Selina Concise Solutions for ICSE Class 10 Chemistry Chapter 9 Study of Compounds Ammonia

Exercise

Question 1. Draw a labelled diagram and give balanced equation for the lab. Preparation of ammonia. Also state physical properties of ammonia.
Answer: Physical properties of ammonia are:
Color: Colourless
Odour: Strong, Pungent chocking smell
Taste: Slightly bitter (alkaline) taste
Physiological action: Non-Poisonous
Density: V.D = 8.5 Lighter than air
Nature: Alkaline
Liquefaction: easily liquefied at 10°C by compressing it at 6 atm. Pressure
Boiling Point: Liquid ammonia boils at −33.5°C
Freezing Point: Solid \( NH_3 \) melts at −77.7°C
Solubility: Highly soluble in water, 1vol of water dissolves about 702 vols. of ammonia at 20°C and 1 atm. pressure.
Reaction:
\( 2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3 \)
In simple words: Ammonia is a colorless gas with a strong smell that easily dissolves in water and can be made liquid by cooling or pressure.

📝 Teacher's Note: Use the fountain experiment demonstration to show ammonia's high solubility. Students often confuse liquid ammonia with ammonia solution - emphasize that one is pure liquefied gas, the other is dissolved in water.

🎯 Exam Tip: Always include the balanced equation and draw the labeled diagram clearly showing the drying agent (CaO) and collection method for full marks.

Question 2. (a) Is ammonia more dense or less dense than air? (b) What property of ammonia is demonstrated by the fountain experiment? (c) Write the balanced equation for the reaction between ammonia and sulphuric acid.
Answer: (a) Ammonia is less dense than air. (b) By Fountain Experiment we demonstrate the high solubility of ammonia gas in water. (c) Balanced equation for the reaction between ammonia and sulphuric acid is:
\( 2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4 \)
In simple words: Ammonia is lighter than air, dissolves very easily in water (like sugar in tea), and reacts with acids to make salts.

📝 Teacher's Note: Demonstrate the fountain experiment with a round-bottom flask - the dramatic water fountain clearly shows ammonia's exceptional solubility compared to other gases.

🎯 Exam Tip: Remember the 1:702 solubility ratio and write balanced equations with correct formulas - (NH₄)₂SO₄, not NH₄SO₄.

Question 3. Pick the odd member from the list giving reasons: (a) Ammonia, sulphur dioxide, hydrogen chloride, carbon dioxide. (b) Copper oxide, aluminium oxide, sodium oxide, magnesium oxide.
Answer: (a) Ammonia is basic in nature. (b) Copper oxide because CuO is less reactive can be reduced by C, CO or by hydrogen whereas \( Al_2O_3 \), \( Na_2O \), \( MgO \) are reduced by electrolysis.
In simple words: Ammonia is the only basic gas among acids, and copper oxide is easier to break down compared to the other very stable metal oxides.

📝 Teacher's Note: Use litmus paper to show ammonia turning red litmus blue, while the other gases turn blue litmus red. This visual demonstration helps students remember the concept.

🎯 Exam Tip: Always give clear reasons for your choice - stating "basic nature" or "reduction method" shows understanding beyond just picking the odd one out.

Question 4. The following reactions are carried out: A: Nitrogen + metal → compound X. B: X + water → ammonia + another compound C: Ammonia + metal oxide → metal + water + N₂ One metal that can be used for reaction A is magnesium. (a) write the formula of the compound X formed (b) write the correctly balanced equation for reaction B where X is the compound formed. (c) what property of ammonia is demonstrated by reaction C?
Answer: (a) The formula of the compound is \( Mg_3N_2 \). (b) Balanced equation: \( Mg_3N_2 + 6H_2O \rightarrow 3Mg(OH)_2 + 2NH_3 \) (c) Ammonia is a reducing agent and reduces less active metal oxide to its respective metal.
In simple words: Magnesium and nitrogen make magnesium nitride, which breaks down with water to give ammonia and magnesium hydroxide. Ammonia can take oxygen away from certain metals.

📝 Teacher's Note: Emphasize the pattern: active metal + nitrogen → nitride, nitride + water → ammonia + hydroxide. This helps students understand the nitrogen cycle connections.

🎯 Exam Tip: Write the subscripts correctly in Mg₃N₂ and balance equations carefully - examiners frequently deduct marks for incorrect formulas and unbalanced equations.

Question 5. Ammonium salts decompose on heating. What other property do ammonium salts have in common?
Answer: Reducing property.
In simple words: Ammonium salts can take away oxygen from other substances, acting like a helper that removes oxygen in chemical reactions.

📝 Teacher's Note: Connect this to everyday examples like how ammonium salts in some fertilizers can react with soil components. The reducing property is often overlooked by students.

🎯 Exam Tip: One-word answers like "reducing property" are sufficient here - don't over-explain unless specifically asked for examples or equations.

Question 6. State what you observe when a piece of moist red litmus paper is placed in a gas jar of ammonia.
Answer: When a piece of moist red litmus paper is placed in a gas jar of ammonia it turns blue.
In simple words: The red litmus paper changes to blue color, showing that ammonia is a basic substance.

📝 Teacher's Note: Emphasize that the paper must be moist - dry ammonia gas won't affect dry litmus paper. This is a crucial detail students often miss in practical exams.

🎯 Exam Tip: Always mention "moist" red litmus paper in your answer and state the color change clearly - "turns blue" gets full marks.

Question 7. A gas 'P' gives dense white fumes with chlorine. Its aqueous solution gives a blue colour with copper (II) hydroxide (a) Name the gas P. (b) Give its formula (c) Give three uses of P.
Answer: (a) The gas is ammonia. (b) The formula is \( NH_3 \). (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. \( NaCl + NH_3 + CO_2 + H_2O \rightarrow NaHCO_3 + NH_4Cl \)
In simple words: The gas P is ammonia, which is used to make acids, fertilizers for plants, and washing soda for cleaning.

