Problem 77 - Chemistry and Chemical Reactivity

Question

Rank the following compounds in order of increasing solubility in water: \(\mathrm{Na}_{2} \mathrm{CO}_{3}, \mathrm{BaCO}_{3}, \mathrm{Ag}_{2} \mathrm{CO}_{3}.\)

Step-by-Step Solution

Answer

The order of increasing solubility is \(\mathrm{BaCO}_{3} < \mathrm{Ag}_{2} \mathrm{CO}_{3} < \mathrm{Na}_{2} \mathrm{CO}_{3}\).

Step 1: Understanding Solubility Concepts

Solubility is determined by a compound's ability to dissolve in solvent, in this case, water. Ionic compounds tend to dissolve based on the solubility rules for anions and cations. Na, K, and NH4 salts are generally soluble, nitrates, acetates and bicarbonates are also soluble, while carbonates are less soluble with exceptions.

Step 2: Analyzing Sodium Carbonate (Na2CO3)

Sodium salts, such as sodium carbonate (\(\mathrm{Na}_{2} \mathrm{CO}_{3}\)), are generally very soluble in water. This is due to the solubility rule that states all alkali metal salts are soluble.

Step 3: Analyzing Barium Carbonate (BaCO3)

Barium carbonate (\(\mathrm{BaCO}_{3}\)) is considered insoluble in water. The solubility rule indicates that most carbonate salts are insoluble except for those of the alkali metals and ammonium. Barium is not an exception.

Step 4: Analyzing Silver Carbonate (Ag2CO3)

Silver carbonate (\(\mathrm{Ag}_{2} \mathrm{CO}_{3}\)) is poorly soluble in water. Given the rules, most silver salts like chlorides except nitrate (which is soluble) are generally insoluble, including its carbonates.

Step 5: Ranking the Compounds based on Solubility

Based on the solubility rules and analysis above, \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) is the most soluble compound, whereas \(\mathrm{BaCO}_{3}\) and \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) are less soluble. Among the two, barium carbonate is less soluble than silver carbonate, though both are not substantially soluble.

Key Concepts

Ionic Compounds

Ionic compounds are formed when metals react with non-metals. They are characterized by the transfer of electrons from the metal to the non-metal, creating ions. These ions are held together by strong electrostatic forces.
Ionic compounds, like sodium carbonate (\(\mathrm{Na}_{2} \mathrm{CO}_{3}\)), barium carbonate (\(\mathrm{BaCO}_{3}\)), and silver carbonate (\(\mathrm{Ag}_{2} \mathrm{CO}_{3}\)), each consist of positive and negative ions.
The structure of these compounds determines their solubility in water, where the positive and negative charges attract and dissolve into ions.

• Example 1: \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) contains two sodium ions and one carbonate ion.
• Example 2: \(\mathrm{BaCO}_{3}\) contains one barium ion and one carbonate ion.
• Example 3: \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) contains two silver ions and one carbonate ion.

While ionic compounds tend to follow solubility rules, not all are equally soluble.

Solubility Rules

Understanding solubility rules helps predict whether a compound will dissolve in water. These rules serve as guidelines based on observed behaviors of various ions in water.
Here are the key points:

• Most halide salts of silver, lead, and mercury are insoluble except when combined with nitrate or acetate.
• Alkali metal salts (like those of sodium, potassium) and ammonium salts are generally soluble.
• Nitrate (\(\mathrm{NO}_{3}^{-}\)), acetate (\(\mathrm{CH}_{3}\mathrm{COO}^{-}\)), and bicarbonate salts are usually soluble.
• Carbonates are typically insoluble except for those with alkali metals or ammonium.

Solubility rules can often predict the solubility of compounds, aiding in problem-solving exercises related to dissolving elements in water.

Alkali Metal Salts

Alkali metal salts, such as those containing sodium, potassium, and other group 1 elements, are known for their high solubility in water. This trait is due to the influence of solubility rules stating that most salts formed with alkali metals are soluble.
This includes compounds like \(\mathrm{Na}_{2} \mathrm{CO}_{3}\), where the sodium ions make the compound dissolve readily.
Key points about alkali metal salts:

• These elements have a +1 charge and easily dissolve due to their ability to separate and interact with water molecules.
• Compounds formed with these metals tend to have a strong presence in various chemical reactions due to their solubility.

The ease of separation into ions in water makes alkali metal salts an important topic in understanding water solubility.

Carbonate Solubility

Carbonate solubility varies significantly based on the metal present in the compound. Carbonate compounds containing alkali metals and ammonium are soluble, whereas most others are not.
Here are specifics:

• \(\mathrm{Na}_{2} \mathrm{CO}_{3}\), an alkali metal carbonate, dissolves well in water.
• \(\mathrm{BaCO}_{3}\) and \(\mathrm{Ag}_{2} \mathrm{CO}_{3}\) exemplify typical carbonates that do not dissolve well in water.
• Understanding the pattern of solubility helps in predicting the behavior of various carbonate compounds in aqueous solutions.

The low solubility of most carbonate compounds is usually due to strong ionic bonds and lattice structures that water cannot easily break.