Selina Concise Solutions for ICSE Class 10 Chemistry Chapter 10 Study of Compounds Nitric Acid

Exercise 1

Question 1. What is: (a) aqua fortis, (b) aqua regia (c) Fixation of Nitrogen?
Answer: (a) Aqua fortis: Nitric acid is called aqua fortis. Aqua fortis means strong water. It is so called because it reacts with nearly all metals.
(b) Aqua Regia: Conc. Nitric acid (1part by volume) when mixed with conc. Hydrochloric acid (3 parts by volume) gives a mixture called aqua regia. It means Royal water.
\( HNO_3 + 3HCl \rightarrow NOCl + 2H_2O + 2[Cl] \)
(c) Fixation of Nitrogen: The conversion of free atmospheric nitrogen into useful nitrogenous compounds in the soil is known as fixation of atmospheric nitrogen.
In simple words: Aqua fortis is just another name for nitric acid (strong water), aqua regia is a special mixture that can dissolve gold, and nitrogen fixation is how nature turns air into useful plant food in soil.

📝 Teacher's Note: Use the Latin names to help students remember - "fortis" means strong and "regia" means royal. Demonstrate how aqua regia dissolves metals that individual acids cannot dissolve alone.

🎯 Exam Tip: Always mention the volume ratio (1:3) for aqua regia and include the chemical equation. For nitrogen fixation, emphasize the conversion from "free" to "useful compounds."

Question 2. During thunderstorm, rain water contains nitric acid. Explain with reactions.
Answer: During lightning discharge, the nitrogen present in the atmosphere reacts with oxygen to form nitric oxide.
\( N_2 + O_2 \rightarrow 2NO \)
Nitric oxide is further oxidized to nitrogen dioxide.
\( 2NO + O_2 \rightarrow 2NO_2 \)
The nitrogen dioxide dissolves in atmospheric moisture in the presence of oxygen of the air and forms nitric acid which is washed down by the rain and combines with the salt present on the surface of the earth.
\( 4NO_2 + 2H_2O + O_2 \rightarrow 4HNO_3 \)
In simple words: Lightning has so much energy that it forces nitrogen and oxygen in the air to combine, creating acid that dissolves in rainwater - this is nature's way of making fertilizer for plants.

📝 Teacher's Note: Connect this to the nitrogen cycle and explain how lightning acts as a natural fertilizer factory. Students often forget the three-step process, so emphasize each reaction separately.

🎯 Exam Tip: Write all three balanced equations in sequence and mention that this process provides natural nitrogen compounds for soil fertility.

Question 3. (a) Write a balanced chemical equation for the laboratory preparation of nitric acid (b) In the preparation of nitric acid from KNO₃ concentrated hydrochloric acid is not used in place of concentrated sulphuric acid. Explain why? (c) Conc. Nitric acid prepared in laboratory is yellow in colour why? How is this colour removed? (d) Give reasons for the following: In the laboratory preparation of nitric acid, the mixture of concentrated sulphuric acid and sodium nitrate should not be heated very strongly above 200°C.
Answer: (a) Chemical equation is:
\( KNO_3 + H_2SO_4 \xrightarrow{< 200°C} KHSO_4 + HNO_3 \)
(b) Concentrated hydrochloric acid cannot replace Conc. Sulphuric acid for the preparation of nitric acid because hydrochloric acid is volatile acid and hence nitric acid vapours will carry HCl vapours.
(c) Conc. Nitric acid prepared in the laboratory is yellow in colour due to the dissolution of reddish brown coloured nitrogen dioxide gas in acid. This gas is produced due to the thermal dissociation of a portion of nitric acid.
\( 4HNO_3 \rightarrow 2H_2O + 4NO_2 + O_2 \)
The yellow colour of the acid is removed:
If dry air or \( CO_2 \) is bubbled through the yellow acid, the acid turns colourless because it drives out \( NO_2 \) from warm acid which is further oxidized to nitric acid.
By addition of excess of water, nitrogen dioxide gas dissolves in water and thus the yellow colour of the acid is removed.
(d) The temperature of the mixture of concentrated sulphuric acid and sodium nitrate should not exceed 200°C because sodium sulphate formed at higher temperature forms a hard crust which sticks to the walls of the retort and is difficult to remove. At higher temperature nitric acid may also decompose.
\( NaNO_3 + NaHSO_4 \xrightarrow{> 200°C} Na_2SO_4 + HNO_3 \)
In simple words: We use sulphuric acid because it's not volatile like HCl, the yellow color comes from nitrogen dioxide gas mixing in, and too much heat creates a hard crust that damages equipment.