📝 Teacher's Note: Show students the white fumes reaction by bringing ammonia and HCl vapors together. The dramatic white smoke formation is memorable and helps with identification questions.

🎯 Exam Tip: Learn the three main industrial uses - nitric acid production, fertilizer manufacture, and Solvay process. These are frequently tested application questions.

Question 8. Ammonia solution in water gives a blue precipitate when it combines with a solution of copper salt. The blue precipitate further dissolves in excess of ammonia solution to give azure blue solution. Explain with equation.
Answer: Equation: \( CuSO_4 + 2NH_4OH \rightarrow Cu(OH)_2 \downarrow + (NH_4)_2SO_4 \) (pale blue). 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. \( Cu(OH)_2 + (NH_4)_2SO_4 + 2NH_4OH \rightarrow [Cu(NH_3)_4]SO_4 + 4H_2O \)
In simple words: First ammonia makes a light blue solid with copper, then more ammonia dissolves this solid to make a dark blue solution - like dissolving blue powder to make dark blue ink.

📝 Teacher's Note: This is an excellent demonstration for complex ion formation. Show students the color change from pale blue precipitate to deep azure blue solution when excess ammonia is added.

🎯 Exam Tip: Write both equations and mention the color changes clearly - "pale blue precipitate" first, then "azure blue solution" with excess ammonia.

Question 9. How do you prove that NH₃ contains nitrogen and hydrogen?
Answer: Ammonia dissociates into nitrogen and hydrogen at high temperature or by electric sparks. \( 2NH_3 \xrightarrow{N_2} N_2 + 3H_2 \)
In simple words: When ammonia gas is heated very strongly or hit with electric sparks, it breaks apart into nitrogen gas and hydrogen gas, proving it contains both elements.

📝 Teacher's Note: Explain that this decomposition requires high energy input, showing that ammonia is quite stable under normal conditions. This connects to the Haber process conditions.

🎯 Exam Tip: Write the balanced decomposition equation and mention the conditions needed - "high temperature or electric sparks" - for complete marks.

Question 10. Give reasons for the following: (a) Liquid ammonia is used as a refrigerant in ice plants. (b) Aqueous solution of ammonia is used for removing grease stains from woolen clothes (c) Aqueous solution of ammonia gives a pungent smell (d) Aqueous solution of ammonia conducts electricity
Answer: (a) Liquid ammonia takes a lot of energy to vaporize. This heat is taken from the surrounding bodies which are consequently cooled down. Thus it is used as a refrigerant in ice plant. (b) Ammonia emulsifies or dissolves fats, grease so it is used to remove grease from woolen clothes. (c) Aqueous solution of ammonia gives pungent smell because of the presence of ammonia. (d) Aqueous ammonia when dissolved in water breaks into ions which help in the conductance of electricity. \( NH_3 + H_2O \rightarrow NH_4OH \rightleftharpoons NH_4^+ + OH^- \)
In simple words: Liquid ammonia absorbs lots of heat when turning to gas (cooling effect), dissolves oily stains easily, keeps its strong smell in water, and makes ions that carry electricity.

📝 Teacher's Note: Connect the refrigeration principle to students' experience with evaporative cooling. The grease removal property can be demonstrated with a small oil stain and dilute ammonia solution.

🎯 Exam Tip: For part (d), always write the ionization equation showing NH₄⁺ and OH⁻ ions formation - this explains the electrical conductivity clearly.

Question 11. Copy and complete the following equations. (a) AlN + H₂O → (b) 2NH₃ + 3PbO → (c) NH₃ + 3Cl₂ → (d) NH₃ + CO₂ → (i) which property of ammonia is illustrated by equation (c)? (ii) what important fertilizer is prepared from equation (d)?
Answer: (a) \( AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3 \) (b) \( 2NH_3 + 3PbO \rightarrow 3Pb + 3H_2O + N_2 \) (c) \( 8NH_3 + 3Cl_2 \rightarrow N_2 + 6NH_4Cl \) (d) \( 2NH_3 + CO_2 \rightarrow NH_2CONH_2 + H_2O \) (i) Ammonia act as reducing agent is explained by equation (c). (ii) Urea the nitrogenous fertilizer is prepared from equation (d).
In simple words: These equations show ammonia reacting with water, metal oxides, chlorine, and carbon dioxide to make different useful compounds including the important fertilizer urea.

📝 Teacher's Note: Emphasize equation (d) as it shows urea formation - one of the most important industrial applications of ammonia. Students should recognize urea as a common fertilizer.

🎯 Exam Tip: Balance equations carefully and remember that equation (c) shows reducing property while equation (d) gives urea fertilizer - these are common follow-up questions.

Question 12. Correct the following: (a) A reddish brown precipitate is obtained when ammonium hydroxide is added to ferrous sulphate. (b) Liquid ammonia is a solution of NH₃ (c) Finely divided platinum is used in Haber process (d) Conc. H₂SO₄ is a drying agent for NH₃ (e) Ammonium salts, on heating, decompose to give ammonia.
Answer: (a) A Dirty green precipitate of \( Fe(OH)_2 \) is obtained when ammonium hydroxide is added to ferrous sulphate. (b) Liquid ammonia is liquefied ammonia. (c) Finely divided Iron is used in Haber process. (d) Quicklime is a drying agent for \( NH_3 \). (e) Ammonium salts when heated with caustic alkali.
In simple words: The corrections show proper colors of precipitates, difference between liquid and dissolved ammonia, correct catalyst for ammonia production, proper drying agent, and complete conditions for ammonia release.

📝 Teacher's Note: Students often confuse ferrous (Fe²⁺) giving green precipitate with ferric (Fe³⁺) giving brown precipitate. Also clarify that concentrated H₂SO₄ would react with ammonia, not dry it.

🎯 Exam Tip: Remember color codes: ferrous = dirty green, ferric = reddish brown. Also, iron catalyst in Haber process, not platinum.

