mod 7 organic states of matter (1 Viewer)

[indeed]

Hi all,

when writing chemical equations, which need physical states of the compounds, for the organic molecules that are not gaseous but liquid OR aqueous, do we state them as liquid or aqeuous?

e.g. carboxylic acids, alcohols, esters etc.

 

[Bob99]

I mostly used aq for those compounds as they're always a 'solution' if that makes sense
i only used liquid for stuff like water

but as long as your states are not completely wrong (like writing solid instead of gas) it should be fine

 

[indeed]

I mostly used aq for those compounds as they're always a 'solution' if that makes sense
i only used liquid for stuff like water

but as long as your states are not completely wrong (like writing solid instead of gas) it should be fine

Oh ok, I remember hearing that you need liquid states for alcohols, and some alkenes (with long C chain), so was unsure whether it also applies for carboxylic acids esters etc.
But thank you anyways

 

[Bob99]

Oh ok, I remember hearing that you need liquid states for alcohols, and some alkenes (with long C chain), so was unsure whether it also applies for carboxylic acids esters etc.
But thank you anyways

Oh yeah its been a year since ive done this lol so im not too sure about those specifics.
Best option will be to email your teacher just to get that reassurance.

 

[SB257426]

Hi all,

when writing chemical equations, which need physical states of the compounds, for the organic molecules that are not gaseous but liquid OR aqueous, do we state them as liquid or aqeuous?

e.g. carboxylic acids, alcohols, esters etc.

alcohols and water def yeah... but carboxylic acids aqueous cuz its a solution

 

[indeed]

alcohols and water def yeah... but carboxylic acids aqueous cuz its a solution

Why's carbo acids a solution and not alcohols (is it solubility in water etc.)

And are the rest of organic molecules e.g. aldehydes,, ketones, esters also solutions

 

[Unovan]

I always just write aq apart from water (l)

 

[SB257426]

Why's carbo acids a solution and not alcohols (is it solubility in water etc.)

And are the rest of organic molecules e.g. aldehydes,, ketones, esters also solutions

If I will be honest I was told by my teacher to write (l) for alcohols and water and (aq) for everything else including esters and aldehyte, ketones.

For esters, when they are produced they are in equilirbium with carboxylic acids and alcohols as the reactions and the ester is a product alongside water so thats how I know its aqeuous because it is in solution WITH water.

However idk why u would do aq for aldehydes and ketones and carboxylic acids

 

[indeed]

If I will be honest I was told by my teacher to write (l) for alcohols and water and (aq) for everything else including esters and aldehyte, ketones.

For esters, when they are produced they are in equilirbium with carboxylic acids and alcohols as the reactions and the ester is a product alongside water so thats how I know its aqeuous because it is in solution WITH water.

However idk why u would do aq for aldehydes and ketones and carboxylic acids

Oh ok yh makes sense all g

 

[SB257426]

If I will be honest I was told by my teacher to write (l) for alcohols and water and (aq) for everything else including esters and aldehyte, ketones.

For esters, when they are produced they are in equilirbium with carboxylic acids and alcohols as the reactions and the ester is a product alongside water so thats how I know its aqeuous because it is in solution WITH water.

However idk why u would do aq for aldehydes and ketones and carboxylic acids

I was just told what to write and not the reason why, however i think for alkanes and alkenes and alkynes you need to put liquid for longer chains

 

[wizzkids]

You state that gases are (g) and liquids are (l). Students are not required to memorise the physical states of organic compounds for the HSC Chemistry exam. You should be able to work these facts out from the context of the question. If a question requires you to write a chemical equation, particularly if it includes thermochemical data, then you must be given the physical states of the compounds. If it is a reaction in the gas phase, you will be told the compounds are gases. If it is combustion of liquids, you will be told they are liquids. If it is a reaction mixture, and the mixture consists of miscible liquids, e.g. a Fischer esterification of a carboxylic acid, then it should be clear that the reagents are all dissolved in an excess of liquid alcohol, so you would state that they are (l).
Does that answer your question?

 

[SB257426]

You state that gases are (g) and liquids are (l). Students are not required to memorise the physical states of organic compounds for the HSC Chemistry exam. You should be able to work these facts out from the context of the question. If a question requires you to write a chemical equation, particularly if it includes thermochemical data, then you must be given the physical states of the compounds. If it is a reaction in the gas phase, you will be told the compounds are gases. If it is combustion of liquids, you will be told they are liquids. If it is a reaction mixture, and the mixture consists of miscible liquids, e.g. a Fischer esterification of a carboxylic acid, then it should be clear that the reagents are all dissolved in an excess of liquid alcohol, so you would state that they are (l).
Does that answer your question?

So then would an ester be a liquid or aqueous

 

[wizzkids]

So then would an ester be a liquid or aqueous

Most esters are liquids at room temperature.

