Question

1) The hydrocarbon C15 H32 burns to form carbon dioxide and water. Write the equation for the reaction.

2) How would you test the products when C15 H32 burns to show that carbon dioxide had been formed.

Answer 1

1) The balanced equation for the combustion of C15H32 (pentadecane) is:

C15H32 + 23O2 → 15CO2 + 16H2O

2) To test for the presence of carbon dioxide (CO2) in the products of the combustion of C15H32, one simple way is to bubble the gas through limewater (aqueous calcium hydroxide solution). When carbon dioxide is passed through limewater, it reacts with the calcium hydroxide to form a white precipitate of calcium carbonate according to the following chemical equation:

Ca(OH)2 + CO2 → CaCO3 + H2O

The formation of a white precipitate indicates the presence of carbon dioxide in the gas. Another way to test for the presence of carbon dioxide is to use a pH indicator, such as universal indicator or litmus paper. When carbon dioxide dissolves in water, it forms a weak acid called carbonic acid. This can be detected by observing a change in the color of the pH indicator. Carbon dioxide will turn universal indicator yellow or litmus paper red, indicating an acidic solution.

Answer 2

`\\ \tt\hookrightarrow C_(15)H_(32)+23O_2\longrightarrow 15CO_2+16H_2O`

• In order to check carbon dioxide we need to pass the gas through lime water then the lime water turn cloudy or milky
• Because it forms calcium carbonate

`\\ \tt\hookrightarrow CO_2+CaO=CaCO_3`