In the previous section, we completed the discussion on acids, alkalies and salts. In this section we will see Compounds of Non-metals.
Ammonia
We know that, nitrogen is an important element required for the growth of plants. Details here. We have also seen that plants do not get the required quantities of nitrogen by natural means alone. We have to supply nitrogen through fertilisers. So we have to produce large quantities of such fertilisers. In other words, we have to produce such fertilisers industrially. For the industrial production of nitrogenous fertilisers, we have to produce ammonia first.
Fig.7.1 shows the diagram for the preparation of ammonia in the laboratory.
1. Ammonium chloride (NH4Cl) and
Calcium hydroxide (Ca(OH)2) are mixed well and heated.
Let us write the equation:
Ammonia is highly soluble
in water. This can be proved using the 'fountain experiment'. The
arrangement is shown in the fig.7.2 below:
• The flask which is placed
in inverted position is filled with ammonia gas. A jet tube enters
the flask from the bottom. The bottom end of the jet tube is dipped
in water contained in a beaker. To this water, some phenolphthalein
is already added.
2. They are made to react with each other. Very high temperature and pressure is required for the reaction to take place. This is because, nitrogen does not take part in reactions very easily, due to it's triple bond.
3. Spongy iron is used as a catalyst.
4. This is known as the Haber process. The equation of the reaction is:
N2 + 3H2 → 2NH3. This is a balanced equation.
In the next section, we will see sulphuric acid.
Ammonia
We know that, nitrogen is an important element required for the growth of plants. Details here. We have also seen that plants do not get the required quantities of nitrogen by natural means alone. We have to supply nitrogen through fertilisers. So we have to produce large quantities of such fertilisers. In other words, we have to produce such fertilisers industrially. For the industrial production of nitrogenous fertilisers, we have to produce ammonia first.
Preparation of ammonia in the laboratory
Fig.7.1 shows the diagram for the preparation of ammonia in the laboratory.
 |
| Fig.7.1 |
Let us write the equation:
Reactants:
♦ Ammonium chloride. One molecule is NH4Cl.
♦ Calcium hydroxide. One molecule is Ca(OH)2.
Products:
♦ Calcium chloride. One molecule is CaCl2.
♦ Water. One molecule is H2O
♦ Ammonia. One molecule is NH3
♦ Ammonia. One molecule is NH3
• So skeletal equation is:
NH4Cl + Ca(OH)2 → CaCl2 + H2O + NH3. This is not a balanced equation. The steps for writing the balanced equation are shown below:
Step 1: NH4Cl + Ca(OH)2 → CaCl2 + H2O + NH3
Step 2: 2NH4Cl + Ca(OH)2 → CaCl2 + H2O + NH3
Step 3: 2NH4Cl + Ca(OH)2 → CaCl2 + H2O + 2NH3
Step 4: 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + NH3
So the balanced equation is: 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + NH3
Step 1: NH4Cl + Ca(OH)2 → CaCl2 + H2O + NH3
Step 2: 2NH4Cl + Ca(OH)2 → CaCl2 + H2O + NH3
Step 3: 2NH4Cl + Ca(OH)2 → CaCl2 + H2O + 2NH3
Step 4: 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + NH3
| Reactants | Products | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| N | H | Cl | Ca | O | N | H | Cl | Ca | O | ||
| Step 1 | 1 | 6 | 1 | 1 | 2 | 1 | 5 | 2 | 1 | 1 | |
| Step 2 | 2 | 10 | 2 | 1 | 2 | 1 | 5 | 2 | 1 | 1 | |
| Step 3 | 2 | 10 | 2 | 1 | 2 | 2 | 8 | 2 | 1 | 1 | |
| Step 4 | 2 | 10 | 2 | 1 | 2 | 2 | 10 | 2 | 1 | 2 | |
2. From the equation, we can see
that water is also formed as a product. So we have to prevent the
newly formed ammonia (NH3) from dissolving in the newly formed water.
3. For that, the test tube is kept in a slanting position. So that, the newly formed water will not collect at the bottom of the test tube.
4. Still, there will be water in the vapour form. This will move out through the delivery tube, along with the NH3. That means, the gas which comes out of the delivery tube will be a mixture of water vapour and ammonia.
5. We have to remove the water vapour. For that, the delivery tube enters a drying tower. The upper chamber of the drying tower contains quick lime (CaO). This CaO, which is a drying agent, will absorb the water vapour. So the delivery tube that comes out of the drying tower will contain NH3 only.
6. This delivery tube enters a gas jar. Thus the ammonia gas is collected in the gas jar. We can see that the gas jar is kept in an inverted position. This is because, ammonia gas is lighter than air. That is., the density of ammonia is lesser than the density of air. So it will rise up. This rising ammonia will displace the air present in the jar, and will occupy it’s top position in the inverted jar.
3. For that, the test tube is kept in a slanting position. So that, the newly formed water will not collect at the bottom of the test tube.
4. Still, there will be water in the vapour form. This will move out through the delivery tube, along with the NH3. That means, the gas which comes out of the delivery tube will be a mixture of water vapour and ammonia.