Question 13. What do you observe when ammonium hydroxide is added to the aqueous solution of: (a) FeSO₄ (b) Iron (III) chloride, (c) Lead nitrate (d) Zinc nitrate?
Answer: (a) Dirty green ppt. of Ferrous hydroxide is formed which is insoluble in excess of \( NH_4OH \). \( FeSO_4 + 2NH_4OH \rightarrow [NH_4]_2SO_4 + Fe(OH)_2 \) (b) Reddish brown ppt. of ferric hydroxide is formed which is insoluble in ammonium hydroxide. \( FeCl_3 + 3NH_4OH \rightarrow 3NH_4Cl + Fe(OH)_3 \) (c) White ppt. of lead hydroxide is formed which is insoluble in \( NH_4OH \). \( Pb(NO_3)_2 + 2NH_4OH \rightarrow 2NH_4NO_3 + Pb(OH)_2 \) (d) White gelatinous ppt. of Zinc hydroxide is formed which is soluble in \( NH_4OH \). \( Zn(NO_3)_2 + 2NH_4OH \rightarrow 2NH_4NO_3 + Zn(OH)_2 \)
In simple words: Different metal salts give different colored precipitates with ammonia - iron compounds give green or brown, lead gives white, and zinc gives white that dissolves in extra ammonia.

📝 Teacher's Note: This is crucial for qualitative analysis. Teach students the memory aid: "Iron green/brown, lead white insoluble, zinc white soluble in excess." Practice with actual solutions when possible.

🎯 Exam Tip: Always mention the color AND solubility behavior in excess NH₄OH. Write balanced equations for full marks - this distinguishes top students.

Question 14. Why is ammonium hydroxide used in qualitative analysis? Give two equations to justify your answer
Answer: When correct amount of ammonium hydroxide is added drop wise to solutions of the metallic salts, ppts. (coloured generally) are formed. They help us to identify their metal ions. Two equations: \( FeSO_4 + 2NH_4OH \rightarrow (NH_4)_2SO_4 + Fe(OH)_2 \)
In simple words: Ammonium hydroxide helps identify different metals by forming colored precipitates that act like fingerprints for each metal.

📝 Teacher's Note: Emphasize that qualitative analysis relies on systematic precipitation patterns. Ammonium hydroxide is preferred over sodium hydroxide because it's a weak base, giving controlled precipitation.

🎯 Exam Tip: Always provide two different metal salt equations as examples, showing different colored precipitates for complete justification of the analytical use.

Question 15. Give a chemical test to distinguish between the following:
(a) Ammonium chloride and sodium chloride
(b) Ferric salt and ferrous salt
(c) Sodium sulphate and ammonium sulphate
Answer:
(a) \( NH_4Cl \) on strong heating sublimes to form dense white fumes which condense to white powdery mass on cooler parts of the tube whereas no white fumes on heating \( NaCl \).
(b) When ammonium hydroxide is added drop wise to solution to be tested:
Ferrous salt gives dirty green precipitate.
Ferric salt gives reddish brown precipitate of their hydroxides.
(c) \( (NH_4)_2SO_4 \) on warming with \( NaOH \) solution gives \( NH_3 \) gas. Sodium sulphate does not liberate \( NH_3 \) gas.
In simple words: These tests help us tell apart similar-looking chemicals by seeing what happens when we heat them or add other chemicals - ammonium salts give off ammonia gas while sodium salts don't.

📝 Teacher's Note: Demonstrate the sublimation test with a test tube and small flame - students love seeing the white smoke appear. Emphasize the characteristic smell of ammonia gas as an additional confirmation test.

🎯 Exam Tip: Always mention both the positive result (what happens with ammonium compounds) AND the negative result (what doesn't happen with other compounds) to get full marks.

Question 16. Give balanced equations for the following conversation:
(a) Ammonia to nitrogen using an acidic gas,
(b) Ammonia to brown gas,
(c) Ammonia to nitrogen trichloride
(d) Ammonia solution to an amphoteric hydroxide
(e) A nitride of a trivalent metal to ammonia
(f) Lead oxide to lead.
Answer:
(a) \( 8NH_3 + 3Cl_2 \rightarrow N_2 + 6NH_4Cl \)
(b) \( 4NH_3 + 5O_2 \xrightarrow{Pt, 800°C} 4NO + 6H_2O + Heat \)
\( 2NO + O_2 \rightarrow 2NO_2 \) (Brown gas)
(c) \( NH_3 + 3Cl_2 \rightarrow 3HCl + NCl_3 \)
(d) \( AlCl_3 + 3NH_4OH \rightarrow 3NH_4Cl + Al(OH)_3 \)
(e) \( AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3 \)
(f) \( 3PbO + 2NH_3 \rightarrow 3Pb + 3H_2O + N_2 \)
In simple words: Ammonia is a very reactive gas that can be converted into many different products depending on what other chemicals it reacts with and under what conditions.

📝 Teacher's Note: Use color coding to highlight the key products in each reaction. Students often confuse the brown gas formation - emphasize it's a two-step process through nitric oxide first.

🎯 Exam Tip: Remember to balance equations properly and include conditions like temperature and catalyst where mentioned in the question.

Question 17.
(a) explain catalytic oxidation of ammonia
(b) Give two reactions to show reducing property of ammonia.
Answer:
(a) In the presence of Platinum at 800°C, ammonia reacts with oxygen to give nitric oxide and water vapour.
Procedure: Pass dry ammonia gas and oxygen gas through inlets over heated platinum placed in the combustion tube, which in the heated state emits reddish glow.
Reaction: \( 4NH_3 + 5O_2 \xrightarrow{Pt, 800°C} 4NO + 6H_2O + Heat \)
\( 2NO + O_2 \rightarrow 2NO_2 \) (Brown gas)
Observation: Reddish brown vapours of nitrogen dioxide are seen in the flask due to the oxidation of nitric oxide. The platinum continues to glow even after the heating is discontinued since the catalytic oxidation of ammonia is exothermic.
(b) Two reactions to show reducing property of ammonia are:
\( 8NH_3 + 3Cl_2 \rightarrow N_2 + 6NH_4Cl \)
\( 2NH_3 + 3CuO \rightarrow 3Cu + 3H_2O + N_2 \)
In simple words: Catalytic oxidation is like a controlled burning of ammonia using platinum as a helper, producing useful chemicals while releasing heat that keeps the reaction going.

