Passage III

Three studies examined the effects of compost (organic matter) on 3 physical properties of soil.

Five soil mixtures (Mixtures 1-5) were prepared (see Table 1).

Study 1

A 1.5 L pot was prepared by placing 500 g of Mixture 1 into the pot, after which the pot was stored at 30°C for 72 hr. The pot and its contents were then baked in a 105°C oven for 24 hr. After cooling, the mixture's bulk density (the dry mass of the mixture per unit volume) was determined.

These procedures were repeated for each of Mixtures 2-5 (see Table 2).

Study 2

Another 1. 5 L pot of Mixture 1 was prepared, stored, and baked as in Study 1.

The dried mixture was ground into powder and passed through a screen with 2 mm diameter openings. Five grams of the screened powder were then mixed with 5 mL of H2O. and the pH of the powder-H2O suspension was determined.

These procedures were repeated for each of Mixtures 2-5 (see Table 3).

Study 3

Another 1. 5 L pot of Mixture 1 was prepared, stored, and baked as in Study 1. The dried mixture was then ground and screened as in Study 2.

Fifty grams of the screened powder were mixed with 5 mL of H2O to form a soil paste, and the paste was placed on a filter. Suction was then applied to the filter. and the extract (the clear, colorless liquid that passed through the filter) was collected. The electrical conductivity of the extract was determined.

These procedures were repeated for each of Mixtures 2-5 (see Table 4).

13. Which of the following is the most likely reason that a given mixture was exposed to a temperature of 105°C in Study 1?

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

Looking at the description of Study 1, the second sentence tells us to bake the container and the mixture inside in an oven at 105 degrees for 24 hours, and then let it cool down, so that we can know the bulk density of the mixture, and the bulk density The definition given in brackets is the quality of dry mass after drying, so the purpose of cooling is to drain water.