Reflux Apparatus with Addition Assembly

In this reflux apparatus with addition assembly post we have briefly explained about reflux apparatus reaction flask, reflux condenser, heat source, coolant source, and drying tubes.

Reflux Apparatus with Addition Assembly

Reflux is a technique that is used in chemical laboratories to dissolve components that are hard to be dissolved. It involves continuous recycling of the solvent. It is very useful in completing a chemical reaction that is difficult to be done.

Refluxing is used in large-scale industries such as petroleum refineries. In laboratory scale, it is used in a simple apparatus which is composed of a round-bottomed flask, a condenser, a water bath and heat source. A mixture of reactants and the solvent is added to the round-bottomed flask. It is connected to a long condenser which is open in its top end.

When the round-bottomed flask with components is heated in the water bath, the reaction mixture starts to boil. Vapours are produced from the mixture. This vapour is condensed by the condenser. Then the droplets return to the reaction mixture due to the force of gravity. This method will thermally accelerate the chemical reaction. The reaction is done at a chemically controlled temperature and ambient pressure.


The basic components for a reflux apparatus are: Reaction Flask, A reflux condenser, a heat source, and coolant source.

Reaction Flask

A reflux condenser

A heat source

A coolant source

Drying tubes

Reflux Apparatus

Reflux Apparatus with Addition Assembly

Reaction Flask

To accommodate the immersion wells, reaction flasks are made of borosilicate glass. The reaction flask form aids with stability and even heating. Certain variants of this reaction flask have flat bottoms to allow magnetic stirrers to be used, and reaction flask can be jacketed or unjacketed. During photolysis, jacketed reaction flasks are used to keep the reactant components cold. With logical volume sizes and varied angled couplings for sparger tubes, condensers, and thermometers to provide simple-to-read measures, robust vessels are durable in design and easy to operate.

Reflux Condenser

Single-surface or double-surface condensers are used for general-purpose work; the double-surface condenser is utilised for low-boiling point solvents like dichloromethane, diethyl ether, or light petroleum.

Reflux condensers are classified into two types: Graham type and coil type. Vapour flows through the central tube of a Graham type condenser and condenses along its walls, allowing it to flow back into the reaction flask.

Water is passed through the central coil as a coolant in the coil condenser, and the vapour flows over the bigger outside jacket. Because the condensed liquid must return to the reaction vessel through a short restricted channel, the Graham type condenser is prone to clogging.

Reflux Apparatus

Types of Reflux Condenser

Allihn Condenser

A ‘bulb condenser’ is another name for the Allihn condenser. It is made up of a water glass jacket on the outside. The central tube is made up of a succession of bulbs that give more surface area for the vapour to condense. The condensed liquid runs down along the bulb walls, avoiding blocking of the rising vapour, which is an advantage over the Graham condenser. When installed vertically, it also has a bigger diameter at the bottom, making it ideal for reflux heating.

While an Allihn condenser is highly recommended for reflux, it is not suitable for distillation. It is possible that the substance will become caught on the sides of the bulbs during the latter phase, especially if the bulbs are in a horizontal posture.

Davies Condenser

A Davies condenser is another name on the list. It works in the same way as the Liebig condenser, but it has three concentric glass tubes. Both the outer jacket and the central tube circulate the coolant. Vapour condenses on the inner tubes and drips into the reflux flask. Condensation of vapours over a wide range of boiling points, including low boiling volatile liquids, is possible using this condenser.

Jacketed Coil Condenser

It’s similar to Davies, but it has a coiled inner tube instead of a straight one. Due to the greater surface area, this condenser outperforms the Davies condenser in terms of condensation. Furthermore, the size remains compact, providing further benefits. As a result, these are thought to be superior to the standard Davies condenser.

Dimroth Condenser

Internal spirals in a Dimroth condenser are doubled. Both the coolant input and exit are located on the top of the unit. Vapour rises from the bottom to the top. Traditional coil condensers are ineffective in comparison to this design.

Friedrichs Condensers

A spiral internal cold finger type capillary within a cylindrical housing characterises Fredrichs condensers. Vapours rise along the spiral path as coolant flows via the interior cold finger. Condensers of this type can be used for both distillation and reflux processes.

A heat source

Water Bath

This is the approach for heating processes up to 100°C that is suggested. It’s crucial to make sure the liquid you’re distilling is suitable for this temperature range. A water bath can be easily made by boiling water in a beaker or pan on a hot plate. It’s critical to use a container large enough to house the reaction flask while also providing a water buffer between the reaction flasks’s outside and the beaker or container.

Steam bath

A steam bath can be made by heating water in a vessel over a hotplate. Steam baths are suitable for heating flammable liquids and can be used to heat low-boiling liquids.

Heating Mantle

When heating liquids above 100° C, this is the approach to use. For these temperatures, heating mantles are the ideal option, as long as the flask is the right size to suit the mantle. Heat is transferred from the hotplate to the reaction vessel via the sand. They take a long time to heat up and cool down, which is a negative. They can also be quite hefty, posing a risk of physical handling.

