Chemistry Notes – Grade 10
National Curriculum Pakistan - NCP
Chapter 7 Nitrogen, Sulphur and Metals
Aligned with National Curriculum Pakistan (Federal Board, NBF, PTB)
- What is photochemical smog?
Photochemical smog is formed when sunlight reacts with nitrogen oxides (NO and NO₂) and unburned hydrocarbons in the atmosphere, producing secondary pollutants like PAN. - What is PAN?
PAN (Peroxyacetyl Nitrate) is a major component of photochemical smog and a stable molecule formed from hydrocarbons and nitrogen oxides in the presence of UV light. - What is the first step in photochemical smog formation?
The first step is the formation of nitrogen dioxide (NO₂) from nitric oxide (NO) and oxygen (O₂) in the atmosphere under UV radiation. - What is the reaction for the formation of NO₂?
2NO(g) + O₂(g) → 2NO₂(g) (in the presence of UV radiation) - What is photolysis of nitrogen dioxide?
NO₂ absorbs UV light and breaks down into nitric oxide (NO) and a nascent oxygen atom [O]. - What is the reaction for photolysis of NO₂?
NO₂(g) → NO(g) + O (in the presence of UV radiation) - How is ozone (O₃) formed in the atmosphere?
Nascent oxygen [O] reacts with oxygen (O₂) to form ozone (O₃) under UV radiation. - Write the reaction for the formation of ozone.
O₂(g) + O → O₃(g) - What are hydrocarbons referred to in the context of smog?
Hydrocarbons are also called volatile organic compounds (VOCs). - How do hydrocarbons react in smog formation?
Hydrocarbons react with nascent oxygen [O] to form intermediate organic radicals (RCO•). - Write the reaction for hydrocarbon oxidation.
Hydrocarbons(g) + O → RCO•(g) - How are peroxyacyl radicals formed?
RCO• reacts with O₂ to form peroxyacyl radicals (RC(O)O₂•). - Write the reaction for formation of peroxyacyl radicals.
RCO•(g) + O₂(g) → RC(O)O₂•(g) - How is PAN formed?
PAN is formed when peroxyacyl radicals react with nitrogen dioxide (NO₂). - Write the reaction for formation of PAN.
RC(O)O₂•(g) + NO₂(g) → RC(O)O₂NO₂(g) (Peroxyacetyl Nitrate) - Why is PAN harmful?
PAN is stable at low temperatures, can travel long distances, and releases NOx and radicals at high temperatures, contributing to smog formation. - What causes acid rain?
Acid rain is caused by SO₂ and NO₂ from fossil fuels and vehicles reacting with rainwater to form acids like H₂SO₄ and HNO₃. - What is the pH of acid rain?
Acid rain has a pH less than 5. - Define acid rain.
Acid rain is rain with a pH lower than 5, formed due to acids like sulfuric and nitric acid in polluted air. - What is the role of NO and NO₂ in acid rain formation?
They contribute by forming nitric acid (HNO₃) through both direct and catalytic reactions. - Why do nitrogen oxides (NO and NO₂) play a key role in environmental chemistry?
Nitrogen oxides are major air pollutants emitted from vehicles and industrial processes. They contribute to the formation of photochemical smog, acid rain, and secondary pollutants like PAN (Peroxyacetyl Nitrate). They also act as intermediates in atmospheric chemical reactions, influencing air quality and climate. - How does photochemical smog affect human health and the environment?
Photochemical smog can cause respiratory problems, eye irritation, and reduced lung function in humans. In the environment, it damages crops, forests, and materials. The ozone formed during smog events is a pollutant at ground level, harming living organisms and degrading rubber and plastics. - What is the significance of UV radiation in the formation of photochemical smog?
UV radiation initiates the photodissociation of NO₂, which produces reactive oxygen species. These reactive atoms and radicals drive the chain reactions that lead to ozone (O₃) formation and the creation of other harmful compounds like PAN. Without sunlight (UV), these reactions cannot occur effectively. - Why is PAN considered a secondary pollutant?
