Video Transcript
Which of the following statements
is correct?
We have been given a flowchart that
gives us four statements. Statement one is in a decomposition
reaction, an oxide breaks down into a carbonate and limewater. Statement two is in a decomposition
reaction, an oxide breaks down into a carbonate and carbon dioxide. Statement three is in a
decomposition reaction, a carbonate breaks down into an oxide and limewater. And statement four is in a
decomposition reaction, a carbonate breaks down into an oxide and carbon
dioxide.
A decomposition reaction involves a
compound breaking down into simpler compounds or even elements. A decomposition reaction often
requires heat, where it is called thermal decomposition. Thermal decomposition is the
breaking down of a substance when heated to form two or more substances. So a substance is broken down into
a simpler substance. An oxide — for example, copper
oxide, lead oxide, or zinc oxide — is a simpler substance than a carbonate, for
example, copper carbonate, lead carbonate, or zinc carbonate. So it make sense for a carbonate to
decompose into an oxide.
An example of this would be copper
carbonate being heated and decomposing into copper oxide. We can now determine that of the
two statements “an oxide breakdown into a carbonate” and “a carbonate breaks down
into an oxide,” “a carbonate breaks down into an oxide” is correct, and “an oxide
breaks down into a carbonate” is incorrect. Some oxides, such as mercury oxide,
will thermally decompose but won’t produce a carbonate. As we have determined that an oxide
does not break down into a carbonate, then both statement one and statement two must
be incorrect.
The next part of the statement
states whether limewater or carbon dioxide is produced in the reaction. As we can see from the equations,
it’s carbon dioxide that’s produced. So carbon dioxide is correct, and
limewater is incorrect. Limewater is composed of aqueous
calcium hydroxide, and it is used as a test for carbon dioxide. We can now tell that statement
three must be incorrect and statement four must be correct.
So the answer to the question
“Which of the following statements is correct?” is statement four. In a decomposition reaction, a
carbonate breaks down into an oxide and carbon dioxide.
