10th Class Chemistry Notes 2026 — Chapter 7
Class 10 Chemistry — Chapter 07: Nitrogen, Sulphur and Metals
Board: Federal Board
1. Multiple Choice Questions (MCQs)
i. What is a key component of photochemical smog formed by the reaction of NO and NO₂ with unburned hydrocarbons?
a. Sulfuric acid
b. Peroxyacetyl nitrate (PAN)
c. Carbon monoxide
d. Ozone
Correct Answer: b. Peroxyacetyl nitrate (PAN)
Concept: Photochemical smog forms when nitrogen oxides (NOₓ) react with volatile unburned hydrocarbons in the presence of sunlight. This produces secondary pollutants such as peroxyacetyl nitrate (PAN) and ground-level ozone (O₃).
ii. Which of the following is the balanced equation for the production of ammonia in the Haber process?
a. \(\mathrm{N_2(g) + H_2(g) \rightleftharpoons NH_3(g)}\)
b. \(\mathrm{N_2(g) + 2H_2(g) \rightleftharpoons 2NH_3(g)}\)
c. \(\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}\)
d. \(\mathrm{2N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}\)
Correct Answer: c. \(\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}\)
Concept: One mole of nitrogen gas reacts reversibly with three moles of hydrogen gas to produce two moles of ammonia gas.
iii. What are the sources of hydrogen and nitrogen in the Haber process?
a. Water and air
b. Methane and air
c. Methane and water
d. Water and methane
Correct Answer: b. Methane and air
Concept: Nitrogen is obtained from air through fractional distillation of liquid air, while hydrogen is obtained by steam reforming of natural gas (methane, CH₄).
iv. Which catalyst is used in the Haber process?
a. Platinum
b. Vanadium(V) oxide
c. Iron
d. Nickel
Correct Answer: c. Iron (finely divided iron with Al₂O₃/K₂O promoters)
Concept: Finely divided iron acts as a heterogeneous catalyst to speed up the reversible formation of ammonia without changing the equilibrium yield.
v. At what temperature is the Haber process typically conducted?
a. 300°C
b. 450°C
c. 600°C
d. 200°C
Correct Answer: b. 450°C
Concept: A temperature of 450°C provides a compromise between a reasonable reaction rate and an acceptable equilibrium yield because the forward reaction is exothermic.
vi. What is the symbol equation for the conversion of sulphur dioxide to sulphur trioxide in the Contact process?
a. \(\mathrm{SO_2(g) + O_2(g) \rightleftharpoons SO_3(g)}\)
b. \(\mathrm{2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)}\)
c. \(\mathrm{SO_2(g) + 2O_2(g) \rightleftharpoons 2SO_3(g)}\)
d. \(\mathrm{2SO_2(g) + O_2(g) \rightleftharpoons SO_3(g)}\)
Correct Answer: b. \(\mathrm{2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)}\)
Concept: Two moles of sulfur dioxide react reversibly with one mole of oxygen to produce two moles of sulfur trioxide.
vii. Which catalyst is used in the Contact process for the conversion of SO₂ to SO₃?
a. Iron
b. Vanadium(V) oxide
c. Platinum
d. Nickel
Correct Answer: b. Vanadium(V) oxide (V₂O₅)
Concept: Vanadium(V) oxide (V₂O₅) acts as an efficient catalyst at 450°C for the oxidation of SO₂ to SO₃.
viii. What are the sources of sulphur dioxide in the Contact process?
a. Burning sulphur or roasting sulphide ores
b. Burning methane
c. Electrolysis of water
d. Combustion of natural gas
Correct Answer: a. Burning sulphur or roasting sulphide ores
Concept: Sulfur dioxide is produced by burning elemental sulfur or roasting sulfide minerals such as zinc blende (ZnS) and iron pyrites (FeS₂) in air.
ix. How do amphoteric oxides react with acids and bases?
a. Forming a salt and water
b. Forming an acid and a gas
c. Forming a base and hydrogen
d. Forming a salt and hydrogen
Correct Answer: a. Forming a salt and water
Concept: Amphoteric oxides react with both acids and bases to produce salts and water.
x. Which of the following oxides is amphoteric?
a. SO₂
b. CO₂
c. CuO
d. Al₂O₃
Correct Answer: d. Al₂O₃
Concept: Aluminum oxide (Al₂O₃) exhibits both acidic and basic properties. It reacts with acids and strong bases to form salts. SO₂ and CO₂ are acidic oxides, while CuO is a basic oxide.
