Disolving solutes in solvents

[nathan]

As I poured sugar into my coffee, I wondered about volumes. Obviously when one adds the sugar, the volume of the mug contents increases -- by the volume of sugar added. Now, when the sugar actually disolves, does the volume decrease from that? Does it return to the volume of the original coffee? I can't remember if I ever learnt this at school.

Oh, and google's not being helpful -- maybe I should drink the coffee and then try again :)

[Reality Check]

WikiAnswers (http://forums.randi.org/Does sugar still have volume when it is dissolved in water?): Says that the volume of the sugar water would be greater than that of water but less than that of the water plus the sugar. So the volume will decrease a bit when the sugar disolves.

[nathan]

Thanks RealityCheck!

Corrected URL:
http://wiki.answers.com/Q/Does_sugar_still_have_volume_when_it_is_dissolved_ in_water

[MrQhuest]

Wow, speaking of coffee, I really need to finish mine. I misread the thread title as "dissolving students in solvents." :confused:

MrQhuest

[Madalch]

Now, when the sugar actually disolves, does the volume decrease from that? Does it return to the volume of the original coffee? I can't remember if I ever learnt this at school.

You wouldn't have- I remember teaching it as part of a second-year physical chemistry course, but it was sufficiently uninteresting that I don't recall any keywords that would lead me to successfully googling up an answer.

I suspect that, with effort, you could find a solute and a concentration such that the total volume would be exactly the same as the original solvent; more than the solvent but less than the total; equal to the unmixed total; or less than the original solvent (pick your favourite).

[fuelair]

Essentially, as the crystal structure of the sugar breaks down (dissolves), the individual sugar molecules - which are still as they were or your coffee would not taste sweeter - can fit in between (or vice-versa) the water molecules so that they do not take up as much space in the solution as they did in their crystal (solid) form. Or, as said above: volume is more than the solvent alone, but less than adding the volume of solute and solvent together with no reference to dissolving. For sugar and water, no combination should result in no volume change or a perfectly equivalent volume change. I am fairly certain - based on what happens in the formation of solutions - that no pairing could work in a way that caused no increase in volume with the two fully mixed - but this is not my area of speciality so I could be quite wrong.

[GreyICE]

Or, take two spheres with different diameters. Take one box of one, and one box of another. Pour the two together, observe that they have less volume than the sum of the volumes they previously occupied.

This example has absolutely nothing to do with solutes and solvents in any way, shape, or form, but it's the typical high school chemistry demonstration of the reduced volume.

[fuelair]

Or, take two spheres with different diameters. Take one box of one, and one box of another. Pour the two together, observe that they have less volume than the sum of the volumes they previously occupied.

This example has absolutely nothing to do with solutes and solvents in any way, shape, or form, but it's the typical high school chemistry demonstration of the reduced volume.That's why I don't use it in mine!:)

[Beerina]

WikiAnswers (http://forums.randi.org/Does sugar still have volume when it is dissolved in water?): Says that the volume of the sugar water would be greater than that of water but less than that of the water plus the sugar. So the volume will decrease a bit when the sugar disolves.

If you've ever made jelly you'd realize this!

A single pot of jelly (about 9" in diameter, 5 inches filled) has something like 27 cups of sugar in it. It's something like 50% sugar by volume after dissolving.

[Madalch]

I am fairly certain - based on what happens in the formation of solutions - that no pairing could work in a way that caused no increase in volume with the two fully mixed - but this is not my area of speciality so I could be quite wrong.

That's a challenge, that is.

<Reaches for bookshelf, grabs rubber bible, turns to page D-253. That's table 66 of Properties of Aqueous Solutions.>

30% silver nitrate has a density of 1.3204 g/mL = 1.3204 kg/L.

So, if we take 1.00 L (1.00 kg) of water, and add 300 g AgNO3 to it, we have 1.30 kg of solution. This will occupy a volume of 1.30 kg divided by 1.32 kg/L = 0.985 L of solution. Less than the water we started with.

