Problem 3 - Chemistry and Chemical Reactivity

Question

Which compound or compounds in each of the following groups is (are) expected to be soluble in water? (a) \(\mathrm{CuO}, \mathrm{CuCl}_{2}, \mathrm{FeCO}_{3}\) (b) \(\mathrm{AgI}, \mathrm{Ag}_{3} \mathrm{PO}_{4}, \mathrm{AgNO}_{3}\) (c) \(\mathrm{K}_{2} \mathrm{CO}_{3}, \mathrm{KI}, \mathrm{KMnO}_{4}\)

Step-by-Step Solution

Answer

(a) \( \mathrm{CuCl}_{2} \); (b) \( \mathrm{AgNO}_{3} \); (c) \( \mathrm{K}_{2} \mathrm{CO}_{3} \), \( \mathrm{KI} \), \( \mathrm{KMnO}_{4} \) are soluble.

Step 1: Evaluate Solubility of Group (a) Compounds

In this group, we have \( \mathrm{CuO} \), \( \mathrm{CuCl}_{2} \), and \( \mathrm{FeCO}_{3} \). Most metal oxides like \( \mathrm{CuO} \) are insoluble in water. Copper(II) chloride is a salt and is typically soluble in water. Iron(II) carbonate, \( \mathrm{FeCO}_{3} \), is generally insoluble in water except when in the presence of a strong acid. Hence, only \( \mathrm{CuCl}_{2} \) is expected to be soluble.

Step 2: Assess Solubility of Group (b) Compounds

For this group, consider \( \mathrm{AgI} \), \( \mathrm{Ag}_{3} \mathrm{PO}_{4} \), and \( \mathrm{AgNO}_{3} \). Most silver halides like \( \mathrm{AgI} \) are insoluble, except \( \mathrm{AgF} \). Silver phosphate, \( \mathrm{Ag}_{3} \mathrm{PO}_{4} \), is also insoluble. However, silver nitrate, \( \mathrm{AgNO}_{3} \), is a salt that is always soluble in water. Thus, only \( \mathrm{AgNO}_{3} \) is expected to be soluble.

Step 3: Check Solubility of Group (c) Compounds

In this group, we have \( \mathrm{K}_{2} \mathrm{CO}_{3} \), \( \mathrm{KI} \), and \( \mathrm{KMnO}_{4} \). Compounds containing alkali metals, like potassium, are generally soluble in water. Thus, \( \mathrm{K}_{2} \mathrm{CO}_{3} \), \( \mathrm{KI} \), and \( \mathrm{KMnO}_{4} \) are all expected to be soluble due to the presence of potassium.

Key Concepts

Inorganic compounds

Inorganic compounds are a class of compounds that typically do not contain carbon-hydrogen (C-H) bonds. These compounds are often formed through ionic or covalent bonding between elements. Common categories include:

• Salts, like sodium chloride (NaCl)
• Oxides, like copper(II) oxide (CuO)
• Carbonates, such as calcium carbonate (CaCO\(_3\))
• Metals, nonmetals, and metalloids

These compounds can exist in solid, liquid, or gaseous states and can have a variety of physical and chemical properties. Some are soluble in water, while others are not. For instance, many metal oxides are not soluble in water, except for a few like sodium oxide. The solubility of inorganic compounds is often influenced by the type of bond, lattice structure, and presence of polar elements.

Water solubility

Water solubility is a key characteristic of chemical substances, referring to the maximum amount of a substance that can dissolve in water at a specified temperature and pressure. It plays a crucial role in determining how substances interact in aqueous environments. Several factors affect water solubility:

• Ionic charge and lattice energy: Compounds with high lattice energy are generally less soluble.
• Temperature: Typically, solubility increases with temperature for most solid substances.
• Polarity of the substance: Water being a polar solvent, dissolves polar substances more readily.

Compounds like salts of alkali metals (e.g., potassium chloride) are readily soluble due to the low lattice energy and the charge distribution conducive for dissolution in polar solvents. Conversely, compounds like silver iodide (AgI) have low solubility because of their high lattice energy and limited ionic interactions with water molecules.

Chemical solutions

Chemical solutions are homogeneous mixtures of two or more substances where components are distributed uniformly. The major component, often water, is called the solvent; the minor component is the solute. The process of forming a solution entails the breaking of intermolecular forces in the solute and solvent, then the formation of new interactions between them. Key aspects of chemical solutions include:

• Saturation: The point at which no more solute can dissolve in the solvent at a given temperature and pressure.
• Concentration: The measure of the amount of solute in a given quantity of solution, commonly expressed in molarity (moles per liter).
• Solubility rules: Guidelines used to predict whether an ionic compound will dissolve in water.

Understanding these concepts helps determine reactions and predict outcomes in various chemical environments. Solutions like silver nitrate in water are crucial in laboratories due to their predictable behavior based on their chemical properties.