Soil has got organic content. Image credit manicapost.com

ZIMSEC O Level Combined Science Notes: Experiment: Calculating the water and organic content of soil

Materials: soil sample, burner, balance, evapourating dish basin, tongs, water bath

Method

1. This burns off the organic content of the soil
2. Roast the soil sample using a hot flame from the burner until there is no further loss in mass. Record the mass repeatedly at intervals to make sure that there is no further loss
3. Record the final mass of the soil
4. Use a water bath to heat the soil thus ensuring that the temperature does not exceed 100ºC
5. Heat the soil at 100ºC until there is no further loss in mass. Measure and record the mass of the soil repeatedly at 5 minute intervals to make sure there is no further loss in mass
6. Weigh a sample of soil and place it into the evapourating dish
7. Record the mass of the evaporating dish
8. Record the mass

Results

• Below are the results obtained in one experiment
• Mass of the evapourating dish 60g
• Mass of the dish with soil in it 100g
• Mass of both the soil and dish after heating in water bath 96g
• Mass of both after roasting 92.3g
• This means that:
• The mass of the soil before heating is 40g
• Mass of water in soil sample 4g
• Percentage of water content in soil 10%
• Mass of organic content in the soil 3.7g
• Percentage of organic content in the soil 9.25%
• The following formula’s were used:
• Mass of soil sample before heating= Mass of dish with soil-mass of dish
• Mass of water content= Mass of dish with soil-Mass of both dish with soil after heating in water bath
• Mass of organic content= Mass of dish after heating with water bath-mass after roasting
• The percentages are calculated using the formula
• (mass of item/mass of soil)x100
• Where mass of item is the mass for the soil component you wish to calculate for example:
• Organic content percentage=(3.7/40)x100

To access more topics go to the Combined Science Notes page.