Problem 71 - Chemistry and Chemical Reactivity

Question

Knowing that the formula of sodium borate is \(\mathrm{Na}_{3} \mathrm{BO}_{3}\) give the formula and charge of the borate ion. Is the borate ion a cation or an anion?

Step-by-Step Solution

Answer

The borate ion is \(\mathrm{BO}_3^{3-}\) and is an anion.

Step 1: Identify Known Compound Structure

The compound sodium borate is given as \(\mathrm{Na}_3\mathrm{BO}_3\), which includes both sodium ions and a borate ion in its structure.

Step 2: Determine Charge of Sodium Ions

Sodium \((\mathrm{Na})\) is an alkali metal and typically has a charge of \(+1\). Since there are three sodium ions, the total positive charge contributed by sodium in \(\mathrm{Na}_3\mathrm{BO}_3\) is \(+3\).

Step 3: Balance the Overall Charge

In ionic compounds, the total positive charge must equal the total negative charge to maintain neutrality. This implies that the charge on the borate ion \(\mathrm{BO}_3\) must be \(-3\) to counterbalance the \(+3\) charge from the sodium ions.

Step 4: Determine the Type of Ion

Ions with a negative charge are known as anions. Since the borate ion has a charge of \(-3\), it is an anion.

Key Concepts

Ion Charge

Atoms can gain or lose electrons to become ions, which have either positive or negative charges. The charge an ion carries is the result of this gain or loss of electrons. Typically:

• Atoms losing electrons become positively charged ions, called cations.
• Atoms gaining electrons become negatively charged ions, known as anions.

In the exercise, we looked at sodium borate (\(\mathrm{Na}_3\mathrm{BO}_3\)) where the sodium (\(\mathrm{Na}\)) carries a \(+1\) charge, indicating it has lost one electron. The borate ion needs to balance the total charge of the compound, ensuring it remains neutral.

Sodium Borate

Sodium borate, commonly referred to as borax, is a compound made up of the metal sodium and the borate ion. Its formula is \(\mathrm{Na}_3\mathrm{BO}_3\), showing it contains three sodium ions (\(\mathrm{Na}^+\)) alongside one borate ion (\(\mathrm{BO}_3^{3-}\)).

• Sodium ions contribute a positive charge to the compound.
• The borate ion contributes a negative charge.
Together, these ions balance each other out, resulting in a neutral compound originally named due to its boron component, borate's unique structure, and wide applications in cleaning and additives.

Anions

Anions play a critical role in balancing ionic compounds. They are negatively charged ions formed by gaining electrons. The number of electrons gained aligns with the negative charge on the anion.

• The borate ion (\(\mathrm{BO}_3^{3-}\)) is an anion.
• Its charge of \(-3\) signifies it has gained three additional electrons.
Anions often pair with cations in ionic compounds to form stable structures. Their presence is pivotal for balancing equations, ensuring the compound is electrically neutral.

Ionic Compounds

Ionic compounds consist of two parts: cations (positive ions) and anions (negative ions), which together create a neutral compound. The charges between these ions need to balance to achieve stability.

• In sodium borate (\(\mathrm{Na}_3\mathrm{BO}_3\)), three sodium cations (\(\mathrm{Na}^+\)) balance one borate anion (\(\mathrm{BO}_3^{3-}\)).
• This ensures the compound itself maintains a neutral overall charge.

Ionic compounds are often solid and crystalline at room temperature due to the strong interaction between the differently charged ions, making them essential in various applications, from salts to minerals.