Question

What is the basic formula of China clay?

• A. $Al_{3}O_{2} \cdot 2SiO_{2} \cdot 6H_{2}O$
• B. $Al_{2}O_{3} \cdot 2SiO_{2} \cdot 2H_{2}O$
• C. $Al_{2}O_{5} \cdot 2SiO_{3} \cdot 2H_{2}O$
• D. $Al_{2}O_{3} \cdot 6SiO_{3} \cdot 2H_{3}O$

Hint:

Logic Tip: Remember the 1:2:2 ratio for Kaolin: 1 Alumina, 2 Silica, 2 Water.

Answer 1

The Correct Option is B

Concept:
China clay, scientifically known as Kaolin, is a primary clay mineral. Understanding its chemical formula is fundamental to calculating glaze and clay body recipes in ceramics.

Step 1:
Kaolin is a hydrated aluminum silicate. This means its molecular structure is composed of alumina ($Al_{2}O_{3}$), silica ($SiO_{2}$), and chemically bound water ($H_{2}O$).

Step 2:
In a theoretically pure sample of kaolinite, the molar ratio of these components is exactly 1 part alumina to 2 parts silica to 2 parts water.

Step 3:
Combining these parts yields the standard theoretical formula for China clay: \[ Al_{2}O_{3} \cdot 2SiO_{2} \cdot 2H_{2}O \]

Step 4:
Options (1), (3), and (4) contain incorrect molecular proportions and non-existent stable chemical combinations for clay minerals (such as $H_{3}O$ in a solid crystal lattice or $Al_{3}O_{2}$).

Step 5:
Matching our derived formula with the given choices, the correct answer is Option 2. \[ \boxed{\text{(2) } Al_{2}O_{3} \cdot 2SiO_{2} \cdot 2H_{2}O} \]