Class 10 SELINA Solutions Chemistry Chapter 9 - Study of Compounds B. Ammonia
Study of Compounds B. Ammonia Exercise Intext 1
Covalent bonding is present in ammonia.
Formula of liquid ammonia is: NH3.
Liquid ammonia is liquefied ammonia and is basic in nature. It dissolves in water to give ammonium hydroxide which ionizes to give hydroxyl ions.
NH3 + H2O NH4OH
NH4OH NH4++ OH-
Therefore it turns red litmus blue and phenolphthalein solution pink.
(a) Lab preparation of ammonia:
2NH4Cl+Ca(OH)2 CaCl2 +2H2O +2NH3
(b) The ammonia gas is dried by passing through a drying tower containing lumps of quicklime (CaO).
(d) Ammonia is highly soluble in water and therefore it cannot be collected over water.
(a) An aqueous solution of ammonia is prepared by dissolving ammonia in water. The rate of dissolution of ammonia to water is very high.
(b)The drying agent used is CaO in case of ammonia.
Other drying agents like P2O5 and CaCl2 are not used. As ammonia being basic reacts with them.
6NH3 + P2O5 +3H2O 2(NH4)3PO4
CaCl2 +4NH3 CaCl2.4NH3
The substance A is Ammonium chloride and 'B' is Ammonia.
2NH4Cl + Ca(OH)2 CaCl2 + 2H2O + 2NH3
(a) Conditions for reactants to combine :
Optimum temperature is 450o-500oC
Above 200 atm pressure
Finely divided iron as catalyst
Traces of molybdenum or Al2O3 as promoters.
Reaction:N2 +3H2 2NH3 + heat
(b) Dry nitrogen and dry hydrogen in the ratio of 1:3 by volume is made to combine.
(c) Source of Hydrogen: Hydrogen is generally obtained from water gas by Bosch process.
(CO + H2) + H2O CO2 +2H2
Source of Nitrogen: It is obtained from fractional distillation of liquid air.
(d) High pressure favours the forward reaction i.e. formation of ammonia.
(e)Two possible ways by which NH3 produced is removed from unreacted N2 and H2 by:
(i)Liquefaction: NH3 is easily liquefiable.
(ii)Absorbing in water: As ammonia is highly soluble in water.
(i)Finely divided iron increases the rate of reaction.
(ii)Molybdenum acts as a promoter to increase the efficiency of the catalyst.
(h) The unchanged nitrogen and hydrogen are recirculated through the plant to get more ammonia. By recirculating in this way, an eventual yield of 98% can be achieved.
(a) Ammonium compounds being highly soluble in water do not occur as minerals.
(b) Ammonium nitrate is not used in the preparation of ammonia as it is explosive in nature and it decomposes forming nitrous oxide and water vapours.
(c) Conc. H2SO4 is not used to dry ammonia, as ammonia being basic reacts with them.
2NH3 + H2SO4 (NH4)2SO4
(d) (i) In order to better mixing of ammonium chloride, calcium hydroxide used in excess.
(ii) The flask is fitted in slatting position because of the water formed in the reaction does not trickle back into the heated flask.
Name of process
Nitrogen and hydrogen
i. 450 - 500°C
ii. 200 -800 atm
iii. Finely divided iron (Fe)
b. Thermal decomposition
An element has 2 electrons in its N shell = Ca (calcium)
It reacts with a non-metal of atomic number 7 = N (nitrogen)
The compound formed is calcium nitride (Ca3N2) which reacts with warm water and produces the basic gas ammonia (NH3).
(a) The formula of the compound is Mg3N2.
(b) Balanced equation :
Mg3N2 + 6 H2O 3 Mg(OH)2 + 2 NH3
(c) Ammonia is a reducing agent and reduces less active metal oxide to its respective metal.
a. A reddish brown precipitate is obtained when ammonium hydroxide is added to ferrous chloride.
b. Aqueous ammonia is a solution of NH3.
c. Finely divided iron is used in Haber process.
d. Quicklime (CaO) is a drying agent for NH3.
e. Ammonium salts, on thermal decomposition, give ammonia and hydrogen chloride.
C.: Magnesium nitride
Study of Compounds B. Ammonia Exercise Ex. 9
(a)Ammonia is less dense than air. By Fountain Experiment, we demonstrate the high solubility of ammonia gas in water.
(b) The high solubility of ammonia gas in water
(c)The balanced equation for the reaction between ammonia and sulphuric acid is:
2NH3 + H2SO4 (NH4)2SO4
(a) Ammonia is basic in nature.
(b) Copper oxide because CuO is less reactive can be reduced by C, CO or by hydrogen whereas Al2O3, Na2O, MgO are reduced by electrolysis.
(a) Liquid ammonia acts as a refrigerant in ice plants. Evaporation needs heat energy, and when liquid ammonia vaporises, it absorbs large quantities of heat without changing its temperature. For these reasons, ammonia is widely used as a refrigerant.
(b) Ammonia is used for removing grease and dirt as it emulsifies or dissolves them.
