Crude petroleum characteristics: A representative average molecular weight for crude petroleum is closest to which value?

Introduction:
Crude petroleum is a complex mixture of thousands of hydrocarbons. Still, an average molecular weight can be quoted for rough engineering calculations and property correlations.

Given Data / Assumptions:

• We seek a rough, representative average value, not the extremes for individual fractions.

Concept / Approach:
Whole crudes typically exhibit average molecular weights in the low hundreds; values around ~200–300 are commonly cited for representative crudes, acknowledging that light vs heavy crudes shift this number.

Step-by-Step Solution:

Verification / Alternative check:
Empirical correlations used in petroleum characterization (e.g., Watson K, density-boiling point) are consistent with average molecular weights near a few hundred for whole crude.

Why Other Options Are Wrong:

• 50: Too low for whole crude mixtures.
• 1500 and 5000: Representative of heavy residues/asphaltenes, not the average of the entire crude.
• 100: Still low for whole crude.

Common Pitfalls:
Confusing the average for the whole crude with the extreme ends of the boiling range.

Final Answer:
250