2. Short Answer Questions
i. What is peroxyacetyl nitrate (PAN) and how is it formed?
Definition: Peroxyacetyl nitrate (CH₃COOONO₂), abbreviated as PAN, is a toxic, eye-irritating secondary pollutant found in photochemical smog.
Formation: It forms in the atmosphere when nitrogen oxides (NOₓ) emitted from vehicle exhausts react with volatile unburned hydrocarbons in the presence of ultraviolet (UV) light from sunlight.
ii. Describe the role of NO and NO₂ in the formation of acid rain.
Answer:
1. Formation of Nitrogen Dioxide:
Nitrogen monoxide (NO), produced at high combustion temperatures in engine cylinders, oxidizes in air to form nitrogen dioxide (NO₂).
2. Formation of Nitric Acid:
NO₂ reacts with atmospheric moisture and oxygen to form nitric acid.
3. Acid Rain:
The nitric acid formed lowers the pH of rainwater below 5.6, resulting in acid rain.
iii. Write the balanced equation for the production of ammonia in the Haber process.
Answer:
iv. What are the typical conditions (temperature, pressure, catalyst) for the Haber process?
Answer:
Temperature: 450°C
Pressure: 200 atm (or 20 MPa)
Catalyst: Finely divided iron (Fe) with aluminum oxide (Al₂O₃) promoter.
v. How is sulphur dioxide produced for the Contact process?
Answer: Sulfur dioxide is produced by the following methods:
1. Direct Burning of Sulfur:
Sulfur is burned in air to produce sulfur dioxide.
2. Roasting Metal Sulfide Ores:
Metal sulfide ores, such as zinc blende (ZnS), are roasted in excess oxygen.
vi. State the balanced chemical equation for the conversion of sulphur dioxide to sulphur trioxide.
Answer:
vii. Describe the role of vanadium(V) oxide in the Contact process.
Answer: Vanadium(V) oxide (V₂O₅) acts as a catalyst in the Contact process. It speeds up the reversible reaction between sulfur dioxide (SO₂) and oxygen (O₂) without changing the position of equilibrium.
It temporarily transfers oxygen to SO₂ and is reduced to V₂O₄. It is then re-oxidized by atmospheric oxygen back to V₂O₅.
viii. What are acidic oxides? Give two examples.
Definition: Acidic oxides are non-metal oxides that react with water to form acidic solutions and neutralize bases to form salt and water.
Examples:
Carbon dioxide (CO₂)
Sulfur dioxide (SO₂)
ix. What are basic oxides? Give two examples.
Definition: Basic oxides are metal oxides that react with acids to form salt and water. When soluble in water, they form basic (alkaline) solutions.
Examples:
Sodium oxide (Na₂O)
Calcium oxide (CaO)
x. What is meant by amphoteric oxides? Provide examples.
Definition: Amphoteric oxides are oxides that display both acidic and basic chemical behaviour. They react with both acids and strong bases to produce salts and water.
Examples:
Aluminum oxide (Al₂O₃)
Zinc oxide (ZnO)
xi. Evaluate the environmental impact of acidic oxides like SO₂ and CO₂.
Answer:
1. Sulfur Dioxide (SO₂):
Causes acid rain.
Acidifies lakes and can harm aquatic life.
Leaches essential nutrients from soils.
Damages forest leaves.
