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Question

Posted on: March 6 2013

After bicarbonate does not dissolve in following preparation: After Salicylate 1 g after bicarbonate 20 g glycerol 50 g aqua menthae 3% BF V AD 300 g Fiat solution UG

This preparation we make very frekwent. But today it fails to rub 20g after baking soda with 50g glycerol and then dissolve in 150mL water. There is precipitation! We Heat the solution after baking soda + glycerol + water in the microwave oven. After salicylate we dissolve separately in water!

Answer

In connection with the solubility of NaHCO 3 in water I find different data. The Merck Index mentions 1 in 10 at 25 °C; On the Internet I find 9g at 100 at 20 °C   but also 10.3 g or 8.6 g in 100 ml at 20 °C. The average of all this is about 9g in 100mL. This means that you need 20g of 222mL of water. You have just!

About the solubility in glycerin NOTHING is mentioned. I also do not expect significant solubility in glycerin.

So in fact it is not surprising that it does not dissolve. We are right on the limit!!

Heating to dissolve bicarbonate is out of the question. There are two cooking options. At first we bring bicarbonate into the bottle with the amount of water (here = 220g) and dissolve under shaking of the closed bottle; At the second, we put the baking soda in a mortar and then slip the powder with water where, after settling, the clear above liquid is given off. This operation is repeated to consumption of 220mL water.

If you have sometimes succeeded in solving the bicarbonate then this is due to the heating of the solution in which the bicarbonate is partially or perhaps even fully converted to the better soluble carbonate. This depends on the temperature of warming up.

Personally I would reduce the bicarbonate to 18g. I expect this amount of cold can be solved.