Gce Model Questions Vol1 2024 Chemistry Question 38

Practice objective / multiple choice question 38 from the 2024 Gce Model Questions Vol1 Chemistry examination.

Gce Model Questions Vol1 2024 Chemistry Objective / Multiple Choice Hard Difficulty
Question 38 GCE_MODEL_QUESTIONS_VOL1 • 2024 • CHEMISTRY • objective

A sample of polyethylene is prepared by polymerising ethylene (\(M_{\text{CH_{2}=CH_{2}}}=28.05\ \text{g\ mol}^{-1}\)) with a degree of polymerisation \(DP = 5000\). (i) Calculate the number‑average molecular weight \(M_{n}\) of the polymer. (ii) The intrinsic viscosity of the sample in a given solvent is measured as \([\eta] = 0.85\ \text{dL\ g}^{-1}\). For this polymer-solvent system the Mark-Houwink equation is \([\eta] = K\,M^{a}\) with \(K = 1.5\times10^{-4}\ \text{dL\ g}^{-1}\,\text{mol}^{-a}\) and \(a = 0.75\). Determine the viscosity‑average molecular weight \(M_{v}\) and state whether \(M_{v}\) is greater than or less than \(M_{n}\), giving a brief explanation.

Answer Options

Correct Answer A. M_{n}=1.40\times10^{5}\ \text{g\ mol}^{-1}; M_{v}\approx1.0\times10^{5}\ \text{g\ mol}^{-1}, which is less than M_{n}
B. M_{n}=1.40\times10^{5}\ \text{g\ mol}^{-1}; M_{v}\approx9.0\times10^{4}\ \text{g\ mol}^{-1}, which is less than M_{n}
C. M_{n}=1.40\times10^{5}\ \text{g\ mol}^{-1}; M_{v}\approx1.2\times10^{5}\ \text{g\ mol}^{-1}, which is greater than M_{n}
D. M_{n}=1.20\times10^{5}\ \text{g\ mol}^{-1}; M_{v}\approx1.0\times10^{5}\ \text{g\ mol}^{-1}, which is less than M_{n}
Correct Answer
A
Correct Option:
M_{n}=1.40\times10^{5}\ \text{g\ mol}^{-1}; M_{v}\approx1.0\times10^{5}\ \text{g\ mol}^{-1}, which is less than M_{n}

About This Question

This is Gce Model Questions Vol1 2024 Chemistry Question 38. It is one of the objective questions from the 2024 Gce Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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