Carbon monoxide (CO) is a major primary air pollutant. State the main source of CO in urban air, write a balanced equation showing how it forms, and explain why it is toxic to humans even at fairly low concentrations.

Question

Accepted Answer

Carbon monoxide is produced mainly by vehicle engines and other combustion sources when the supply of oxygen is insufficient to burn the fuel completely: $2\text{C} + \text{O}_2 \rightarrow 2\text{CO}$ (compare this with complete combustion, $\text{C} + \text{O}_2 \rightarrow \text{CO}_2$ , which needs more oxygen for the same amount of fuel). CO is dangerous because it binds to the iron centre of haemoglobin roughly 200 times more strongly than oxygen does, forming stable carboxyhaemoglobin. Since haemoglobin's only job is to shuttle oxygen from the lungs to body tissues, haemoglobin tied up as carboxyhaemoglobin can no longer carry oxygen, so tissues throughout the body become starved of oxygen even though the lungs themselves are functioning normally.

✓Final answer

2\text{C} + \text{O}_2 \rightarrow 2\text{CO}

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2022Set ANNUAL3 marks
$Q. How is SO2 an air pollutant?$
›Reveal solutionSolution
SO2 is a major air pollutant because it directly irritates lungs/plants and, once oxidised, forms acid rain, which damages ecosystems, crops and stone buildings.

Sulfur dioxide (SO2) is released mainly from the combustion of sulfur-containing fossil fuels (coal, diesel) in power plants, vehicles, and industries (e.g. smelting of sulfide ores). It is considered an air pollutant for several reasons:

Direct toxicity: SO2 irritates the mucous membranes of the respiratory tract, causing coughing, bronchitis, and worsening asthma; at high concentrations it can damage lung tissue.

Acid rain formation: SO2 dissolves in atmospheric moisture to form sulfurous acid, and is further oxidised (often catalysed by dust or ozone) to sulfur trioxide, which forms sulfuric acid:

$SO_2 + H_2O \rightarrow H_2SO_3$

$2SO_2 + O_2 \rightarrow 2SO_3 \qquad SO_3 + H_2O \rightarrow H_2SO_4$

This acidified rain lowers the pH of soil and water bodies, harming aquatic life and vegetation.

Damage to buildings/monuments: acid rain reacts with the calcium carbonate in marble/limestone structures ("marble cancer"): $CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2$ , slowly corroding monuments.

Damage to plants: SO2 causes chlorosis (yellowing) and necrosis (death) of leaf tissue, reducing crop yield.

✓Final answer
$SO2 is an air pollutant because it irritates the respiratory system directly and, on oxidation and reaction with atmospheric water, forms sulfurous/sulfuric acid — the main cause of acid rain, which damages plants, water bodies, and stone buildings.$

> [!ANSWER]
> CO forms by incomplete combustion ($2	ext{C} + 	ext{O}_2 ightarrow 2	ext{CO}$) and is toxic because it binds haemoglobin ~200 times more strongly than oxygen, blocking the body's oxygen supply.

Q.Carbon monoxide (CO) is a major primary air pollutant. State the main source of CO in urban air, write a balanced equation showing how it forms, and explain why it is toxic to humans even at fairly low concentrations.

Concept understanding — Air Pollution — Primary and Secondary Pollutants

Q.Carbon monoxide (CO) is a major primary air pollutant. State the main source of CO in urban air, write a balanced equation showing how it forms, and explain why it is toxic to humans even at fairly low concentrations.

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