Understanding the Chemical Formula of Sodium Carbonate

The question asks for the chemical formula of Sodium Carbonate. To determine the chemical formula of an ionic compound like Sodium Carbonate, we need to know the charges of the ions involved.

Sodium Carbonate is made up of Sodium ions and Carbonate ions.

• The Sodium ion is derived from the element Sodium (Na), which is an alkali metal and typically forms a cation with a +1 charge. Its symbol is Na⁺.
• The Carbonate ion is a polyatomic ion composed of carbon and oxygen atoms. Its formula is CO₃ and it carries a -2 charge. Its symbol is CO₃²⁻.

To form a neutral compound, the total positive charge must balance the total negative charge. We need to find the smallest whole number ratio of Na⁺ ions to CO₃²⁻ ions that results in a neutral compound.

Let the number of Na⁺ ions be $x$ and the number of CO₃²⁻ ions be $y$. The total positive charge is $x \times (+1)$ and the total negative charge is $y \times (-2)$. For a neutral compound, the sum of charges is zero:

$x(+1) + y(-2) = 0$

$x - 2y = 0$

$x = 2y$

The simplest ratio of $x$ to $y$ is when $y=1$, which gives $x=2$. This means we need 2 Sodium ions for every 1 Carbonate ion.

Alternatively, using the criss-cross method:

• Write the symbols of the ions with their charges: Na⁺ and CO₃²⁻.
• The magnitude of the charge on the Carbonate ion (2) becomes the subscript for Sodium.
• The magnitude of the charge on the Sodium ion (1, though usually omitted) becomes the subscript for Carbonate.

This gives Na₂CO₃.

Let's examine the given options:

1. Na₃CO₂: This formula suggests 3 sodium ions and a CO₂ group. CO₂ is carbon dioxide, not a carbonate ion. This is incorrect.
2. Na₂CO: This formula suggests 2 sodium ions and a CO group. CO is carbon monoxide, not a carbonate ion. This is incorrect.
3. NaCO₃: This formula suggests 1 sodium ion and 1 carbonate ion. With Na⁺ and CO₃²⁻, the charges do not balance (+1 + -2 = -1). This would be a charged species, not a neutral compound. This is incorrect.
4. Na₂CO₃: This formula suggests 2 sodium ions and 1 carbonate ion. With two Na⁺ ions (total charge +2) and one CO₃²⁻ ion (total charge -2), the charges balance (+2 + -2 = 0). This is the correct chemical formula for Sodium Carbonate.

Therefore, the correct chemical formula for Sodium Carbonate is Na₂CO₃.

Revision Table: Chemical Formulas and Ionic Compounds

Understanding how to write chemical formulas for ionic compounds is key. Here's a quick summary:

• Ionic compounds are formed between metals (usually forming positive ions) and nonmetals or polyatomic ions (usually forming negative ions).
• The chemical formula represents the simplest whole-number ratio of cations to anions needed to make the compound electrically neutral.
• The subscripts in the formula indicate the number of ions of each type.
• Use the criss-cross method: The magnitude of the cation's charge becomes the subscript for the anion, and the magnitude of the anion's charge becomes the subscript for the cation. Simplify subscripts if they have a common divisor.

Additional Information about Sodium Carbonate

Sodium Carbonate, Na₂CO₃, is an important industrial chemical. It is also known as soda ash or washing soda.

• It is a white, odorless powder.
• It is soluble in water and forms an alkaline solution, which is why it's used in detergents and cleaning products.
• It is used in the manufacturing of glass, paper, and soaps.
• It can absorb moisture from the air to form a hydrated form, Sodium Carbonate decahydrate (Na₂CO₃·10H₂O), also known as washing soda.