Question

If the moist and oven dried weights of a soil sample are 100 gram and 80 gram, respectively, the moisture content of the sample on dry weight basis will be:

• A. 10%
• B. 15%
• C. 25%
• D. 30%

Hint:

The most common mistake is to divide the mass of water by the total (moist) mass. Remember, for the standard (dry weight basis) moisture content, the denominator is always the mass of the dry soil solids.

Answer 1

The Correct Option is C

Step 1: Define the formula for moisture content on a dry weight basis.
Moisture content (\(w\)) is calculated as the ratio of water mass (\(M_w\)) to dry soil solids mass (\(M_s\)), expressed as a percentage.\[ w (%) = \frac{M_w}{M_s} \times 100 \] Step 2: Determine the mass of water and the mass of solids using the provided data.
- Total mass of moist soil: \(M_t = 100\) g
- Mass of oven-dried soil (solids): \(M_s = 80\) g
- Mass of water: \(M_w = M_t - M_s = 100 - 80 = 20\) g
Step 3: Compute the moisture content.
\[ w (%) = \frac{20 \text{ g}}{80 \text{ g}} \times 100 = \frac{1}{4} \times 100 = 25% \]