Question

Explain the possible hazards that could be associated with each scenario during distillation

a. Running hot water through a condenser during a large scale distillation

b. Having no boiling stones in the still pot during a large scale distillation

Answer 1

a) Running hot water through a condenser during a large scale distillation

         The condenser must generally be connected to a source of running water to provide cooling for the vapours.

• The proper method is to connect the input hose to the condenser at the end furthest from the heated flask and the outflow hose nearest the heated flask, if it is not done then the hottest vapors from contacting the coldest water and creating a large thermal shock to the glassware.

• The section on flowing water, the hoses must be connected tightly enough to the condenser that they will not come loose if the water pressure should increase during the distillation, usually this means that something like copper wire is twisted around the tubing at the joint to prevent it from coming away.

• The flow of water must be sufficient to accomplish condensation without being so fast as to cause undue hose pressure or splashing of outflow water, remembering that flow rates can change during the day after they have initially been set.

b) Having no boiling stones in the still pot during a large scale distillation              

                                      Liquids that have been degassed will not boil when heated, but vaporize suddenly and explosively if heated sufficiently, a hazard known as bumping. Adding small chips / boiling stones of unglazed porcelain or carborundum directly into the liquid before heating begins prevents bumping. These so called boiling chips have pockets of trapped air, which; upon heating of the liquid, provide a fine stream of bubbles that act as nuclei for the formation of vapor rising from the liquid. Without boiling chips / boiling stones the liquid may bump, with very large bubbles leaving the liquid, sometimes with considerable violence.Thus, never distill a liquid without first adding boiling chips / boiling stones, If a hot liquid containing boiling chips / boiling stones cools, vapor will condense and fill the pores of the chips, rendering them ineffective. Consequently, fresh boiling chips must be added if heating is interrupted and the liquid cools at all. It is noted that never add boiling chips / boiling stones to hot water otherwise stones will initiate sudden and violent boiling.