[munchkiness]

Ok,
currently studying my chem segment on my university science course,

Question is:

Zinc and element X form a solid compound which has the chemical formula Zn₃X₂ The compound reacts with waterr to produce the aqueous ions Zn²⁺, OH^- and a gas XH₃
Write a balanced chemical equation to represent this reaction including the physical states of the reactants and products in your equation. Identify element X which lies in the second row of the periodic table.


Now, i worked out that the chemical equation would be:

Zn₃X₂ (s) + 2H₂O (l) = 3Zn²⁺ (aq) + OH^- (aq) + ZXH₃ (g)

I  thought the element X would be phosphorous, but im guessing thats wrong as its on the 3rd row of the periodic table.

Firstly is the balanced equation correct? if not where have i gone wrong, and secondly, How do i work out which compound forms a solid with zinc? I've read and re-read my text books, and its all confusing.

P.S. I study at home and my tutor out the country for the next 10 days or i would of harrassed him into helping :-)

[vhpk]

Zn₃X₂(s) + 3H₂O(l) -> 3Zn(OH)₂(s) + 2XH₃(g)
Zn(OH)2 is precipitated so, to make the basic solution, the agent must be XH₃ -> X must be nitrogen
NH₃ + H₂O --> NH₄⁺ + OH^-

[munchkiness]

thanks for answering so quickly, but can you explain so an idiot ( ME ) can understand for future similar questions.

[Borek]

Zn(OH)2 is precipitated so, to make the basic solution, the agent must be XH₃ -> X must be nitrogen

This logic doesn't make any sense, even if  X seems to be nitrogen. No connection between solution basicity and X identity.

Let's start with the original reaction equation, as posted by munchkiness:

Zn₃X₂(s) + 2H₂O(l) = 3Zn²⁺(aq) + OH^-(aq) + ZXH₃(g)

First of all - it is not balanced yet, and there is something wrong on the far right - no idea what ZXH₃. But let's just ignore it. Your products are more or less correct - and as vhpk correctly signalled, you have Zn²⁺ and OH^- in the same solution, knowing a little bit about solubilites you should be able to identify that they will immediately form insoluble Zn(OH)₂.

The simplest approach to identify X is to look at the second row of the periodic table and at the Zn₃X₂ formula. We know Zn is divalent, there are three Zn atoms, so they hava 6 bonds. The same number of bonds must be created by 2 atoms of X. This means X is trivalent. Which non-metals can be trivalent? Only those from 5^th column. There is only one element that is both in 5^th column and 2^nd period. And if you take a look at its chemical properties you will see that zinc nitride and ammonia fit the question perfectly.

If you will look further, you will find that the reaction of zinc nitride and water doesn't yield Zn(OH)₃... But that's a lesson on using Google and wikipedia.

[feiying]

I like Borek's style, couldn't have said it better.

[washey]

Study this yourself to see if this makes sense to you. From what I can see, this is an Oxidation reduction reaction. Element X appears to be Oxygen. Find a section in your book that gives the deatils on this type of reaction. That section should give you direction is how to identify the types of reactions, and how to balance them as well.

[munchkiness]

Firstly, just noticed an error in my original post, equation should have read:

Zn3X2(s) + 2H2O(l) = 3Zn2+(aq) + OH-(aq) + 2XH3(g)

But it was late and i was tired so my eyes read the Z as a 2.

Gone back over my text books as washey said, and found a small paragraph which gave me some idea of what im supposed to do.

(still unsure of how to work out the element X though)

I am reasonably sure now that is not a metal, and if its on the second row as the original question asked, is going to be either C, N, O, F, Ne.



So, is the above equation balanced now?

and finally, Big thanks guys, Expect more questions off me soon.