General chemistry question

[Ferferi]

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A 0.60 M solution is made by dissolving solid compound X in water. After ten seconds, the
concentration of X is 0.40 M. All of the following could account for these results
EXCEPT one. Which one is this EXCEPTION?
A. Precipitation
B. Neutralization
C. Evaporation
D. Decomposition
E. Disproportionation



The answer is A
Can somebody please explain it to me, I just don't get it.

It's question 61 in OAT sample test

 

[Dotoday]

Yes it is true. The concentration of the compound clearly decreased because it went from 0.6 to 0.4. That cannot be precipitation, because if it was the concentration would not change. It is like saying if you put a table spoon if sand into a glass of water, it will precipitate, but there will still be one table spoon of sand in th glass, nothing less.

Hope this helps.

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[Ferferi]

Thanks
Your example really helped


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[imbackasd]

Yes it is true. The concentration of the compound clearly decreased because it went from 0.6 to 0.4. That cannot be precipitation, because if it was the concentration would not change. It is like saying if you put a table spoon if sand into a glass of water, it will precipitate, but there will still be one table spoon of sand in th glass, nothing less.

Hope this helps.

Sent from my MB855 using Tapatalk

I was thinking along the lines of that precipitation is an increase rather than a decrease, is that a valid logic?

 

[premac]

no, that wouldn't be a valid logic. let's say there were 2 mol of a dissolved compound (in an aqueous state) in 4 L of solution.
if that compound goes through "precipitation" and becomes solid, there's still 2 mol of the same compound (now in a solid state) in 4 L of solution.
this would mean:
start: 2mol / 4L = 0.5 M
end: 2mol / 4L = 0.5 M
thus, precipitation wouldn't result in any change in molarity.