Question

Which of the following elements would from oxides which would indicate pH values less than seven, using moist pH paper?
Magnesium, Carbon, Sulphur, Hydrogen, Copper

Answer 1

Sulphur and Carbon burn in the air to form sulphur dioxide and carbon dioxide. Both are acidic oxides that indicate pH values less than 7 when moist pH paper is used.

S + O₂ → SO₂
C + O₂ → CO₂

Hydrogen is also a non-metal, but forms water, which has a neutral pH of 7, after reacting with oxygen. The oxides of magnesium and copper do not have pH values less than 7.