PAN is not emitted directly into the atmosphere. Instead, it forms through complex reactions involving NO₂, hydrocarbons, and oxygen under sunlight. Since it results from atmospheric reactions rather than direct emission, it's classified as a secondary pollutant. - What properties make PAN a long-distance air pollutant?
PAN is chemically stable at low temperatures, allowing it to persist in the atmosphere and be transported over long distances from urban or industrial areas. When temperatures rise, it decomposes and releases nitrogen oxides and organic radicals, contributing to smog even far from its origin. - How does lightning contribute to the formation of acid rain?
During thunderstorms, lightning causes the high-temperature formation of nitrogen oxides (NO and NO₂) from atmospheric nitrogen and oxygen. These gases dissolve in rainwater, forming nitric acid (HNO₃), thereby increasing the acidity of rainwater and contributing to acid rain. - Why is the pH of rainwater lower in polluted areas?
In polluted areas, large quantities of sulfur dioxide (SO₂) and nitrogen oxides are released from vehicles and power plants. These gases dissolve in atmospheric moisture to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃), which significantly reduce the pH of rainwater, often below 5. - What is the difference between direct and catalytic roles of NO and NO₂ in acid rain formation?
In the direct role, NO and NO₂ react with water to form nitric acid (HNO₃). In the catalytic role, they help convert SO₂ into SO₃, which then forms sulfuric acid (H₂SO₄). Thus, they contribute to acid rain both by forming their own acids and by catalyzing the formation of other acids. - Why do nitrogen oxides (NO and NO₂) play a key role in environmental chemistry?
Nitrogen oxides are major air pollutants emitted from vehicles and industrial processes. They contribute to the formation of photochemical smog, acid rain, and secondary pollutants like PAN (Peroxyacetyl Nitrate). They also act as intermediates in atmospheric chemical reactions, influencing air quality and climate. - How does photochemical smog affect human health and the environment?
Photochemical smog can cause respiratory problems, eye irritation, and reduced lung function in humans. In the environment, it damages crops, forests, and materials. The ozone formed during smog events is a pollutant at ground level, harming living organisms and degrading rubber and plastics. - What is the significance of UV radiation in the formation of photochemical smog?
UV radiation initiates the photodissociation of NO₂, which produces reactive oxygen species. These reactive atoms and radicals drive the chain reactions that lead to ozone (O₃) formation and the creation of other harmful compounds like PAN. Without sunlight (UV), these reactions cannot occur effectively. - Why is PAN considered a secondary pollutant?
PAN is not emitted directly into the atmosphere. Instead, it forms through complex reactions involving NO₂, hydrocarbons, and oxygen under sunlight. Since it results from atmospheric reactions rather than direct emission, it's classified as a secondary pollutant. - What properties make PAN a long-distance air pollutant?
PAN is chemically stable at low temperatures, allowing it to persist in the atmosphere and be transported over long distances from urban or industrial areas. When temperatures rise, it decomposes and releases nitrogen oxides and organic radicals, contributing to smog even far from its origin. - How does lightning contribute to the formation of acid rain?
During thunderstorms, lightning causes the high-temperature formation of nitrogen oxides (NO and NO₂) from atmospheric nitrogen and oxygen. These gases dissolve in rainwater, forming nitric acid (HNO₃), thereby increasing the acidity of rainwater and contributing to acid rain. - Why is the pH of rainwater lower in polluted areas?
In polluted areas, large quantities of sulfur dioxide (SO₂) and nitrogen oxides are released from vehicles and power plants. These gases dissolve in atmospheric moisture to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃), which significantly reduce the pH of rainwater, often below 5. - What is the difference between direct and catalytic roles of NO and NO₂ in acid rain formation?
