[Smokaz]

Thank you for reading this post.

I am an IB student investigating a trend in the homologous series of alcohol. I am attempting to design a lab where I can determine the solubility of the primary alcohols butan-1-ol to octan-1-ol. Unfortunately, the equipment available at our lab is crude at best.

My solvent is water, and the concentrations of the stock alcohol is roughly 96-99%. I have taken a volumetric approach to determine the solubility. Using a burette, known amounts of alcohol is dispensed into a beaker filled with distilled water. I have used green food coloring, a drop added to the water, to better discern the concave meniscus formed between the layer of the saturated alcohol solution and the excess alcohol.

However, I have not been able to obtain any precise measurements this way. It has been very hard for me to know when the solution is saturated by looking for the meniscus, as I am not sure which meniscus it is. After mixing and stirring, the solution will eventually settle forming three layers. The uncertainty of the beaker is about +-0.25mL.

The bottom layer is the layer of the colored water with dissolved alcohol. The middle layer is white in color and often contain small bubbles, I am not sure what this is. So far, I believe it is a sort of endpoint where the h-bonds broken in the water can barely facilitate the alcohol. The top layer is clear, i presume this is the excess alcohol.

Here, the question is, should I include the middle layer? Or simply read off the increase in volume in the beaker up to the middle layer and assume this is how much alcohol it takes to create a saturated solution?

If anyone of you have a suggestion to do this differently (using school-lab equipment), or can appropriately argue for why the middle layer should or should not be included please respond and comment on this post. Included is an attachment of a drawing illustrating the three layers formed when the solution is left alone for visualization purposes.

Thank you very much,
Smokaz.

[skbuncks]

Ho Smokaz,

To determine the solubility of butanol in water is really quite simple, you have almost got it but have overcomplicated the situation.
The simplest way would be to measure 100g of water and 20g of butanol into a separating funnel. Shake vigorously with periodic venting and then allow to settle.
If after performing this you have only one layer then the solution is not saturated and more butanol should be added. If you have two layers then the aqueous layer is saturated.
Once a saturated solution has been obtained simply run off the lower aqueous layer and reweigh. This will tell you the mass of butanol that has been solubilised per 100g water.

*remember solubility will vary with temperature
*n-butanol has a solubility of around 7.7g/100ml and n-octanol is insoluble.

skb