Why Does Adding Salt Mix Increase Volume

[BZOFIQ]

Live-n-Learn!

Thank you @Randy Holmes-Farley

 

[AngryOwl]

I would have never thought this would need 40 posts of discussion ;Hilarious

 

[BZOFIQ]

I would have never thought this would need 40 posts of discussion ;Hilarious

me neither, but re-read and some things are rather interesting...if not magical.

 

[Cory]

I gave the exact data for seawater. It rises. That's the summation of many effects, but mostly Na+, Cl-, Mg++, and SO4--.

But, there are chemicals that actually cause a decrease, emphasizing that it can decrease and is not "simple physics".

Dissolving a small amount of magnesium sulfate in fresh water results in a smaller final volume than the starting volume of fresh water. That is because magnesium and sulfate strongly bind water ions, pulling them closer and increasing the density.

See this article:

9.2 Partial Molar Quantities

chem.libretexts.org

.

from it:

" It is possible for a partial molar volume to be negative. Magnesium sulfate, in aqueous solutions of molality less than 0.07mol kg−10.07mol kg−1, has a negative partial molar volume. Physically, this means that when a small amount of crystalline MgSO44 dissolves at constant temperature in water, the liquid phase contracts. This unusual behavior is due to strong attractive water–ion interactions. "


This article has highly detailed data for true enthusiasts:

Densities and apparent molar volumes of aqueous magnesium sulfate and sodium sulfate to 473 K and 100 bar

https://pubs.acs.org/doi/10.1021/je00045a018

This was too interesting but the volume may decrease because of what you stated, however the weight would increase. Correct?

 

[Chewbacca]

I think the word is

DISPLACEMENT

 

[Randy Holmes-Farley Verified Community Expert]

This was too interesting but the volume may decrease because of what you stated, however the weight would increase. Correct?

Mass is always conserved, except in nuclear reactions. Combine two things and the mass is the simple addition of the two.

 

[Randy Holmes-Farley Verified Community Expert]

I think the word is

DISPLACEMENT

Word for what?

That word does not correctly characterize what happens when salts dissolve in water.

 

[Chewbacca]

Word for what?

That word does not correctly characterize what happens when salts dissolve in water.

That is what the heading is asking not all your scientific marbles

 

[Randy Holmes-Farley Verified Community Expert]

That is what the heading is asking not all your scientific marbles

lol

If you read his questions in his post, he is asking far more complex questions for which the answer is not the ultra simplistic idea of displacement.

 

[tvan]

+1 for the scientific marbles.

 

[Chewbacca]

lol

If you read his questions in his post, he is asking far more complex questions for which the answer is not the ultra simplistic idea of displacement.

I guess ULTRA SIMPLISTIC is just to much

 

[Randy Holmes-Farley Verified Community Expert]

I guess ULTRA SIMPLISTIC is just to much

I'm not sure what that means.

Bear in mind, this is a science forum at reef2reef and we strive for detailed and technically accurate discussions. Sometimes they go into much more detail than the average user is interested in, but for those who are, or for those who want some assurance that what is being stated is not just a random opinion but something that can be backed up with valid scientific facts and theories, we often delve into the underlying principles of reefkeeping practices.

 

[canadianeh]

When you add air into water filled ballon, it increases the volume of the balloon.

 

[Chewbacca]

I'm not sure what that means.

Bear in mind, this is a science forum at reef2reef and we strive for detailed and technically accurate discussions. Sometimes they go into much more detail than the average user is interested in, but for those who are, or for those who want some assurance that what is being stated is not just a random opinion but something that can be backed up with valid scientific facts and theories, we often delve into the underlying principles of reefkeeping practices.

Well pardon me I by no way mean to insult you intelligence

 

[Randy Holmes-Farley Verified Community Expert]

When you add air into water filled ballon, it increases the volume of the balloon.

Yes, but the more pertinent question to salts raising or lowering volume when they dissolve is what happens if you only add air that dissolves in the water, with zero actual gas volume.

I suspect the volume rises, but let's pull out some more marbles and look into it...

Found this paper:

The Influence of Dissolved Gases on the Density of Water

The Influence of Dissolved Gases on the Density of Water - IOPscience

The Influence of Dissolved Gases on the Density of Water, H Watanabe, K Iizuka

iopscience.iop.org

from it:

" As is seen from the results, the dissolved nitrogen decreases the density of water, and the others increase it. "

If dissolving nitrogen (the majority of "air") decreases the density of water it is dissolving into, then the volume must rise. Same is true for "air" as shown in the paper..

But for the other components of air (e.g., oxygen), the effect is more subtle. An increase in density "might" more than compensate for the added mass of gas and thus the volume may decline. Does it? I cannot tell from the data in the paper.

 

[tvan]

When you add air into water filled ballon, it increases the volume of the balloon.

But does the air increase the volume of water inside the balloon?

 

[Randy Holmes-Farley Verified Community Expert]

But does the air increase the volume of water inside the balloon?

it does , as I showed with a paper that measured it (ignoring the complication of the pressure effect from the balloon on the density of the water).