📝 Teacher's Note: Demonstrate with a diagram showing the experimental setup. Explain why the platinum glows - it's like a self-sustaining fire once started.

🎯 Exam Tip: Include both the procedure AND observations for full marks. Don't forget to mention the exothermic nature of the reaction.

Question 18. Choose the correct word or phrase from the brackets to complete the following sentences and write balanced equations for the same.
(i) ammonium chloride is a soluble salt prepared by ………………. [precipitation, neutralization]
(ii) when ammonium chloride is heated, it undergoes …………….. [thermal decomposition/ dissociation].
(iii) Heating ammonium chloride with sodium hydroxide produces …………. [ammonia, nitrogen].
Answer:
(i) Neutralization
\( NH_3 + HCl \rightarrow NH_4Cl \)
(ii) Thermal dissociation
\( NH_4Cl \rightarrow NH_3 + HCl \)
(iii) Ammonia
\( NH_4Cl + NaOH \rightarrow NH_3 + NaCl + H_2O \)
In simple words: Ammonium chloride can be made by mixing ammonia with acid, breaks apart when heated, and releases ammonia gas when mixed with a strong base.

📝 Teacher's Note: Clarify the difference between decomposition (permanent breakdown) and dissociation (reversible separation). Use the analogy of ice melting vs wood burning.

🎯 Exam Tip: Write balanced equations for each part - many students lose marks by forgetting the chemical equations even when they choose correct words.

Question 19. Name:
(a) the gas which is prepared by Haber process,
(b) two gases which give dense white fumes with ammonia,
(c) one salt of ammonia in each case which is used in: (i) dry cell (ii) explosive (iii) medicine.
(d) an acidic gas which reacts with a basic gas liberating a neutral gas,
(e) a metallic chloride soluble in ammonium hydroxide,
(f) the gas obtained when ammonia burns in an atmosphere of oxygen without any catalyst
(g) a nitride of a divalent metal which reacts with warm water liberating ammonia
(h) an amphoteric oxide reduced by the basic gas.
(i) a white salt produced by an acid gas and a basic gas.
Answer:
(a) Ammonia
(b) Hydrogen chloride and chlorine gas.
(c) (i) Ammonium chloride (ii) Ammonium nitrate (iii) Ammonium carbonate
(d) Acidic gas: HCl, Basic gas: Ammonia, Neutral gas: \( NH_4Cl \)
(e) Silver chloride
(f) Nitrogen
(g) Magnesium nitride
(h) Lead oxide
(i) Ammonium chloride
In simple words: This question tests knowledge of ammonia's many uses and reactions - from making fertilizers to batteries to medicines.

📝 Teacher's Note: Create a mind map showing ammonia at the center with all its applications branching out. This helps students visualize the versatility of this compound.

🎯 Exam Tip: Learn the specific uses of ammonium salts - dry cell uses NH₄Cl, explosives use NH₄NO₃, medicine uses (NH₄)₂CO₃. These are commonly tested.

Question 20. When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This pale blue precipitate dissolves in excess ammonium hydroxide giving an inky blue solution. What is the cation [positive ion] present in solution B? what is the probable colour of solution B.
Answer:
\( CuSO_4 + 2NH_4OH \rightarrow (NH_4)_2SO_4 + Cu(OH)_2 \) [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.
\( Cu(OH)_2 + (NH_4)_2SO_4 + 2NH_4OH \rightarrow [Cu(NH_3)_4]SO_4 + 4H_2O \)
In simple words: This is a classic test for copper ions - they make a pale blue solid first, then dissolve to give a beautiful deep blue solution when more ammonia is added.

📝 Teacher's Note: This is an excellent demonstration - the color change from pale blue to deep blue is dramatic and memorable. Explain how copper forms a complex with ammonia molecules.

🎯 Exam Tip: Always mention both the initial pale blue precipitate AND the final deep blue complex. The question asks for both observations.

Question 21. When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved. State three ways in which you could identify this gas.
Answer:
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.
In simple words: Ammonia has a strong smell, makes white smoke with acid, and turns indicator papers different colors because it's a basic gas.

📝 Teacher's Note: Demonstrate the glass rod test - it's visual and impressive. Warn students about the strong smell and ensure good ventilation during practicals.

🎯 Exam Tip: Give three DIFFERENT types of tests - smell, chemical reaction, and indicator tests. Don't repeat similar tests.

Question 22. Complete the following equations. What property of ammonia is illustrated by the reaction in (b)?
(a) \( Mg_3N_2 + 6H_2O \rightarrow \)
(b) \( 2NH_3 + 3CuO \rightarrow \)
(c) \( 8NH_3 + 3Cl_2 \rightarrow \)
(d) \( 4NH_3 + 5O_2 \rightarrow \)
What important process starts with the reaction in (d) above? Name the catalyst used.
Answer:
(a) \( Mg_3N_2 + 6H_2O \rightarrow 3Mg(OH)_2 + 2NH_3 \)
(b) \( 2NH_3 + 3CuO \rightarrow 3Cu + 3H_2O + N_2 \)
Ammonia acts as a reducing agent. It reduces metallic oxide to give metals, water vapour and nitrogen.
(c) \( 8NH_3 + 3Cl_2 \rightarrow N_2 + 6NH_4Cl \)
(d) \( 4NH_3 + 5O_2 \rightarrow 6H_2O + 4NO + Heat \)
Ostwald process starts with the catalytic oxidation of ammonia to manufacture nitric acid in the presence of catalyst platinum.
In simple words: These reactions show ammonia can be made from other compounds, can help extract metals from their oxides, and is the starting material for making nitric acid industrially.

