use magnetic shields
What causes environmental errors?
due to external condition effecting the measurement including
surrounding area condition such as change in temperature, humidity, barometer pressure, etc
What are the most common observational errors
parallax error and estimation error (while reading the scale)
It is the accumulation of small effect, require at high degree of accuracy;
Random Error
How to avoid Random errors?
a) increasing number of reading;
b) use statistical means to obtain best approximation of true value
Standard reference materials (SRMs)
These are substances sold by the National Institute of Standards and Technology (NIST) and certified to contain specified concentrations of one or more analytes.
Blank
solution contains the solvent and all of the reagents in an analysis
Whenever feasible, blanks may also contain added constituents to simulate the _________________.
sample matrix