(c) Ammonia is formed by bacterial decomposition of urea, so ammonia has a pungent smell.
(d) An aqueous solution of ammonia is a weak electrolyte. It dissociates partially to give hydroxyl ions, and ions conduct electricity. So an aqueous solution of ammonia conducts electricity.
(a) The gas is ammonia.
(b) The formula is NH3.
(c) Uses of ammonia:
It is used in the industrial preparation of nitric acid by Ostwald process.
It is used in the manufacture of fertilizers such as ammonium sulphate, ammonium nitrate, ammonium phosphate.
It is used in the manufacture sodium carbonate by Solvay process.
NaCl + NH3 + CO2 + H2O NaHCO3 +NH4Cl
CuSO4 +2NH4OH Cu(OH)2 + [NH4]2SO4
Ammonia solution in water gives a blue precipitate when it combines with a solution of copper salt.
The pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming tetraamine copper[II] sulphate, an azure blue(deep blue)soluble complex salt.
Cu(OH)2 +(NH4)2SO4 +2NH4OH [Cu(NH3)4]SO4 + 4H2O
This reaction is reversible and exothermic. From the reaction, it is proved that ammonia contains nitrogen and hydrogen.
Ammonia burns with a yellowish flame. It produces water vapour and nitrogen. This shows that ammonia contains nitrogen and hydrogen.
(a) AlN + 3H2O Al(OH)3 +NH3
(b) 2NH3 + 3PbO 3Pb + 3H2O + N2
(c) 8NH3 +3Cl2 N2 + 6NH4Cl
(d) 2NH3 + CO2 NH2CONH2 + H2O
(i) Ammonia act as reducing agent is explained by equation (c).
(ii) Urea the nitrogenous fertilizer is prepared from equation (d).
(a) Dirty green ppt. of Ferrous hydroxide is formed which is insoluble in excess of NH4OH.
FeSO4 + 2NH4OH [NH4]2SO4 + Fe(OH)2
(b) Reddish brown ppt. of ferric hydroxide is formed which is insoluble in ammonium hydroxide.
FeCl3 + 3NH4OH 3NH4Cl + Fe(OH)3
(c) White ppt. of lead hydroxide is formed which is insoluble in NH4OH.
Pb(NO3)2 + 2NH4OH 2NH4NO3 + Pb(OH)2
(d)White gelatinous ppt. of Zinc hydroxide is formed which is soluble in NH4OH.
Zn(NO3)2 + 2NH4OH 2NH4NO3 + Zn(OH)2
- Calcium chloride and zinc chloride
Calcium chloride does not react with ammonium hydroxide.
On adding ammonium hydroxide drop by drop to a solution of zinc salt a white precipitate is formed which is soluble in excess of ammonium hydroxide.
- Ferric salt and ferrous salt:
When ammonium hydroxide is added drop wise to solution to be tested.
Ferrous salt gives dirty green ppt.
Ferric salt gives reddish brown ppt of their hydroxides.
- Zinc nitrate and lead nitrate
When ammonium hydroxide is added drop wise to solution to be tested.
Zinc nitrate gives white gelatinous ppt. of their hydroxides which is soluble on adding excess of ammonium hydroxide.
Whereas, lead nitrate gives white ppt. of their hydroxides which is insoluble on adding excess of ammonium hydroxide.
- 8NH3 + 3Cl2 → N2 + 6NH4Cl
- 4NH3 + 5O2 4NO + 6H2O + Heat
2NO + O2 → 2NO2
- NH3 + 3Cl2 → 3HCl + NCl3
- AlCl3 + 3NH4OH → 3NH4Cl + Al(OH)3
- AlN + 3H2O → Al(OH)3 + NH3
- 3PbO + 2 NH3 → 3Pb + 3H2O + N2
(b) Hydrogen chloride and chlorine gas.
(c) (i) Ammonium chloride
(i) Ammonium nitrate
(ii) Ammonium carbonate
(d) Acidic gas: HCl
Basic gas: Ammonia
Neutral gas: NH4Cl
(e) Silver chloride
(g) Magnesium nitride
(h) Lead oxide
(i) Ammonium chloride
CuSO4 + 2NH4OH (NH4)2SO4 +Cu(OH)2 [Pale blue]
The cation present in solution B is Copper (Cu+2).
The colour of solution B is Blue.
The pale blue precipitate of copper hydroxide dissolves in excess of ammonium hydroxide forming tetraamine copper[II] sulphate, an azure blue(deep blue) soluble complex salt.
Cu(OH)2 + (NH4)2SO4 +2NH4OH [Cu(NH3)4]SO4 + 4H2O
Three ways in which ammonia gas can be identified is:
It has a sharp characteristic odour
When a glass rod dipped in HCl is brought in contact with the gas white colour fumes of ammonium chloride are formed
It turns moist red litmus blue, moist turmeric paper brown and phenolphthalein solution pink.
As the 'A' turns red litmus blue it is a base.Now the gas 'A' combines with 'B' in presence of Catalyst to give colourless gas Nitrogen monoxide. It reacts with oxygen to give brown gas which is Nitrogen dioxide.