Corrodes limestone structures and metal bridges.
Causes respiratory distress in humans.
2. Carbon Dioxide (CO₂):
Acts as a greenhouse gas by trapping infrared radiation in the atmosphere.
Contributes to global warming and climate change.
Causes ocean acidification.
Contributes to polar ice melting.
xii. Evaluate the significance of controlling the emission of oxides like NO₂ and SO₂ in industrial processes.
Answer: Controlling these emissions is important for the following reasons:
Prevent Acid Rain: Protects terrestrial ecosystems, crops, and aquatic habitats from harmful decreases in pH.
Reduce Photochemical Smog: Prevents the formation of harmful secondary pollutants such as PAN and tropospheric ozone.
Protect Human Health: Minimizes respiratory problems such as asthma, bronchitis, and lung irritation.
Preserve Infrastructure: Reduces acid-induced corrosion of buildings, monuments, and metallic structures.
3. Long Answer Questions
i. Explain the environmental impact of nitrogen oxides in the atmosphere, particularly focusing on photochemical smog and acid rain.
Answer:
Sources of Nitrogen Oxides:
Nitrogen oxides (NOₓ, primarily NO and NO₂) are generated in internal combustion engines and power plants when atmospheric nitrogen and oxygen combine at extremely high temperatures.
1. Photochemical Smog:
In the presence of ultraviolet radiation from sunlight, NO₂ photodecomposes into NO and reactive oxygen atoms (O).
These atomic oxygen species combine with molecular oxygen to form tropospheric ozone (O₃).
Ozone and NOₓ react further with unburned hydrocarbons from exhaust fumes to produce peroxyacetyl nitrate (PAN).
Environmental Impact:
Photochemical smog causes:
Severe eye irritation.
Reduced visibility.
Respiratory damage.
Crop degradation.
2. Acid Rain:
Nitrogen dioxide reacts with oxygen and atmospheric water droplets to form nitric acid.
The dissolved nitric acid lowers the pH of rainwater.
Environmental Impact:
Acid rain causes:
Acidification of lakes.
Damage to leaves and vegetation.
Corrosion of building materials.
ii. Discuss the Haber process, including the chemical reaction, sources of reactants, conditions required, and its significance in the production of ammonia.
Answer:
1. Chemical Reaction:
The Haber process is used for the industrial production of ammonia from nitrogen and hydrogen.
2. Sources of Reactants:
Nitrogen (N₂): Extracted from air through fractional distillation of liquid air.
Hydrogen (H₂): Obtained through steam methane reforming.
3. Industrial Conditions:
Temperature (450°C): Since the forward reaction is exothermic, lower temperatures favour a higher ammonia yield. However, lower temperatures greatly slow down the reaction. A temperature of 450°C provides a balance between reaction rate and yield.
Pressure (200 atm): High pressure shifts the equilibrium towards the right because fewer gas molecules are present on the product side. This increases ammonia yield and reaction rate.
Catalyst (Iron): Finely divided iron increases the rate of reaching equilibrium without changing the equilibrium yield.
4. Significance:
Ammonia is an important raw material for producing:
Synthetic nitrogenous fertilizers, such as urea and ammonium nitrate.
Nitric acid.
Explosives.
Industrial cleaning products.
Nitrogenous fertilizers are essential for global agriculture.
iii. Describe the Contact process for sulphuric acid production, detailing the chemical reactions involved, the sources of reactants, and the industrial conditions used.
Answer:
The Contact process is an industrial method used to manufacture sulfuric acid (H₂SO₄).
1. Sources of Reactants:
Sulfur (S): Obtained from underground deposits or extracted from natural gas and petroleum.
Oxygen (O₂): Supplied by atmospheric air.
2. Process Steps and Chemical Reactions:
Stage 1: Combustion of Sulfur
Sulfur is burned in air to produce sulfur dioxide.
Stage 2: Catalytic Oxidation of SO₂ to SO₃
Sulfur dioxide reacts with oxygen to produce sulfur trioxide.
