Water Chem Question (1 Viewer)

[superjan]

Hi,
Can someone please help me answer this question:
Explain the effect of temperature and ion concentration on the solubility of substances.


Thanks for the help all.

 

[pomsky]

Yoooo

Temperature will increase solubility of the substance. This is because an increase in temperature leads to an increase in kinetic energy (since temperature is really just average kinetic energy of the molecules). Since molecules are vibrating fast and moving more quickly, they're more likely to bump into each other creating strong dispersion forces between them (because their closer together and electron clouds can attract/repel more). If they're polar, it will also lead to a higher likelihood of forming stronger dipole dipole forces and/or hydrogen bonding. As strength of the bond increases, the substance is more likely to form a bond with the solvent (which is usually water) than itself. Thus it will dissolve more easily/ is more soluble in high temperatures.

Not really sure what you mean about ion concentration. The higher the ion concentration in the solvent before dunking the solute in, the more concentrated the solvent already is. As the solvent (water/ alcohol/ etc) will only dissolve an x amount of solute before it reaches saturation, then you're not going to get as much stuff dissolved into the solvent.

 

[Librah]

Yoooo

Temperature will increase solubility of the substance. This is because an increase in temperature leads to an increase in kinetic energy (since temperature is really just average kinetic energy of the molecules). Since molecules are vibrating fast and moving more quickly, they're more likely to bump into each other creating strong dispersion forces between them (because their closer together and electron clouds can attract/repel more). If they're polar, it will also lead to a higher likelihood of forming stronger dipole dipole forces and/or hydrogen bonding. As strength of the bond increases, the substance is more likely to form a bond with the solvent (which is usually water) than itself. Thus it will dissolve more easily/ is more soluble in high temperatures.

Not really sure what you mean about ion concentration. The higher the ion concentration in the solvent before dunking the solute in, the more concentrated the solvent already is. As the solvent (water/ alcohol/ etc) will only dissolve an x amount of solute before it reaches saturation, then you're not going to get as much stuff dissolved into the solvent.

That's not always true.

I have an explanation for this, but it doesn't use HSC chemistry, otherwise i think i'm just overthinking the question.

 

[Librah]

Question is a little ambiguous, but i'm guessing what it's getting at, is if you had an equilibrium, the effect of temperature will depend on whether the reaction is exo/endothermic and if you had a specific ion in the equilibria, adding more of that ion (increasing concentration) will shift to remove some of those ions and that will depend on the value of the equilibrium constants.

 

[porcupinetree]

if you had an equilibrium, the effect of temperature will depend on whether the reaction is exo/endothermic

+1

e.g., an increase in temperature leads to a decreased solubility of CO2(g), because the reaction is exothermic and the CO2 molecules have less ability to become 'trapped' within water molecules, because everything is vibrating more energetically

 

[pomsky]

Question is a little ambiguous, but i'm guessing what it's getting at, is if you had an equilibrium, the effect of temperature will depend on whether the reaction is exo/endothermic and if you had a specific ion in the equilibria, adding more of that ion (increasing concentration) will shift to remove some of those ions and that will depend on the value of the equilibrium constants.

+1, my bad ahaha. Assumed OP was a 2016'er doing the water topic in prelim (prolly cos of the title)

Yiis, so a (slightly) more indepth explanation of Librah's answer is that when an equilibrium encounters a temperature, pressure or concentration change (generally we talk about those three factors) it will react according to Le Chatelier's Principle. LCP states that an equilibrium will shift to minimize the effects of a disturbance. Therefore if you increase the temperature, the equilibrium would shift to lower the temperature, thus favouring the endothermic reaction (because that will absorb heat.) Likewise, if you decrease the temperature, the equilibrium would want to increase the temperature and thus favouring the exothermic reaction.

An equilibrium is a state when the forward and backward reactions (not not all chemical reactions are equilibriums) occur at equal rates. When this happens there will be no discernible change to the system despite chemical reactions/ collisions still occuring.

As for the increasing ion thingo:
If the equilibrium involves a specific ion and you add more of said ion (aka increase concentration of that ion), then by Le Chatelier's Principle, the equilibrium would shift to decrease the ion concentration. This means the equilibrium will shift to favour the forward or backward reaction that uses the ion as a reactants. (decreasing concnetration by using up some of that ion).

Also note that the equilibrium will never be able to completely counter the disturbance, it can only minimize it. For example if we're talking about temperatures and you drop the temp. from 300K (at equilibrium) to 273K, the equilibrium can't ever bring it back to 300K, but it could probably shift to hit a new equilibrium of 290K.

To OP: If my initial hunch was right and you're actually in prelim, don't worry about this lol.

 

[Librah]

I actually think the OP might be in prelim. That's why i was skeptical.