Laboratory Equipment and Safety

What is it?

A chemistry lab is a safe place when everyone follows the same rules. Two skills go together:

Safety: recognizing hazards, wearing the right protection and working in a way that prevents accidents.
Equipment: knowing what each piece of apparatus is for and how precisely it measures, so that results are reliable.

Hazards are communicated worldwide with the GHS (Globally Harmonized System) pictograms: red-bordered diamonds printed on bottles and on safety data sheets (SDS).

Pictogram	Meaning	Example
Flame	Flammable	Ethanol, propanone (acetone)
Flame over circle	Oxidizer: makes fires burn more fiercely	Concentrated hydrogen peroxide, potassium nitrate
Exploding bomb	Explosive or self-reacting	Some peroxides
Gas cylinder	Gas under pressure	Oxygen and nitrogen cylinders
Corrosion	Destroys skin, eyes or metal	Concentrated acids, sodium hydroxide
Skull and crossbones	Toxic: can kill in small amounts	Mercury compounds
Exclamation mark	Harmful or irritant	Dilute ammonia solution
Health hazard	Long-term harm (e.g. cancer, damage to organs)	Benzene
Environment	Toxic to aquatic life	Copper(II) sulfate

The signal word shows severity: Danger for the more serious hazards, Warning for the less serious ones.

Key idea

Before any practical, ask three questions: What are the hazards? (read the label and the SDS), How could I be harmed? and What will I do to reduce the risk? This is a risk assessment, and every professional chemist does one.

Why does it matter?

Your safety and others’. Most lab accidents come from a few avoidable causes: no eye protection, spills, heating carelessly and mixing up bottles.
Reliable results. Using a beaker to measure 25.00 mL, or reading a burette from above, gives results that no calculation can rescue.
Every later practical depends on it, from making solutions (molarity) to titrations.

How does it work?

1. Protective equipment and safe habits

Wear safety goggles at all times while chemicals are in use; add a lab coat and, when needed, gloves. Tie back long hair; wear closed shoes.
No eating or drinking in the lab, and never taste or directly sniff a chemical: waft the vapour gently towards your nose if told to smell it.
Use a fume cupboard for toxic or smelly gases and volatile solvents.
When heating a test tube, point it away from everyone. Keep flammable liquids away from flames; use a water bath or hot plate instead.
To dilute a concentrated acid, add acid to water, slowly, never water to acid: the mixing releases heat, and adding water to acid can make it boil and spit.
Never pipette by mouth; use a pipette filler.
Report every spill, breakage and injury at once. Know where the eyewash, safety shower and fire blanket are. Dispose of waste as instructed, not down the sink by default.

2. Equipment and its precision

Apparatus	Use	Typical tolerance (class A)
Beaker	Holding, mixing, heating	Marks only approximate (about ±5 %)
Conical flask	Swirling, titrations	Marks only approximate
Measuring cylinder, 100 mL	Measuring volumes roughly	±0.5 mL
Burette, 50 mL	Adding a variable, measured volume (titration)	±0.05 mL
Volumetric pipette, 25 mL	Delivering one fixed volume	±0.03 mL
Volumetric flask, 250 mL	Making a solution of exact volume	±0.15 mL
Top-pan balance	Weighing	±0.01 g
Analytical balance	Accurate weighing	±0.0001 g

The percent uncertainty compares equipment fairly:

\begin{aligned} &\text{percent uncertainty} \\[4pt] &= \frac{\text{uncertainty}}{\text{measured value}} \times 100\% \end{aligned}

3. Reading a scale

Liquids in narrow glassware form a curved surface, the meniscus. For water and most solutions, read the bottom of the meniscus.
Your eye must be level with the meniscus. Reading from above or below gives a parallax error.
Record one more digit than the smallest graduation by estimating between the lines: a burette marked every 0.1 mL is read to two decimal places, for example 23.35 mL.
A burette reads downwards from 0.00 mL at the top. The volume delivered (the titre) is the final reading minus the initial reading.

