curiouschemist82
Member
OK. Continuing on from my earlier post...
I could wax intellectual about the 'likelihood' of certain amounts of water being present in this reaction to prevent the formation of alkoxide salts. I was going to reason that the fact we see bubbles at all actually shifts the position of equilibrium in the favour of 'the forward reaction' (as discussed earlier), driving the formation of more alkoxides. However, believe it or not, I'm not all that interested in the theoretical ifs and buts. I'm a practical scientist - and I realised that there was an experiment I could do to find out FOR SURE whether or not the bubbles seen in this reaction were solely from the water initially present in the KOH or whether the water was being produced in the process (which would confirm that we are generating alkoxides)...
I had a bit of spare time today, so I did it. Here it is:
The experiment I am about to describe is really quite simple. It just involves preparing a mixture of KOH and glycerin (in the correct proportions of course), heating it (and recording the temperature using an infrared thermometer) and then weighing the total mixture periodically. The loss in weight must be due to water boiling off - as long as the temperature stays below 290 oC (which is the boiling point of glycerin).
So if we assume that the KOH I used contains 9% water by mass, we can calculate how much weight *should* be lost and compare that to the actual observed weight loss of the mixture. If the mixture loses 9% of its mass (or less) and stops boiling, then it means that the only water present was the 9% impurity in the KOH to start with. If, on the other hand, more than 9% weight loss is observed, then it confirms that water is being produced in the process and indicates that the glycerin is actually reacting with KOH (to form alkoxide species and water).
Here are some of the details of the experiment set up;
Amount of glycerin used: 62.40 g
Amount of KOH used: 19.83 g
Container: 250 mL borosilicate glass beaker
Heating method: kitchen hob (electric)
Temperature measurement: Infrared thermometer
Now, the situation is slightly complicated. I am using a very sensitive balance and it cannot be used to weigh things which are hot. So it simply means I have to allow the mixture to cool before weighing it. For that reason, the experiment is being broken down into four stages of heating (with cooling and weighing in between each stage). I have included the results and some pics of the experiment as attachments.
The scatter graphs might look a little complicated, but the blue dots simply show the temperature of the mixture (temperature is shown on the left vertical axis and the thick vertical red lines show the point at which heating was ceased) with time shown along the horizontal axis. The orange dotted line shows the amount of weight lost (in grams) - the axis used for this weight loss measurement is on the right hand side - which is bound to confuse a few of you.
The bar chart is a much more simplified representation of the weight loss over the four heating stages. We were expecting no more that 9% (of the KOH mass) to be lost from the mixture if the only water present was that impurity in the KOH as supplied. In fact I have measured a whopping 59% (over 11 g) lost over the four heating stages!
This means that water is indeed being produced by the reaction of glycerin and KOH!
Which means alkoxide species are indeed being generated. Now, exactly what kind of mischief these alkoxides get up to when they are added to a mixture of plant oils is still up for debate... I think we'll leave that for another time.
CONCLUSIONS:
Please don't anyone panic! I heated this KOH glycerin mixture excessively to prove that there is indeed a reaction between the two chemicals. In fact, by the end of this experiment, my mixture was starting to turn a light yellow colour (see attachment) and started producing a nasty 'burning plastic' smell (of course I had adequate ventilation so no worries about safety). In the methods I have seen, i.e. if people are careful with the temperature of the mixture and the time for which it is heated, this unwanted chemical reaction will be minimised. It is certainly going on though, so my advice to anyone using the new KOH/ Glycerin method is to keep the temperature and heating time as low as possible. Boiling for two (or three) minutes should be enough to dissolve the KOH.
Thank you topofmurrayhill for inspiring me to get off my chair and put on my lab specs once again! I feel like I accomplished something today and also - now there is some empirical evidence to support my hypothesis about alkoxide salts!
More experiments to come in the future, guys... Thanks for reading.
Happy soaping!
