Problem 83 - 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

\(\mathrm{Ag}_2 \mathrm{CO}_3\) < \(\mathrm{BaCO}_3\) < \(\mathrm{Na}_2 \mathrm{CO}_3\) in solubility.

Step 1: Understand Solubility Rules

The solubility of ionic compounds in water can be predicted using solubility rules. One of the main rules is that most carbonate (\(\mathrm{CO}_3^{2-}\)) compounds are insoluble in water, except when paired with alkali metals (such as sodium), or ammonium. This means that sodium carbonate (\(\mathrm{Na}_2 \mathrm{CO}_3\)) will be more soluble than other carbonates.

Step 2: Examine Solubility of \(\mathrm{Na}_2 \mathrm{CO}_3\)

\(\mathrm{Na}_2 \mathrm{CO}_3\) is a carbonate compound. According to solubility rules, all sodium salts are soluble in water. Therefore, we can infer that sodium carbonate is highly soluble in water.

Step 3: Examine Solubility of \(\mathrm{BaCO}_3\)

\(\mathrm{BaCO}_3\) is a carbonate compound, where barium is an alkaline earth metal. Carbonates of alkaline earth metals, like barium, are generally insoluble in water. Therefore, \(\mathrm{BaCO}_3\) is expected to have low solubility in water.

Step 4: Examine Solubility of \(\mathrm{Ag}_2 \mathrm{CO}_3\)

\(\mathrm{Ag}_2 \mathrm{CO}_3\) is a carbonate compound of silver. Silver carbonate is known to be poorly soluble in water, due to the general rule that carbonates are insoluble unless paired with highly soluble cations like alkali metals.

Step 5: Rank Compounds from Least to Most Soluble

From the analysis, \(\mathrm{Na}_2 \mathrm{CO}_3\) is the most soluble because sodium salts are always soluble. Between \(\mathrm{BaCO}_3\) and \(\mathrm{Ag}_2 \mathrm{CO}_3\), \(\mathrm{BaCO}_3\) is slightly more soluble than \(\mathrm{Ag}_2 \mathrm{CO}_3\), though both are largely insoluble. So, the ranking from least to most soluble is: \(\mathrm{Ag}_2 \mathrm{CO}_3\), \(\mathrm{BaCO}_3\), \(\mathrm{Na}_2 \mathrm{CO}_3\).

Key Concepts

Ionic Compounds

Ionic compounds are chemical compounds composed of ions held together by ionic bonds. Each ion is a charged particle that has either donated or accepted electrons to achieve a full outer shell. Typically, ionic compounds form between metals and non-metals. Metals tend to lose electrons, becoming positively charged cations, while non-metals gain electrons, forming negatively charged anions.

• The resulting ionic bond is due to the electrostatic attraction between these oppositely charged ions.
• Ionic compounds are usually solid at room temperature, forming crystals with high melting and boiling points.
• They conduct electricity when dissolved in water or melted, as the free-moving ions facilitate the flow of charge.

The solubility of ionic compounds in water depends on the nature of the ions and the solubility rules, which help predict whether a compound will dissolve or remain solid.

Carbonate Compounds

Carbonate compounds contain the carbonate ion \[\mathrm{CO}_3^{2-}\], which is a polyatomic ion composed of one carbon atom covalently bonded to three oxygen atoms. These compounds often result in lattice structures when they form with various cations. Solubility Insights:

• Carbonate compounds are generally insoluble in water, except for those formed with alkali metals (like lithium, sodium, and potassium) and ammonium.
• This characteristic makes compounds like sodium carbonate \(\mathrm{Na}_2\mathrm{CO}_3\) highly soluble, while others like barium carbonate \(\mathrm{BaCO}_3\) and silver carbonate \(\mathrm{Ag}_2\mathrm{CO}_3\) are not.

Carrying a negative charge, the carbonate ion can bond with various cations, influencing the stability and solubility of the resulting compound. For instance, the insolubility of barium carbonate reflects the poor interaction between the relatively large barium ion and the carbonate ion in water.

Water Solubility

Water solubility refers to the ability of a substance to dissolve in water, forming a homogeneous solution. This property is essential for various biological, environmental, and chemical processes. Key Considerations:

• Water, being a polar solvent, tends to dissolve polar substances as well as ionic compounds, due to positive and negative ends attracting ions or polar molecules.
• Solubility rules provide a guideline to determine the likelihood of an ionic compound dissolving.
• Compounds with highly soluble counterions, such as alkali metal ions, are usually water-soluble. For example, sodium carbonate is soluble because sodium ions help overcome lattice energy forces, dispersing carbonate ions effectively in water.

Learning about water solubility is crucial to understanding reactions in aqueous solutions, predicting chemical behavior, and applying these principles in real-world scenarios like medicine and environmental science.