Paraffin wax is a mixture of (virtually) straight chain hydrocarbons. Note the word “mixture”. Unless one goes to the enormous lengths of purifying or searching for a fine chemical supplier, the wax will always be a mixture. I used a “pure” wax once as a standard for gas chromatographic studies on paraffin waxes. There is a relationship between hydrocarbon chain length and melting point, but as the waxes are always mixtures, melting points are never exact, either in the compounding or the measuring.