Crude petroleum characteristics: A representative average molecular weight for crude petroleum is closest to which value?
-
A50
-
B250
-
C1500
-
D5000
-
E100
Answer
Correct Answer: 250
Explanation
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:
Step 1: Eliminate very small numbers like 50 (too low for whole crude).Step 2: Eliminate very large numbers like 1500 or 5000 (more typical of asphaltenes or extremely heavy fractions).Step 3: Select the mid-range choice around a few hundred, i.e., 250.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