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: State the formula for moisture content (dry weight basis).
The moisture content (\(w\)) is the ratio of the mass of water (\(M_w\)) to the mass of dry soil solids (\(M_s\)), expressed as a percentage. \[ w (%) = \frac{M_w}{M_s} \times 100 \] Step 2: Calculate the mass of water and mass of solids from the given data.
- Mass of moist soil (total mass), \(M_t = 100\) g
- Mass of oven-dried soil (mass of solids), \(M_s = 80\) g
- Mass of water, \(M_w = M_t - M_s = 100 - 80 = 20\) g
Step 3: Calculate the moisture content. \[ w (%) = \frac{20 \text{ g}}{80 \text{ g}} \times 100 = \frac{1}{4} \times 100 = 25% \]