📝 Teacher's Note: Demonstrate the volatility difference by showing how HCl fumes escape while H₂SO₄ doesn't. Use analogy of "unwanted guests" for HCl vapours contaminating the product.

🎯 Exam Tip: Always mention "volatile" for HCl, write the decomposition equation for the yellow color, and explain both temperature effects - crust formation and acid decomposition.

Question 4. Nitric acid cannot be concentrated beyond 68% by the distillation of a dilute solution of HNO₃. State the reason.
Answer: Nitric acid forms a constant boiling mixture with water containing 68% acid. This mixture boils constantly at constant boiling point without any change in its composition. At this temperature, the gas and the water vapour escape together. Hence the composition of the solution remains unchanged. So nitric acid cannot be concentrated beyond 68% by distillation of dilute solution of \( HNO_3 \).
In simple words: At 68% concentration, nitric acid and water become like best friends who always want to stay together - they boil at the same temperature and escape together, so you can't separate them further.

📝 Teacher's Note: Explain azeotropic mixtures using the analogy of dancing partners who move in perfect sync. This concept appears in many acid preparations.

🎯 Exam Tip: Use the exact term "constant boiling mixture" or "azeotrope" and mention both the 68% composition and that vapors escape together.

Question 5. What is passive iron? How is passivity removed?
Answer: Iron becomes inert when reacted with nitric acid due to the formation of extremely thin layer of insoluble metallic oxide which stops the reaction. Passivity can be removed by rubbing the surface layer with the sand paper or by treating with strong reducing agent.
In simple words: Nitric acid creates a protective invisible shield on iron that prevents further reaction - like putting a raincoat on iron to protect it from getting damaged.

📝 Teacher's Note: Demonstrate with iron nail in nitric acid showing initial reaction then stopping. Connect this to stainless steel and aluminum's natural passivation in air.

🎯 Exam Tip: Mention "thin oxide layer," "inert/inactive," and give both methods of removal - mechanical (sandpaper) and chemical (reducing agents).

Question 6. Name the products formed when: (a) carbon and conc. Nitric acid is heated (b) dilute HNO₃ is added to copper.
Answer: (a) When carbon and conc. Nitric acid is heated the products formed are Carbon dioxide, Nitrogen dioxide and water.
\( C + 4HNO_3 \rightarrow CO_2 + 2H_2O + 4NO_2 \)
(b) Copper when reacts with dilute \( HNO_3 \) forms Copper nitrate, Nitric oxide and water.
\( 3Cu + 8HNO_3 \rightarrow 3Cu(NO_3)_2 + 4H_2O + 2NO \)
In simple words: Nitric acid is so powerful that it can burn carbon to make carbon dioxide and turns copper into blue copper nitrate solution while releasing different nitrogen gases.

📝 Teacher's Note: Point out the difference in nitrogen oxides produced - NO₂ (brown) with concentrated acid vs NO (colorless) with dilute acid. This pattern repeats with many metals.

🎯 Exam Tip: Remember the gas products change with concentration - NO₂ for concentrated HNO₃ and NO for dilute HNO₃. Always balance equations completely.

Question 7. Give two chemical equations for each of the following: (a) Reactions of nitric acid with non-metals (b) Nitric acid showing as acidic character (c) Nitric acid acting as oxidizing agent
Answer: (a) Reaction of nitric acid with non-metals:
\( C + 4HNO_3 \rightarrow CO_2 + 2H_2O + 4NO_2 \)
\( S + 6HNO_3 \rightarrow H_2SO_4 + 2H_2O + 6NO_2 \)
(b) Nitric acid showing acidic character:
\( K_2O + 2HNO_3 \rightarrow 2KNO_3 + H_2O \)
\( ZnO + 2HNO_3 \rightarrow Zn(NO_3)_2 + H_2O \)
(c) Nitric acid acting as oxidizing agent
\( P_4 + 20HNO_3 \rightarrow 4H_3PO_4 + 4H_2O + 20NO_2 \)
\( 3Zn + 8HNO_3 \rightarrow 3Zn(NO_3)_2 + 4H_2O + 2NO \)
In simple words: Nitric acid can burn non-metals to their highest oxides, neutralize bases like any normal acid, and steal electrons from elements to oxidize them.