Industrial Conditions:
Temperature: 450°C
Pressure: 1–2 atm
Catalyst: Vanadium(V) oxide (V₂O₅)
Stage 3: Absorption of SO₃
Sulfur trioxide is dissolved in concentrated sulfuric acid to form oleum (H₂S₂O₇). Direct addition of SO₃ to water is avoided because it is highly exothermic and produces an uncontrollable acid mist.
Stage 4: Dilution of Oleum
Oleum is safely mixed with water to produce concentrated sulfuric acid.
iv. Compare and contrast acidic, basic, and amphoteric oxides with suitable examples for each type.
Answer:
Oxides are classified according to their chemical behaviour when they react with acids, bases, and water.
Parameter | Acidic Oxides | Basic Oxides | Amphoteric Oxides |
|---|---|---|---|
Origin | Non-metals | Metals | Selected metals |
Reaction with acids | Generally no reaction | Form salt and water | Form salt and water |
Reaction with bases | Form salt and water | Generally no reaction | Form salt and water |
Effect on water | Form acidic solutions | Form basic solutions (if soluble) | Generally insoluble in water |
Examples | CO₂, SO₂, SO₃, NO₂ | Na₂O, CaO, CuO, MgO | Al₂O₃, ZnO, PbO |
v. How do industrial processes like the Haber and Contact processes contribute to environmental pollution, and what measures can be taken to minimize their impact?
Answer:
1. Environmental Contributions:
Haber Process:
High energy requirements for methane reforming release carbon dioxide (CO₂), a greenhouse gas.
Runoff of synthetic nitrogen fertilizers can cause eutrophication in water bodies.
Contact Process:
– Leakage of unconverted sulfur dioxide (SO₂) directly contributes to acid rain and localized air pollution.
2. Mitigation Measures:
Flue Gas Desulfurization (FGD): Scrubbing waste gases with wet limestone (CaCO₃) or lime (CaO) to trap leftover SO₂ before it is released into the atmosphere.
Double Absorption Systems: Using Double Contact Double Absorption (DCDA) plants increases SO₂-to-SO₃ conversion efficiency to more than 99.8%.
Green Hydrogen: Producing hydrogen through renewable-powered water electrolysis instead of steam methane reforming reduces the carbon dioxide footprint.
vi. Compare the roles of NO and NO₂ in the formation of acid rain. How do their chemical behaviours contribute to both direct acid formation and the oxidation of sulphur dioxide?
Answer:
1. Direct Acid Formation:
– Nitrogen monoxide (NO) oxidizes in air to form nitrogen dioxide (NO₂).
– Nitrogen dioxide reacts with atmospheric water vapour and oxygen to form nitric acid (HNO₃).
2. Catalytic Oxidation of SO₂:
Nitrogen oxides also contribute to the oxidation of sulfur dioxide into sulfur trioxide.
– Nitrogen dioxide reacts with sulfur dioxide:
– The NO formed reacts with atmospheric oxygen to regenerate NO₂:
– The sulfur trioxide formed dissolves in cloud water to produce sulfuric acid (H₂SO₄), accelerating acid rain formation.
vii. Analyse the classification of oxides. Why are oxides like SO₂ considered acidic, while oxides like CuO are considered basic? Discuss how the metallic or non-metallic character of the element influences this classification.
Answer:
1. Influence of Non-Metallic Character (SO₂):
Non-metals generally have high electronegativities and hold electrons tightly. Their covalent bonds with oxygen produce oxides that react with water to form acidic solutions.
For example, sulfur dioxide reacts with water to form sulfurous acid:
Therefore, SO₂ is classified as an acidic oxide.
2. Influence of Metallic Character (CuO):
Metals generally have lower electronegativities and readily donate electrons to oxygen, forming ionic compounds containing oxide ions (O²⁻). These oxide ions accept protons from acids.
