Question

When an element is burnt in excess oxygen, is the oxide formed always:

1. a crystalline solid
2. greater in mass than the element
3. soluble in water
4. white in color

alright, i know that most oxides are not soluble in water other than group 1 elements and calcium and barium. (correct me if i'm wrong) And not all oxides are white in color. So, what about option 1 and 2? The correct answer is 2, but i don't get it, why must the oxide formed be heavier than the element?? And what kind of oxide isn't a crystalline solid?

Help, thanks!

Answer 1

The oxide must have a greater mass than the element as O atoms have been added. Thus CuO must have a great mass than Cu.

For 1. I suspect that they are thinking of room temperature and pressure. Thus CO2 is a gas, H2O is a liquid.

Answer 2

ans 3

Answer 3

It should be answer 3 as suppose we take magnesium and oxygen
The mass of magnesium would obviously be less than when magnesium reacts with oxygen to form magnesium oxide.
Hope this helps