Question

Predict which compounds are soluble in water. (a) \(\mathrm{HgBr}_{2}\) (b) \(\mathrm{Sr}\left(\mathrm{NO}_{3}\right)_{2}\) (c) \(\mathrm{Hg}_{2} \mathrm{Br}_{2}\) (d) ammonium phosphate (e) lead(II) iodide (f) lead(II) acetate

Short answer

(a) Insoluble, (b) Soluble, (c) Insoluble, (d) Soluble, (e) Insoluble, (f) Soluble

Step-by-step solution

Use Solubility Rules

To predict the solubility of the given compounds in water, utilize a set of solubility rules. These guidelines typically state that all nitrates (NO3-) and most ammonium (NH4+) salts are soluble. Halides (Cl-, Br-, I-) are soluble except when paired with Ag+, Pb2+, Hg2 2+, and Hg22+. Sulfates (SO4 2-) are generally soluble, with exceptions for Ba2+, Sr2+, Pb2+, Ag+, and Ca2+.

Apply Solubility Rules to Each Compound

For each given compound, apply the solubility rules to determine if they are soluble in water. (a) HgBr2: Mercury(II) bromide is a halide, but since it is paired with Hg2+, it is insoluble. (b) Sr(NO3)2: Strontium nitrate contains the nitrate ion, which is always soluble. (c) Hg2Br2: Mercury(I) bromide is also insoluble due to the mercury ion. (d) Ammonium phosphate contains the ammonium ion, which makes it soluble. (e) Lead(II) iodide is a halide but with Pb2+, therefore it is insoluble. (f) Lead(II) acetate, despite being a lead compound, is an exception and is soluble due to the acetate anion.

Key concepts

Chemical Solubility

Understanding chemical solubility is fundamental when studying chemistry and carries practical significance in fields like pharmacology and environmental science. At its core, solubility refers to the capacity of a substance, known as the solute, to dissolve in a solvent and form a homogeneous solution. Solubility depends on various factors, including temperature, pressure, and the chemical nature of the solute and solvent.

Compounds that dissolve in water to a significant extent are considered soluble, forming aqueous solutions that are important for biological and chemical processes. Inorganic compounds' solubility in water is generally predicted by solubility rules, which are based on empirical data and can be used as quick references for predicting whether a compound will be solvable.

Soluble Compounds

When we refer to soluble compounds, we are discussing those substances which can dissolve in a solvent to a considerable degree. In the context of water as the solvent—the most common scenario in chemistry—solubility rules help us determine which ionic compounds will readily dissociate and mingle with the water molecules.

• Nitrates (NO_3^-) and acetates (CH_3COO^-) are classic examples of ions that form soluble compounds with most metals.
• Compounds containing the ammonium ion (NH_4^+) are also typically soluble.
• Alkali metal ions and the halides (notably, chloride, bromide, and iodide ions), barring a few exceptions, tend to form soluble compounds as well.

Remembering these patterns can simplify the process of identifying which substances will dissolve in water in chemical reactions and various industrial processes.

Insoluble Compounds

In contrast to their soluble counterparts, insoluble compounds do not dissolve in water or do so extremely poorly. In the realm of solubility rules, certain ions tend to form insoluble compounds with specific exceptions. For instance:

• Compounds containing carbonate (CO_3^2-) and phosphate (PO_4^3-) ions are generally insoluble, with the notable exceptions of those that also contain alkali metal ions or the ammonium ion.
• Halides are well known for their solubility, but when bonded with metal ions like lead (Pb^2+), silver (Ag+), or mercury (Hg2^2+), the resulting compounds are typically insoluble.
• Sulfates (SO_4^2-) form insoluble compounds with barium (Ba^2+), strontium (Sr^2+), and lead (Pb^2+), among others.

Recognizing these patterns is vital for predicting reaction outcomes and understanding the behavior of substances in aqueous environments.

Predicting Compound Solubility

The ability to predict whether a compound is soluble or insoluble in water can be incredibly valuable. Various fields, such as environmental science, biochemistry, and engineering, often require an understanding of a substance's solubility. You can employ a set of empirical rules known as solubility rules, which serve as a guide to the solubility of ionic compounds in water.

These guidelines summarize years of experimental observations and are framed in a way to facilitate easy memorization and application. When predicting solubility, recall that factors such as temperature and the common ion effect can also influence solubility; thus, while the rules provide a solid starting point, they are not definitive for every possible scenario.

The key is to analyze the ions present in a compound and apply the relevant solubility rules. For example, nitrates are generally soluble, but if you're dealing with a compound that includes a nitrate ion and a typically insoluble ion, the solubility rule for the nitrate takes precedence, predicting that the compound will be soluble.