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Offline Blue212

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Need help with finding equations
« on: February 19, 2011, 07:25:14 PM »
Hey, I am new here and I was wondering if I could get some help on deriving a couple equations.

I have to test Ti 3+ with the following but I don't know how I would get the chemical equation of the reactions

(a) granulated zinc
(b) 2 M ammonia solution
(c) acidified potassium dichromate solution*
With and without the prior addition of N-phenylanthranilic acid
(d) acidified hydrogen peroxide solution (add dropwise with mixing
between additions).

observations:
a) solution bubbled
b) dark blue/black precipitate formed
c) with N-phenylanthranilic acid, light blue solution formed
without, no reaction
d) orange/yellow solution

I know this is a lot to ask but it is difficult to try and find the right equations. Is there a way to predict the product or must I do extensive research on the internet to try and find the equations?

Thank you

Offline DevaDevil

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Re: Need help with finding equations
« Reply #1 on: February 21, 2011, 10:16:41 AM »
you must have some idea of chemistry that could occur?
I assume you have a solution with Ti3+ ions in it and you see a reaction, then you have to name the reaction, right? (aka in all solutions the was indeed Ti3+ present, which would mean all are acidic solutions?)

Offline Blue212

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Re: Need help with finding equations
« Reply #2 on: February 21, 2011, 04:03:12 PM »
Unfortunately no, it pretty much just says predict what the products are. There was not even an introduction to the experiment either, just method.

Offline DevaDevil

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Re: Need help with finding equations
« Reply #3 on: February 21, 2011, 04:21:45 PM »
well then, that sounds very strange and not enough explanation. For example: what was the anion that was present with the titanium (III), oxide?

Still, let's see if we can help you out a little bit to get you to get to the answers for yourself.

For the first one: what does the observed bubbling mean for the product(s)?

For the next ones: can you tell me the colors that titanium oxides have?


(and I have to leave the exact answers for your teacher, because without knowing more about the anions that are present I can only guess as well.)

Offline Blue212

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Re: Need help with finding equations
« Reply #4 on: February 21, 2011, 06:05:31 PM »
Sorry, I guess I could have been more clear on the experiment. It's adding a solution of hexaaquatitanium (III) chloride to the tests that I listed.

As for your questions,

A) Formation of bubbles signals the formation of a gas. I am thinking H2 or O2 is the most likely culprits.

B) I know Titanium 3+ has a violet color and Ti (iv) is clear, at least when it is as TiCl4 because I used that in the lab. The other oxidation states aren't as common.

Thanks for your time. I am not exactly looking for you to spoon feed me the equations, I would be more interested in learning how to derive the equations myself if it is possible unless this type of stuff relies more on hours of research than chemical intuition.

Offline DevaDevil

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Re: Need help with finding equations
« Reply #5 on: February 21, 2011, 07:14:24 PM »
let's focus on the first one then: what kind of reaction can make H2 or O2 from water?
Which one is more likely with Zinc?

Offline Blue212

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Re: Need help with finding equations
« Reply #6 on: February 21, 2011, 07:49:39 PM »
I would probably guess a redox reaction. I think maybe the zn would react with the oxygen to produce a zinc oxide leaving the identity of the gas as hydrogen. However, I think it is possible for zinc to react with the chloride to produce zinc chloride but then you would probably see white precipitate and this reaction seems pointless if we are testing for Ti (III).

I think the Ti (III) would get oxidized to Ti(IV) and so would the Zn solid to form (Zn2+) and the hydrogen is being reduced in the process to balance everything out?

Offline DevaDevil

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Re: Need help with finding equations
« Reply #7 on: February 22, 2011, 10:10:01 AM »
so you expect both to get oxidized at the same time. What would have prevented the titanium to oxidize without zinc present?

Here is what I think may happen:

Zinc (E0 of Zn/Zn2+=-.8 will reduce titanium to Ti2+ (E0 of Ti(II)/(III)=-0.37) , which is not stable in water and will quickly oxidize back to Ti3+, while forming hydrogen.

zinc by itself in water forms a passivating layer to prevent quick oxidation, the addition of titanium prevents that

Offline Blue212

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Re: Need help with finding equations
« Reply #8 on: February 22, 2011, 12:50:49 PM »
So you think the overall reaction sequence would be something like

Zn + 2H20 = Zn(OH)2 + 2H2

The titanium half reactions would just cancel out because it gets reduced and oxidized immediately?

Offline DevaDevil

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Re: Need help with finding equations
« Reply #9 on: February 22, 2011, 01:55:00 PM »
a good possibility, but I am not saying that is what WILL happen

Offline Blue212

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Re: Need help with finding equations
« Reply #10 on: February 22, 2011, 02:50:20 PM »
It's better than nothing. Now for the 2nd equation. Do you think this is a fair possibility?

The ammonia dissociates into ammonium which creates a white precipitate with the Cl- ions and the Ti3+ just makes the precipitate appear dark in solution?

I am not too sure about this because I don't think the hexa aqua titanium (III) chloride compound would dissociate like that. What do you think?

Offline DevaDevil

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Re: Need help with finding equations
« Reply #11 on: February 22, 2011, 05:31:20 PM »
your original solution of TiCl3 is colorless (almost), right?

Titanium in basic solution can form oxides... which are insoluble
Ti2O3 just happens to be violet.

Offline Blue212

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Re: Need help with finding equations
« Reply #12 on: February 22, 2011, 06:40:00 PM »
TiCl3 is actually violet. However, that seems possible as well making the overall equation

2Ti3+ + 6OH- = 2Ti2O3 + 3H2

A data sheet I consulted said this was black which makes the inference even more likely. Is it hydrogen that gets produced? I tried balancing it with water but that didn't really work. The reaction looks weird because hydrogen is getting reduced but nothing is getting oxidized. I tried putting Cl- into the equation producing HCl but it became unbalancable.

Offline DevaDevil

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Re: Need help with finding equations
« Reply #13 on: February 23, 2011, 11:46:56 AM »
No gas bubbling, right? So I would expect more along the line of:

4 Ti3+ + 12 OH- = 2 Ti2O3 + 6 H2O

the reason you didn't manage to balance is that you did not balance the Titanium in your equation.
No reduction/oxidation taking place here

Offline Blue212

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Re: Need help with finding equations
« Reply #14 on: February 23, 2011, 01:59:25 PM »
Oh yeah, thanks. That was a dumb mistake. I figured out the rest. Thanks a lot for your *delete me*

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