Which of the following oxides, when dissolved in water, will produce a solution with a pH less than 7?
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Correct answer
C. SO3
Principle or equation
Metal oxides are basic and react with water to form bases, increasing pH. Non-metal oxides are acidic and react with water to form acids, decreasing pH.
Why this answer is correct
SO3 is a non-metal oxide. It reacts with water to form sulfuric acid (H2SO4), which dissociates to produce H+ ions, making the solution acidic (pH < 7). Na2O, CaO, and K2O are metal oxides that form strong bases in water, giving pH > 7.
Example
SO3(g) + H2O(l) -> H2SO4(aq). The resulting solution has a pH below 7.
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