What precautions should be observed when an aqueous sodium carbonate solution is used to extract an organic solution containing traces of acid?

The biggest precaution that should be followed is to not wall the separatory funnel off too tightly. When the sodium carbonate solution is used, the acid will react with it to create carbon dioxide. This can build up in the funnel, leading to an increase in pressure that could cause a rupture if enough is created.

Most smaller stars don't have a radiative zone.