Oil baths

For temperatures above 100° C, oil baths are employed. In most cases, the bath is magnetically agitated and heated on a hotplate. The two most commonly used oils are silicon oil and mineral oil. Silicon oils are non-flammable, have no offensive odours, and are extremely stable. Mineral oil is a lot cheaper, but it’s combustible. It should not be heated over 175 degrees Celsius. Silicon fluids are arguably the best liquids for oil baths, but they’re also the most expensive.

Heat Guns

These reach extremely high temperatures (up to 500° C) very quickly. In the presence of flammable organic solvents, they work by sucking air over red-hot heating components, increasing the risk of fire. During operation, the nozzle of a heat gun also serves as an ignition source. They should never be used near flammable substances or in situations with flammable vapours. Furthermore, this method makes it difficult to create equal heating.

Bunsen Burners

Only non-flammable liquids should be heated with a Bunsen burner. Steam distillations of essential oils, ink solutions, sea water, and copper (II) sulphate solutions are all examples of distillations where Bunsen burners are safe to use.

A coolant source

A coolant (typically chilled water) is cycled through the condenser’s outer jacket. The temperature of the solvent vapours is reduced by the circulating water, which causes the vapours to condense and fall back into the reaction vessel. The condenser is connected to the rubber tubing for coolant water in two ways:

Reflux Apparatus

Plastic connectors for condensers.

Wet the inside of the rubber tube with a little water and slip it onto the pipe and past the ‘knuckle’ if the condenser has glass inlet and output pipes with a ‘knuckle.’ The rubber tubing needs to be a tight fit, or it will slide off over time.

Modern condensers contain plastic adapters that may be screwed on the threaded inlet and output pipes after being joined to the tubing. Screw the adapter onto the condenser after sliding the rubber tubing onto the moistened ‘pipe’ on the adaptor. Otherwise, water will leak at the condenser intake or outlet unless the adapter has a rubber gasket on the inside of the threaded section.

Drying tubes

Condensation from the atmosphere or condensation of steam created in a water bath can both introduce water into your reaction. Fit a guard tube with a solid drying agent like anhydrous calcium chloride or calcium sulphate to the top of the condenser to keep water out.

Reflux with addition of chemicals

Instead of halting the reaction and opening the apparatus, you can use an addition or ‘dropping’ funnel to add the new chemicals. There are two varieties of addition funnels, which are separatory funnels with a ground-glass junction on the stem.

Reflux Apparatus

Adding chemicals to a reflux apparatus: (a) addition funnel; (b) pressureequalizing funnel.

Addition funnels

You must remove the stopper before adding a liquid or solution from the funnel to the reaction flask; otherwise, a vacuum will build and the liquid will not flow out. This is a disadvantage when working with substances that produce irritating or hazardous vapours or are sensitive to air. The simplest solution to this problem is to replace the stopper on the addition funnel with a guard tube, which will allow the liquid or solution to flow freely into the reaction flask.

Dropping funnels

Pressure-equalizing dropping funnels have a side arm that connects the funnel’s reservoir to the input stem below the tap. Even with the stopper in place in the funnel, the pressures in the reservoir and the reaction flask are equal, and liquid will flow into the reaction flask. Pressure-equalizing dropping funnels are extremely expensive and are often reserved for reactions that take place in an inert atmosphere.

Setup Process

1. Fill a round bottomed flask with the solution to be refluxed and fasten it to the ring stand or latticework with an extension clamp. Only half of the flask should be filled.

2. For bump prevention, use a stir bar or a few hot stones. When refluxing concentrated sulfuric or phosphoric acid solutions do not use boiling stones because they will colourize the solution.

3. Place rubber hoses on a condenser (wet the ends first to help them glide on), then connect the condenser to the flask vertically. Clamp the condenser to the ring stand or latticework if using a tall condenser.

4. Connect the water faucet to the hose on the lower arm of the condenser, and let the hose on the upper arm to drain to the sink. It is critical that water flows from the bottom to the top of the condenser; otherwise, the condenser will be useless since it will not fill entirely.

5. Start circulating water through the hoses in a steady stream. Check that the glassware components are tightly connected before placing the heat source beneath the flask. If you’re using a stir bar, turn on the stirring plate.

6. The solution should begin to boil within five minutes if the heat source was warmed (optional). If it doesn’t, increase the heating speed. When the solution is actively boiling and a “reflux ring” can be seen around one-third of the way up the condenser, the heating rate is appropriate. The upper limit of where hot vapours are actively condensing is called a “reflux ring.” The reflux ring is evident in some solutions (e.g. aqueous solution) with plainly visible droplets in the condenser.

7. If you’re following a process that requires you to reflux for a set amount of time (e.g. “reflux for one hour”), the time period should start when the solution is actively refluxing in the bottom third of the condenser, not just boiling.

8. If the reflux ring reaches half-way up the condenser or higher, the heat should be lowered down to prevent vapours from escaping the flask.

9. Turn off the heat source and remove the flask from the heat by either lifting the reflux apparatus up or dropping the heat source down after the reflux is complete.

Further Readings