Carbon Dioxide
Carbon dioxide is a acidic gas/ Dry ice. It is because as it reacts with water it gives carbonic acid. i.e
Molecular Weight of co2 gas is c+2O= 12+ 2*16= 44amu
co2 is polar covalent compound because it is formed by mutual sharing of valence electron between atom of different non-metal.
Molecular structure of co2 :
General methods of preparations of carbon dioxide gas
- By reacting carbon with oxygen
Rxn:
c + o $\rightarrow$ co2
2. By heating metallic carbonate
Rxn;
3. By reacting acid with metallic carbonate and bicarbnate
Rxn ;
Laboratory preparations of co2 gas ;
(principle of lab-preparations of co2 gas)
Principle ;
In lab co2 is prepared by reacting limestone and dilute hydrochloric acid.
Rxn ;
Testing of hydrogen gas in lab ;
As we insert blue litmus paper inside the gas jar than it truns into red . This verifies that the gas is co2 .
Q. Why co2 gas is collected by upward displacement of gas jar?
Ans: It is because co2 gas is heavier than air.
Q. What is dry ice?
Ans: When co2 gas is sufficiently cooled up to -78.c , then it solidifies and become just like hard solid .
Q. Why is co2 gas called acidic gas?
Ans: It is because as the co2 reacts with water then it gives carbonic acid .
Rxn:
Q. How do you surely verified that co2 is acidic in nature ?
Ans; We can verify co2 as acidic gas as if we insert blue litmus paper into gas jar it turns into red .
Physical properties of co2 gas:
- It is colorless , tasteless and odorless.
- It truns blue litmus into red.
- It is heavier than air.
- It helps to put out the fire.
Chemical properties of co2 :
- It reacts with water to give carbonic acids.
Reaction;
2. It reacts with Cao (Quicklime) to give limestone.
Reaction;
3. It reacts with ammonia to give urea.
Reaction;
4. It reacts with Ca(OH)2 for long time to give colorless calcium bicarbonate.
Reaction;
5. It reacts with carbon (red hot coke) at 900 degree centigrade, to give carbon monoxide.
Reaction;
6. It reacts with water in presence of sunlight to give glucose (carbohydrate) and oxygen.
Reaction;
Uses of carbon dioxide :
- It is used to make urea.
- It is used in fire extinguisher.(Artificial Use)
- It is used by green plant for photosynthesis. (Natural Use Of Carbon dioxide)
- It is used for purification of sugarcane juice during manufacturing it. (Carbonation)
NOTE:
Carbonation:
The process of purification of sugarcane juice in industry while manufacturing it is called carbonation.
Q. How does fire extinguisher works to put out fire?
Ans: In fire extinguisher sodium bicarbonate reacts with sulphuric acid to produce carbon dioxide gas to put out fire.
Reaction;
Ammonia gas:
It is lighter gas which is also called marsh gas because of bacterial decomposition of dead material or in swamp/ marshy land.
Molecular weight of ammonia:
Molecular structure:
General preparation of ammonia gas in lab:
- By Haber process:
When nitrogen reacts with hydrogen under suitable condition as 200-900 atmosphere, 500 degree centigrade as temperature , Fe as catalyst and Mo as promoter in the ratio of 1:3 then ammonia is produced which is called Haber process.
Reaction;
2. By decomposition of ammonium salt:
Laboratory Preparation of Ammonia gas
Principle :
It states that , “when a finely crushed mixture of dry solid ammonium chloride and calcium hydroxide (slaked lime) is heated into the ratio of 2:1, they react with each other and release ammonia gas.
Reaction;
Fig: laboratory preparation of ammonia gas.
Q. Why is lime tower used in lab preparation of ammonia gas?
Ans; It is done because lime tower helps to obtained dry ammonia gas.
Q. How do we test the ammonia gas in gas jar?
Ans; As we insert red litmus paper into gas jar then it truns into blue. This verifies that the gas is ammonia gas.
Q. Why is ammonia gas not collected in water?
Ans: It is because as the ammonia is collected in water than it reacts with water to give liquor ammonia.
Reactions:
Q. Why is ammonia gas collected by downward displacement of gas jar?
Ans: Ammonia gas is lighter than air. So, it is collected by downward displacement of gas jar.
What is Liquor Ammonia?
Ammonia reacts with water to give ammonium hydroxide which is called liquor ammonia.
Reaction:
$\text{NH}_3 + 2\text{H}_2\text{O} \rightarrow \text{NH}_4\text{OH} + \text{H}_2\text{O}$
Physical Properties of Ammonia gas
- It is lighter than air.
- It gives ” pungent” smell.
- It truns red litmus into blue.
- It is tasteless, colorless etc .
Chemical Properties of Ammonia gas
- It reacts with acids to gives ammonium salts.
$\text{HCl} + \text{NH}_3 \rightarrow \text{NH}_4\text{Cl}$
2. Ammonia reacts with carbon dioxide to give urea.
Reaction;
3. Ammonia reacts with water to give ammonium hydroxide ( liquor ammonia)
Reaction:
4. Ammonia reacts with oxygen to give greenish yellow flame of nitrogen.
Reaction;
5. When excess ammonia reacts with chlorine then it give ammonium chloride and nitrogen.
Reaction;
Uses of Ammonia
- It is used to manufactured urea.
- It is used for making blue prints map.
- Liquor ammonia is used in refrigerator.
- It is used for manufacturing salt containing nitrogen.
- It is used to make rayon and nylon.
Important Questions on Some Gases
Q. How do you verify that ammonia gas is produced in gas jar by using foundation of R.B flask.
Ans: First of all, as we take a round bottom flask filled with ammonia gas such that a delivery tube is inserted inside it. When we invert the R.B flask and put it in water filled beaker then water comes in contact with ammonia and ammonium hydroxide ( liquor ammonia is formed due to which vacuum is created inside B.R flask). The pressure inside R.B flask is extremely lesser as compared to that of water pressure and hence water raises up as fountain inside it. This clarifies that ammonia is highly soluble in water.
Fig: R:B flask.
Q. Dilute sulphuric is not used in preparation of carbon dioxide . Why?
Ans: It is because it from thin protective insulating layer so the reaction is not forwarded.
Q. When a glass rod dipped in the ammonia solution is brought near hydrochloric acid gas, a dense white fume of ammonium chloride is formed why?
Ans: It is because ammonia reacts with the fumes of HCL to gives ammonium chloride.
Reaction;
Q. Why is the mouth of hard glass test tube inclined downward?
Ans: It is because as we incline the mouth of hard glass tube then it prevents from cracking and the water drops will pass out easily as well.
Q. It is dangerous to clean well remaining closed for long time, why?
Ans: It is because there is deficiency of oxygen as go to higher depth from ground level. So it might be very difficult to breathe and it may cause death as well.