Chem - solubility

anpanman SG

Hi!

when you cool the saturated solution of NaCl and NaNO3 (say from 70 deg to room temperature), from which solution would you obtain more crystals? My guess is NaCl because its solubility varies very little with changing temperature which means not a lot of its solute would dissolve, hence more excess solid would be crystallise out. Not sure but that's my reasoning and it sounds wrong.

From some net research, i also found out that crystallization is never used to separate NaCl mixture of NaCl and water.... why?

dkcx SG

Hi!

From some net research, i also found out that crystallization is never used to separate NaCl mixture of NaCl and water.... why?

NaCl and water mixture can just heat since NaCl won't react/decompose under heat.

yiha093 SG

Hi!

From some net research, i also found out that crystallization is never used to separate NaCl mixture of NaCl and water.... why?

because hor . do u wan

a) u heat 10mins get ur product

b) heat 5min wait 1 day to get that product. sumore crystallisation got chance of impurity.

doesnt make economical sense la . maybe thats why thats nvr usedd

anpanman SG

Hmm.

First part of the question not yet answered. So more NaCl will be crystallised out? Thanks!

dkcx SG

Hmm.

First part of the question not yet answered. So more NaCl will be crystallised out? Thanks!

Base on solubility, NaNO3 is more than twice more soluble than NaCl.

Due to that, i would say more NaNO3 might crystalised out.

As NaCl's solubilty vary little with temperature, it would mean that changes in temperature does little to affect the solubility and thus there should be less crystalisation.

anpanman SG

Base on solubility, NaNO3 is more than twice more soluble than NaCl.

Due to that, i would say more NaNO3 might crystalised out.

As NaCl's solubilty vary little with temperature, it would mean that changes in temperature does little to affect the solubility and thus there should be less crystalisation.

Ok, shall confirm my concept with you.

If more of the solute of a particular substance dissolves than the other, then crystalization of this substance will yield more crystals than a substance whose solute is less soluble. Is it because if more solute dissolves, then upon evaporation of the water and cooling, more crystals form?

dkcx SG

Ok, shall confirm my concept with you.

NaCl 5g dissolve in 100ml of water at 25 degrees
NaNO3 50g dissolves in 100ml of water at 25 degrees

NaCl 9g dissolves in 100ml of water at 100 degrees
NaNO3 90g dissolves in 100ml of water at 100 degrees.

From the above, you can see that when water is cooled, you will get 4g of NaCl and 40g of NaNO3.

For O's, you will will consider evaporation as neglegible so only take into account the cooling.