In this explainer, we will learn how to identify different laboratory apparatus and discern how and when they should be used.
Let us begin by learning how to measure mass, volume, and gas in the laboratory. We measure mass using a balance. There are two main types of balances that we can choose from: top-loading balances and analytical balances. Examples of both types of balances are shown below.
Top loader balances tend to be less precise and give masses to the nearest gram, a tenth of a gram, or a hundredth of a gram, depending on the balance. Analytical balances are held in a protective housing and typically give masses to the nearest ten-thousandth of a gram.
Chemicals should never be massed directly on the pan of the balance. Instead, they should be placed in a weigh boat or another open container, such as the one shown below.
We can extract solid chemicals from a reagent bottle and add them to the weigh boat using a spatula, as shown below.
We can measure the volume of a liquid with a variety of equipment. Graduated cylinders are narrow, cylindrical pieces of glassware that have markings or graduations to indicate the volume of liquid in the cylinder. The image below shows a typical graduated cylinder.
Graduated cylinders can typically hold anywhere from 10 mL to 1 000 mL. As the sizes vary, so do the graduations. It is always important to be aware of the major and minor scales of the cylinder in use.
When we want to accurately and precisely transfer or deliver a small volume of liquid, we should use a pipet. There are many types of pipets, but they all operate by drawing a liquid into a narrow cylinder using suction. Glass and plastic pipets may be graduated or volumetric. Graduated pipets have many markings and can be used to measure several volumes, while a volumetric pipet has only one marking and can only be used to measure one specific volume. The image below shows graduated and volumetric pipets.
Suction can be applied to the top of the pipet using a bulb, a three-way safety bulb, or a pump, as shown below.
When we are unsure of the volume of liquid needed in an experiment, such as in a titration experiment, we can use a buret. A buret, shown below, looks very similar to a graduated pipet.
However, we do not use suction to draw liquid into a buret. Instead, we fill the buret with liquid and open the stopcock at the bottom to allow the liquid to drain. Burets are numbered from the top down so that we can easily determine the amount of liquid released. It is important when filling a buret to always ensure that the stopcock is in the closed position, perpendicular to the column, before adding any liquid. This is illustrated in the diagram below.
The volume of a gas can be measured using a gas syringe, as shown below. The tube of the syringe is graduated to indicate the volume. Tubing is used to connect the syringe to a reaction vessel. As gas is produced; it will displace the plunger and the volume can be recorded.
Example 1: Identifying the Purpose of a Balance
What would the following laboratory setup be used for?
- Measuring the pH of a solution
- Measuring the temperature of a substance
- Measuring the mass of a substance
- Measuring the volume of a liquid or gas
- Measuring time
The pH of a solution can be measured with a pH probe. The temperature of a substance is measured using a thermometer. The mass of a substance is measured using a balance. The volume of a liquid can be measured using a graduated cylinder, pipet, or buret, while the volume of a gas can be measured with a gas syringe. Time is measured with a clock or stopwatch.
Pictured is a top-loading balance with a beaker. This setup is used to measure the mass of a substance. The correct answer is C.
Example 2: Recognizing a Buret
Which of the following images shows a buret?
A buret is a cylindrical piece of equipment used to dispense a liquid, particularly when we are unsure of the total volume of liquid needed in an experiment. A buret has graduations on the glass that indicate the volume and a stopcock, an adjustable valve, at the bottom that can be turned to release the liquid.
Answer A has graduations but does not have a stopcock. This is an image of a syringe. Answer B has no visible graduations or stopcock. This is an image of a volumetric pipet with a pipet pump attached. Answer C has graduations but does not have a stopcock nor a way to release liquid from the bottom of the container. This is an image of a graduated cylinder. Answer D has graduations and a stopcock. Answer D is a buret.
There are many pieces of equipment that we can choose when we need to transport or contain chemicals or react them together. Beakers are cylindrical containers with a spout. A typical beaker is shown in the image below.
They are commonly used as temporary storage vessels when performing an experiment or as containers in which to heat water. Beakers sometimes have volume markings on the side; however, these markings are not accurate. As such, a beaker should never be used for exact volume measurements.
Beakers do not have lids, but we can place a watch glass on a beaker to act as a cover.
Watch glasses can also be used in place of a weigh boat when massing solids or as surfaces on which to evaporate small amounts of liquid.
If we wish to evaporate larger amounts of liquid (10 mL–100 mL), we can use an evaporating dish. Evaporating dishes, such as the one shown below, are typically ceramic and have a large liquid surface to encourage evaporation.
There are many times when we need to dissolve a solid into a liquid to produce a solution with a specific volume. In these instances, we can use a volumetric flask, shown in the following image.
The shape allows for easy mixing of the solid into the liquid without splashing. There is a single graduation on the neck. Filling to the graduation produces a solution with a very accurate volume. As volumetric flasks can only produce a solution of a specific volume, they come in a variety of sizes ranging from one millilitre to several litres.
An Erlenmeyer flask, also known as a conical flask, is a common reaction vessel. The image below shows two different types of Erlenmeyer flasks.
The base of an Erlenmeyer flask is like that of a beaker. Likewise, although Erlenmeyer flasks often have volume markings, they should not be used for accurate measurement. Unlike beakers, Erlenmeyer flasks are tapered. This makes the flask an excellent choice for reactions that need to be stirred or swirled, as the narrow neck helps reduce splashing.