📝 Teacher's Note: Emphasize the industrial importance of the Ostwald process - it's how we make nitric acid for fertilizers and explosives on a large scale.

🎯 Exam Tip: For reaction (b), clearly state that ammonia is acting as a reducing agent. For (d), mention both the process name (Ostwald) AND the catalyst (platinum).

Question 23. A gas 'A' reacts with another gas 'B' in the presence of a catalyst to give a colourless gas 'C'. the gas 'C' when comes in contact with air produces a brown gas 'D'. The solution of 'A' in water turns red litmus blue. Explain the observations.
Answer:
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.
A = \( NH_3 \)
B = \( O_2 \)
C = NO
D = \( NO_2 \)
Reactions:
\( 4NH_3 + 5O_2 \xrightarrow{Pt, 800°C} 4NO + 6H_2O + Heat \)
\( 2NO + O_2 \rightarrow 2NO_2 \)
\( NH_3 \) in water forms \( NH_4OH \) which turns red litmus blue.
In simple words: This is like a detective story - we use clues (turns litmus blue, makes brown gas) to figure out that gas A must be ammonia going through the industrial process to make nitric acid.

📝 Teacher's Note: Present this as a problem-solving exercise. Teach students to work backwards from the clues given to identify unknown substances.

🎯 Exam Tip: Always identify what each letter represents clearly, then write the balanced chemical equations to support your answer.

Question 24. Name the common refrigerant. How does it deplete ozone layer?
Answer:
Hydroxide ion.
The alkaline behavior of aqueous solution of ammonia is due to the hydroxyl ion.
\( NH_3 + H_2O \rightarrow NH_4OH \)
\( NH_4OH \rightleftharpoons NH_4^+ + OH^- \)
An aqueous solution of ammonia turns moist red litmus paper blue.
In simple words: This answer seems to be mismatched with the question - it talks about hydroxide ions rather than refrigerants and ozone depletion.

📝 Teacher's Note: This appears to be an error in the source material - the answer doesn't match the question about refrigerants. Use this as a teaching moment about carefully reading questions.

🎯 Exam Tip: Always ensure your answer directly addresses what the question is asking. If something seems wrong, double-check the question.

Question 25.
(a) What is the alternative of chlorofluoro carbon?
(b) State the advantages of using ammonia as refrigerant?
Answer:
(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.
\( CF_2Cl_2(g) \xrightarrow{ultraviolet} CF_2Cl(g) + Cl(g) \) free radical
The free radical [Cl] reacts with ozone and chlorine monoxide is formed.
\( Cl(g) + O_3(g) \rightarrow ClO(g) + O_2(g) \)
This causes depletion of ozone layer and chlorine monoxide so formed reacts with atomic oxygen and produces more chlorine free radicals.
\( ClO + O \rightarrow Cl + O_2 \)
Again this free radical destroys ozone and the process continues thereby giving rise to ozone depletion.
In simple words: CFCs break down in the upper atmosphere and release chlorine atoms that destroy ozone molecules in a chain reaction, creating a hole in our protective ozone layer.

📝 Teacher's Note: Use diagrams to show the chain reaction mechanism. Explain how one chlorine atom can destroy thousands of ozone molecules, making this such a serious environmental problem.

🎯 Exam Tip: Focus on the chain reaction aspect - show how the chlorine radical is regenerated and continues destroying ozone. Include the UV radiation trigger.

Question 26. Ammonia is a good refrigerant but it shows some disadvantages when used as refrigerant. State the disadvantages.
Answer: Disadvantages of ammonia as a refrigerant are as follows:
(i) It is not compatible with copper, so it cannot be used in any system with copper pipes.
(ii) It is poisonous in high concentration although it is easily detectable due to its peculiar smell and since it is less dense than air it goes up in the atmosphere not affecting the life too much on earth.
In simple words: Ammonia can't be used with copper pipes and is toxic in large amounts, though its strong smell helps detect leaks quickly.

📝 Teacher's Note: Use a simple demonstration showing how ammonia reacts with copper strips to make students understand the incompatibility. Emphasize safety protocols when handling ammonia in lab.

🎯 Exam Tip: Always mention both the copper incompatibility AND the toxicity with detection advantage to score full marks in disadvantage questions.

Question 27. Name a compound prepared by ammonia and is used as:
(a) Explosive, (b) fertilizers
(c) Medicine (d) laboratory reagent
Answer:
(a) Explosive: ammonium nitrate
(b) Medicine: ammonium carbonate
(c) Fertilizers: ammonium sulphate
(d) Laboratory reagent: ammonia solution
In simple words: Ammonia forms different compounds that are used in explosives, medicines, farming, and lab work.

📝 Teacher's Note: Connect this to real-world applications - show fertilizer packets containing ammonium sulphate and explain how ammonium nitrate is used in mining explosives.

🎯 Exam Tip: Learn the specific compound names, not just "ammonia compounds" - examiners want exact chemical names like ammonium nitrate, not general terms.

Question 28. Ammonia is used in the Ostwald process,
(a) Give the sources of reactants used in this process.
(b) Name the catalyst used in the process
(c) Name the oxidizing agent used in this process
(d) What is the ratio of ammonia and air taken in this process?
(e) Why is quartz used in this process?
Answer:
(a) Dry air free from carbon dioxide and dry ammonia from Habers process.
(b) The catalyst used in the process is Platinum.
(c) The oxidizing agent used in the process is oxygen.
(d) Ratio of ammonia and air is 1:10.
(e) Quartz is acid resistant and when packed in layers help in dissolving nitrogen dioxide uniformly in water.
In simple words: The Ostwald process uses ammonia and clean air with platinum catalyst to make nitric acid, using quartz because it doesn't get damaged by acids.

