Writing equations (working out formulae) (1 Viewer)

[YBK]

Hey, I can't figure out how to do this question:

Solid phosphorus (V) oxide dissolves in water to form phosphoric acid. Write a balanced equation for this reaction


Now, my problem is actually finding the correct formula for phosphorus oxide... in the answer it is P4 O10 but how come it isn't P2O5?

Thanks

 

[pkc]

At a high school level I suspect both would be marked correct.

I've never heard of a rule for determining whether molecules hang around in multiples of the lowest common denominators - in this case P2O5.
Its something you've just got to be told.

http://home.clara.net/rod.beavon/oxides.htm

 

[Riviet]

Phosphorus(III) oxide and phosphorus(V) oxide have molecular formulae P4O6(s) and P4O10(s) but are often seen written as P2O3(s) and P2O5(s).

In the HSC, I guess either's fine.

 

[YBK]

Cool, thanks.

Is there any trick to memorising all the acids? The list is too long.

 

[YBK]

Actually, it's okay, I just memorised them... *off to work out how to get the salts from the acids*