Test Tube with Stopper

Quick Answer: A test tube with stopper is a test tube supplied with a closure that seals its mouth, so the contents can be shaken, kept or carried without spilling or evaporating. It is used for shaking tests, sample storage and reactions that must be kept away from air.

Why a Test Tube Needs a Stopper

Many classroom tests are shaking tests. Hard water is compared with soft water by shaking each with soap solution and measuring the lather; an alkene decolourises bromine water when the two are shaken together; and one liquid is extracted into another by shaking and letting the layers settle. An open tube cannot safely be shaken with a thumb over its mouth when the contents are corrosive, so a stoppered tube is the proper way to do it.

A stopper also turns a test tube into a small sample container for a water sample taken on a field trip, a portion of a prepared reagent, or a precipitate kept until the next lesson. Sealed, the contents lose less to evaporation and pick up less dust or carbon dioxide from air. The stopper material, whether rubber, cork, plastic or ground glass, and the tube size and glass are not stated in the listing.

A stoppered tube must never be heated. Warming the closed tube raises the pressure inside until the stopper blows out or the glass bursts, so remove the stopper before any heating and replace it only after the tube has cooled.

Specifications

Applications

• Comparing hard and soft water by shaking with soap solution and measuring lather height
• The bromine water test for unsaturation, shaken safely in a closed tube
• Collecting and keeping water or soil extract samples for later tests
• Small-scale solvent extraction and observing the layers that separate

Care & Handling

• Hold the stopper in place with a finger while shaking, since a loose stopper can be pushed out.
• Match the stopper material to the contents: rubber swells in many organic solvents, and cork can absorb liquids.
• Label stoppered samples on the tube, not the stopper, so the label stays with the contents.
• Wash stoppers separately from tubes and let both dry before reassembling.

Why Choose LabEquip

Schools buy stoppered test tubes for shaking tests and for passing samples between classes, often with disposable Pasteur pipettes for adding reagents drop by drop. LabEquip lists them in the chemistry lab equipment range; send sizes and quantities via the LabEquip contact page.

Frequently Asked Questions

Can I heat a test tube with the stopper on?

No. Heating a sealed tube raises the pressure of the air and vapour inside, which can blow the stopper out or burst the glass. Remove the stopper before heating and replace it after cooling.

Which stopper suits organic solvents?

Rubber swells and softens in many organic solvents, so use a glass, cork or chemically resistant plastic stopper for liquids such as hexane or propanone. Rubber is fine for most aqueous solutions.

How do I carry out the soap test for hard water?

Put equal volumes of each water sample into stoppered tubes, add soap solution a little at a time and shake after each addition. Hard water needs more soap before a lasting lather forms, and it gives a scum.

Why release the stopper slowly after shaking?

Shaking can release dissolved gas or vapour, and some reactions produce gas, so pressure may have built up. Opening slowly, with the tube pointed away from people, stops liquid spraying out.

Is a stoppered tube airtight enough for storing samples?

It suits short-term storage and protects samples from dust and spills. For long-term storage or volatile liquids, a screw-cap bottle gives a more reliable seal.

How full should the tube be for a shaking test?

Fill it no more than about one-third full, so there is room for the liquids to mix when shaken. An overfilled tube mixes poorly and is more likely to leak around the stopper.

Last Updated: September 2026