📝 Teacher's Note: Explain that this process is how we make nitric acid industrially - connect it to fertilizer production and show students the importance of the 1:10 ratio for efficiency.

🎯 Exam Tip: Remember the exact ratio 1:10 (ammonia:air) and that platinum is the catalyst - these are frequently tested specific details.

Question 29. Write the equation for the action of heat on:
(a) Ammonium chloride (b) Ammonium nitrate
State whether each reaction is an example of thermal decomposition or thermal dissociation.
Answer:
(a) Ammonium chloride
\( NH_4Cl \rightleftharpoons NH_3 + HCl \)
(b) Ammonium nitrate
\( NH_4NO_3 \rightleftharpoons N_2O + 2H_2O \)
Both are examples of Thermal dissociation.
In simple words: When heated, both compounds break apart into simpler substances, and this process is called thermal dissociation because the reaction can be reversed when cooled.

📝 Teacher's Note: Demonstrate the reversible nature by showing how the products recombine when cooled. Use the double arrow to emphasize reversibility.

🎯 Exam Tip: Use double arrows (\( \rightleftharpoons \)) for dissociation reactions and remember that dissociation is reversible while decomposition is not.

Question 1(2003). (a) Write the equation for the formation of ammonia by the action of water on magnesium nitride
(b) How is ammonia collected?
(c) why is ammonia not collected over water?
(d) Which compound is normally used as a drying agent for ammonia?
Answer:
(a) \( Mg_3N_2 + 6H_2O \rightarrow 3Mg(OH)_2 + 2NH_3 \)
(b) Ammonia gas is collected in inverted gas jars by the downward displacement of air.
(c) Ammonia is not collected over water because it is highly soluble in water.
(d) Quicklime is used as a drying agent for ammonia.
In simple words: Magnesium nitride reacts with water to produce ammonia, which is collected using upside-down jars because it's lighter than air and dissolves easily in water.

📝 Teacher's Note: Show students how ammonia's low density (lighter than air) determines the collection method. Demonstrate ammonia's solubility by bubbling it through water.

🎯 Exam Tip: Remember that ammonia is collected by downward displacement of air (not water) due to its high solubility and low density.

Question 1(2004). (a) Write the equation for the reaction in Haber process that forms ammonia.
(b) state the purpose of liquefying the ammonia produced in the process.
Answer:
(a) Equation:
\( 2NH_3 \rightleftharpoons N_2 + 3H_2 \) (450-500°C, 200atm)
(b) Compared to nitrogen and hydrogen, ammonia is easily liquefiable and to increase the forward reaction.
In simple words: The Haber process combines nitrogen and hydrogen to make ammonia under high pressure and temperature, and liquefying the ammonia helps produce more of it.

📝 Teacher's Note: Explain Le Chatelier's principle - removing ammonia by liquefying it shifts the equilibrium forward to produce more ammonia.

🎯 Exam Tip: Include the conditions (450-500°C, 200atm) in the equation and mention that liquefying removes ammonia from the equilibrium mixture.

Question 1(2005). (a) which feature of ammonia molecule leads to the formation of the ammonium ion when ammonia dissolves in water?
(b) Name the other ion formed when ammonia dissolves in water.
(c) Give one test that can be used to detect the presence of the ion produced in (b)
Answer:
(a)It is the basic nature of ammonia molecule.
(b)Hydroxyl ion (\( NH_3 + H_2O \rightarrow NH_4^+ + OH^- \))
(c) The red litmus paper turns blue in the solution.
In simple words: Ammonia acts like a base when it dissolves in water, forming ammonium and hydroxyl ions, which makes the solution basic and turns red litmus blue.

📝 Teacher's Note: Emphasize that ammonia accepts protons (H+) from water molecules due to the lone pair on nitrogen, making it a Brønsted-Lowry base.

🎯 Exam Tip: Always write the complete equation showing ion formation and mention the litmus test specifically - "red litmus turns blue."

Question 2(2005). Write the equations for the following reactions which result in the formation of ammonia.
(a) A mixture of ammonium choride and slaked lime is heated.
(b) Aluminium nitride and water.
Answer:
Equations are:
(a) \( 2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3 \)
(b) \( AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3 \)
In simple words: Both reactions produce ammonia gas - one by heating ammonium chloride with lime, and the other when aluminum nitride reacts with water.

📝 Teacher's Note: These are classic lab preparations of ammonia. Demonstrate the first reaction in a test tube and show students how the gas can be detected by its smell.

🎯 Exam Tip: Balance the equations carefully - note that the first equation needs coefficient 2 for NH4Cl and the products.

Question 1(2006) State what is observed when: Excess of ammonia is passed through an aqueous solution of lead nitrate.
Answer:
\( Pb(NO_3)_2 + NH_4OH \rightarrow 2NH_4NO_3 + Pb(OH)_2 \)
The chalky white ppt. of lead hydroxide is formed.
In simple words: A white chalky precipitate appears when ammonia solution reacts with lead nitrate, forming lead hydroxide.

📝 Teacher's Note: This is a classic precipitation reaction. Show students how the white precipitate settles and explain that ammonia acts as a base to precipitate metal hydroxides.

🎯 Exam Tip: Describe the observation first ("chalky white precipitate"), then write the equation - this shows you understand what happens visually.

Question 1(2007). (a) Of the two gases, ammonia and hydrogen chloride which is more dense? Name the method of collection of this gas.
(b) Give one example of a reaction between the above two gases which produces a solid compound.
Answer:
(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) \( NH_3 + HCl \rightarrow NH_4Cl \)
In simple words: Hydrogen chloride is heavier than ammonia, so it's collected differently, and when these two gases meet, they form solid ammonium chloride.

📝 Teacher's Note: Compare the vapor densities to help students understand why collection methods differ. Demonstrate the white fumes formation when NH3 and HCl meet.

