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Why is camphor preferred as a solvent fo...

Why is camphor preferred as a solvent for measuring the molecular mass of naphthalene by Rast method?

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Camphor has a large `K_(f)` value `(39.8^(@))`, and therefore, it causes large depression in the melting point of a solution with very small amount of solute (naphthalene).
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Assertion (A): Camphor is used as a solvent in the determination of the molecular mass of naphthalene and anthracene. Reason (R ): camphor has high molal elevation constant.

What is osmotic pressure and how is it related with the molecular mass of a non-volatile substance? What advantage the osmotic pressure method has over the elevation of boiling point method for determining molecular masses?

Knowledge Check

  • The molecular mass of Kci determined by osmotic pressure method will be

    A
    the same as normal mol. mass
    B
    higher than normal mol. mass
    C
    lower than normal mol. mass.
    D
    can not be predicted unless data are given

  • Camphor is often used in molecular mass determination because

    A
    it has a very high cryoscopic constant.
    B
    it is volatile
    C
    it is solvent for organic substances
    D
    it is readily available

  • In the Victor Meyer's method for the determination of molecular mass of an organic compound, what is measured ?

    A
    Volume of displaced air
    B
    Volume of vapours of substance produced
    C
    Volume of water vapours produced
    D
    None of these

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    Give equation to calculate molecular mass of a solute using osmotic pressure method.

    A system of greater disorder of molecules is more probable. The disorder of molecules is reflected by the entropy of the system. A liquid vapourizes to form a more disordered gas. When a solute is present, there is additional contribution to the entropy of the liquid due to increased randomness. As the entropy of solution is higher than that of pure liquid, there is weaker tendency to form the gas. Thus, a solute (non-volatile) lowers the vapour pressure of a liquid, and hence a higher boiling point of the solution. Similarly, the greater randomness of the solution opposes the tendercy to freeze. In consequence, a lower temperature must be reached for achieving the equilibrium between the solid (frozen solvent) and the solution. The elevation in boiling point (DeltaT_(b)) and depression in freezing point (DeltaT_(f)) of a solution are the colligative properties which depend only on the concentration of particles of the solute and not their identity. For dilute solutions, (DeltaT_(b)) and (DeltaT_(f)) are proportional to the molarity of the solute in the solution. A liquid possessing which of the following characteristics will be most suitable for determining the molecular mass of a compound by cryoscopic measurements?

    A liquid possessing which of the following characteristics will be most suitable for determining the molecular mass of a compound by cryoscopic measurements? a.That having low freezing point and small enthalpy of fusion b.That having high freezing point and small enthalpy of fusion c.That having hifh freezing point and small enthalpy of vapourization d.That having large surface tension

    Camphor is often used in molecular mass determination because

    Molecular mass of a volatile substance may be measured by :

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