Problem 145 - Chemistry and Chemical Reactivity

Question

The formula of barium molybdate is BaMoO_{ } Which of the following is the formula of sodium molybdate? (a) \(\mathrm{Na}_{4} \mathrm{MoO}\) (c) \(\mathrm{Na}_{2} \mathrm{MoO}_{3}\) (b) NaMoO (d) \(\mathrm{Na}_{2} \mathrm{MoO}_{4}\) (e) \(\mathrm{Na}_{4} \mathrm{MoO}_{4}\)

Step-by-Step Solution

Answer

The formula of sodium molybdate is \( \text{Na}_2\text{MoO}_4 \), option (d).

Step 1: Understand Barium Molybdate Formula

Barium molybdate has the formula \( \text{BaMoO}_4 \). This indicates that barium, which has a charge of \( +2 \), combines with molybdate, \( \text{MoO}_4^{2-} \), to form a neutral compound.

Step 2: Determine Sodium Charge

Sodium \( \text{Na} \) is an alkali metal and typically has a \( +1 \) charge.

Step 3: Analyze Molybdate Ion Charge

Molybdate ion \( \text{MoO}_4^{2-} \) is common in such compounds and carries a \( -2 \) charge, similar to the one in barium molybdate.

Step 4: Balance Charges for Sodium Molybdate

To form a neutral compound with molybdate \( \text{MoO}_4^{2-} \), you need two sodium ions, each \text{Na} with a charge of \( +1 \), to balance the \( -2 \) charge of molybdate. Thus, the correct formula is \( \text{Na}_2\text{MoO}_4 \).

Step 5: Select the Correct Formula from Options

Based on the charge balance, the formula \( \text{Na}_2\text{MoO}_4 \) corresponds to option (d).

Key Concepts

Ionic Compounds

Ionic compounds are formed when metals and non-metals come together to create a neutral compound. This happens through the transfer of electrons from one atom to another.
The metal atoms, which often have only one or a few electrons in their outer shells, are inclined to lose these electrons. When they lose electrons, they become positively charged ions known as cations.

• The non-metal atoms, on the other hand, usually have more electrons in their outer shell. They are inclined to gain electrons to fill up their outer shells, becoming negatively charged ions known as anions.
• As a result, the positive and negative charges from these ions attract each other, which holds the compound together.

In the case of barium molybdate or sodium molybdate, the barium or sodium cations balance the charge of the molybdate anion, forming a stable ionic compound. The resulting compound is electrically neutral, which is a key feature of ionic substances.

Charge Balancing

Charge balancing is a crucial step when forming ionic compounds because the compounds need to be electrically neutral. Each positive charge should be offset by a negative charge.
This is often done through a careful determination of how many ions of each element are needed to balance out the charges.

• For barium molybdate ( \( \text{BaMoO}_4 \) ), barium (\( \text{Ba}^{2+} \)) bonds with one molybdate ion (\( \text{MoO}_4^{2-} \)), as their charges directly cancel each other out.
• For sodium molybdate, sodium (\( \text{Na}^+ \)) has a +1 charge, and you would need two sodium ions to balance the -2 charge of one molybdate ion (\( \text{MoO}_4^{2-} \)).

Without balancing these charges, the compound would be unstable and wouldn't exist naturally in this form. Charge balancing is fundamental in predicting the formula of ionic compounds and understanding the ratios between the participating ions.

Alkali Metals

Alkali metals, which include lithium, sodium, potassium, and others, are found in Group 1 of the periodic table.
These metals are highly reactive and are known for their tendency to lose one electron, forming positively charged ions (\( \text{Na}^+ \), \( \text{K}^+ \), etc.).

• Because they have only one electron in their outer shell, they can easily lose this one electron to achieve a full outer electron shell, like those of the inert gases.
• Once they lose this electron, they form cations with a +1 charge, making them ideal for forming ionic compounds with anions that have a negative charge.

In the case of sodium molybdate ( \( \text{Na}_2\text{MoO}_4 \) ), the sodium ions balance the molybdate ion's charge, highlighting their role as essential components in the formation of ionic compounds. Their reactivity and charge characteristics make them versatile in chemical reactions.

Polyatomic Ions

Polyatomic ions are those charged species that consist of two or more atoms bonded together, carrying a net positive or negative charge as a whole.
These ions play a critical role in the structure and formation of various chemical compounds.

• An example of a polyatomic ion is the molybdate ion \( \text{MoO}_4^{2-} \).
• This ion is made of a central molybdenum atom surrounded by oxygen atoms, carrying an overall charge of -2.

Polyatomic ions are interesting because, despite being a cluster of atoms, they behave as a single charged entity which participates in ionic bonds just like monatomic ions do. They add a layer of complexity to compounds, but their behavior in reactions is predictable, which makes them integral to understanding complex chemical formations like barium molybdate and sodium molybdate.