(COC) Important Base Units for Chemists Lesson

Important Base Units for Chemists

Length

The base unit for length, or distance, in the metric system, is the meter.  A meter stick is used to measure length.  When measuring smaller or larger distances, prefixes are used.  For instance, 1 kilometer is equal to 1000 meters. For measuring smaller items, millimeters are used.  One meter is equal to 1000 millimeters.  A kilometer would be used to measure long distances, like those equivalent to a mile.  A millimeter would be used to measure short distances, like the width of a dime.  When using the metric system, you must be familiar with the prefixes used to denote the size of the unit as seen in the table below:

Base Units

Prefix	Size Compared to Base Unit	Abbreviation
Kilo	1000 x's Larger	k
Hecto	100 x's Larger	h
Deca	10 x's Larger	da
Base Unit	1	Meter (m), Liter (L), Gram (g)
Deci	.1 x's Smaller	d
Centi	.01 x's Smaller	c
Milli	.001 x's Smaller	m

Here are some good examples of when to use the varying units:

• The size of an ant would be measured in centimeters
• The length of your deck would be measured in meters.
• The distance to your school would be measured in kilometers.

Mass

Mass is another important measurement made by scientists. Mass is the amount of matter in an object.  In other words, it's the amount of stuff that the object is made up of.  The base unit for mass is grams.  Mass is measured by using a triple-beam balance.  Mass and weight are not the same thing, although they are commonly referenced interchangeably.    Mass is the amount of matter (stuff) that makes up an object while weight is the measurement of the force due to gravity.  It can be confusing to see the difference between the two because everything we do takes place on Earth.  However, if you traveled to the moon you would be able to see the difference.  Your mass on the moon would remain the same (how much matter you are made up of).  However, your weight on the moon would be significantly less because the force of gravity is less on the moon.  We will visit this topic again in the next module. Here are some examples of when you would use the varying units:

1. The mass of a strand of hair would be measured in milligrams.

2. The mass of a raisin would be measured in grams.

3. The mass of your dog would be measured in kilograms.

Volume

Volume is a measurement of how much space an object takes up.  The base unit for volume is the liter. Liquid volume is measured by using a graduated cylinder.  The volume of a regularly shaped object, like a cube, is measured by multiplying length x height x width.  When you multiply these 3 dimensions (centimeters x centimeters x centimeters) you get centimeters cubed.   It is important to know that 1 cm³   = 1 mL.  Sometimes these units are used interchangeably for volume.  To find the volume of an irregularly shaped object, like a rock, you would need to use the water displacement method.  Since you cannot easily measure the length, height, and width; you would want to see how much space it takes up by seeing how much space it takes up in water.  To do this, you measure a certain amount of water; let's say 20 mL.  Then you place the irregularly shaped object in the given amount of water and see how much the water rises.   Let's say when we place the rock in 20 mL of water, the water rises to 23 mL.  What does this tell us? What is the volume of the rock?   Since the water rose 3 mL that means the volume of the rock is 3 mL.  Here are some examples of when you would use the varying units:

• The amount of liquid a medicine dropper holds would be measured in milliliters.
• The amount of liquid in a Coke-cola bottle would be measured in liters.

Temperature

Temperature is a measure of how hot or cold an object is. The SI unit for temperature is Celsius.  A thermometer is used to measure temperature.  The Celsius scale is easy to use it is based off of the freezing and boiling points of water, being the freezing point of water is 0 °C and the boiling point of water is 100 °C. The Kelvin scale is also favored among scientists as absolute zero (0 Kelvin), is the lowest possible temperature an object can acquire.  

• The temperature water freezes can be measured at 0°C   or 32°F.
• The average body temperature of a human is measured at 98.6 °F or 37 °C.

[CC BY 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION