Q23 · CSIR NET Chemistry, December 2011
Paper: CSIR NET December 2011 · Subject: Physical Chemistry · Chapter: Polymer Chemistry · Topic: Molecular Weight Averages · Marks: 2 · Difficulty: Medium
The osmotic pressure ($\pi$) of a polymer sample at different concentrations (c) was measured at T(K). A plot of ($\pi$/c) versus c gave a straight line with slope (m) and intercept (c'). The number average molecular weight of the ploymer is (R = gas constant).
(a)$\frac{Rt}{c'}$
(b)$\frac{c'}{RT}$
(c)RT
(d)mRT
Answer
Answer (as printed): B
Explanation
Osmotic pressure, 𝜋 = C₁RT (1+ BC1 + ...) Where C₁ = concentration of polymer in mol L-1 unit and B = constant. When concentration is expressed in terms of 'c' (gL-1) then, C₁ = Mc 2 𝜋 = MRTc(1+MBc+...) ⇒ = MRT+BM2RTc+... 3 2 Vs c graph will give intercept (c')= MRT 3 3/ M= 45
Explanation as extracted from the printed page; notation may be imperfect.
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