What do you understand by downward displacement of air?

In the laboratory, ammonia gas s prepared byheating the mixture of ammonium chloride andcalcium hydroxide in the ratio 2:1.
2NH₄CL + Ca(OH)₂ ---------> Cacl₂ +2H₂O + 2NH₃

We can identifyammonia gas by the following ways:
-Treating moist red litmus paper withammonia.It turns blue since ammonia is basic in nature.
-It has a strong pungent odor.
-When a glass rod dipped in conc. Hcl is broughtincontact with ammoniagas,it forms a white fumeof NH₄cl.

Any four physical properties of ammonia gas are:
-It is colorless, tastelessgas having strong pungent odor.
-It is lighter than air.
-It is highly soluble in water.
-It is basic in nature.
-It is non-combustible gas.

Any three chemical properties of ammonia gas are:
- Ammonia dissolves in water and forms analkali ie, ammonium hydroxide.
NH₃ + H₂O ------> NH₄OH
-Ammonia is a basic gas. So, it reacts with acidto give salt.
NH₃ + Hcl -------> NH₄CL
-Ammonia reacts with water and Forms nitrogengas and water.
4NH₃ + 3O₂ -------> 2N₂ + 6H₂O

For commercial purpose, ammonia gas is manufacturedby Harber's process. In this process, a mixture of nitrogen and hydrogen (1:3) is combined directly at500ºc temperature and 200 to600 atm. For this reactionfinely powdered iron is taken as a catalyst andmolybdenumas apromoter.
N₂ + 3H₂ -----------> 2NH₃

We all know, a hard glass test tube is slightlyinclined during preparation of ammonia gas, otherwisethe steam produced during the reaction exerts pressure, which maycrack the test tube. So, the HGTT isslanted to prevent it from cracking.

We all know, ammonia is lighter than air. So, itflows upward in the free state. Therefore, the gas jar isinverted to collect the ammoniagas by downwarddisplacementof air.

Moist red litmus paper is brought near the mouth ofgas jar filled with ammonia to testwhether the gasis ammonia or not. Since, ammoniagas is basicinnature, it turns moist red litmus paper to blue.

Ammonia gasis not collected by downward displacementof water because it is highly soluble in water andgives ammonium hydroxide.
NH₃ + H₂O ----------> NH₄OH

Urea is produced when ammonia and carbon dioxidereact together at about 1500Cunder certain pressure(30atom).
2NH₃ + CO₂----------> NH₂ - CO - NH₂ + H₂O

The uses of ammoniagas are:
-It is used to manufacture chemical fertilizers.
-Liquidammoniais used in refrigerators.
-It is used to develop blueprint of maps.
-It is used to make medicines.
-It is used as laboratory reagent.

Ammonia gas prepared by heating a mixture ofNH₄CL and CA(OH)₂.
2NH₄Cl + Ca(OH)₂---------> CaCl₂ + 2H₂O + 2NH₃

When a glass rod is dipped in conc. HCl is brought incontact with ammonia gas, it forms a white fumeof ammonium chloride (NH₄Cl).
HCl + NH₃ ------------>NH₄Cl

In the laboratory, carbon dioxide gas is preparedby the reaction of dilute hydrochloric acid withcalcium carbonate (limestone or marble).
CaCO₃ + 2HCl ----------> CaCl₂ + H₂O + CO₂

The different methods to test the carbon dioxide are:
-Putting the burning matchstick into the jar containing CO₂. If it extinguishes.
-When CO₂ is passed through lime water, it turnsmilky white due to the formation of insoluble CaCo₃.When CO₂ is passed in lime water for long time, themilky color disappearsdue to the formation of solubleCa(HCO₃)₂.
-CO₂ turns blue litmus paper to red because it isacidicin nature.

The precautions needed during the laboratorypreparation of CO₂ are:
-The apartus should be made air tight.
-The Lower end of deliverytube should not touch thesolution within the woulfe's bottle.
-The lower end of thistle funnel should be dipped inthe solution.
-Carbon dioxide is collected in the gas jar by theupward displacementof air.

