An ecology student needs to determine the percentage moisture content of a freshly collect… — JAMB UTME

An ecology student needs to determine the percentage moisture content of a freshly collected soil sample from a terrestrial habitat. What is the correct sequence of steps the student must perform to measure this edaphic factor accurately?

1Weigh the freshly collected wet soil sample in a clean evaporating dish to record its initial mass ( $M_1$ ).
2Place the evaporating dish containing the soil sample in an oven maintained at $105^\circ\text{C}$ until a constant dry mass is attained.
3Transfer the dish to a desiccator containing a dry silica gel agent and allow it to cool to room temperature.
4Re-weigh the dry soil sample to record its final mass ( $M_2$ ) and calculate the moisture content using $\frac{M_1 - M_2}{M_1} \times 100\%$ .

Answer

The correct sequence begins with weighing the wet soil sample to find its initial mass (

M_1

), followed by drying the sample in an oven at

105^\circ\text{C}

to constant weight, cooling the sample inside a desiccator, and finally re-weighing the cooled sample to find the dry mass (

M_2

) and calculate percentage moisture content.

The proper laboratory procedure for determining soil moisture content requires establishing initial fresh weight first, driving off all moisture through controlled oven drying at

105^\circ\text{C}

, cooling in a moisture-free desiccator environment, and lastly recording the constant dry weight to calculate mass loss.

Step-by-Step Solution

Measure the initial wet mass of the soil sample.

Obtain initial mass value

M_1

This establishes the total baseline mass of soil solids plus moisture before any evaporation takes place.

Dry the soil in an oven at

105^\circ\text{C}

until constant mass.

Evaporate all free moisture from the soil matrix.

Oven drying at

105^\circ\text{C}

ensures all water escapes without destroying or burning soil organic components.

Cool the dried soil in a desiccator.

Prevent hygroscopic soil from reabsorbing moisture from humid air while cooling.

Hot containers set out on an open laboratory bench will absorb moisture from the surrounding air as they cool, causing inaccurate mass readings.

Weigh the dry soil sample to record

M_2

and compute moisture content.

Calculate percentage moisture as

\frac{M_1 - M_2}{M_1} \times 100\%

The difference between

M_1

and

M_2

equals the total mass of evaporated soil water.

Key Concept

Edaphic Factor Measurement (Soil Moisture Determination by Gravimetric Oven-Drying)

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