🎯 Exam Tip: Remember the vapor densities (HCl = 18.25, NH3 = 8.5) and that denser gases are collected by upward displacement.

Question 2(2007). Write a balanced equation for a reaction in which ammonia is oxidized by:
(a) a metal oxide
(b) a gas which is not oxygen
Answer:
Balanced equation:
(a) \( 2NH_3 + 3CuO \rightarrow 3Cu + 3H_2O + N_2 \)
(b) \( 2NH_3 + 3Cl_2 \rightarrow N_2 + 6HCl \)
In simple words: Ammonia can be oxidized by copper oxide (producing copper metal) or by chlorine gas (producing hydrogen chloride).

📝 Teacher's Note: These show ammonia acting as a reducing agent. In both cases, nitrogen goes from -3 oxidation state to 0, demonstrating oxidation.

🎯 Exam Tip: Check that equations are balanced - count atoms on both sides and ensure coefficients are in lowest terms.

Question 1(2008). Write equation for the following: Aluminum nitride and water.
Answer:
Equation:
\( AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3 \)
In simple words: When aluminum nitride reacts with water, it produces aluminum hydroxide and ammonia gas.

📝 Teacher's Note: This is a hydrolysis reaction where the nitride ion reacts with water to form ammonia. Point out the pattern in nitride hydrolysis reactions.

🎯 Exam Tip: Remember the 1:3 ratio of AlN to H2O and that the products are always the metal hydroxide plus NH3.

Question 2(2008). Choose the correct from the following: Ammonia can be obtained by adding water to
A : Ammonium chloride
B : Ammonium nitrite,
C : Magnesium nitride
D : Magnesium nitrate
Answer: (C) Magnesium nitride
In simple words: Only magnesium nitride produces ammonia when water is added - the other compounds don't release ammonia gas with just water.

📝 Teacher's Note: Emphasize that nitrides (not nitrates or ammonium salts) react with water to produce ammonia directly. Show the difference between nitride and nitrate.

🎯 Exam Tip: Don't confuse nitride with nitrate - only nitrides like Mg3N2 release NH3 when water is added.

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Question 1. State the type of bonding present in ammonia, show by a diagram.
Answer: Covalent bonding is present in ammonia.
In simple words: Ammonia molecules are held together by covalent bonds where nitrogen and hydrogen atoms share electrons.

📝 Teacher's Note: Draw the Lewis structure showing the lone pair on nitrogen and the three N-H bonds. This lone pair is crucial for ammonia's basic properties.

🎯 Exam Tip: Always mention "covalent bonding" specifically and draw the structure showing shared electron pairs if asked for a diagram.

Question 2. Name the different forms of ammonia.
Answer: The different forms of ammonia:
Gaseous ammonia(dry ammonia gas)
Liquid ammonia
Liquor ammonia fortis
Laboratory bench reagent
In simple words: Ammonia exists in different forms - as a gas, as a liquid, as a strong solution, and as a common lab chemical.

📝 Teacher's Note: Show students actual ammonia solution bottles and explain that "liquor ammonia fortis" means strong ammonia solution. Emphasize safety when handling.

🎯 Exam Tip: List all four forms clearly - examiners often ask for complete lists and partial answers lose marks.

Question 3. What is the formula of liquid ammonia? Account for the basic nature of this compound.
Answer: Formula of liquid ammonia is: \( NH_3 \).
Liquid ammonia is liquefied ammonia and is basic in nature. It dissolves in water to give ammonium hydroxide which ionizes to give hydroxyl ions.
\( NH_3 + H_2O \rightarrow NH_4OH \)
\( NH_4OH \rightleftharpoons NH_4^+ + OH^- \)
Therefore it turns red litmus blue and phenolphthalein solution pink.
In simple words: Liquid ammonia has the same formula as gas ammonia but is compressed into liquid form, and it's basic because it produces hydroxide ions when dissolved in water.

📝 Teacher's Note: Clarify that liquid ammonia is just the physical state - the chemical formula remains NH3. Demonstrate with litmus paper and phenolphthalein.

🎯 Exam Tip: Write both equations showing the formation of NH4OH and its ionization, plus mention both indicator tests (litmus and phenolphthalein).

Question 4. Ammonia gas can be prepared by warming an ammonium salt with caustic alkali. Give two equations.
Answer:
\( 2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3 \)
\( 2NH_4SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O + 2NH_3 \)
In simple words: Heating ammonium salts with strong bases like calcium hydroxide or sodium hydroxide releases ammonia gas.

📝 Teacher's Note: This is the standard lab preparation method. Show students how the reaction works by using ammonium chloride and calcium hydroxide in a test tube.

🎯 Exam Tip: Balance equations carefully and use common ammonium salts like NH4Cl or (NH4)2SO4 with strong bases like Ca(OH)2 or NaOH.

Question 5.
(a) Write a balanced chemical equation for the lab preparation of ammonia.
(b) How is ammonia dried and collected in the laboratory?
(c) Ammonia cannot be collected over water. Give reason.
Answer:
(a) Lab preparation of ammonia:
\( 2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3 \)
(b) The ammonia gas is dried by passing through a drying tower containing lumps of quicklime (CaO).
(c) Ammonia is highly soluble in water and therefore it cannot be collected over water.
In simple words: When we make ammonia in the lab, we use ammonium chloride with calcium hydroxide. We dry it using quicklime, and we cannot collect it over water because ammonia dissolves completely in water like sugar dissolves in tea.

📝 Teacher's Note: Demonstrate the high solubility of ammonia by showing how a few drops create an alkaline solution instantly. Emphasize why CaO is chosen over other drying agents due to ammonia's basic nature.

🎯 Exam Tip: Always write the balanced equation with proper chemical formulas and state symbols. Mention "highly soluble in water" as the key reason for not collecting over water.

