Question

How are gases prepared in chemistry?

Answer 1

Depending on the nature of gases, they are prepared by various methods that may involve heating a compound to break it down i.e. pyrolysis, Collection of lighter gas over heavier one, dissolving a gas in a solvent that selectively prefers its dissolution without changing its chemical properties and releasing as soon as the need comes.

Complete answer:
Various gases are prepared by various means, here are some of the most come common gases and their preparations:
$1)$Methane gas$\left( {C{H_4}} \right)$ is prepared by reacting sodium Ethanoate with Soda lime and collecting the gas released over water.
$2)$Oxygen gas$\left( {{O_2}} \right)$ is prepared by reaction between Hydrogen peroxide and Manganese$IV$oxide and is also collected over water like methane.
$3)$Carbon Dioxide gas$\left( {C{O_2}} \right)$ is prepared by adding dilute hydrochloric acid to Calcium carbonate powder or chips and is collected by downward delivery because it is gas heavier than air and so it preferably condenses downwards.
$4)$Chlorine gas$\left( {C{l_2}} \right)$ is obtained by heating hydrochloric acid with Manganese$\left( {IV} \right)$oxide and similar to $C{O_2}$ it is collected by downward delivery.
$5)$Hydrogen gas$\left( {{H_2}} \right)$ is prepared by adding a dilute acid to Zinc Granules, It is collected over water like oxygen and methane gases.
$6)$Hydrogen Sulphide$\left( {{H_2}S} \right)$ is generally prepared by adding dilute acid to Iron$\left( {II} \right)$ oxide and similar to hydrogen, oxygen and methane it is collected over water.

Note: The preparation of gases should be done generally near a fume hood especially if the gas to be prepared is a toxic one for example chlorine and hydrogen sulphide. Other than the above mentioned methods there are many more methods available in literature but their feasibility is either low or are just too unsafe to be done in labs.