4NH3 + 5O2 4NO + 6H2O + Heat
2NO + O2 2NO2
NH3 in water forms NH4OH which turns red litmus blue.
(a) The main refrigerants used are Freon chlorofluorocarbons (CFC). They deplete ozone layer. The chlorofluorocarbons are decomposed by ultraviolet rays to highly reactive chlorine which is produced in the atomic form.
The free radical [Cl] reacts with ozone and chlorine monoxide is formed.
This causes depletion of ozone layer and chlorine monoxide so formed reacts with atomic oxygen and produces more chlorine free radicals.
ClO + OCl + O2
Again this free radical destroys ozone and the process continues thereby giving rise to ozone depletion.
(b) Liquid ammonia can be used as a refrigerant, as an alternative for chlorofluorocarbons.
(c) Advantages of ammonia as refrigerant:
(i) Ammonia is environmentally compatible. It does not deplete ozone layer and does not contribute towards global warming.
(ii) It has superior thermodynamic qualities as a result ammonia refrigeration systems use less electricity.
Ammonia has a recognizable odour and so leaks are not likely to escape.
(a) Explosive: ammonium nitrate
(b) Medicine: ammonium carbonate
(c) Fertilizers: ammonium sulphate
(d) Laboratory reagent: ammonia solution
(a) Ammonium chloride
NH4Cl NH3 +HCl
(b) Ammonium nitrate
NH4NO3 N2O +2H2O
Both are examples of Thermal dissociation.
(a)It is the basic nature of ammonia molecule.
(b)Hydroxyl ion (NH3 +H2O NH4+ + OH-)
(c) The red litmus paper turns blue in the solution.
(a) HCl gas is more dense [V.D.=18.25,V.D. of ammonia =8.5] and it is collected by the upward displacement of air.
(b) NH3 + HCl → NH4Cl
(c) Balanced equation:
(a) 2NH3 +3CuO 3Cu +3H2O +N2
(b) 2NH3 +3Cl2 N2 + 6HCl
A. Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3
B. NH3 + HCl → NH4Cl
8NH3 + 3Cl2 → 6NH4Cl + N2
C. NH4Cl + NaOH → NaCl + NH3 + H2O
- Ammonia reacts with excess chlorine to form nitrogen trichloride.
- Ammonium hydroxide is added to ferrous sulphate solution.
2NH4OH + FeSO4⟶ Fe(OH)2 ↓ + (NH4)2SO4
- When ammonia gas is passed over heated copper (II) oxide, black copper oxide is reduced to greyish metallic copper.
b. C.: Magnesium nitride
c. 'Q' is ammonium chloride.
v. Dirty green
b. Ammonia burns with a yellowish flame. It produces water vapour and nitrogen.
i. Haber's process
ii. 1 part of nitrogen gas and 3 parts of hydrogen gas
iii. Finely divided iron (Fe)
i. Ammonia and hydrogen chloride gas
ii. High solubility of gases in water
a. In small quantity: A bluish white ppt. is obtained.
In excess quantity: A deep blue solution is obtained.
iii. By downward displacement of air
v. Bring a moist red litmus paper to the mouth of the inverted jar if it immediately turns blue.
Bring a glass rod dipped in hydrochloric acid to the mouth of the inverted jar. If it produces dense white fumes, then the jar is full of gas.
d. Pungent smelling basic gas called ammonia is evolved.
b. Magnesium nitride reacts with boiling water to liberate ammonia.
i. Ammonium nitrate is a highly explosive substance and cannot be heated.
iii. By the downward displacement of air or upward delivery as it is lighter than air.
It is not collected over water because it easily dissolves in water.
a. A yellow-coloured explosive is formed.
b. Ammonium nitrite
i. When added in small quantity, it forms a gelatinous white ppt.
ii. When added in excess, it dissolves to form a complex salt.
Name of the process
Equation for the catalysed reaction
Finely divided iron (Fe)
a. Downward displacement of air.
i. Iron(II) sulphate: Gives dirty green ppt. with ammonium hydroxide insoluble in excess.
ii. Iron(III) sulphate: Gives reddish brown ppt. with ammonium hydroxide insoluble in excess.
d. A colourless pungent-smelling ammonia gas is obtained.
i. Hydroxyl (OH-) ion other than ammonium ion
ii. Red litmus turns blue, methyl orange turns yellow and phenolphthalein turns pink.
f. In the presence of platinum catalyst at 800°C.
(i) 2NH4Cl + Ca (OH)2 → CaCl2 + 2H2O + 2NH3
(ii) NH3 + 3Cl2→ NCl3 + 3HCl
(iii) 2NH3 + H2SO4→ (NH4)2SO4
(b) Ammonia (NH3)
Solution 2016 (a)
Solution 2016 (b)
(i) 8NH3 + 3Cl2→ N2 + 6NH4Cl
(ii) 3PbO + 2NH3→3Pb + 3H2O + N2