Question 6. Name a drying agent for ammonia. Why are other drying agents such as \( P_2O_5 \) and \( CaCl_2 \) are not used?
Answer: The drying agent used is CaO in case of ammonia. Other drying agents like \( P_2O_5 \) and \( CaCl_2 \) are not used. As ammonia being basic reacts with them.
\( 6NH_3 + P_2O_5 + 3H_2O \rightarrow 2(NH_4)_3PO_4 \)
\( CaCl_2 + 4NH_3 \rightarrow CaCl_2.4NH_3 \)
In simple words: We use quicklime (CaO) to dry ammonia because other drying agents like phosphorus pentoxide and calcium chloride actually react with ammonia instead of just removing water, which defeats the purpose.

📝 Teacher's Note: Show students that the choice of drying agent depends on chemical compatibility. Use this as an example of how chemical properties determine practical applications.

🎯 Exam Tip: Write the chemical equations showing why P₂O₅ and CaCl₂ cannot be used - this demonstrates understanding rather than just memorization.

Question 7. A substance 'A' was heated with slaked lime and a gas 'B' with a pungent smell was obtained. Name the substances A and B and give a balanced equation.
Answer: The substance A is Ammonium chloride and 'B' is Ammonia.
Reaction:
\( 2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2H_2O + 2NH_3 \)
In simple words: When you heat ammonium chloride with slaked lime, you get ammonia gas which has a very strong, sharp smell that makes your nose sting - that's the pungent smell mentioned.

📝 Teacher's Note: This is a classic identification question. Emphasize the characteristic pungent smell of ammonia and connect it to the lab preparation method students should know.

🎯 Exam Tip: The key clue is "pungent smell" which immediately points to ammonia. Always write both the names and the balanced equation for full marks.

Question 8. Ammonia is manufactured by Haber process.
(a) Under what condition do the reactants combine to form ammonia? Give a balanced equation for the reaction.
(b) In what ration by volume, are the above gases used?
(c) state one possible source of each reactant used in haber process.
(d) state whether the formation of ammonia is promoted by the use of high pressure or low pressure?
(e) Mention two possible ways by which ammonia produced is removed from unchanged gases
(f) What is the function of:
(i) finely divided iron
(ii) molybdenum in the above process?
Answer:
(a) Conditions for reactants to combine:
Optimum temperature is 450°-500°C
Above 200 atm pressure
Finely divided iron as catalyst
Traces of molybdenum or \( Al_2O_3 \) as promoters.
Reaction: \( N_2 + 3H_2 \rightleftharpoons 2NH_3 + heat \)
(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.
\( (CO + H_2) + H_2O \xrightarrow{Fe/Fe_2O_3, 500°C} CO_2 + 2H_2 \)
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 \( NH_3 \) produced is removed from unreacted \( N_2 \) and \( H_2 \) by:
(i) Liquefaction: \( NH_3 \) is easily liquefiable.
(ii) Absorbing in water: As ammonia is highly soluble in water.
(f)
(i) Finely divided iron increases the rate of reaction.
(ii) Molybdenum acts as a promoter to increase the efficiency of the catalyst.
In simple words: The Haber process is like cooking ammonia under very high pressure and temperature, using iron as a helper (catalyst) to speed up the reaction. We mix nitrogen and hydrogen in a 1:3 ratio, and then separate the ammonia by cooling it down or dissolving it in water.

📝 Teacher's Note: Use Le Chatelier's principle to explain why high pressure favors ammonia formation (fewer molecules on product side). Connect this industrial process to everyday fertilizer production.

🎯 Exam Tip: Remember the specific conditions: 450-500°C, 200+ atm pressure, Fe catalyst, 1:3 ratio. The reversible arrow in the equation is crucial for showing this is an equilibrium process.

Question 9. Given reasons:
(a) Ammonium compounds do not occur as minerals
(b) Ammonium nitrate is not used in the preparation of ammonia
(c) Conc \( H_2SO_4 \) is a good drying agent, yet it is not used to dry \( NH_3 \).
Answer:
(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. \( H_2SO_4 \) is not used to dry ammonia, as ammonia being basic reacts with them.
\( 2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4 \)
In simple words: Ammonium compounds dissolve completely in rainwater so they wash away from rocks. Ammonium nitrate is too dangerous to use because it can explode. Sulfuric acid reacts with ammonia instead of just drying it, like trying to use soap to dry your hands.

📝 Teacher's Note: Connect part (a) to why we don't find ammonium salts in nature despite their importance in chemistry. Emphasize safety concerns with ammonium nitrate in part (b).

🎯 Exam Tip: For each part, give both the reason and any relevant chemical equation. The key is understanding chemical compatibility and safety considerations.

Question 10. Explain with a diagram the preparation of aqueous ammonia.
Answer: Preparation of Aqueous Ammonia: An aqueous solution of ammonia is prepared by dissolving ammonia in water. The rate of dissolution of ammonia in water is very high; therefore, back suction of water is possible. To avoid this, a funnel is attached to the outer end of the delivery tube with rubber tubing.
Procedure: Water is taken in a container and only a small portion of the mouth of funnel is dipped in water.
As ammonia dissolves in water at a higher rate than its production in the flask, the pressure in the funnel above water level decreases for a moment and water rushes into the funnel. As a result, the rim of the funnel loses its contact with water. Since, ammonia produced pushes the water down, the funnel comes in contact with water again. In this way, ammonia dissolves in water without back suction of water.
In simple words: When making ammonia water, we use a special funnel setup because ammonia dissolves so fast in water that it creates a vacuum effect. The funnel prevents water from being sucked back into the gas-making apparatus, which would spoil the experiment.

📝 Teacher's Note: Demonstrate or draw how the funnel setup prevents back suction. This is a classic example of practical problem-solving in chemistry lab techniques.

🎯 Exam Tip: Draw a clear, labeled diagram showing the funnel arrangement. Explain both why back suction occurs (high solubility) and how the funnel prevents it (breaks contact with water).