The API gravity formula API = (141.5 / SG) - 131.5 is used to relate API gravity to what property?

The API gravity formula API = (141.5 / SG) - 131.5 is used to relate API gravity to what property?

• A. Molecular weight
• B. Vapor pressure
• C. Viscosity
• D. Specific gravity

Answer: (D)

The main idea here is that API gravity is built from density relative to water. The formula shows API as a function of specific gravity (SG): API equals 141.5 divided by SG, minus 131.5. Because SG sits in the denominator, liquids that are denser than water (higher SG) yield a smaller first term and thus a lower API, while lighter liquids (lower SG) produce a higher API. This is why API gravity serves as a density-related scale: higher API numbers mean lighter liquids, and lower API numbers mean heavier ones. For example, water has SG of 1.0, giving API = 10; a lighter hydrocarbon with SG 0.75 would have API ≈ (141.5/0.75) − 131.5 ≈ 57. A quick way to relate the two is SG = 141.5 / (API + 131.5).

The main idea here is that API gravity is built from density relative to water. The formula shows API as a function of specific gravity (SG): API equals 141.5 divided by SG, minus 131.5. Because SG sits in the denominator, liquids that are denser than water (higher SG) yield a smaller first term and thus a lower API, while lighter liquids (lower SG) produce a higher API. This is why API gravity serves as a density-related scale: higher API numbers mean lighter liquids, and lower API numbers mean heavier ones. For example, water has SG of 1.0, giving API = 10; a lighter hydrocarbon with SG 0.75 would have API ≈ (141.5/0.75) − 131.5 ≈ 57. A quick way to relate the two is SG = 141.5 / (API + 131.5).