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Topic: Which provides the most F^- in 1.0 L of water?  (Read 1176 times)

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Molthisok

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Which provides the most F^- in 1.0 L of water?
« on: August 27, 2020, 10:43:53 AM »
.10 mol NaF
.10 mol IF_3
.10 mol HF

My best guess was IF_3 because it had the largest molar mass, but my professor’s key says I’m wrong
« Last Edit: August 27, 2020, 02:05:32 PM by Borek »

Offline AWK

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Re: Which provides the most F^- in 1.0 L of water?
« Reply #1 on: August 27, 2020, 11:37:10 AM »
Why do you consider IF3 to be a stable ionic compound in the water? You will never get an aqueous solution of this compound - it decomposes completely at -28°C.
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Re: Which provides the most F^- in 1.0 L of water?
« Reply #2 on: August 27, 2020, 02:05:22 PM »
The answer could depend on what are the the IF3 decomposition products. However, there is definitely an error in your reasoning, as

because it had the largest molar mass

molar mass doesn't matter here at all.

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Offline AWK

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Re: Which provides the most F^- in 1.0 L of water?
« Reply #3 on: August 27, 2020, 04:04:19 PM »
The chemistry of interhalogen compounds is very far from general chemistry.
IF3 at -28°C disproportionates to form iodine and iodine pentafluoride. IF5 is fairly stable but reacts vigorously with water to form iodic acid (HIO3) and hydrofluoric acid (this reaction can be found in Wikipedia).
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Offline OrganicH2O

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Re: Which provides the most F^- in 1.0 L of water?
« Reply #4 on: August 31, 2020, 01:09:48 PM »
If we ignore the IF3 decomposition, we could say:

NaF is an ionic compound with full water solubility. Each mole of NaF creates one mole of F- in water.

HF is a weak acid, so 1 mole of HF will dissociate partially to create less than one mole of HF is water.

IF3 is a covalent compound, so it will not dissociate in water at all, making zero moles of F- in water.

The molar mass does not matter because have already been given moles as your unit.
I have a Master's in organic chemistry and I am exposed to a LOT of different introductory organic chem classes in the course of my work, ranging from very basic to Harvard. I am here to refine my knowledge and consult with other organic chemistry nerds.

Offline AWK

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Re: Which provides the most F^- in 1.0 L of water?
« Reply #5 on: August 31, 2020, 03:38:42 PM »
If we ignore the IF3 decomposition, we could say:

IF3 is a covalent compound, so it will not dissociate in water at all, making zero moles of F- in water.
This is chemical nonsense. We will never introduce IF3 into the water, but possibly the equivalent (taking into account fluorine) amount of IF5 that decompose in the water giving 0.3 M HF.
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Offline OrganicH2O

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Re: Which provides the most F^- in 1.0 L of water?
« Reply #6 on: August 31, 2020, 07:38:54 PM »
If we ignore the IF3 decomposition, we could say:

IF3 is a covalent compound, so it will not dissociate in water at all, making zero moles of F- in water.
This is chemical nonsense. We will never introduce IF3 into the water, but possibly the equivalent (taking into account fluorine) amount of IF5 that decompose in the water giving 0.3 M HF.

If the professor is asking a question like this, I assume this is the answer they want. For all we know, the person assigning the question doesn't even know IF3 is unstable. Generally, non-acidic and non-basic covalent compounds do not make ions in water. I assume based on the fact that this is undergraduate general chemistry forum.
I have a Master's in organic chemistry and I am exposed to a LOT of different introductory organic chem classes in the course of my work, ranging from very basic to Harvard. I am here to refine my knowledge and consult with other organic chemistry nerds.

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