**Study 1** Students determined the soil organic matter (SOM) percentage of a soil sample … — ACT

Study 1
Students determined the soil organic matter (SOM) percentage of a soil sample using a loss-on-ignition (LOI) procedure. The apparatus consisted of an analytical balance, porcelain crucibles, a drying oven ( $105^\circ\text{C}$ ), a high-temperature muffle furnace ( $550^\circ\text{C}$ ), and a desiccator containing active silica gel desiccant.

Based on standard laboratory procedures for analyzing soil composition and controlling moisture error, in what chronological sequence should the students perform the steps below?

1Cool the empty porcelain crucible in a desiccator and record its baseline tare mass on the analytical balance.
2Heat the crucible containing the raw soil sample at $105^\circ\text{C}$ in the drying oven until constant mass is achieved.
3Place the crucible with dry soil in the muffle furnace at $550^\circ\text{C}$ to oxidize and burn off organic compounds.
4Cool the crucible and remaining mineral ash in the desiccator before recording the final mass on the balance.

Answer

The correct procedural sequence is: first, cool the empty crucible in a desiccator and record its tare mass; second, heat the sample at

105^\circ\text{C}

to remove moisture; third, combust the dry soil at

550^\circ\text{C}

in a muffle furnace; and fourth, cool the remaining ash in a desiccator before obtaining the final mass.

The procedural steps follow a strict logical sequence to isolate variables: first, establish a baseline tare mass for the apparatus; second, remove water at

105^\circ\text{C}

to isolate dry soil weight; third, combust organic content at

550^\circ\text{C}

; and fourth, cool the mineral ash in a desiccator to prevent water reabsorption prior to final weighing.

Step-by-Step Solution

Determine initial tare mass of the crucible

Obtained empty crucible mass (

m_{\text{tare}}

)

Establishing an accurate tare mass after desiccator cooling prevents room humidity from skewing initial measurements.

Evaporate soil moisture at low temperature

Obtained dry soil sample mass (

m_{\text{dry}}

)

Heating at

105^\circ\text{C}

removes water content so moisture loss is not falsely measured as organic matter loss.

Combust organic compounds at high temperature

Thermal breakdown of organic matter leaving inorganic mineral ash (

m_{\text{ash}}

)

Muffle furnace temperature (

550^\circ\text{C}

) selectively ignites organic material while leaving inorganic mineral residue intact.

Cool in desiccator and perform final gravimetric weighing

Accurate mass measurement of mineral ash

Desiccator cooling prevents hot ash from absorbing ambient moisture during cooling, ensuring valid organic mass loss calculations.

Key Concept

Sequential procedural analysis and apparatus role in gravimetric loss-on-ignition testing

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic