Hydrides

vector

WJEC

Recall the formatio and chemical properties of the saline hydrides of Groups I and II

Can anyone help?

Thanks :smile:

Reply 1

Swyn

Indeed I can! Just been cramming the whole of CH5 in one day. Here goes:

For group I:

2Na + H2 ----> 2NaH on heating

Hydrides are easily formed for all group I members, because of their high elecropositive nature. On electrolysis of their molten form, hydrogen is evolved at the anode. The hydrides are very powerful reducing agents, illustrated by their reaction with water:

NaH + H2O ----> NaOH + H2

Note that water has been reduced to hydrogen gas.

For group II:

Ca + H2 ----> CaH2

Only the most electropositive members of group II (i.e. Ca, Sr and Ba) form hydrides. Again, on electrolysis of their molten form hydrogen is evolved at the anode and again they're powerful reducing agents as illustrated by their reaction with water:

CaH2 + 2H2O ----> Ca(OH)2 + H2

And that's everything I know about the hydrides of group I and II. I'm doing WJEC - there might be more with other exam boards. Hope it helps anyway!

Reply 2

vector

I'm WJEC as well - that's great - thanks!

Reply 3

vector

Another question - when you add ammonia to hexaaqua copper (II), why do only 4 of the H20 molecules get substituted rather than all 6?

Reply 4

Swyn

I have absolutely no idea! I don't think that we really need to know that - well I hope not anyway. I've got the orange revision book published by WJEC, and it doesn't mention anything about knowing how they're formed. Oh well - it'll only be a mark if they bother asking!