View attachment weight loss koh gly.pdf
View attachment % of KOH Mass Lost.pdf
I could wax intellectual about the 'likelihood' of certain amounts of water being present in this reaction to prevent the formation of alkoxide salts. I was going to reason that the fact we see bubbles at all actually shifts the position of equilibrium in the favour of 'the forward reaction' (as discussed earlier), driving the formation of more alkoxides. However, believe it or not, I'm not all that interested in the theoretical ifs and buts. I'm a practical scientist - and I realised that there was an experiment I could do to find out FOR SURE whether or not the bubbles seen in this reaction were solely from the water initially present in the KOH or whether the water was being produced in the process (which would confirm that we are generating alkoxides)...
I had a bit of spare time today, so I did it. Here it is:
The experiment I am about to describe is really quite simple. It just involves preparing a mixture of KOH and glycerin (in the correct proportions of course), heating it (and recording the temperature using an infrared thermometer) and then weighing the total mixture periodically. The loss in weight must be due to water boiling off - as long as the temperature stays below 290 oC (which is the boiling point of glycerin).
So if we assume that the KOH I used contains 9% water by mass, we can calculate how much weight *should* be lost and compare that to the actual observed weight loss of the mixture. If the mixture loses 9% of its mass (or less) and stops boiling, then it means that the only water present was the 9% impurity in the KOH to start with. If, on the other hand, more than 9% weight loss is observed, then it confirms that water is being produced in the process and indicates that the glycerin is actually reacting with KOH (to form alkoxide species and water).
Here are some of the details of the experiment set up;
Amount of glycerin used: 62.40 g
Amount of KOH used: 19.83 g
Container: 250 mL borosilicate glass beaker
Heating method: kitchen hob (electric)
Temperature measurement: Infrared thermometer
Now, the situation is slightly complicated. I am using a very sensitive balance and it cannot be used to weigh things which are hot. So it simply means I have to allow the mixture to cool before weighing it. For that reason, the experiment is being broken down into four stages of heating (with cooling and weighing in between each stage). I have included the results and some pics of the experiment as attachments.
The scatter graphs might look a little complicated, but the blue dots simply show the temperature of the mixture (temperature is shown on the left vertical axis and the thick vertical red lines show the point at which heating was ceased) with time shown along the horizontal axis. The orange dotted line shows the amount of weight lost (in grams) - the axis used for this weight loss measurement is on the right hand side - which is bound to confuse a few of you.
The bar chart is a much more simplified representation of the weight loss over the four heating stages. We were expecting no more that 9% (of the KOH mass) to be lost from the mixture if the only water present was that impurity in the KOH as supplied. In fact I have measured a whopping 59% (over 11 g) lost over the four heating stages!
This means that water is indeed being produced by the reaction of glycerin and KOH!
Which means alkoxide species are indeed being generated. Now, exactly what kind of mischief these alkoxides get up to when they are added to a mixture of plant oils is still up for debate... I think we'll leave that for another time.
CONCLUSIONS:
Please don't anyone panic! I heated this KOH glycerin mixture excessively to prove that there is indeed a reaction between the two chemicals. In fact, by the end of this experiment, my mixture was starting to turn a light yellow colour (see attachment) and started producing a nasty 'burning plastic' smell (of course I had adequate ventilation so no worries about safety). In the methods I have seen, i.e. if people are careful with the temperature of the mixture and the time for which it is heated, this unwanted chemical reaction will be minimised. It is certainly going on though, so my advice to anyone using the new KOH/ Glycerin method is to keep the temperature and heating time as low as possible. Boiling for two (or three) minutes should be enough to dissolve the KOH.
Thank you topofmurrayhill for inspiring me to get off my chair and put on my lab specs once again!
I feel like I accomplished something today and also - now there is some empirical evidence to support my hypothesis about alkoxide salts!More experiments to come in the future, guys... Thanks for reading.
Happy soaping!
View attachment weight loss koh gly.pdf
View attachment % of KOH Mass Lost.pdf
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