<span>Condensation takes place when gas molecules lose heat and kinetic energy. The warmer molecules are the faster they move. Gas molecules move very quickly and have a lot of kinetic energy and heat energy. As the gas molecules lose heat they also lose kinetic energy. As the molecules slow down they move closer together to form liquids.</span>
The purpose of using distilled water in the cuvette of the spectrophotometer is to calibrate the instrument. It is generally considered that distilled water shows zero absorbance and 100 % transmittance. So, to zero out the absorbance of compounds other than the analyte being determined, distilled water is used as a blank.
If the unknown being determined is prepared using ethanol as the base solution, the blank used must be ethanol. This is because absorbance if any from the solvent, ethanol must be zeroed out as when the measurement of the actual unknown is being made, the absorbance of the solvent does not interfere.
