Accepted organic length to be soluble in water (1 Viewer)

TheShy

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Whats the accepted organic length for an alcohol or acid to be soluble in water? Would you say around 3 carbon length? Or would they provide us with that information?
 

icycledough

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With regards to alcohols, the link here --> https://www.solubilityofthings.com/water/alcohols , mentions that up to propanol is where it is 'miscible' , or dissolves in water, due to the short hydrophobic carbon chain. After that, it becomes decreasingly soluble (or increasingly insoluble). You wouldn't be required to remember the exact figures, but if you can remember that alcohols up to propanol or butanol are soluble, it should be enough.

With regards to acids, I believe it's the same; so up to propanoic acid (for butanoic acid, it states that it is miscible in ethanol or slightly miscible in CCl4, which would be far past the scope of the course).
 

tito981

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they are all soluble just to a lower extent the longer the carbon chain
 

Eagle Mum

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they are all soluble just to a lower extent the longer the carbon chain
Octanol and decanoic acid both have water solubility < 0.005 M (ie. less than 1 percent).
They would each appear as an immiscible layer floating on top of water, so for practical intents & purposes, they are water insoluble.

I agree with you that many chemical properties lie on a continuum and ‘cut offs’ can seem quite arbitrary, so one has to define the sought cut off - <1% is commonly used, but higher values can be appropriate, so icycledough’s reply is also helpful.
 
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someth1ng

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I agree with you that many chemical properties lie on a continuum and ‘cut offs’ can seem quite arbitrary, so one has to define the sought cut off - <1% is commonly used, but higher values can be appropriate, so icycledough’s reply is also helpful.
This is what I hate about borderline cases. I'd consider octanol to be "slightly soluble" but there's a problem if we're just going with soluble or insoluble.
 

Eagle Mum

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This is what I hate about borderline cases. I'd consider octanol to be "slightly soluble" but there's a problem if we're just going with soluble or insoluble.
In most scenarios, it’s a matter of defining specifications which determine the appropriate cut off value on a continuous spectrum. It makes it easier to determine if a case is within or outside specifications (PhD level of chemistry applications would be very different to secondary school and simple everyday applications). I appreciate it’s also not always possible to define appropriate specifications, still it’s worthwhile encouraging approaches that are as systematic and critical as possible.

ETA: Related to this concept, I am wary that the secondary school curriculum has its own definition of how cases should fit within specific conceptual frameworks, so I sometimes refrain from answering posted questions to avoid creating confusion, but if someone with better knowledge of NESA requirements doesn’t respond, I might then add my two cents worth.
 
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someth1ng

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In most scenarios, it’s a matter of defining specifications which determine the appropriate cut off value on a continuous spectrum. It makes it easier to determine if a case is within or outside specifications (PhD level of chemistry applications would be very different to secondary school and simple everyday applications). I appreciate it’s also not always possible to define appropriate specifications, still it’s worthwhile encouraging approaches that are as systematic and critical as possible.

ETA: Related to this concept, I am wary that the secondary school curriculum has its own definition of how cases should fit within specific conceptual frameworks, so I sometimes refrain from answering posted questions to avoid creating confusion, but if someone with better knowledge of NESA requirements doesn’t respond, I might then add my two cents worth.
The funny thing is, I don't think most chemists care whether you call it soluble/insoluble/slightly soluble when you have the exact value, and quite frankly, I had no idea there was a cutoff to define whether something was soluble or not. It's definitely context-dependent because I've seen catalysts where you only need ppm solubility and you might say that was soluble even though it may saturate at 10 mg/L.

I agree that creating definitions might be unproductive when people go beyond HS and realize there are varying interpretations. IMO, it's far more important for students to understand why chemical processes and techniques are performed the way they are.
 

Eagle Mum

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The funny thing is, I don't think most chemists care whether you call it soluble/insoluble/slightly soluble when you have the exact value, and quite frankly, I had no idea there was a cutoff to define whether something was soluble or not. It's definitely context-dependent because I've seen catalysts where you only need ppm solubility and you might say that was soluble even though it may saturate at 10 mg/L.

I agree that creating definitions might be unproductive when people go beyond HS and realize there are varying interpretations. IMO, it's far more important for students to understand why chemical processes and techniques are performed the way they are.
I wasn’t suggesting that there is a specific cut off for whether something is soluble or not - that is the original question posted. We agree that it’s context dependent.
 

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