Question

Compare the density of \[{{HCl}}\] gas with air:
A. ${{HCl}}$ gas is more dense than air
B. ${{HCl}}$ gas is less dense than air
C. ${{HCl}}$ is a liquid acid
D. None of these

Answer 1

Hint: For gases that are less dense than air it is collected by upward delivery and if the gas is denser than air than it is collected by downward delivery. These gases can also be collected over water, but it works for gases that are insoluble in water.

Complete step by step answer:
Density is given as mass by volume. When we are unsure about the density of the gas than we can collect it over water. All gases are less dense than water, displacement of water is possible.
Hydrogen chloride dissolves in water to produce Hydrochloric acid, so collecting over water is not possible, since it is denser than air it can be collected by a downward delivery.
${{HC}}{{{l}}_{\left( {{g}} \right)}}{{ + }}{{{H}}_{{2}}}{{{O}}_{\left( {{l}} \right)}}\xrightarrow{{}}{{{H}}_{{3}}}{{{O}}^{{ + }}}_{\left( {{{aq}}} \right)}{{ + C}}{{{l}}^{{ - }}}_{\left( {{{aq}}} \right)}$

So, the correct answer is Option A.

Additional Information:
Gas syringe is used for all gases and also it could be used to measure the volume of the gas. In case of upward delivery, the collection vessel is inverted so that the gas is able to displace the air inside it as it rises upwards. Since air is pushed downward this method is also called downward displacement. Hydrogen gas and Ammonia are collected over this method. In case of downward delivery, the collection vessel is placed upright so that the gas collected is able to displace the air inside it, since air is pushed upwards this method is also called upward displacement. Using this method it is possible to collect chlorine gas and Carbon dioxide. If the density of the gas is unsure then it is possible to collect it over water. This method doesn’t work for gases that are soluble in water such Ammonia.

Note: If the solubility and density of gases is not known the method to collect the gas irrespective of these properties is by using a Gas syringe. It is a closed container so the density of the gas does not need to be taken to consideration. It can also be used when the volume of gas produced needs to be measured.