📝 Teacher's Note: Emphasize that nitric acid rarely produces hydrogen gas due to its strong oxidizing nature. Show how oxidation state of nitrogen changes from +5 to +4 or +2.

🎯 Exam Tip: For oxidizing reactions, always show the nitrogen oxide product (NO₂ or NO). For acidic character, use oxide + acid → salt + water pattern.

Question 8. Write balanced equations and name the products formed when: (a) Sodium hydrogen carbonate is added to nitric acid (b) cupric oxide reacts with nitric acid (c) zinc reacts with dilute nitric acid (d) concentrated nitric acid is heated
Answer: (a) When Sodium hydrogen carbonate is added to nitric acid sodium nitrate, carbon dioxide and water is formed.
\( NaHCO_3 + HNO_3 \rightarrow NaNO_3 + H_2O + CO_2 \)
(b) When Cupric oxide reacts with dilute nitric acid, it forms Copper nitrate.
\( CuO + 2HNO_3 \rightarrow Cu(NO_3)_2 + H_2O \)
(c) Zinc reacts with nitric acid to form Zinc nitrate, nitric oxide and water.
\( 3Zn + 8HNO_3 \rightarrow 3Zn(NO_3)_2 + 4H_2O + 2NO \)
(d) \( 4HNO_3 \rightarrow 2H_2O + 4NO_2 + O_2 \)
In simple words: Nitric acid reacts with carbonates to produce fizzing gas, dissolves metal oxides to make colorful solutions, and when heated, breaks down to release brown toxic gas.

📝 Teacher's Note: Demonstrate the effervescence with bicarbonate and explain why metals don't produce hydrogen with HNO₃. Show the brown gas evolution when heating concentrated HNO₃.

🎯 Exam Tip: Remember bicarbonate reactions always produce CO₂, metal reactions with dilute HNO₃ give NO gas, and thermal decomposition gives NO₂ + O₂.

Question 9. Write equation for the following conversions A, B, C and D.
Answer: A: Copper can be converted into copper nitrate.
\( 3Cu + 8HNO_3 \rightarrow 3Cu(NO_3)_2 + 4H_2O + 2NO \)
B: \( 2Cu(NO_3)_2 \xrightarrow{\Delta} 2CuO + 4NO_2 + O_2 \)
C: \( 2Cu + O_2 \xrightarrow{\Delta} 2CuO \)
D: By reduction
\( 2CuO + C \rightarrow 2Cu + CO_2 \)
In simple words: This shows a complete cycle - copper dissolves in acid, the salt decomposes to oxide, copper burns to oxide, and oxide reduces back to metal.

📝 Teacher's Note: Use this cycle to show reversible chemical processes and how metals can be extracted and purified. Connect to metallurgy principles.

🎯 Exam Tip: Label each step clearly (A, B, C, D) and show the conditions like heat (Δ) where required. This type of cycle question is common in exams.

Question 10. How will you prepare the following from nitric acid? (a) Sodium nitrate (b) copper nitrate (c) Lead nitrate (d) Magnesium nitrate (e) Ferric nitrate (f) Aqua regia
Answer: (a) Sodium nitrate:
\( NaOH + HNO_3 \rightarrow NaNO_3 + H_2O \)
Sodium hydroxide reacts with nitric acid to form sodium nitrate.
(b) Copper nitrate:
\( CuO + 2HNO_3 \rightarrow Cu(NO_3)_2 + H_2O \)
Copper oxide reacts with nitric acid to form copper nitrate.
(c) Lead nitrate:
\( Pb + 4HNO_3 \rightarrow Pb(NO_3)_2 + 2H_2O + 2NO_2 \)
Lead reacts with conc. nitric acid to form lead nitrate.
(d) Magnesium nitrate:
\( Mg + 2HNO_3 \rightarrow Mg(NO_3)_2 + H_2 \)
Magnesium with dil. nitric acid to form magnesium nitrate.
(e) Ferric nitrate:
\( Fe + 6HNO_3 \rightarrow Fe(NO_3)_3 + 3H_2O + 3NO_2 \)
Iron reacts with conc. nitric acid to form ferric nitrate.
(f) Aqua regia:
\( HNO_3 + 3HCl \rightarrow NOCl + 2H_2O + 2[Cl] \)
Nitric acid reacts with hydrochloric acid to form a mixture called aqua regia.
In simple words: You can make different nitrate salts by reacting nitric acid with metals, metal oxides, or bases - each gives you the metal nitrate plus water and sometimes gas.

