Lab Safety, Measurement, and Units

By the end of this lesson, you will be able to follow the safety rules that matter and say why each exists, read an instrument to the right number of digits, and tell accuracy from precision.

Safety Rules Exist Because Someone Was Hurt

Every rule below comes from an accident. Knowing the reason is what makes the rule stick when nobody is watching.

Goggles, always, from the moment anyone in the room starts. Splashes travel, and an eye does not heal the way skin does. This is the one rule with no exceptions, because the cost of being wrong once is permanent.

Add acid to water, never water to acid. Mixing concentrated acid with water releases a great deal of heat. Pouring acid into a large volume of water spreads that heat through the water. Pouring water onto acid concentrates it in the few drops that landed, which can boil instantly and spit acid out of the container.

Never taste, and smell only by wafting. Fan the vapor toward your face with a hand rather than putting your face over the container, so you get a trace rather than a lungful.

Know where the eyewash, shower, extinguisher and exits are before you start. In an emergency there is no time to look, and the seconds spent finding an eyewash are the seconds that decide the outcome.

Never return a reagent to its bottle, because whatever it picked up in your container is now contaminating everyone's supply.

Tie hair back, no loose sleeves, closed shoes. Bunsen flames are nearly invisible, and spills go downward.

Sort It: Safe or Not

SI Units and Prefixes

Science uses one system so that results travel between laboratories without translation.

Quantity	Unit	Symbol
length	meter	m
mass	kilogram	kg
time	second	s
amount	mole	mol
temperature	kelvin	K

Prefixes scale a unit by powers of ten, so no new units are needed:

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