For example:
Therefore, CuO is classified as a basic oxide.
4. Think Tank
1. Explain why gold and platinum are often used in jewellery despite their high cost.
Answer: Gold and platinum are found near the bottom of the reactivity series and are known as noble metals. They are extremely unreactive and resistant to chemical attack by air, water, oxygen, and atmospheric pollutants.
Consequently, they do not easily tarnish, corrode, or rust. They maintain their lustrous appearance over time, making them suitable for jewellery despite their high cost.
2. If a new metal was discovered and found to react with steam but not cold water, where would you place it in the reactivity series? Justify your placement.
Placement: It would be positioned below calcium and magnesium, which react with cold water, and above iron and lead, which do not react rapidly with steam. It would be placed alongside metals such as aluminum and zinc.
Justification: Reacting with steam (H₂O(g)) requires higher thermal energy than reacting with cold water. This indicates an intermediate level of reactivity in displacing hydrogen from water molecules.
3. Give the expected reactivity series from the following data for the following three metals. Justify your placement.
Data Summary:
Metal A: Reacts slowly with cold water, vigorously with steam, and quickly with dilute acid.
Metal B: Does not react with cold water or steam but reacts slowly with dilute acid.
Metal C: Does not react with cold water, steam, or dilute acid.
Reactivity Order:
Justification:
Metal A: It is the most reactive because it reacts with cold water and dilute acid.
Metal B: It is moderately reactive. It does not react with water or steam but can displace hydrogen from dilute acid.
Metal C: It is the least reactive because it cannot displace hydrogen even from dilute acids.
4. How can the knowledge of basic oxides, such as CaO, be applied to neutralize acidic pollutants in industrial wastewater treatment?
Answer: Acidic industrial wastewater containing excess hydrogen ions (H⁺), such as wastewater containing H₂SO₄ or HCl, can be treated by adding controlled amounts of calcium oxide (CaO), also known as quicklime, or calcium hydroxide (Ca(OH)₂), also known as slaked lime.
Reaction:
This reaction neutralizes harmful acidity and raises the wastewater pH towards neutral levels (6.5–8.5) before safe discharge into water bodies.
5. Evaluate the choice of 450°C and 200 atm for the Haber process.
Answer:
1. Choice of 450°C:
The Haber process is exothermic:
According to Le Chatelier’s Principle, lower temperatures favour a higher percentage conversion into ammonia. However, lower temperatures greatly slow down the reaction rate.
A temperature of 450°C provides a compromise between reaction speed and ammonia yield when used with an iron catalyst.
2. Choice of 200 atm:
Four moles of gaseous reactants produce two moles of gaseous products. Therefore, increasing pressure shifts the equilibrium towards ammonia formation, increasing both yield and reaction rate.
A pressure of 200 atm is selected because operating at higher pressures requires extremely expensive reinforced equipment and safety infrastructure.
6. Evaluate the environmental impact of acidic oxides.
Answer: Acidic oxides such as SO₂, NO₂, and CO₂ contribute to environmental degradation.
1. Acid Deposition:
SO₂ and NO₂ cause acid rain, which:
Destroys aquatic ecosystems.
Leaches essential soil minerals such as Mg²⁺ and Ca²⁺.
Damages vegetation.
Dissolves structural stonework.
2. Global Warming:
The accumulation of CO₂ in the atmosphere intensifies the greenhouse effect, raising global surface temperatures and altering weather patterns.
7. Evaluate the significance of controlling the emission of oxides like NO₂ and SO₂ in industrial processes.
Answer: Industrial emission-control methods, such as catalytic converters and flue gas scrubbers, are important for reducing environmental pollution.
Controlling these emissions helps prevent:
Acidification of freshwater reservoirs and loss of biodiversity.
Urban photochemical smog and hazardous breathing conditions.
Respiratory problems caused by polluted air.
Expensive structural maintenance caused by acid corrosion.
Notes by Sir Dilawar
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