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The pH of unpolluted rainwater is about 6.0 - HSC - SSCE Chemistry - Question 5 - 2001 - Paper 1
Question 5
The pH of unpolluted rainwater is about 6.0. Which substance contributes most to this? (A) CO₂ (B) N₂ (C) NO₂ (D) O₃
Worked Solution & Example Answer:The pH of unpolluted rainwater is about 6.0 - HSC - SSCE Chemistry - Question 5 - 2001 - Paper 1
Step 1
Identify the substance contributing to the pH
Answer
The pH of unpolluted rainwater is typically around 6.0 due to the presence of dissolved carbon dioxide (CO₂). When CO₂ dissolves in water, it forms carbonic acid (H₂CO₃), which slightly lowers the pH, making the rainwater naturally acidic. Therefore, the substance that contributes most to the pH of unpolluted rainwater is CO₂.