Moisture (water) content from wet and dry masses: An unsaturated soil sample (volume 100 cm³) weighs 190 g in the field. After oven drying, it weighs 160 g. What is the water content w of the soil?

Introduction / Context:
Water content (also called moisture content) is a fundamental index property in soil mechanics, needed for compaction control, shear strength correlations, and consolidation predictions. It compares the mass of water in a soil to the mass of dry soil solids.

Given Data / Assumptions:

• Wet (natural) mass M_wet = 190 g.
• Dry mass M_dry = 160 g (after oven drying).
• Standard definition w = (mass of water) / (mass of dry solids).
• Sample volume is provided but not required for w.

Concept / Approach:

Water content w is the ratio of the mass of water removed by drying to the mass of soil solids left after drying. It is commonly expressed as a decimal or percentage. Use simple subtraction to find water mass, then divide by dry mass.

Step-by-Step Solution:

Verification / Alternative check:

A result under 0.20 is typical for an unsaturated compacted soil. If expressed in percent, w ≈ 18.8%.

Why Other Options Are Wrong:

0.288, 0.388, 0.488, and 0.588 imply much more water relative to solids than given by the mass difference.

Common Pitfalls:

Dividing by wet mass instead of dry mass, or forgetting to subtract to find water mass.

Final Answer:

0.188