A sample of wet garden soil of known weigh was heated to constant weight. The loss of weight is due to loss of

Analyze the question: A wet soil sample is weighed, then heated until its weight stops changing (constant weight). We need to identify what is lost.

Concept: Soil analysis is done in stages:

1. Water content: Heat the soil gently (about 100-105°C) to constant weight. Water evaporates and the loss in weight equals the water that was in the soil.
2. Organic matter (humus) content: Heat the dried soil very strongly (burning or ignition). The organic matter burns off, and the loss in weight gives the organic matter content.

So the temperature and the stage matter. Heating wet soil to constant weight in this basic experiment is the method for finding the water content. Once all the water has evaporated, the weight stops changing, which is why "constant weight" is the sign that the water has gone.

Solution:

• Wet soil, heated gently, loses water by evaporation.
• When the weight no longer changes, all the water is gone.
• Organic matter only burns off at much higher temperatures, with strong heating (ignition) of the dried soil, which is a separate step.
• Inorganic matter (sand, clay, mineral salts) does not burn off or evaporate under these conditions.

So options B, C and D are wrong. The loss of weight is due to loss of water.

Answer: A. water

Exam tip: Remember the order: dry first (water), burn next (organic matter). If a question says "heated to constant weight", think water. If it says "strongly heated or burnt", think organic matter (humus).