# 2: Measurements

- Page ID
- 171902

In 1983, an Air Canada airplane had to make an emergency landing because it unexpectedly ran out of fuel; ground personnel had filled the fuel tanks with a certain number of pounds of fuel, not kilograms of fuel. In 1999, the Mars Climate Orbiter spacecraft was lost attempting to orbit Mars because the thrusters were programmed in terms of English units, even though the engineers built the spacecraft using metric units. In 1993, a nurse mistakenly administered 23 units of morphine to a patient rather than the “2–3” units prescribed (the patient ultimately survived). These incidents occurred because people weren’t paying attention to quantities.

Chemistry, like all sciences, is quantitative. It deals with *quantities*, things that have amounts and units. Dealing with quantities is very important in chemistry, as is relating quantities to each other. In this chapter, we will discuss how we deal with numbers and units, including how they are combined and manipulated.

- 2.1 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.

- 2.2 Expressing Numbers - Significant Figures
- Significant figures properly report the number of measured and estimated digits in a measurement. There are rules for applying significant figures in calculations.

- 2.3 The International System of Units
- Recognize the SI base units. Combining prefixes with base units creates new units of larger or smaller sizes.

- 2.4 Converting Units
- The ability to convert from one unit to another is an important skill. A unit can be converted to another unit of the same type with a conversion factor.

- 2.5 Other Units - Temperature and Density
- Chemistry uses the Celsius and Kelvin scales to express temperatures. A temperature on the Kelvin scale is the Celsius temperature plus 273.15. The minimum possible temperature is absolute zero and is assigned 0 K on the Kelvin scale. Density relates a substance’s mass and volume. Density can be used to calculate volume from a given mass or mass from a given volume.