In the direct role, NO and NO₂ react with water to form nitric acid (HNO₃). In the catalytic role, they help convert SO₂ into SO₃, which then forms sulfuric acid (H₂SO₄). Thus, they contribute to acid rain both by forming their own acids and by catalyzing the formation of other acids. - Why are oxides classified as acidic, basic, or amphoteric?
Oxides are classified based on their chemical behavior when reacting with water, acids, or bases. This classification helps in understanding the nature of the element forming the oxide—whether it's metallic (forms basic or amphoteric oxides) or non-metallic (forms acidic oxides). - Why are acidic oxides generally non-metallic?
Non-metals tend to gain electrons and form covalent bonds with oxygen. Their oxides dissolve in water to form acids. For example, CO₂ reacts with water to form carbonic acid (H₂CO₃), showing acidic behavior. - What is the difference in behavior between basic and acidic oxides when reacting with water?
Acidic oxides form acids in water (e.g., SO₂ + H₂O → H₂SO₃), while basic oxides form hydroxides (bases), such as CaO + H₂O → Ca(OH)₂. Acidic oxides come from non-metals, basic from metals. - What are amphoteric oxides, and why are they important?
Amphoteric oxides can react with both acids and bases, showing dual nature. They are typically oxides of elements that have both metallic and non-metallic characteristics, like Al₂O₃ and ZnO. This makes them useful in neutralizing both acidic and basic environments. - How does aluminum oxide react differently with acids and bases?
Aluminum oxide reacts with HCl (acid) to form aluminum chloride and water, showing basic character. It also reacts with NaOH (base) to form sodium aluminate, showing acidic character. This dual reactivity proves its amphoteric nature. - Why do some metals not react with dilute acids?
Metals like copper, silver, and gold are less reactive and lie below hydrogen in the reactivity series. They cannot displace hydrogen ions from acids, so no reaction occurs. - What is the role of reactivity series in metal-acid reactions?
The reactivity series ranks metals by their tendency to lose electrons. Highly reactive metals like Mg, Zn, and Fe can displace hydrogen from acids, while less reactive ones like Cu and Ag cannot. - Why do potassium and sodium react explosively with water?
These alkali metals are highly reactive. When they contact water, the reaction is extremely exothermic, producing hydrogen gas and metal hydroxide quickly and often explosively. - How does the reaction of metals with steam differ from cold water?
Metals like Mg, Zn, and Fe that do not react much with cold water can react with steam to form oxides and hydrogen. Steam provides the heat needed to activate the reaction. - Why is steam used instead of cold water to test the reactivity of certain metals?
Cold water doesn’t provide enough energy for moderate-reactivity metals (like Zn and Fe) to react. Steam, being hotter, speeds up the reaction, allowing formation of oxides and hydrogen. - How are metal oxides formed, and what determines their nature?
Metal oxides form when metals react with oxygen. The nature (basic or amphoteric) depends on the metal's reactivity and position in the periodic table. More reactive metals tend to form strongly basic oxides. - What is the significance of reactions of metals with steam in industrial processes?
Reactions with steam are important in metallurgy and hydrogen production. For example, passing steam over hot iron produces iron oxide and hydrogen gas, used in various chemical processes. - What is oleum and how is it formed?
Oleum (H₂S₂O₇) is formed by the reaction of sulfur trioxide (SO₃) with concentrated sulfuric acid (H₂SO₄). It is an intermediate used to produce more concentrated sulfuric acid. - How is concentrated sulfuric acid obtained from oleum?
By adding a calculated amount of water to oleum (H₂S₂O₇), two moles of concentrated sulfuric acid (H₂SO₄) are formed. - What is the significance of the oleum tower in the Contact Process?
The oleum tower is used to absorb SO₃ gas into H₂SO₄ to form oleum. It is lined with bricks and filled with 98% sulfuric acid to enhance absorption. - Why is the acid obtained by the Contact Process considered pure?
It is extremely pure because the process involves controlled conditions and does not introduce impurities, making it suitable for industrial applications. - What are the sources of hydrogen and nitrogen in the Haber Process?
