Physical Properties of Alkynes :
(i)Lower members (C2 to C4) are gases; middle one (C5 to C12) are liquids; higher are solids.
(ii)The b.pt., m.pt. and specific gravity of alkynes show a regular increase with increase in molecular weight; however less volatile than alkene. The order of b.pt. in hydrocarbons has been explained in terms of polarity. Alkynes possess more polarity and thus have higher b.pt.
b.pt. Alkyne > Alkene > Alkane
(iii)All are colourless & possess no characteristic odour; however C2H2 has garlic odour due to the impurities of PH3, H2S etc. Pure C2H2 has ethereal odour.
(iv)Soluble in organic solvents like acetone, alcohol & sparingly soluble in water.
(v)The b.pt. of acetylene is -84oC. Liquid acetylene is dangerously explosive and therefore storage and transportation of liquid acetylene is prohibited by law. That is why acetylene is stored and transported by dissolving it in acetone soaked on porous material like asbestos packed in steel cylinders, under high pressure.