Using solubility guidelines, predict whether each of the following compounds is soluble or insoluble in water: (a) MgBr₂ (b) NH₄OH (c) Ni(CH₃COO)₂ (d) AgNO₃ (e) FeCO₃.

Verified step by step guidance

1. Step 1: Understand the solubility rules. Some of the key rules are: (1) All nitrates (NO3-) are soluble. (2) All salts of alkali metals (Group 1 elements) and ammonium (NH4+) are soluble. (3) All chlorides (Cl-), bromides (Br-), and iodides (I-) are soluble, except those of silver (Ag+), lead (Pb2+), and mercury (Hg2+). (4) All sulfates (SO4^2-) are soluble, except those of barium (Ba2+), strontium (Sr2+), lead (Pb2+), calcium (Ca2+), silver (Ag+), and mercury (Hg2+).
2. Step 2: Identify the ions in the compound. In this case, MgBr2 is made up of Mg2+ and Br- ions.
3. Step 3: Apply the solubility rules to the ions in the compound. According to the rules, all bromides (Br-) are soluble except those of silver (Ag+), lead (Pb2+), and mercury (Hg2+). Since Mg2+ is not one of the exceptions, MgBr2 is soluble in water.

Key Concepts

Solubility Rules

Solubility rules are a set of guidelines used to predict whether ionic compounds will dissolve in water. These rules take into account the nature of the ions involved, such as their charge and size, and categorize them into soluble and insoluble groups. For example, most salts containing alkali metal ions or ammonium ions are soluble, while many metal hydroxides and carbonates are generally insoluble.

Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between positively charged cations and negatively charged anions. Their solubility in water depends on the strength of these ionic bonds compared to the interactions with water molecules. Compounds like MgBr₂ consist of magnesium cations and bromide anions, and their solubility can be assessed using established solubility rules.

Hydration Energy

Hydration energy refers to the energy released when ions are surrounded by water molecules. This process is crucial for the dissolution of ionic compounds in water. If the hydration energy is greater than the lattice energy (the energy holding the ions together in the solid), the compound will dissolve. For MgBr₂, the hydration energy of the magnesium and bromide ions plays a significant role in determining its solubility.