Question

Holmes signals can be given by using

• A. ${\mathrm{CaC}}_2+{\mathrm{CaCN}}_2$
• B. ${\mathrm{CaC}}_2+{\mathrm{Ca}}_3{\mathrm{P}}_2$
• C. ${\mathrm{CaC}}_2+{\mathrm{CaCO}}_3$
• D. ${\mathrm{Ca}}_3{\mathrm{P}}_2+{\mathrm{CaCN}}_2$

Answer 1

The correct option is B

${\mathrm{CaC}}_2+{\mathrm{Ca}}_3{\mathrm{P}}_2$

Explanation:

Option (B) ${\mathrm{CaC}}_2+{\mathrm{Ca}}_3{\mathrm{P}}_2$

• Holmes signal is the bright red colored signal which is shown on the ocean surface.
• Holmes signal contains a mixture of compounds that can react with water to give fumes.
• A container is used which is filled up with a mixture of two compounds that reacts with water to give a signal.
• For example, Calcium carbide and Calcium phosphide react with water

$$\begin{gathered} \underset{\mathrm{Calcium}\mathrm{carbide}}{{\mathrm{CaC}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Ethyne}}{{\mathrm{C}}_2{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)} \\ \underset{\mathrm{Calcium}\mathrm{phosphide}}{{\mathrm{Ca}}_3{\mathrm{P}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Phosphine}}{2{\mathrm{PH}}_3\left(\mathrm{g}\right)}+\underset{\mathrm{Calcium}\mathrm{hydroxide}}{3\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)} \end{gathered}$$

• Here Ethyne is produced by the reaction of Calcium carbide with water and Phosphine is produced by the reaction of Calcium phosphide with water.
• The Phosphine gets ignited immediately when it comes in contact with air, and the Acetylene produced by the Calcium phosphide which is flammable also burns with bright red-colored flames which are also followed by fumes.
• Thus, the mixture of Calcium carbide and Calcium phosphide is used as a Holmes signal.

Hence, Option (B) is correct.