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Scientific Measurements Review
Accuracy:
How close a measured value is to the accepted or real value.
Precision:
The degree of reproducibility of a measured quantity; how close a series of measurements of the same quantity are to one other.
Scientific measurements generally adhere to the International System of Units (SI).
SI Base Units
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Note: Precise definitions of the SI units are not necessary to memorize. Rather, the relationships between the units and how to use them are the important parts to know.
| Quantity | Unit | Symbol |
|---|---|---|
| Length | Meter | m |
| Temperature | Kelvin | K |
| Time | Second | s |
| Mass | Kilogram | kg |
| Amount of Substance | Mole | mol |
| Electric Current | Ampere | A |
| Luminous Intensity | Candela | cd |
SI Derived Units
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Volume
Volume is a measure of space. It is a unit of length raised to the third power.
The SI unit of length is the meter. One meter cubed is equivalent to 1000 L. Litres, which are a convenient unit for scientific measurements, are a more common measurement unit than meters cubed.
1 L = 1 dm\(^{3}\)
1 L = 1000 mL
1 cm\(^{3}\) = 1 ml
Density
A ratio of mass (m) to volume (V) of a substance.
\(\text{Density} = \frac{\text{Mass}}{\text{Volume}}\)
SI Prefixes: Units of Measure for All Sizes
Multipliers that change unit values by multiples of ten.
| \(1\,nm = \frac{1\,um}{1000\,nm} = \frac{1\,mm}{1000\,um} = \frac{1\,m}{1000\,mm} = \frac{1\,km}{1000\,m} = 0.000\,000\,000\,001\,km\) |
| \(1\,km = \frac{1000\,m}{1\,km} = \frac{1000\,mm}{1\,m} = \frac{1000\,um}{1\,mm} = \frac{1000\,nm}{1\,um} = 1\,000\,000\,000\,000\,nm\) |
Examples
Scientific Measurements Examples
When making scientific measurements it is important to be as precise as possible. Precision is the degree of reproducibility of a measured quantity; how close a series of measurements of the same quantity are to one other. A measurement value with a high degree of precision will have a larger number of digits.
Example Problem 1
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A length of rope is measured several times, the measured value is 10.5 cm. However, the length of the rope is actually 12.1 cm. How is this possible?
Example Problem 2
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An experiment is conducted five times and the following volumes are recorded: 1.9 mL, 2.1 mL, 2.0 mL, 1.9 mL, and 2.0 mL. The actual volume is 2.0 mL. Are the recorded volumes: a) accurate, b) precise, c) accurate and precise, d) neither accurate nor precise?
Example Problem 3
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Chemical experiments involve the precise measuring of liquids. These measurements are generally completed with cylindrical glassware. To read the volume of liquid using a cylindrical measuring apparatus use the bottom of the meniscus. The meniscus is the curved surface of the liquid. For example, a volumetric flask is designed to precisely measure one exact volume of liquid, and has only one marker.
What is the volume of liquid in the pictured graduated cylinder?
Problem Set
Scientific Measurements Problem Set
Below are two documents. One is practice problems, the second is the same problems with solutions.
They can be downloaded and changed to suit your needs.
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Practice Problems
Problem Solutions
Quiz
Scientific measurements are communicated using...
What is the SI unit of length?
Scientific Measurements Quiz
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