📝 Teacher's Note: Point out the different methods - base neutralization for alkali nitrates, oxide dissolution for most metals, and direct metal reaction for reactive metals. Note the exception with Mg producing H₂.

🎯 Exam Tip: Choose the easiest method for each nitrate - use hydroxides for Group 1 metals, oxides for most others, and direct metal reaction when specified. Remember aqua regia ratio 1:3.

Question 11. Correct the following, if required: (a) HNO₃ is strong reducing agent. (b) NaNO₃ gives Na₂ and O₂ on heating. (c) Constant boiling nitric acid contains 80% nitric acid by weight. (d) Nitric acid remains colourless even when exposed to light.
Answer: (a) \( HNO_3 \) is strong oxidizing agent.
(b) \( NaNO_3 \) gives \( NaNO_2 \) and oxygen on heating.
(c) Constant boiling nitric acid contains 68% nitric acid by weight.
(d) Nitric acid turns yellow solution when exposed to light.
In simple words: Nitric acid takes electrons (oxidizes), sodium nitrate loses some oxygen when heated, the constant boiling mixture is 68% not 80%, and light makes nitric acid turn yellow.

📝 Teacher's Note: Use common student mistakes to reinforce correct concepts. Emphasize that HNO₃ is always an oxidizing agent due to nitrogen in +5 oxidation state.

🎯 Exam Tip: Remember key numbers - 68% for azeotrope composition, and that HNO₃ decomposes in light to form brown NO₂ which dissolves back making yellow solution.

Question 12. Name: (a) a nitrate of metal which on heating does not give nitrogen dioxide (b) a nitrate which on heating leaves no residue behind. (c) a metal nitrate which on heating is changed into metal oxide (d) a metal nitrate which on heating is changed into metal (e) a solution which absorbs nitric oxide (f) the oxide of nitrogen which turns brown on exposure to air. How is it prepared?
Answer: (a) Sodium nitrate
\( 2NaNO_3 \rightarrow 2NaNO_2 + O_2 \)
(b) A nitrate which on heating leaves no residue behind- Ammonium nitrate.
(c) A metal nitrate which on heating is changed into metal oxide- Calcium nitrate
(d) A metal nitrate which on heating is changed into metal- Silver nitrate
(e) A solution which absorbs nitric oxide- Freshly prepared ferrous sulphate
(f) The oxide of nitrogen which turns brown on exposure to air. - nitric oxide
By catalytic oxidation of ammonia.
\( 4NH_3 + 5O_2 \xrightarrow{Pt, 800°C} 4NO + 6H_2O + Heat \)
In simple words: Different nitrates behave differently when heated - some just lose oxygen, others break down completely, and some even give back the original metal.

📝 Teacher's Note: Relate thermal stability to the reactivity series - more reactive metals form more stable nitrates. Show how NO (colorless) + air → NO₂ (brown).

🎯 Exam Tip: Learn these specific examples as they're commonly asked. Remember that NO turns brown in air because it forms NO₂, and ferrous sulfate forms a brown ring test with NO.

Question 13. Give the chemical name and formula of the substance formed as a brown ring in the test for nitrate radical.
Answer: The chemical name of the brown ring is Nitroso ferrous sulphate. Formula: \( \text{FeSO}_4 \cdot \text{NO} \)

📝 Teacher's Note: Help students remember this by explaining that the brown ring is actually a complex compound where NO attaches to iron. Show the test practically if possible to make it memorable.

🎯 Exam Tip: Always write both the chemical name and formula clearly. The formula should show the dot notation to indicate it's a complex compound.

Question 14. Mention three important uses of nitric acid. Give the property of nitric acid involved in the use.
Answer: Three important uses of Nitric acid and the property of nitric acid involved is:

📝 Teacher's Note: Connect each use to the oxidizing property of nitric acid. Demonstrate how etching works by showing before and after pictures of copper plates.

🎯 Exam Tip: Present your answer in tabular format as shown - it's clearer and shows good organization to the examiner.

