1. Soi Section A Il colloids play an important role in the adsorption of a. Cati

Question

1. Soi Section A Il colloids play an important role in the adsorption of a. Cations b. Anions c. Water molecule d. a and b e. a, b, and c 2. Soil colloids are, by definition, a. made up of mineral matter b. larger than 10 or 20 micrometers in diameter c. made up of organic (humic) matter and clay particles d. crystalline in nature e. only negatively charged 3. Which of these is not one of the four major types (composition) of soil colloids? a. Inorganic humus b. Crystalline Silicate Clays C. Noncrystalline Silicate Clays d. Iron and Aluminum Oxides (Non silicate clays) e. Organic (humus) Soil colloids have small external surface area per unit mass, but some silicate clays possess ext internal surface area between the layers of their platelike crystal units. 4. a. True b. False 5. Which of the following is a cation? a. O2 b. ??2 ?. ?032- d. Cl- e. K* 6. In general, clay minerals have well defined crystalline structure a. True

Explanation / Answer

1) E in soild colloids cations anions and water molecules plays an important role in the adsorption

2) C, made up of organic (humic) matter and clay particles.

3) A, where crystalline silicate clays, non crystallinne silicate clays and iron and aluminium comes under inorganic humus

4) A, Because of their small size, all soil colloids have a larger external surface area per unit mass. The external surface area of 1 g of colloidal clay is 1000 times that of 1 g of coarse sand. Certain silicate clays have extensive internal surfaces occurring between plate like crystal units that make up each particle and often greatly exceed the external surface area.

5) E,K^+ is an cation

6) TRUE, clay minerals have well defined crystalline structure, Clay minerals are generally classified into three layer types based upon the number and arrangement of tetrahedral and octahedral sheets in their basic structure. These are further separated into five groups that differ with respect to their net charge. Kaolinite mineral of layer type 1:1 contains one tetrahedral and one octahedral sheet in their basic structural unit . This two-sheet mineral type is represented by the kaolin group, with the general formula Al2Si205(0H)4. Kaolinite, the most common mineral in this group, is dioctahedral, exhibiting Al3+ octahedral and Si4+ tetrahedral coordination. The sheets are held together by van der Waals bonds between the basal oxygens of the tetrahedral sheet and the hydroxyls of the octahedral sheet. Layers are held together tightly by hydrogen bonding, which restricts expansion and limits the reactive area to external surfaces. Isomorphic substitution for Si4+ and Al3+ in this mineral is negligible. As such, soils dominated by 1:1 minerals exhibit a low capacity for adsorbing cations and have low fertility.

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