Video Transcript
In the diagram, mercury oxide is
being heated strongly to cause thermal decomposition. Which gas is being collected over
water?
Many substances undergo thermal
decomposition when heated to high temperatures. Thermal decomposition is the
breaking down of a substance when heated to form two or more other substances. This generic equation represents
what occurs during a thermal decomposition reaction. The reaction has one reactant,
represented here by AB. The reactant is heated to a high
temperature, which we can represent using a Δ symbol above the reaction arrow. The reactant then breaks down into
at least two new substances.
In this question, solid mercury
oxide is heated in the test tube. Mercury oxide is an oxide, which is
a chemical compound that contains at least one oxygen atom chemically bonded to an
atom of another element. A metal oxide when heated strongly
decomposes into a pure metal and oxygen gas. In the diagram, mercury oxide is
being heated over a Bunsen burner. The metal produced would be mercury
metal in its standard state as a liquid. Oxygen gas would also be produced,
which can be collected over water as shown in the diagram.
The equation shown is the balanced
symbol equation for the thermal decomposition of mercury oxide. We can see that the gas formed is
oxygen gas. Therefore, in the diagram, the gas
being collected over water when mercury oxide is heated strongly to cause thermal
decomposition is oxygen.
