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Topic: *delete me*! (chemical identification problem)  (Read 6918 times)

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Offline StephB

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*delete me*! (chemical identification problem)
« on: December 23, 2013, 01:13:29 PM »
Can someone please help me with the following?

Identify the following substances and explain any chemical changes involved:

A) a is a very good conductor of heat and electricity. It dissolves separately in hot aq sodium hydroxide and in a strong solution of h2so4 with the liberation of a colorless explosive gas. It reacts with chlorine gas to form a vapour which condenses into a white product. The relative molecular mass of the vapour changes with temperature.

B) B is a white powder which, on heating in the presence of dry halogen halide gas, produces a white solid c. A cream coloured precipitate is formed when c is dissolved in water and treated with a mixture of dilute nitric acid and aq silver nitrate. On warming c with concentrated h2so4 and mno2, a red vapour is formed.

! Give as much detail as you can :)

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« Last Edit: December 23, 2013, 01:22:41 PM by billnotgatez »

Offline billnotgatez

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Re: *delete me*! (chemical identification problem)
« Reply #1 on: December 23, 2013, 01:23:15 PM »
@StephB
You must show your attempts to solve this problem.
Then we can see where you need help.
This is a forum rule.
Please read forum rules!

Offline StephB

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Re: *delete me*! (chemical identification problem)
« Reply #2 on: December 24, 2013, 12:11:53 PM »
Well I know the first one is a metal if it is a good conductor of heat and electricity... The exploding gas is probably hydrogen gas...But as for anything else I have no idea

The cream colored precipitate indicated the presence of bromide ions being present in solution

Offline Borek

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Re: *delete me*! (chemical identification problem)
« Reply #3 on: December 24, 2013, 07:10:39 PM »
You are right about A being a metal. However, it reacts with acids and bases. What metals do you know that would behave this way?
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Offline StephB

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Re: *delete me*! (chemical identification problem)
« Reply #4 on: December 27, 2013, 06:16:08 PM »

Sodium, Magnesium, aluminium, iron, tin, zinc I think

Offline StephB

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Re: *delete me*! (chemical identification problem)
« Reply #5 on: January 02, 2014, 02:17:17 PM »
Can some one please reply? :(

Offline Corribus

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Re: *delete me*! (chemical identification problem)
« Reply #6 on: January 02, 2014, 02:52:24 PM »
For A, based on the last hint you'll need a metal that reacts vigorously with chlorine gas to produce a metal chloride, and it has to be a metal that can adopt several different oxidation states - this is really the only way the mass of the product vapor can change depending on an external factors like temperature (since presumably the elemental composition won't change).  This should help you eliminate a few of the choices you listed your previous post.  Then, with a little sleuthing on wikipedia, you should be able to guess at a reasonable answer.
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Offline Borek

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Re: *delete me*! (chemical identification problem)
« Reply #7 on: January 02, 2014, 02:59:00 PM »
You are right about A being a metal. However, it reacts with acids and bases. What metals do you know that would behave this way?

Sodium, Magnesium, aluminium, iron, tin, zinc I think

Check the details again. For example, magnesium doesn't react with bases.

it has to be a metal that can adopt several different oxidation states - this is really the only way the mass of the product vapor can change depending on an external factors like temperature (since presumably the elemental composition won't change)

I don't think different oxidation states are necessary.
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Offline Corribus

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Re: *delete me*! (chemical identification problem)
« Reply #8 on: January 02, 2014, 03:57:09 PM »
Ok, but to me it is the most obvious way, if the reaction is strictly between the metal and chlorine.

e.g., X + Cl2  :rarrow: XnClm

There is a metal which reacts accordingly, with the oxidation state of the metal cation in the product chloride changing as a function of temperature.
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Offline Borek

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Re: *delete me*! (chemical identification problem)
« Reply #9 on: January 02, 2014, 04:56:15 PM »
For me the obvious metal that works the way given in the question doesn't change the oxidation state in the gaseous phase.

Obviously we think about different metals, and to be honest, I have no idea what metal you mean  ::) I can think of several possible candidates, but I am not sure they will dissolve in hydroxide (and I am too busy with other things ATM to check the details).
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Offline Corribus

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Re: *delete me*! (chemical identification problem)
« Reply #10 on: January 02, 2014, 05:34:31 PM »
StephB: after private discussion, I see my previous posts may have been unintentionally misleading. Pls disregard my earlier posts about changing oxidation state. I had the right metal in mind but there is a simpler behavior of it that I was overlooking. Definitely the last part about changing molecular mass as a function of temperature is your most important clue. Try to think of a metal chloride that exhibits this behavior in the vapor phase.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline Corribus

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Re: *delete me*! (chemical identification problem)
« Reply #11 on: January 02, 2014, 05:43:48 PM »
For "B", I think "red vapor" is giving you a clue about what the dry halogen gas is.  And the mention of silver should help you figure out what c might be.  From this I can make a guess at B but let's see what you can come up with.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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