Question 15. Choose the correct answer:
(a) The nitrate salt which does not give a mixture of \( \text{NO}_2 \) and \( \text{O}_2 \) on heating is:
(i) \( \text{AgNO}_3 \)
(ii) \( \text{KNO}_3 \)
(iii) \( \text{Cu(NO}_3\text{)}_2 \)
(iv) \( \text{Zn(NO}_3\text{)}_2 \)
(b) The chemical used in the brown ring test is:
(i) \( \text{CuSO}_4 \)
(ii) \( \text{FeSO}_4 \)
(iii) \( \text{Fe}_2\text{(SO}_4\text{)}_3 \)
(iv) \( \text{N}_2\text{O}_5 \)
Answer: (a) (ii) KNO₃ (b) (ii) FeSO₄
In simple words: Potassium nitrate only gives oxygen when heated, while other nitrates give nitrogen dioxide too. Iron(II) sulphate is specifically needed for the brown ring test because iron(III) won't work.

📝 Teacher's Note: Explain that alkali metal nitrates (like KNO₃) behave differently from other metal nitrates due to their high thermal stability. This is a key concept in salt decomposition.

🎯 Exam Tip: Remember the pattern - alkali metal nitrates give only oxygen, while heavy metal nitrates give both NO₂ and O₂ when heated.

Question 16. (a) Explain with the help of a balanced equation, the brown ring test for nitric acid. (b) Why is freshly prepared ferrous sulphate solution used for testing the nitrate radical in the brown ring test?
Answer:
(a) Brown ring test
Procedure:
(i) Add freshly prepared saturated solution of iron (II)sulphate to the aqueous solution of nitric acid.
(ii) Now add concentrated sulphuric acid carefully from the sides of the test tube, so that it should not fall drop wise in the test tube.
(iii) Cool the test tube in water.
(iv) A brown ring appears at the junction of the two liquids.
\( 6\text{FeSO}_4 + 2\text{HNO}_3 + 3\text{H}_2\text{SO}_4 \rightarrow 3\text{Fe}_2\text{(SO}_4\text{)}_3 + 2\text{NO} + 4\text{H}_2\text{O} \)
(b) A freshly prepared ferrous sulphate solution is used because on exposure to the atmosphere, it is oxidized to ferric sulphate which will not give the brown ring.

📝 Teacher's Note: Emphasize the careful addition of concentrated H₂SO₄ - it must flow down the sides to create layers. Practice the technique with water and colored solutions first.

🎯 Exam Tip: For the balanced equation, make sure coefficients are correct. For part (b), clearly state that Fe²⁺ oxidizes to Fe³⁺ in air, which is why fresh solution is needed.

Question 17. From the following list of substances, choose one substance in each case which matches the description given below: Ammonium nitrate, calcium hydrogen carbonate, copper carbonate, lead nitrate, potassium nitrate, sodium carbonate, sodium hydrogen carbonate, zinc carbonate. (a) A nitrate which gives off only oxygen when heated (b) A nitrate which on heating decomposes into dinitrogen oxide [nitrous oxide] and steam. (c) A nitrate which gives off oxygen and nitrogen dioxide when heated.
Answer:
(a) Potassium nitrate
(b) Ammonium nitrate
(c) Lead nitrate

📝 Teacher's Note: Create a simple chart showing different types of nitrate decomposition patterns - alkali metal nitrates vs heavy metal nitrates vs ammonium nitrate. Each has a distinct pattern.

🎯 Exam Tip: Remember the three patterns: KNO₃ → only O₂; NH₄NO₃ → N₂O + H₂O; heavy metal nitrates → NO₂ + O₂.

Question 18. Fill in the blanks: (a) Aqua regia is a mixture of 3 parts ________ and one part ________. (b) The catalytic oxidation of ammonia to nitric oxide is ________ (exothermic / endothermic) process. (c) Magnesium gives ________ (O₂, H₂, NO) with very dilute nitric acid. (d) ________ (iron / copper) become passive in concentrated nitric acid
Answer:
(a) Aqua regia is a mixture of 3 parts Hydrochloric acid and one part Nitric acid.
(b) The catalytic oxidation of ammonia to nitric oxide is exothermic.
(c) Magnesium gives H₂ with very dilute nitric acid.
(d) Iron become passive in concentrated nitric acid

📝 Teacher's Note: For aqua regia, explain that the 3:1 ratio is critical for its ability to dissolve gold and platinum. For passivation, show how a protective oxide layer forms.

🎯 Exam Tip: Remember aqua regia ratio as "3 parts HCl : 1 part HNO₃". For passivation, only iron and aluminum become passive, not copper.