Think of it like this

Using the right glassware is like choosing the right kitchen tool: you can measure a teaspoon of salt with a mug, but you wouldn’t expect the cake to come out the same twice. A beaker is the mug; a volumetric pipette is the measuring spoon.

More precisely

Glassware is made to two standards: class A (tighter tolerances, for accurate analysis) and class B (about twice the tolerance). The tolerance is printed on the glass. Pipettes and flasks are calibrated at a stated temperature, usually 20 °C, and are marked “Ex” (calibrated to deliver) or “In” (calibrated to contain). The tolerance is a limit on the systematic error of the item; replicate measurements show the random error of your technique.

Visualise it

A burette scale with a curved meniscus. An eye level with the bottom of the meniscus reads 23.35 mL correctly. An eye above or below the meniscus lines it up with the wrong mark: a parallax error. — Read the bottom of the meniscus with your eye level with it.

Worked example

Worked example: Choosing equipment by percent uncertainty

Question: You need 25.0 mL of a solution. Compare the percent uncertainty using a 100 mL measuring cylinder (±0.5 mL) and a 25 mL volumetric pipette (±0.03 mL).

Measuring cylinder:
$\begin{aligned} &\frac{0.5\ \text{mL}}{25.0\ \text{mL}} \times 100\% \\[4pt] &= 2\% \end{aligned}$
Volumetric pipette:
$\begin{aligned} &\frac{0.03\ \text{mL}}{25.0\ \text{mL}} \times 100\% \\[4pt] &= 0.12\% \end{aligned}$
The pipette is far more precise. Use it whenever an exact volume matters, for example in a titration.

Worked example: Finding a titre

Question: A burette reads 0.50 mL at the start of a titration and 23.35 mL at the end. What volume was delivered?

\begin{aligned} &\text{titre} = 23.35\ \text{mL} - 0.50\ \text{mL} \\[4pt] &= 22.85\ \text{mL} \end{aligned}

Both readings are recorded to two decimal places, so the titre is also given to two decimal places.

Worked example: Planning a safe method

Question: A student plans to warm ethanol over a Bunsen burner and to dilute concentrated sulfuric acid by pouring water into it. Identify the hazards and improve the plan.

Ethanol carries the flame pictogram: its vapour catches fire easily. Warm it in a water bath (hot water from a kettle, or a beaker of water on a hot plate), with no flames nearby.
Concentrated sulfuric acid carries the corrosion pictogram, and mixing it with water releases a lot of heat. Add the acid slowly to the water, stirring, wearing goggles and gloves.

Common mistake

Common mistake: Measuring with a beaker

The marks on a beaker are only a rough guide. “50 mL” in a beaker could be several millilitres out. Use a measuring cylinder for rough volumes and a pipette or burette for accurate ones.

Common mistake: Reading the top of the meniscus, or from an angle

For water-based solutions, read the bottom of the curve, with your eye level with it. Looking from above or below shifts the reading (parallax).

Common mistake: Adding water to concentrated acid

The heat released can make the water boil instantly and spray acid. Always add acid to water, slowly.

Notation note

Record a burette reading to two decimal places even when the last digit is zero: 24.00 mL, not 24 mL.
“±0.05 mL” is the tolerance of the item; a result is reported as mean ± standard deviation of replicates.

Remember this

Read the label and the SDS; know the GHS pictograms; Danger is more severe than Warning.
Goggles on; no eating or drinking; fume cupboard for harmful vapours; add acid to water.
Beakers and flasks are for holding; cylinders for rough volumes; pipettes, burettes and volumetric flasks for accurate ones.
Percent uncertainty = uncertainty ÷ measured value × 100 %.
Read the bottom of the meniscus at eye level; a burette is read to two decimal places; titre = final − initial.

Practise this topic with flashcards and a quiz at chemistryclarity.com/chemistry/laboratory-equipment-and-safety/