Any 4 physical properties of CO₂ gasare:
-It is colorless, odorless and tasteless gas.
-It is heavier than air.
-It is acidic in nature.
-It is neithercombustible nor a supporter ofcombustion.
-It is soluble in wader and produce carbonic acid when dissolved in water.

Any 3 chemical properties of carbon dioxide gas are:
-CO₂ reacts with water and gives carbonic acid.
CO₂ + H₂O ----------> H₂CO₃
-Green plants concert solar energy into chemicalenergy by photosynthesis. In this process CO₂ andwater react to give starch and oxygen.
6CO₂ + 6H₂O ----------> C₆H₁₂O₆ + 6O₂
- CO₂ reacts with lime water and gives insolublecalciumcarbonate (CaCO₃), which makes the solution milky white.
CO₂ + Ca(OH)₂ ----------> CaCO₃ + H₂O

For commercial purpose, carbon dioxidegas ismanufactured by heating calcium carbonate. During thisprocess, calcium oxide i.e. lime or quick lime is alsoproduced.
CaCO₃ -------------> CaO + CO₂

When we pass CO₂ in lime water, it becomesmilkywhite due to the formation of insoluble calcium carbonate (CaCO₃).

Whencarbon dioxide is passed in lime water for a long time, themilky colordisappearsslowly due to the formation of watersoluble calcium bicarbonate [Ca(HCO₃)₂].
CaCO₃ + H₂O + CO₂ --------> Ca(HCO₃)₂

Carbon dioxide gas is collected in the gas jar by the downward ofair because it is heavier than air which cause itto flow to the surface.

We all know, carbon dioxide gas is heavier than air which causeit to flow to the lower surface. Therefore,carbon dioxide gas isfound in lower surface like deep wells, mines, caves,etc.

Dry ice is the solid substance formed when CO₂ gasis cooled to below -78c.
-It is used as a refrigerantto preserve foods.

Lime water turns milky in color due to theformationof insoluble calcium carbonate (CaCO₃).
CO₂ + Ca(OH)₂ -------------> CaCO₃ + H₂O

The ribbon burns in CO₂gaswith dazzling light.

A balloon filled with CO₂ left free in the air will fall on the surface of the land because CO₂ cause it to fall due to its higher density than that of air.

When Ca(HCO₃)₂ solution is heated, it gives calciumcarbonate, water and CO₂.
Ca(HCO₃)₂ -------------> CaCO₃ + H₂O + CO₂

We all know, CO₂ gas is acidic in nature and wateris neutral. When a mixture of CO₂ and H₂O is madethe mixture will have acidicPH. which stimulates thetaste buds with sour taste.

The uses of carbon dioxidegas are:
-Green plants use CO₂ during photosynthesis.
-It is used on fire extinguishers.
-It is used to manufacture fertilizers.
-It is used to make soft as well as hard drinks.
-It used in carbonation process to purifysugarcanejuice.

We know, fire extinguisher has a red metallic vesselcontaininga sodium bicarbonate solution and a bottleof sulphuric acid. When we need carbon dioxide gas toextinguisha fire, the vessel is inverted. Afterwards, thebottle of concentrated sulpheric acid strikes againstthe floor. The plug of the acid bottle falls down andand comes in contact with the sodium bicarbonatesolution. When those chemical react together, they givecarbon dioxide gas.
2NaHCO₃ + H₂SO₄ ----------> Na₂SO₄ + 2H₂O + 2CO₂
The...

During collection of gases in laboratory, if the freshly prepared gas settles at the bottom of the vessel or container (used to collect the gas), such that it displaces (moves) the air present in the container upwards. This is called upward displacement of air.

During preparation of Carbon Dioxide gas, as CO₂ is heavier than air, it settles at the bottom. This causes the earlier gases to move upward or displace upward.