Cause of carbonate error?

Question

Cause of carbonate error?

Answer 1

The failure to degas the NaOH solutions will allow dissolved CO2 in the water to react with the NaOH forming NaHCO3 and Na2CO3 both of which are weaker bases than NaOH, Na2CO3 also is diprotic and will consume HCl differently than NaOH. Also, importantly, these weaker bases make the endpoint by phenolphthalein, drift and fade ,,,introducing an inaccurate estimate of the equivalence point.