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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: mark1029 on September 13, 2017, 02:56:04 AM

Title: what gas is forming when mixing NaCl into water?
Post by: mark1029 on September 13, 2017, 02:56:04 AM

Hi all,

I'm not very familiar with chemistry but have a question on mixing salt (NaCl) in (tap) water.
I notice that small bubbles are forming when mixing, is this a gas that formed during the mixing process and what is the gas?
Or Is it air that was already in the water that is escaping?

Thanks,

Mark

Title: Re: what gas is forming when mixing NaCl into water?
Post by: clarkstill on September 13, 2017, 03:37:40 AM

Hi Mark,

When NaCl is dissolved in water there should be no by-products (gaseous or otherwise):

NaCl (s) --> Na+ (aq) + Cl- (aq.)

So it follows that any gas released must have been in the water to start with (i.e. air). But there are still a couple of reasons why bubbles might form: (i) the reaction above is exothermic and the heating of the water decreases gas solubility or (ii) gases are less soluble in water containing NaCl so are driven out of solution. Dissolving NaCl is actually endothermic (https://socratic.org/questions/why-is-solvation-of-nacl-endothermic) so the answer must be (ii).

In fact, there is a brief discussion here:

http://www.freedrinkingwater.com/water_quality/water-science/j-9-08-does-salt-concentration-salinity-water-affect-solubility-oxygen.htm

Hope this makes sense.

Title: Re: what gas is forming when mixing NaCl into water?
Post by: mark1029 on September 13, 2017, 10:27:29 AM

Makes sense, thanks for the response

Title: Re: what gas is forming when mixing NaCl into water?
Post by: Flatbutterfly on September 13, 2017, 01:10:46 PM

I think you will find that the dissolution of NaCl is an endothermic process.
I believe that because the H2O molecules solvate the ions there is less water to solvate the N2/O2 in air and hence the excess bubbles out.
Check what you can find regarding the solubility of air is salt or sea water.

Title: Re: what gas is forming when mixing NaCl into water?
Post by: clarkstill on September 15, 2017, 04:48:58 PM

Quote from: Flatbutterfly on September 13, 2017, 01:10:46 PM

I think you will find that the dissolution of NaCl is an endothermic process.

Isn't that what I said?

Title: Re: what gas is forming when mixing NaCl into water?
Post by: Flatbutterfly on September 19, 2017, 10:18:36 AM

clarkstill: My apologies I misread your reply.