Differences between the properties of metals and non-metals
2 marks · EasyWhen 0.1 mol of sodium oxide (a metal oxide) is dissolved in water, it produces sodium hydroxide solution, which is alkaline. When 0.1 mol of sulfur dioxide (a non-metal oxide) is dissolved in water, it forms an acidic solution. Calculate the total number of moles of hydroxide ions, OH⁻, produced from the sodium oxide, and the total number of moles of hydrogen ions, H⁺, produced from the sulfur dioxide, after complete reaction in water. State which oxide forms a solution with pH greater than 7, explaining your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Also accept: States sodium oxide forms a basic/alkaline solution and sulfur dioxide forms an acidic solution; shows correct ionic calculation for each.
Common mistakes: Incorrectly identifying which oxide is acidic or basic; Mixing up H+ and OH- produced; Calculating double moles for SO2 from 1:1 reaction
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Correctly calculates moles of OH⁻ or H⁺ produced: 0.2 mol OH⁻ from Na2O, 0.2 mol H⁺ from SO2 (must show correct working from balanced equations or clear calculation).
A1 · 1 mark · States and explains which oxide forms a solution with pH greater than 7 (sodium oxide, because it produces hydroxide ions making the solution alkaline).
Worked solution
Sodium oxide reacts with water:
Each 1 mol Na2O forms 2 mol NaOH, which provides 2 mol OH⁻. For 0.1 mol Na2O:
Sulfur dioxide reacts with water:
H2SO3 is a diprotic acid, so 1 mol gives 2 mol H⁺. For 0.1 mol SO2:
Sodium oxide forms a solution with pH greater than 7 because its oxide is basic (alkaline) and produces hydroxide ions.