Hydrogen is obtained from the decomposition of methane (natural gas), and nitrogen is obtained from the air. - At what pressure and temperature does the Haber process occur?
The reaction occurs at a high pressure of 200–500 atm and a temperature of around 450°C. - Why is refrigerated brine used in the Haber Process?
Refrigerated brine is used to cool and condense ammonia gas from the mixture of gases coming out of the catalytic chamber. - What catalyst is used in the Haber Process?
A mixture of iron (Fe) and molybdenum (Mo) is used as a catalyst in the Haber Process. - What is the chemical equation for ammonia formation in the Haber Process?
N₂ + 3H₂ ⇌ 2NH₃ (in the presence of Fe/Mo catalyst at 450°C and 200 atm). - Why is high pressure favored in the Haber Process?
According to Le Chatelier's Principle, high pressure favors the formation of ammonia since it results in a decrease in the volume of gases. - Explain how the Contact Process ensures the continuous production of sulfuric acid.
The Contact Process involves several steps where sulfur dioxide (SO₂) is first produced, then oxidized to sulfur trioxide (SO₃) using a vanadium pentoxide catalyst. This SO₃ is absorbed into H₂SO₄ to form oleum, which is then diluted to form highly pure sulfuric acid. The entire process is continuous, efficient, and ensures high yield due to controlled conditions and catalyst use. - What are the advantages of using oleum in sulfuric acid production?
Oleum allows for safe and efficient absorption of SO₃, which is otherwise difficult to dissolve directly in water due to its highly exothermic reaction. It also permits precise control over acid concentration and improves purity. - Discuss why the Contact Process uses vanadium pentoxide instead of platinum as a catalyst.
Vanadium pentoxide (V₂O₅) is preferred because it is less expensive, more durable under industrial conditions, and effectively catalyzes the oxidation of SO₂ to SO₃ at a lower cost compared to platinum. - How does the Haber Process reflect Le Chatelier’s Principle in industrial settings?
The Haber Process uses high pressure to shift the equilibrium toward the product (ammonia) because fewer gas molecules are formed. Additionally, although the reaction is exothermic, a moderately high temperature is used (450°C) to balance the rate of reaction and yield, while a catalyst is used to enhance efficiency. - Why is ammonia liquefied after production in the Haber Process?
Liquefying ammonia makes it easier to store and transport. It also allows for separation from unreacted hydrogen and nitrogen, which are recycled, improving the efficiency of the process. - What are the environmental and industrial significances of the Haber and Contact Processes?
The Haber Process is crucial for producing ammonia used in fertilizers, which supports global food production. The Contact Process provides sulfuric acid, essential in countless industries. However, both processes must be controlled to minimize environmental impacts like acid rain and greenhouse gas emissions. - What are oxides?
Oxides are binary compounds of elements with oxygen, e.g., CaO, CO₂, SO₂. - How are oxides classified?
Oxides are classified as acidic, basic, or amphoteric based on chemical properties. - What do acidic oxides form when they react with water?
They form acids and are typically non-metal oxides. - Give an example of an acidic oxide and its reaction with water.
SO₂ + H₂O → H₂SO₃ (Sulphurous acid). - What acid is formed when CO₂ reacts with water?
H₂CO₃ (Carbonic acid) is formed. - What do basic oxides form when they react with water?
They form bases and are typically metal oxides. - Give an example of a basic oxide reacting with water.
CaO + H₂O → Ca(OH)₂ (Calcium hydroxide). - What happens when Na₂O reacts with HCl?
Na₂O + 2HCl → 2NaCl + H₂O. - What are amphoteric oxides?
Oxides that react with both acids and bases. - Give an example of an amphoteric oxide.
Al₂O₃ (Aluminum oxide) or ZnO (Zinc oxide). - Write the reaction of Al₂O₃ with HCl.
