Why should the test tubes be dry when testing the solubility

Why should the test tubes be dry when testing the solubility of a substance in ethanol?

Solution

Dry test tubes should be used while determing the solubilty of a substance in ethanol to avoid any interference with the results. If the test tubes are wet, the aqueous part can interfere with the chemical bondings of the substance ( ionic bonding as well as Vander waal\'s forces of attraction). Thereby the moisture influences the result by either decreasing or increasing the solubility depending on the polarity of the substances.