Round-bottom flasks are typically used for apparatus setups that involve multiple glassware connections or when a reaction needs to be more uniformly heated. An example of a round-bottom flask is shown below.
As the bottoms are round, the flasks need to be clamped or set on a cork ring to stand upright.
For smaller-scale reactions, multiple sample storage, or the heating of small amounts of substances, we can use a test tube. When heating a small amount of substance, it is best to choose a boiling tube, a slightly larger version of a test tube. Both types of test tubes are shown below. The increased size helps to prevent the heated substance and potential bubbles from exploding out of the tube.
Test tube racks are used to store multiple sets of test tubes.
When transferring substances from one vessel to another, we can use a stem funnel, shown below, to prevent spills.
While we can heat beakers, Erlenmeyer flasks, round-bottom flasks, and test tubes, we can only safely raise their temperature to about . If we need to exceed , we should use a crucible.
Crucibles are typically made of porcelain or stainless steel and can withstand temperatures upward of .
Example 3: Identifying a Piece of Labware
What piece of labware is shown in the image below?
This piece of labware is flat on the bottom. Beakers, graduated cylinders, volumetric flasks, and Erlenmeyer flasks have flat bottoms. The top of the piece of labware tapers to a narrow neck. Volumetric flasks and Erlenmeyer flasks have tapered necks. The base of a volumetric flask is more rounded than that of an Erlenmeyer flask. The neck of a volumetric flask is tall and skinny, while the neck of an Erlenmeyer flask is short and stout. Volumetric flasks have a single marking on the neck, while Erlenmeyer flasks may have no markings or several graduations on the base. Pictured here is an Erlenmeyer flask.
There are a few ways of heating substances in the laboratory. Beakers, evaporating dishes, and Erlenmeyer flasks can easily be heated by placing them on a hot plate.
Simple hot plates have one dial that, when turned, increases the heat produced. Some hot plates have a second dial that can be used to control a magnetic stir bar for constant and consistent stirring.
Beakers, Erlenmeyer flasks, round bottom flasks, test tubes, and crucibles can be heated with a Bunsen burner. A Bunsen burner typical looks like the following image.
The hose barb near the base of the Bunsen burner is connected via gas tubing to a gas inlet that provides a flammable gas, typically propane or butane.
When the gas is flowing, the Bunsen burner can be lit with a match, stick lighter, wooden splint, or spark lighter, also known as a striker.
The flame produced may vary in color from orange to deep blue, depending on the amount of air that is allowed to mix with the flammable gas. We can control the amount of air by rotating the collar.
When the air vent is closed, the combustion will be incomplete, and the flame will appear orange. When the air vent is fully open, the combustion will be complete and the flame will appear blue. An orange flame, sometimes called a safety flame, is less hot than a blue flame. We should use a blue flame when heating substances and revert to an orange flame between heatings.
When using a Bunsen burner, we need to ensure that it is placed on a heatproof mat or table and that the area around the burner is clear. We should not use a Bunsen burner to heat flammable substances but use a hot plate instead. Regardless of the heating source, it is important that we never heat a closed vessel, as the pressure can build and the vessel may explode.
Example 4: Identifying the Color of a Bunsen Burner Flame
What color flame will a Bunsen burner have if the air hole is fully open?
The air vent or collar on a Bunsen burner can be turned to control the amount of air allowed to mix with the flammable gas. When the air vent is closed, the combustion of the gas is incomplete and the flame will appear orange. When the air vent is open, the gas will completely combust and the flame will appear blue. When the Bunsen burner air hole is fully open, there will be a blue flame.
There are a number of ways to position glassware above a Bunsen burner. Wire mesh can be placed on a tripod set over a Bunsen burner, then we can position vessels with flat bottoms on the wire mesh. This setup is shown in the image below.
A clay triangle can be placed on the tripod to hold crucibles.
We must always take care when heating substances. Hot glassware and cold glassware look the same. Tongs can be used to pick up and move hot glassware. A selection of different tongs is shown below.
Test tube tongs can also be used to hold a test tube over the Bunsen burner. The test tube should be held at an angle with the opening pointing away from those in the laboratory, as illustrated below.
We can also use clamps to hold equipment above the Bunsen burner. The various clamps and supports we can choose from can be attached to a retort stand or ring stand, as shown below.
An iron ring can attach directly to the stand by tightening the screw clamp, as shown below.
Like a tripod, wire mesh and clay triangles can be placed on the ring to support beakers and crucibles.
Two-prong and three-prong clamps can be attached to the ring to hold test tubes, round-bottom flasks, and other narrow-necked glassware. These clamps may have a screw clamp for direct attachment, or they may need to be connected to the retort stand with a boss.
A boss is simply two screw clamps. One is tightened around the retort stand, and one is tightened around the arm of the clamp. The screw clamp holding the arm should always be pointed with the opening facing upward so that if the screw were to fail, the clamped object would be less likely to fall.
Any clamps added to the retort stand should be placed so that the equipment that they hold is directly above the base of the retort stand. This helps prevent the stand from falling over.
Let us summarize what we have learned about scientific equipment.
- The mass of a substance can be measured with a balance.
- The volume of a liquid can be measured with a graduated cylinder, pipet, or buret.
- The volume of a gas can be measured with a gas syringe.
- Various pieces of glassware can be used to contain or transport chemicals including beakers, Erlenmeyer flasks, and test tubes.
- Bunsen burners and hot plates are common heat sources in the laboratory.
- Glassware can be secured using various clamps attached to a retort stand.