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O. - Write the reaction of Al₂O₃ with NaOH.
Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄. - What is formed when ZnO reacts with NaOH?
Na₂[Zn(OH)₄] (Sodium zincate) is formed. - How do metals react with dilute acids?
They form salt and hydrogen gas. - Write the reaction of magnesium with HCl.
Mg + 2HCl → MgCl₂ + H₂. - Which metals react explosively with dilute acids?
Potassium and sodium. - Which metals do not react with dilute acids?
Copper, silver, and gold. - What is formed when reactive metals react with cold water?
Metal hydroxide and hydrogen gas. - Give an example of a metal reacting with cold water.
2Na + 2H₂O → 2NaOH + H₂. - Which metals react vigorously with cold water?
Potassium, sodium, and calcium. - Do zinc and iron react with cold water?
No, they do not react significantly. - What is formed when metals react with steam?
Metal oxide and hydrogen gas. - Write the reaction of iron with steam.
3Fe + 4H₂O → Fe₃O₄ + 4H₂. - Which metals react readily with steam?
Magnesium, zinc, and iron. - Do copper and lead react with steam?
No, they do not. - What do metals form when they react with oxygen?
They form metal oxides. - Give an example of a metal reacting with oxygen.
2Mg + O₂ → 2MgO. - Which metals form protective oxide layers?
Magnesium and aluminium form protective oxide layers. - Which metals do not react with oxygen under normal conditions?
Gold and platinum do not react with oxygen normally. - What is the reactivity series based on?
It is based on how metals react with acids, cold water, and steam. - Name three highly reactive metals.
Potassium, sodium, and calcium. - What do highly reactive metals form with cold water?
They form metal hydroxides and hydrogen gas. - What happens when potassium reacts with HCl?
2K + 2HCl → 2KCl + H₂. - Name two moderately reactive metals.
Magnesium and zinc. - How do moderately reactive metals react with steam?
They form metal oxides and hydrogen gas. - Do less reactive metals react with cold water or steam?
No, they do not react with cold water or steam. - Name a metal that reacts slowly with strong acids.
Lead reacts slowly with strong acids. - Which metals are unreactive?
Gold and platinum are unreactive. - Write the simplified order of reactivity series.
K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au - Why do some metals form a protective oxide layer while others don’t?
Metals like aluminium and magnesium form a tightly bonded oxide layer that prevents further oxidation. This layer acts as a barrier to oxygen and moisture, making them more resistant to corrosion compared to metals like iron or copper. - What determines the position of a metal in the reactivity series?
A metal’s position depends on how easily it loses electrons to form positive ions. Metals that lose electrons easily (like potassium) are highly reactive, while those that don’t (like gold) are unreactive. - How do the reactions of highly reactive and moderately reactive metals with water differ?
Highly reactive metals like potassium and sodium react violently with cold water, while moderately reactive metals like magnesium and zinc react slowly, or only with steam, not cold water. - Why do less reactive metals like copper and silver not react with acids?
These metals are below hydrogen in the reactivity series, so they cannot displace hydrogen ions from acids, making them unreactive in such conditions. - What is the significance of hydrogen gas release in these reactions?
The release of hydrogen gas indicates a redox reaction where the metal is oxidized and hydrogen ions are reduced. It's used to test metal reactivity. - Why are potassium and sodium not tested with steam?
These metals react too violently with water or steam, often causing explosive reactions, so they are avoided for safety. - Why is the reactivity series important in practical chemistry?
It helps predict how metals will behave in reactions, such as extraction processes, corrosion resistance, and displacement reactions. - What does the simplified order of reactivity tell us about metal use?
It shows which metals are more likely to corrode or react. For instance, gold is used in jewelry because of its low reactivity, while reactive metals like sodium need careful storage.
Tags
acid rain causes
Contact Process
Haber Process
metal reactivity series
nitrogen oxides
PAN pollutant
photochemical smog
reactions of metals with acids
sulfuric acid production