Why must a solid be dry to obtain meaninful melting point?

Answer 1

when u have a damp crystal then water molecules act as impurities and break bonds between molecules of solid in order to find a place there. thus the ordered arrangement of the crystal gets disturbed as at some places water may get connected with atoms of crystals as shown below and hence due to lower forces of attraction at bonds become weaker and it takes less amount to break them. hence melting point gets lowered.

a a a a a a a a a a a a a w a a w a a a w a a w a w

a a a a a a a a a a a w a a a a a w w a a a a a w a

a a a a a a a a a a w a w w a a a a w w w a a a a w

here a repersent a crystal structure while the picture on right hand side show the intermixing of water molecules(w) with a's

Answer 2

Moisture can affect the melting point of a solid by introducing impurities that alter its chemical composition or create eutectic mixtures, resulting in inaccurate readings. To obtain reliable melting point data, solids must be dried to remove any moisture that could interfere with the purity of the substance being tested.

Answer 3

It must be dry as if its wet it might not be a fair test and accurate as it will be if it was dry. If it is wet it could be closer to a liquid.