Understanding Formula Mass in Chemistry

Formula mass is a fundamental concept in chemistry, representing the sum of the atomic masses of all atoms in a chemical formula. For ionic compounds and network solids that do not exist as discrete molecules, the term "formula unit mass" is often used, but "formula mass" is also commonly applied. It is expressed in atomic mass units (u).

The question asks for the formula mass of anhydrous sodium carbonate. Anhydrous means without water. The chemical formula for anhydrous sodium carbonate is \(\text{Na}_2\text{CO}_3\).

To calculate the formula mass of anhydrous sodium carbonate, we need the atomic masses of the constituent elements: sodium (Na), carbon (C), and oxygen (O). The question provides these atomic masses:

• Atomic mass of Sodium (Na) = 23 u
• Atomic mass of Carbon (C) = 12 u
• Atomic mass of Oxygen (O) = 16 u

Calculating Anhydrous Sodium Carbonate Formula Mass

The chemical formula \(\text{Na}_2\text{CO}_3\) indicates that one formula unit of anhydrous sodium carbonate contains:

• 2 atoms of Sodium (Na)
• 1 atom of Carbon (C)
• 3 atoms of Oxygen (O)

To find the total formula mass, we multiply the number of atoms of each element by its respective atomic mass and sum these values.

Formula Mass of \(\text{Na}_2\text{CO}_3\) = (Number of Na atoms \(\times\) Atomic mass of Na) + (Number of C atoms \(\times\) Atomic mass of C) + (Number of O atoms \(\times\) Atomic mass of O)

Let's plug in the values:

Formula Mass = \((2 \times 23 \text{ u}) + (1 \times 12 \text{ u}) + (3 \times 16 \text{ u})\)

First, calculate the total mass contributed by each element:

• Mass from Sodium = \(2 \times 23 \text{ u} = 46 \text{ u}\)
• Mass from Carbon = \(1 \times 12 \text{ u} = 12 \text{ u}\)
• Mass from Oxygen = \(3 \times 16 \text{ u} = 48 \text{ u}\)

Now, sum these masses to get the total formula mass of anhydrous sodium carbonate:

Formula Mass = \(46 \text{ u} + 12 \text{ u} + 48 \text{ u}\)

Formula Mass = \(58 \text{ u} + 48 \text{ u}\)

Formula Mass = \(106 \text{ u}\)

Anhydrous Sodium Carbonate Formula Mass Result

The calculated formula mass of anhydrous sodium carbonate (\(\text{Na}_2\text{CO}_3\)) is 106 u.

Let's compare this result with the given options:

Our calculated formula mass of 106 u matches Option 2.

Revision Table: Key Concepts for Formula Mass

Additional Information on Sodium Carbonate

Sodium carbonate (\(\text{Na}_2\text{CO}_3\)) is an important chemical compound. It is a sodium salt of carbonic acid. The anhydrous form, \(\text{Na}_2\text{CO}_3\), is a white, odorless powder.

• It is commonly known as washing soda or soda ash.
• The hydrated form, \(\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}\) (sodium carbonate decahydrate), is the most common form.
• Sodium carbonate is widely used in various industries, including glass manufacturing, soap and detergent production, water softening, and in chemical synthesis.
• Calculating formula mass is crucial for stoichiometric calculations, such as determining the amount of substance needed for a reaction or the yield expected.