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JAMB Biology 2011 Paper

Question : 22

Total: 48

The percentage of humus in the soil sample is

Solution:

Concept:

Humus is the organic matter lost when the dried soil is roasted.

Explanation:

First, find the mass of the original soil sample.

Mass of soil =

101.5\text{g} - 80.5\text{g} = 21.0\text{g}

The soil loses water in the oven, then loses humus when roasted.

Mass after oven drying =

99.0\text{g}

Mass after roasting =

95.5\text{g}

Loss in mass due to burning off humus =

99.0\text{g} - 95.5\text{g} = 3.5\text{g}

Percentage of humus =

\frac{\text{mass of humus}}{\text{mass of soil}} \times 100

\frac{3.5}{21.0} \times 100 = 16.7\%

Answer:

16.7\%

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