5. We have to remove the water vapour. For that, the delivery tube enters a drying tower. The upper chamber of the drying tower contains quick lime (CaO). This CaO, which is a drying agent, will absorb the water vapour. So the delivery tube that comes out of the drying tower will contain NH3 only.
6. This delivery tube enters a gas jar. Thus the ammonia gas is collected in the gas jar. We can see that the gas jar is kept in an inverted position. This is because, ammonia gas is lighter than air. That is., the density of ammonia is lesser than the density of air. So it will rise up. This rising ammonia will displace the air present in the jar, and will occupy it’s top position in the inverted jar.
Drying agent
Drying agents are substances
capable of absorbing moisture from substances. After the absorbtion,
ths substances will become ‘dry’. In the above experiment, CaO
is used as the drying agent. CaO is alkaline. The ammonia is also
alkaline. The two will not react with each other, and so, the ammonia
comes out of the drying tower.
 |
| Fig.7.2 |
• A few drops of water is added
into the flask using the syringe. We can see a fountain of pink water
in the flask. How is this fountain formed? Why is it pink coloured?
Let us analyse:
1. When a few drops of water is
added into the flask using the syringe, Some of the ammonia gas
dissolves in that water. This will create some vacuum in the flask.
So the out side atmospheric pressure will be greater than the
pressure inside the flask. This atmospheric pressure will push down
on the water in the beaker. So the water rushes up through the jet
tube.
2. When more water enters the flask in this way, more ammonia gas will dissolve in that water. Thus new vacuum is created. Because of this additional vacuum, the atmospheric pressure will again push down on the water in the beaker.
3. This continues as a cyclic process. Thus a fountain will be formed. The cycle will continue until all the ammonia is dissolved. When all the ammonia is dissolved, there will not be any formation of 'new vacuum'.
2. When more water enters the flask in this way, more ammonia gas will dissolve in that water. Thus new vacuum is created. Because of this additional vacuum, the atmospheric pressure will again push down on the water in the beaker.
3. This continues as a cyclic process. Thus a fountain will be formed. The cycle will continue until all the ammonia is dissolved. When all the ammonia is dissolved, there will not be any formation of 'new vacuum'.
■ Now we will see the reason for
the pink colour: The ammonia gas present in the flask dissolves in the water which rushes into the flask. So the water becomes a
solution. A ‘solution of ammonia in water’. This solution is
alkaline in nature. So the phenolphthalein that is already present,
will turn pink. Thus we get a pink fountain.
A video showing the demonstration can be seen here.
This experiment shows that
ammonia gas is readily soluble in water. The equation is:
A video showing the demonstration can be seen here.
NH3 + H2O → NH4OH. This is a balanced equation.
A highly concentrated solution
of ammonia in water is called liquor ammonia.
Ammonia gas can be easily
liquefied by applying pressure. Liquefied ammonia is called liquid
ammonia.
We know that, ammonia is
alkaline in nature. So let us see it’s reaction with an acid:
■ Introduce the tip of a glass
rod which is dipped in concentrated hydrochloric acid, into a glass
jar filled with ammonia. We can see the formation of thick white
fumes. This is due to the formation of ammonium chloride (NH4Cl). Let us
write the equation:
NH3 + HCl → NH4Cl
This is a balanced equation
• The white fumes are caused by small white particles of NH4Cl
NH3 + HCl → NH4Cl
This is a balanced equation
• The white fumes are caused by small white particles of NH4Cl
■ In this way, ammonia reacts with acids
yielding ammonium salts, which are used as chemical fertilisers
Properties of ammonia
• It has no colour
• It has a pungent smell
• It is alkaline in nature
• It is highly soluble in water
• It is lighter than air
Identification of ammonia gas
We can use the following
tests:
1. The basic test is by the
smell. Ammonia has a characteristic pungent smell.
2. Ammonia turns wet red litmus paper into blue colour, showing it’s alkaline property
3. When the tip of a glass rod
which is dipped in concentrated hydrochloric acid is introduced into
a glass jar filled with ammonia, thick white fumes are formed.
Identification of ammonium salts
1. Prepare a solution of the
given ammonium salt. Take 5 ml of nesslers reagent in a test tube.
2. Add a few drops of the prepared salt solution into this.
3. If a brownish orange precipitate is formed, then the given salt is a salt of ammonia.
2. Add a few drops of the prepared salt solution into this.
3. If a brownish orange precipitate is formed, then the given salt is a salt of ammonia.
Industrial preparation of Ammonia
1. Nitrogen and hydrogen are taken in the ratio 1:3. This ratio is obvious because, in the final product which is ammonia (NH3), There are 3 atoms of hydrogen for every one atom of nitrogen.2. They are made to react with each other. Very high temperature and pressure is required for the reaction to take place. This is because, nitrogen does not take part in reactions very easily, due to it's triple bond.
3. Spongy iron is used as a catalyst.
4. This is known as the Haber process. The equation of the reaction is:
N2 + 3H2 → 2NH3. This is a balanced equation.
In the next section, we will see sulphuric acid.
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