1.1 What is Chemistry?

http://www.ck12.org Chapter 3. Measurement

temperature (25°C). The densities of some common materials are listed in theTable3.5.

TABLE3.5:

Material Density (g/mL)

hydrogen 0.00009

oxygen 0.0014

water 1.0

aluminum 2.7

iron 7.9

gold 19.3

Mass vs. Weight

The terms mass and weight, while often used interchangeably, are technically different terms.Massis the quantity
of inertia possessed by an object. Weightrefers to the gravitational force acting on a mass, as measured on a
scale. On the surface of the earth, the numerical values of mass and the corresponding force of gravity (weight) are
approximately equivalent. For now, we will use the terms mass and weight interchangeably although mass is the
more appropriate scientific term.

Determining the Volume of Regularly Shaped Objects

In order to calculate density, we must know the volume the object occupies. We can calculate the volumes of some
regularly shaped objects using the following expressions inTable3.6.

TABLE3.6: Formulas for Calculating Volumes of Regularly Shaped Objects

Volume of a cube l×w×h

Volume of a sphere

4

3

πr^3

Volume of a cylinder πr^2 h

Volume of a cone

1

3

πr^2 h

Determining the Volume of Irregularly Shaped Objects

If a solid is irregularly shaped, we can determine its volume by measuring the volume of water displaced by the solid.
For example, say you want to measure the volume of the toy dinosaur inFigure3.7. After placing the dinosaur in
the water, the volume measured in the container increases by an amount that is equal to the total volume of the
dinosaur. Note that this method only works for solids that do not dissolve in water. If you tried to measure the
volume occupied by a pile of salt, the salt would dissolve in the water and this method would not work very well.

Temperature Scales

There are three temperature scales that are commonly used in measurement. Their units are °F (degrees Fahrenheit),
°C (degrees Celsius), and K (Kelvin). TheFahrenheit scale, which is the most commonly used scale in the United
States, defines the normal freezing point and boiling point of water as 32°F and 212°F, respectively. TheCelsius
scaledefines the normal freezing point and boiling point of water as 0°C and 100°C, respectively. The Celsius