Question 19. The action of heat on the blue crystalline solid A, gives a reddish brown gas B, a gas which relight a glowing splint and leaves a black residue. When gas C, which has a rotten egg smell, is passed through a solution of A, a black precipitate is formed. (a) Identify A, B and C (b) Write equation for action of heat on A. (c) Write equation between solution of A and gas C.
Answer:
(a) A = copper nitrate, B = nitrogen dioxide, C = hydrogen sulphide
(b) \( 2\text{Cu(NO}_3\text{)}_2 \rightarrow 2\text{CuO} + 4\text{NO}_2 + \text{O}_2 \)
(c) \( \text{Cu(NO}_3\text{)}_2 + \text{H}_2\text{S} \rightarrow \text{CuS} + 2\text{HNO}_3 \)

📝 Teacher's Note: This is a good problem-solving question. Help students identify compounds step by step using the clues given - blue color, rotten egg smell, etc.

🎯 Exam Tip: Use the clues systematically: blue crystalline = copper compound; reddish brown gas = NO₂; rotten egg smell = H₂S; black precipitate with Cu = CuS.

Question 1(2004). X, Y and Z are three crystalline solids which are soluble in water and have a common anion. To help you to identify X, Y and Z you are provided with the following experimental observations. Copy and complete the corresponding inferences in (a) to (f). (a) A reddish-brown gas is obtained when X, Y and Z are separately warmed with concentrated sulphuric acid and copper turning added to the mixture. INFERENCE 1: The common anion is the ________ ion. (b) When X is heated, it melts and gives off only one gas which re-lights a glowing splint. INFERENCE 2: The cation in X is either ________ or ________ (c) The action of heat on Y produces a reddish-brown gas and a yellow residue which fuses with the glass of the test tube. INFERENCE 3: The metal ion present in Y is the ________ ion (d) When Z is heated, it leaves no residue. Warming Z with sodium hydroxide solution liberates a gas which turns moist red litmus paper blue. INFERENCE 4: Z contains the ________ cation. (e) Write the equations for the following reactions: (1) X and concentrated sulphuric acid (below 200° C). (One equation only for either of the cations given in INFERENCE 2). (2) Action of heat on Y. (3) Concentrated nitric acid is added to copper turnings kept in a beaker.
Answer:
(a) Nitrate
(b) Sodium or potassium
(c) Lead
(d) Ammonia
(e) (1) \( \text{KNO}_3 + \text{H}_2\text{SO}_4 \xrightarrow{<200°C} \text{KHSO}_4 + \text{HNO}_3 \)
(f) \( 2\text{Pb(NO}_3\text{)}_2 \xrightarrow{\Delta} 2\text{PbO} + 4\text{NO}_2 + \text{O}_2 \)
(g) \( \text{Cu} + 4\text{HNO}_3 \rightarrow \text{Cu(NO}_3\text{)}_2 + \text{H}_2\text{O} + 2\text{NO}_2 \)

📝 Teacher's Note: This systematic identification problem teaches logical deduction. Work through each clue methodically and show how elimination helps identify the compounds.

🎯 Exam Tip: Use the process of elimination: reddish-brown gas = nitrates; only O₂ on heating = alkali metal nitrate; yellow residue that fuses = lead oxide; no residue + ammonia = ammonium salt.

Question 1(2005). (a) Dilute acid is generally considered a typical acid except for its reaction with metals. In what way is dilute nitric acid different from other acids when it reacts with metals? (b) Write the equation for the reaction of dilute nitric acid with copper.
Answer:
(a) Dilute acid is generally considered a typical acid except for its reaction with metals since it does not liberate hydrogen. It is a powerful oxidizing agent and the nascent oxygen formed oxidizes the hydrogen to water.
(b) \( 3\text{Cu} + 8\text{HNO}_3 \rightarrow 3\text{Cu(NO}_3\text{)}_2 + 4\text{H}_2\text{O} + 2\text{NO} \)

📝 Teacher's Note: Emphasize that nitric acid is unique among acids because it acts as an oxidizing agent. Show students that H₂ is oxidized to H₂O instead of being released as gas.

🎯 Exam Tip: Always mention that nitric acid doesn't release H₂ because it oxidizes the hydrogen to water. This is its key distinguishing property from other acids.

Question 1(2006). Explain why: (a) Only all-glass apparatus should be used for the preparation of nitric acid by heating concentrated sulphuric acid and potassium nitrate. (b) Nitric acid is kept in a reagent bottle for a long time.
Answer:
a) All glass apparatus are used because nitric acid vapours are highly corrosive in nature and corrodes cork and rubber etc.
b) Nitric acid is kept in reagent bottle because nitric acid is a highly fuming liquid; it spreads in air and is highly corrosive.