 

[SB257426]

Most esters are liquids at room temperature.

so just to confirm we call esters liquids at room temperature because they result from the reaction of liquid alcohol?

 

[wizzkids]

Ahh, no. We call them liquids because that is their standard state at 25^oC. If the ester coincidentally happens to be dissolved in a reaction mixture like an alcohol, then you still call it a liquid. The adjective "aqueous" (aq) should be reserved for substances that are dissolved in water, or in which water makes up the majority of the mass.

 

[SB257426]

Ahh, no. We call them liquids because that is their standard state at 25^oC. If the ester coincidentally happens to be dissolved in a reaction mixture like an alcohol, then you still call it a liquid. The adjective "aqueous" (aq) should be reserved for substances that are dissolved in water, or in which water makes up the majority of the mass.

Thank you so much, I get it now

 

[Luukas.2]

This is not correct. Just as we reserve the term "aqueous" for situations where the solvent is water, we reserve the term "liquid" for a pure substance or for the solvent.

In an esterification process where the reaction mixture contains several different liquid substances that are miscible and mixed together, neither the states (l) nor (aq) is appropriate. The proper state of matter in this situation is (sol), meaning that the substances are solvated and the solvent is not water.

 

[wizzkids]

In an esterification process where the reaction mixture contains several different liquid substances that are miscible and mixed together, neither the states (l) nor (aq) is appropriate. The proper state of matter in this situation is (sol), meaning that the substances are solvated and the solvent is not water.

Thanks for that contribution, you got me thinking that can't be right because IUPAC has reserved the term "sol" for colloidal suspensions, so I went to the references.
In the Journal of Pure Appl. Chem., Vol. 80, No. 2, pp. 233–276, 2008. doi:10.1351/pac200880020233 © 2008 IUPAC they give the approved references for all the Physical Chemistry terms, and this paper recommends the term "sln" for state of solution.

 

[Luukas.2]

Thanks for that contribution, you got me thinking that can't be right because IUPAC has reserved the term "sol" for colloidal suspensions, so I went to the references.
In the Journal of Pure Appl. Chem., Vol. 80, No. 2, pp. 233–276, 2008. doi:10.1351/pac200880020233 © 2008 IUPAC they give the approved references for all the Physical Chemistry terms, and this paper recommends the term "sln" for state of solution.

Thanks for that information.

I can't say that I am surprised that IUPAC decided to declare a new practice that differs from one already in use. It doesn't mean that many will follow it, however. It can see the sense in not using a single term (sol) with different meanings, but that doesn't mean the recommendation will be followed - and it is one that I don't recall having heard.

In any case, whether using "(sol)" or "(sln)", the important point for the HSC is that it is inappropriate to use the "(l)" state for other than pure liquids or a solvent. It leads to confusion.

For example, if I dissolve sodium chloride into water, I write:

NaCl (s) -----> Na⁺ (aq) + Cl^- (aq)​

If I heat and melt solid sodium chloride, I write:

NaCl (s) -----> Na⁺ (l) + Cl^- (l)​

If I dissolve sodium chloride into liquid ammonia, writing any of

NaCl (s) -----> Na⁺ (sol) + Cl^- (sol)​

or

NaCl (s) -----> Na⁺ (sln) + Cl^- (sln)​

or

NaCl (s) -----> Na⁺_{(in NH3, l)} + Cl^-_{(in NH3, l)}​

is preferable to the highly misleading option of

NaCl (s) -----> Na⁺ (l) + Cl^- (l)​

which looks like melting. I might clarify a little by putting something over the arrow, like:

NaCl (s) --H₂O--> Na⁺ (aq) + Cl^- (aq)

NaCl (s) --heat--> Na⁺ (l) + Cl^- (l)

NaCl (s) --NH₃--> Na⁺ (l) + Cl^- (l)​

but the opportunities for confusion remain high.

It also makes confusing a case like Fischer esterification where the solvent is the mixture of components, albeit with generally the higher concentration of the alcohol, because a system like

CH₃COOH (sln) + CH₃CH₂OH (sln) <--- ---> CH₃COOCH₂CH₃ (sln) + H₂O (sln)​

having an equilibrium constant of

​

is a lot more intuitively obvious for an HSC student than making the same claim about an equilibrium system written as

CH₃COOH (l) + CH₃CH₂OH (l) <--- ---> CH₃COOCH₂CH₃ (l) + H₂O (l)
​

I hope you agree.

 

[wizzkids]

I think any further debate will likely result in arcane hair-splitting. However, for students sitting their HSC Chemistry exam, there will be just three states of matter, they are solid, liquid and gas and the only other mixture they are likely to be examined on is the aqueous mixture, and we should leave it at that.