Connecting apparatuses in series minimizes the use of water, as water exiting one condenser enters the next. Several reflux setups can be connected in series, and the water flow should be monitored to ensure that all setups are adequately cooled. Begin circulating a steady stream of water through the hoses not so strong that the hose flops around from the high water pressure. Check again that the pieces of glassware securely fit together, then position the heat source under the flask.
Turn on the stirring plate if using a stir bar. If using a heating mantle, hold it in place with an adjustable platform e. Allow a few inches below the mantle so when the reaction is complete, the mantle can be lowered and the flask cooled. If the heating mantle is not a perfect fit for the size of the round bottomed flask, surround the flask with sand to create a better contact Figure 1.
If using a sand bath, bury the flask in the sand so that sand is at least as high as the level of liquid in the flask Figure 1. If the setup will eventually be left unattended for a long period of time e. If the heat source was preheated optional , the solution should begin to boil within five minutes.
If it does not, increase the rate of heating. The appropriate heating rate occurs when the solution is vigorously boiling and a " reflux ring " is seen roughly one-third of the way up the condenser. A "reflux ring" is the upper limit of where hot vapors are actively condensing. With some solutions e. This video will explain the basics of a reflux experiment and demonstrate how to perform the technique in the laboratory with appropriate glassware and equipment. The Arrhenius equation states that by increasing the temperature of a reaction, the reaction rate increases.
A reflux system operates under the dynamic balance between the evaporation and condensation rates of the solvent, reactant, and product molecules within the flask.
The condenser is continually flushed with cold water and the round bottom flask is then placed into a heated bath. Upon heating, the solution evaporates and the condenser column cools the vapor molecules. The vapor is condensed on the internal glass sidewall and then returns back down to the reaction flask as liquid condensate.
If the vapor condenses too high in the condenser loss of solvent can occur and the flow rate of cold water must be increased. As time progresses and the reaction proceeds, all vaporized species are recovered and no loss occurs among the reactants, solvents, or products within the flask.
For this protocol the entire reaction setup should be performed in a well-ventilated chemical hood with access to a nearby cold water source. Now that you understand the basics of reflux let's see how to setup and perform a simple transesterification reaction under heat and reflux conditions with the appropriate glassware.
Before performing the procedure inspect all glassware for signs of possible chemical contaminants from previous reactions. Eliminate all moisture by drying the glassware in an oven for 30 min. Remove the glassware once it has cooled to room temperature. Next, apply a small amount of acetone to a clean lab tissue and wipe all ground-glass joints to remove chemical- and particle-contaminants. The clean flask and condenser column are now ready to be assembled into a reflux system.
With a suitable solvent dissolve the chemical reagents inside the round-bottom flask. After adding a magnetic stir bar to the flask, connect the reflux condenser by joining the ground-glass ports of the glassware. Attach a Keck clip to the joint. Connect a tube between the cold-water source and the bottom port of the condenser column. Then, make another tube connection between the top of the condenser column and the lab sink.
Finally, turn on the water slowly and fill the condenser column with circulating cold water. Adjust the water flow to prevent over-pressurizing the tube connections. To complete the reflux setup, submerge the reaction vessel into a heating bath.
Depending on the desired temperature range, these are filled with water or oil. For optimal heating, the level of the bath should be just above the meniscus of the reactants inside the flask. Secure the condenser and flask combination in place using a ring stand and clamps with bosses.
Begin the reaction by turning on the stirrer and hotplate. Once equilibrium between evaporation and condensation has been reached a steady drip of condensed solvent will start falling back into the reaction vessel from the condenser column. When the chemical reaction is complete turn off the hot plate and re-clamp the apparatus higher up the ring stand. Allow cold water to continue circulating throughout the condenser until the setup has cooled to room temperature.
Then, turn off the cold-water source and disconnect the condenser from the reaction flask. You can also do a keyword search using the search box at the top right hand corner.
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Click here for instructions on how to enable JavaScript in your browser. So what really is Reflux? To solve this issue, the tip of the pipet should be bent slightly in a flame. Once removed, the liquid is transferred to a small vial and capped with a Teflon-sealed cap.
If there is more than one volatile compound in the vial, it will be necessary to start with low heat to distill the lower boiling compound first. This way, compounds with a difference of boiling point of at least 50 oC can be separated relatively cleanly.
The conical vial should not be more than half filled in order to leave enough room for the liquid to boil. Otherwise the solution will spill out or over when it starts to boil. A good seal between the joints minimizes the loss of target compound during the distillation. It also prevents dripping of a compound onto the hotplate, and a possible fire accident.
An appropriate temperature setting has to be used. Often times, a water or oil bath is used for better temperature control. If a heating mantle is used as heat source, it has to be plugged into a variable power control. Skip to main content. Reflux Your browser does not support the embed tag What is Reflux? As shown in figure 2, a hot plate should be used in place of a heating mantle when a magnetic stir bar is used because it contains a magnetic stirrer allowing the bar to be spun automatically while the reflux is taking place The condenser is always completely filled with water to ensure efficient cooling.
The liquid that drains downward collects in the circular well at the bottom of the still.
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