Question

A mixture of \[C{a_3}{P_2}\] and \[Ca{C_2}\], is used in making Holmes signal.
Explain.

Answer 1

Hint: \[C{a_3}{P_2}\] and \[Ca{C_2}\] are inorganic compounds. These are known as calcium phosphide and calcium carbide respectively. In these compounds phosphorus and carbon have negative oxidation states. Holmes signals are a mixture of compounds in a container which reacts with water to produce gases, which burn and guide the ships in sea.

Complete step by step answer:
In case of Holmes’s signal, a spontaneous combustion of phosphine is used technically . It is also used in smoke screens. Containers containing calcium carbide and calcium phosphide are made a hole in and thrown into the sea. After that the gases evolved from that hole and burn which serves as a signal. Water enters the containers through the bottom and reacts to give acetylene and phosphine gases. Phosphine gets burned spontaneously when it comes in contact with air and also burns acetylene. As a result, a bright red flame is produced which is accompanied by huge smoke due to the burning of phosphine. This serves as a signal to the ships.
The reactions of this signal is as follows,
\[
  Ca{C_2} + 2{H_{2}}O\;\; \to Ca{\left( {OH} \right)_{2}}\; + {\text{ }}\;{C_{2}}{H_{2{\text{ }}}} \\
  C{a_3}{P_2} + 6{H_{2}}O \to 3Ca{\left( {OH} \right)_{2}} + 2P{H_3} \\
  \]

Note:
Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of \[{\text{Ca}}{{\text{C}}_{\text{2}}}\]. Its main use industrially is in the production of acetylene and calcium cyanamide. This can be formed in electric arc furnace by treating lime with coke as follows,
\[CaO + 3C \to Ca{C_2} + CO\].