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Unpolluted rain water in New South Wales is slightly acidic - HSC - SSCE Chemistry - Question 2 - 2009 - Paper 1
Question 2
Unpolluted rain water in New South Wales is slightly acidic. Which substance is the major contributor to this acidity? (A) Ozone (B) Sulfur dioxide (C) Carbon dioxi... show full transcript
Worked Solution & Example Answer:Unpolluted rain water in New South Wales is slightly acidic - HSC - SSCE Chemistry - Question 2 - 2009 - Paper 1
Step 1
Which substance is the major contributor to this acidity?
Answer
To determine the major contributor to the acidity of unpolluted rainwater, we need to consider the chemical reactions involved. Rainwater is naturally slightly acidic due to the presence of carbon dioxide (CO₂) in the atmosphere.
When CO₂ dissolves in water, it forms carbonic acid (H₂CO₃), which can dissociate to release hydrogen ions (H⁺), contributing to acidity:
ightleftharpoons ext{H}_2 ext{CO}_3$$ $$ ext{H}_2 ext{CO}_3 ightleftharpoons ext{H}^+ + ext{HCO}_3^-$$ While sulfur dioxide (SO₂) can also contribute to acidity when it forms sulfurous acid, its concentration is generally lower compared to carbon dioxide. Thus, the primary contributor to the slight acidity observed in natural rainwater is carbon dioxide. Therefore, the correct choice is: **(C) Carbon dioxide**