Question

Indicate which of the following copper(II) salts are soluble in water and which are insoluble: \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) \(\mathrm{CuCO}_{3}, \mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}, \mathrm{CuCl}_{2}\).

Short answer

\(\mathrm{Cu(NO_3)_2}\) and \(\mathrm{CuCl_2}\) are soluble; \(\mathrm{CuCO_3}\) and \(\mathrm{Cu_3(PO_4)_2}\) are insoluble.

Step-by-step solution

Understanding Solubility Rules

To determine solubility, we use solubility rules that specify the solubility of various compounds in water.

Analyzing Copper(II) Nitrate, \(\mathrm{Cu(NO_3)_2}\)

Compounds containing the nitrate ion \((\mathrm{NO_3}^-)\) are always soluble. Therefore, \(\mathrm{Cu(NO_3)_2}\) is soluble in water.

Analyzing Copper(II) Carbonate, \(\mathrm{CuCO_3}\)

Carbonates \((\mathrm{CO_3}^{2-})\) are generally insoluble in water, except for those of alkali metals and ammonium. Thus, \(\mathrm{CuCO_3}\) is insoluble.

Analyzing Copper(II) Phosphate, \(\mathrm{Cu_3(PO_4)_2}\)

Phosphates \((\mathrm{PO_4}^{3-})\) are generally insoluble in water, except for those of alkali metals and ammonium. Hence, \(\mathrm{Cu_3(PO_4)_2}\) is insoluble in water.

Analyzing Copper(II) Chloride, \(\mathrm{CuCl_2}\)

Compounds containing chloride ions \((\mathrm{Cl}^-)\) are typically soluble, except when paired with silver, lead, or mercury. So, \(\mathrm{CuCl_2}\) is soluble in water.

Key concepts

Water Solubility

Water solubility is a key idea in chemistry and refers to the ability of a substance to dissolve in water. When a compound is soluble, it can dissolve to form a homogeneous solution. Solubility depends on many factors, including the nature of the solute and solvent, temperature, and pressure. For ionic compounds, solubility rules help predict whether a compound will dissolve in water.

These rules are a set of guidelines that simplify the process of determining the solubility of various ionic compounds. For example:

• Nitrates, represented by the ion \((\mathrm{NO}_3^-)\), are generally soluble.
• Most carbonates \((\mathrm{CO}_3^{2-})\) are insoluble, except those of alkali metals and ammonium.
• Chlorides are typically soluble, with notable exceptions like silver, lead, and mercury chlorides.

Recognizing these patterns makes it easier to predict whether a copper(II) salt will dissolve in water.

Copper(II) Salts

Copper(II) salts contain copper in the +2 oxidation state and are often found in various chemical reactions and applications. Understanding their solubility is important for practical uses in industry and research.

Typical copper(II) salts include:

• Copper(II) nitrate \(\mathrm{Cu(NO_3)_2}\), which is water-soluble due to the presence of nitrate ions.
• Copper(II) carbonate \(\mathrm{CuCO_3}\), usually insoluble in water because carbonates tend to have low solubility unless combined with alkali metals or ammonium.
• Copper(II) chloride \(\mathrm{CuCl_2}\), soluble in water as chlorides are commonly soluble, excluding a few exceptions.

These properties are crucial for understanding the behavior of copper in different chemical environments.

Nitrate Ions

Nitrate ions \(\mathrm{NO}_3^-\) possess a unique property—they are always considered soluble in water. This helps in predicting the behavior of many compounds in aqueous solutions.

The nitrate ion's solubility is incredibly beneficial in a variety of chemical contexts, providing stability and dissolvability. That is why salts like copper(II) nitrate \(\mathrm{Cu(NO_3)_2}\) easily dissolve, resulting in a clear solution when added to water.

• Nitrates are used extensively in fertilizers due to their excellent solubility and ability to provide essential nutrients to plants.
• The solubility of nitrates remains so regardless of particle size, temperature, or concentration.

Understanding this aspect enhances how we handle these compounds in practical applications.

Carbonate Solubility

Carbonate solubility is a concept focused on the insoluble nature of most carbonates in water. The carbonate ion \(\mathrm{CO}_3^{2-}\) typically forms precipitates, making most carbonates insoluble unless they are paired with alkali metals or ammonium.

This general rule simplifies predicting which carbonates remain undissolved in water. For example, copper(II) carbonate \(\mathrm{CuCO_3}\) typically does not dissolve in water, creating an undissolved sediment instead.

• Common carbonates, like calcium carbonate (chalk), also exhibit this insolubility trait.
• Some carbonates will dissolve in acidic solutions, transforming into soluble compounds.

By comprehension of these solubility patterns, one can anticipate the behavior of carbonate compounds in certain chemical settings.