📝 Teacher's Note: Demonstrate the corrosive nature by showing how nitric acid affects different materials. Emphasize safety precautions when handling concentrated acids.

🎯 Exam Tip: For apparatus choice, always mention "corrosive nature" and "attacks organic materials". For storage, mention "fuming" and "corrosive" properties.

Question 2(2006). Write a chemical equation to illustrate the acidic nature of nitric acid.
Answer: The chemical equation: \( \text{HNO}_3 \rightleftharpoons \text{H}^+ + \text{NO}_3^- \)

📝 Teacher's Note: Explain that this ionization equation shows how nitric acid releases H⁺ ions in solution, which is the definition of an acid according to Arrhenius theory.

🎯 Exam Tip: Use the equilibrium arrow (⇌) to show the reversible ionization. This demonstrates your understanding of acid-base equilibrium.

Question 3(2006). Name the products formed when ammonium nitrate is heated.
Answer: When ammonium nitrate is heated the products formed are nitrous oxide and steam.

📝 Teacher's Note: Connect this to the unique decomposition pattern of ammonium nitrate - it's different from other nitrates because both the cation and anion contribute to the products.

🎯 Exam Tip: Write the products as "nitrous oxide (N₂O) and steam (H₂O)" to be completely clear about what forms.

Question 1(2007). The figure given below illustrates the apparatus used in the laboratory preparation of nitric acid. (a) Name A (a liquid), B (a solid) and C (a liquid). (Do not give the formulae) (b) Write an equation to show how nitric acid undergoes decomposition (c) Write the equation for the reaction in which copper is oxidized by concentrated nitric acid
Answer:
(a) A = Concentrated Sulphuric acid, B = potassium nitrate, C = nitric acid
(b) Nitric acid undergoes decomposition as follows: \( 4\text{HNO}_3 \rightarrow 4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \)
(c) Copper is oxidized by concentrated nitric acid: \( \text{Cu} + 4\text{HNO}_3 \rightarrow \text{Cu(NO}_3\text{)}_2 + 2\text{H}_2\text{O} + 2\text{NO}_2 \)

📝 Teacher's Note: Use the apparatus diagram to explain the distillation process. Show how the less volatile H₂SO₄ displaces the more volatile HNO₃ from its salt.

🎯 Exam Tip: For apparatus questions, identify reagents based on their physical states and positions. Remember concentrated HNO₃ gives NO₂ with copper, while dilute gives NO.

Question 1(2008). (a) A dilute acid B does not normally give hydrogen when reacted with metals but does give a gas when reacts with copper. Identify B. Write equation with copper.
Answer: B is dilute nitric acid. The equation with copper is: \( 3\text{Cu} + 8\text{HNO}_3 \rightarrow 3\text{Cu(NO}_3\text{)}_2 + 4\text{H}_2\text{O} + 2\text{NO} \)

📝 Teacher's Note: This question tests understanding of nitric acid's unique behavior. Emphasize that even dilute HNO₃ acts as an oxidizing agent, unlike other dilute acids.

🎯 Exam Tip: The key clue is "does not give hydrogen" - only nitric acid has this property among common acids. With copper, dilute HNO₃ produces colorless NO gas.

Question. (b) Complete the table:

(c) What is the property of nitric acid which allows it to reacts with copper.

Answer:

(a) B is nitric acid

Its reaction with copper:

\( Cu + 4HNO_3 \rightarrow Cu(NO_3)_2 + 2H_2O + 2NO_2 \)

(b)

(c) Nitric acid is a very good oxidizing agent. Its oxidizing property is responsible for its reaction with copper.

In simple words: Nitric acid acts like a powerful substance that can steal electrons from metals like copper, making them react and form new compounds. The Ostwald process converts ammonia into nitric acid through three main steps involving heating and adding oxygen.

📝 Teacher's Note: Demonstrate the color change when copper reacts with nitric acid - students can see the brown NO₂ gas forming. Emphasize that oxidizing agents are electron acceptors, making this concept concrete through visual observation.

🎯 Exam Tip: Always mention "oxidizing property" when explaining why nitric acid reacts with metals. For the Ostwald process, write all three equations in sequence and mention the catalyst (Pt) and temperature conditions for full marks.