Stirring & heating

When stirring a reaction, clamp your setup directly above the centre of the stirrer-hotplate. A lab jack is not necessary when just stirring as we only raise our setup when we heat so that we can effectively lower the hotplate away, quickly removing the heat from our system when appropriate. The cable is wound round the framing, removing it out of the way of our fumehood space and so that it is not caught in the lab jack.

After turning the hotplate on, it is good practice to check the dials as sometimes these are left at a certain temperature by a previous user, which could inadvertently begin heating our reaction.

Gently slide the magnetic stirrer bar into the glassware you wish to clamp, as dropping it in may cause damage to the glassware. A moderate stirring rate is sufficient, selecting a higher rate may splash solvent or spray solid material against the sides of the reaction flask, removing them from the system and so remain unreacted.

When heating a reaction, a heating block is used to create a larger surface area over which the system is heated, increasing efficiency. For this to have this effect, there must be good contact between the reaction flask and the block. Take care in raising the lab jack in order to establish this contact – avoid applying too much force to the clamped glassware, this shouldn’t be raised along with the lab jack as this will put strain on the glass joint that is clamped. Alternatively, setting the lab jack position too low will result in a gap between the flask and the heating block, leading to uneven and inefficient heating. Instead, the reaction flask should sit comfortably within the heating block with good surface contact.