Thank you, thank you, I'll be here all week.

[DavidS]

That's a challenge, that is.

<Reaches for bookshelf, grabs rubber bible, turns to page D-253. That's table 66 of Properties of Aqueous Solutions.>

30% silver nitrate has a density of 1.3204 g/mL = 1.3204 kg/L.

So, if we take 1.00 L (1.00 kg) of water, and add 300 g AgNO3 to it, we have 1.30 kg of solution. This will occupy a volume of 1.30 kg divided by 1.32 kg/L = 0.985 L of solution. Less than the water we started with.

Thank you, thank you, I'll be here all week.
Great! You can interpolate that table for us.

300g AgNO3 in 1300g of solution is only 23%. I have neither the table to hand nor the immediate Google-fu inclination, but I'll bet a twelve-pack the density at reasonable conditions will be less than 1.3 g/ml and the volume will therefore be something larger than 1000 ml.

[Madalch]

300g AgNO3 in 1300g of solution is only 23%.
Reaches for CRC Handbook, gives self a large smack in the head with it.

You are, of course, correct. I'll just eat my previous post, and get back to you.

[Madalch]

Alright, alright.

5% NaOH solution has a density of 1.0538 kg/L.
This is comprised of 0.95 kg water (950 mL) and 0.05 kg NaOH = 1.00 kg mixture.
This solution has a volume of 1.00 kg divided by 1.0538 kg/L = 0.949 L.

This is very slightly less than the water we started with.

(ETA: The densities given are for 20oC, so the pure water we start with will actually have a volume of 952 mL, since the density of water at 20 oC is not exactly 1.000 g/mL. So we lose 3 whole millilitres.)

[DavidS]

Reaches for CRC Handbook, gives self a large smack in the head with it.

<shrug>
It happens. You won't be the last. You weren't the first. My empirical basis for these assertions is left as an exercise for the reader :o

[ddt]

Cool effect - solve something in water and end up with less volume than the water you started with. Does this effect only occur with water or also with other solvents? You've got a rubber bible, Madalch :).

And what's the explanation for this counter-intuitive phenomenon? Has it to do with hydrogen bonds? I faintly remember something about hydrogen bonds in water actually keeping the water molecules further apart then would be the case without them, from high-school chemistry.

[Madalch]

Cool effect - solve something in water and end up with less volume than the water you started with. Does this effect only occur with water or also with other solvents? You've got a rubber bible, Madalch. The CRC Handbook only gives data for aqueous solutions. (Well, it gives data for some non-aqueous solutions, but only when the solute is water. 90% ethanol isn't an aqueous solution, but it's just a logical continuation of the ethanol-dissolved-in-water data.)

And what's the explanation for this counter-intuitive phenomenon? Has it to do with hydrogen bonds? I faintly remember something about hydrogen bonds in water actually keeping the water molecules further apart then would be the case without them, from high-school chemistry.
In the case of sodium hydroxide, both the cation and anion are very strongly solvated. The sodium ion will have four or six water molecules attached to it, and this clump will take up less volume than four (or six) individual water molecules bouncing around. Same with the hydroxide ion.

[ddt]

The CRC Handbook only gives data for aqueous solutions.
OK, sorry. I've only seen it stand in friends' book cases :).


In the case of sodium hydroxide, both the cation and anion are very strongly solvated. The sodium ion will have four or six water molecules attached to it, and this clump will take up less volume than four (or six) individual water molecules bouncing around. Same with the hydroxide ion.
The reason for this is the water molecules are highly polar, and sufficiently small?

[fuelair]

You've got a rubber bible, Madalch :).

. Doesn't everybody?!!?:)

[Evilgiraffe]

Doesn't everybody?!!?:)

Mine's a 59th edition. Which makes it older than I am (but only just).
Must've only cost £4-5 on ebay and was invaluable for 2nd/3rd year physical labs.