The chemical formula of borax is .
Understanding the Chemical Formula of Borax
Borax is a common mineral and a salt of boric acid. It is also known as sodium borate, sodium tetraborate, or disodium tetraborate. It is an important boron compound, a mineral, and a salt of boric acid. In chemistry, it is often encountered in its hydrated form.
The question asks for the chemical formula of borax. Let's look at the common hydrated forms of sodium tetraborate.
Identifying the Correct Borax Chemical Formula
The most common form of borax is the decahydrate, which means it contains 10 molecules of water of crystallization. This is the form typically found in household products and referred to simply as "borax". Its chemical name is sodium tetraborate decahydrate.
The chemical formula for sodium tetraborate decahydrate is $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$. Let's examine the given options to find the correct formula.
Analyzing Borax Formula Options
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Option 1: $\text{Na}_2\text{B}_5\text{O}_7 \cdot 10\text{H}_2\text{O}$
This formula shows 5 boron atoms, which is not correct for sodium tetraborate. Sodium tetraborate contains 4 boron atoms. -
Option 2: $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$
This formula shows 2 sodium atoms, 4 boron atoms, 7 oxygen atoms in the borate part, and 10 water molecules. This matches the chemical formula for sodium tetraborate decahydrate, the most common form of borax. -
Option 3: $\text{Na}_2\text{B}_4\text{O}_7 \cdot 5\text{H}_2\text{O}$
This formula shows 5 water molecules. This represents the pentahydrate form of sodium tetraborate, also known as cotton ball. While a form of sodium tetraborate, it is not the chemical formula commonly referred to as "borax" without further specification (which usually implies the decahydrate). -
Option 4: $\text{Na}_2\text{B}_4\text{O}_7 \cdot 12\text{H}_2\text{O}$
This formula shows 12 water molecules. This form is not a commonly encountered or stable hydrate of sodium tetraborate.
Based on the analysis, the chemical formula for the most common form of borax is $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$.
Borax Chemical Formula Summary
| Compound Name | Chemical Formula | Notes |
|---|---|---|
| Sodium tetraborate decahydrate (Common Borax) | $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$ | Most common form |
| Sodium tetraborate pentahydrate (Cotton ball) | $\text{Na}_2\text{B}_4\text{O}_7 \cdot 5\text{H}_2\text{O}$ | Less common form |
| Anhydrous sodium tetraborate | $\text{Na}_2\text{B}_4\text{O}_7$ | Heated form, no water |
Therefore, the correct chemical formula for borax, referring to the decahydrate, is $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$.
Revision Table: Key Boron Compounds
| Compound | Formula | Common Name |
|---|---|---|
| Borax | $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$ | Sodium tetraborate decahydrate |
| Boric Acid | $\text{H}_3\text{BO}_3$ | Orthoboric acid |
| Boron Trioxide | $\text{B}_2\text{O}_3$ | Diboron trioxide |
Additional Information on Borax Structure and Uses
The chemical formula $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$ might seem simple, but the actual structure of the borate anion in the decahydrate form is more complex. It is better represented as $\text{Na}_2[\text{B}_4\text{O}_5(\text{OH})_4] \cdot 8\text{H}_2\text{O}$. This shows that within the crystal structure, there is a complex tetraborate anion $[\text{B}_4\text{O}_5(\text{OH})_4]^{2-}$ and 8 separate water molecules, plus 2 sodium ions coordinated with water. However, the empirical formula $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$ is the widely accepted and used representation, especially for general purposes.
Borax has many uses, including:
- As a cleaning product.
- In laundry boosters.
- As a flux in metallurgy.
- In making enamel glazes.
- As an ingredient in slime recipes.
- In fertilizers.
Understanding the correct chemical formula, $\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$, is fundamental to studying its properties and reactions.
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