9: Measurements, Unit Conversions, and Density
- Page ID
- 381243
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- 9.1: Expressing Numbers - Scientific Notation
- Scientific notation is a system for expressing very large or very small numbers in a compact manner. It uses the idea that such numbers can be rewritten as a simple number multiplied by 10 raised to a certain exponent, or power. Scientific notation expressed numbers using powers of 10.
- 9.2: Significant Figures
- Significant figures in a quantity indicate the number of known values plus one place that is estimated. There are rules for which numbers in a quantity are significant and which are not significant. In calculations involving addition and subtraction, limit significant figures based on the rightmost place that all values have in common. In calculations involving multiplication and division, limit significant figures to the least number of significant figures in all the data values.
- 9.3: Units for Measurements
- Measurements provide quantitative information that is critical in studying and practicing chemistry. Each measurement has an amount, a unit for comparison, and an uncertainty. Measurements can be represented in either decimal or scientific notation. Scientists primarily use the SI (International System) or metric systems. We use base SI units such as meters, seconds, and kilograms, as well as derived units, such as liters (for volume) and g/cm3 (for density).
- 9.4: Converting Units
- Units can be converted to other units using the proper conversion factors. Conversion factors are constructed from equalities that relate two different units. Conversions can be a single step or multistep. Unit conversion is a powerful mathematical technique in chemistry that must be mastered. Exact numbers do not affect the determination of significant figures.
- 9.5: Solving Multistep Conversion Problems
- Sometimes you will have to perform more than one conversion to obtain the desired unit.
- 9.6: Density
- Density is a physical property that is defined as a substance’s mass divided by its volume. Density is usually a measured property of a substance, so its numerical value affects the significant figures in a calculation. Notice that density is defined in terms of two dissimilar units, mass and volume. That means that density overall has derived units, just like velocity.