Question

Predict which of the following compounds are soluble in water: (a) ammonium sulfide, ${\left({\mathrm{NH}}_4\right)}_2\mathrm{S}$ (b) zinc carbonate, ${\mathrm{ZnCO}}_3$ (c) tin(II) chromate, ${\mathrm{SnCrO}}_4$ (d) lead(II) acetate, $\mathrm{Pb}{\left({\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_2\right)}_2$

Short answer

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

Step-by-step solution

Understanding Solubility Rules

To determine the solubility of the given compounds, we need to apply general solubility rules for ionic compounds in water. Common rules include: 1. Salts containing ammonium ions ${\mathrm{NH}}_4^{+}$ are generally soluble. 2. Carbonates ${\mathrm{CO}}_3^{2-}$ are generally insoluble except when paired with alkali metals or ammonium.3. Lead salts are generally insoluble, except for nitrates and acetates. 4. Chromates are generally insoluble except for chromium(III), strontium, and most alkali metals.

Evaluating Ammonium Sulfide

According to Rule 1, since ammonium sulfide contains the ammonium ion (${\mathrm{NH}}_4^{+}$), it is soluble in water.

Evaluating Zinc Carbonate

According to Rule 2, carbonates are typically insoluble except with alkali metals or ammonium. Since zinc carbonate does not contain ammonium or alkali metal ions, it is generally insoluble in water.

Evaluating Tin(II) Chromate

Based on Rule 4, chromates are generally insoluble. Tin(II) chromate does not contain any of the exceptions listed (such as alkali metals), so it is insoluble in water.

Evaluating Lead(II) Acetate

According to Rule 3, lead salts are generally insoluble but an exception exists for acetates. Therefore, lead(II) acetate is soluble in water.

Key concepts

Understanding Ionic Compounds

Ionic compounds are made of positive and negative ions. These ions are held together by strong electrostatic forces. This creates a solid lattice structure. In water, these compounds usually dissolve by dissociating into their individual ions.
Not all ionic compounds dissolve equally in water. Monitoring solubility is critical. Specific rules help predict this solubility.

• Compounds with certain ions like ammonium (${\mathrm{NH}}_4^{+}$) are typically soluble.
• This rule helps in identifying compounds that will dissolve in water, important for understanding reactions.

Understanding these patterns is key in chemistry. It aids in determining how substances will interact.

Role of Ammonium Ions in Solubility

Ammonium ions are integral in determining the solubility of some compounds. They carry a positive charge, ${\mathrm{NH}}_4^{+}$. This charge contributes to the compound's ability to dissolve in water. Most compounds containing these ions are soluble.
The presence of ammonium ions often overrides the insolubility of accompanying ions. For example, while sulfide ions (${\mathrm{S}}^{2-}$) might be generally insoluble, the association with ammonium makes ammonium sulfide (${\left({\mathrm{NH}}_4\right)}_2\mathrm{S}$) soluble.

• Ammonium ions are an exception to many solubility rules.
• This characteristic is exploited in various chemical processes.

Recognizing this influence is crucial when predicting reactions and overall compound behavior in solutions.

Carbonates and Their Solubility Exceptions

Carbonates are a fascinating group of compounds when discussing solubility. They typically include a ${\mathrm{CO}}_3^{2-}$ ion. Most carbonates are insolvable in water except for those formed with ions like alkali metals or ammonium.
Zinc carbonate (${\mathrm{ZnCO}}_3$), for instance, is not soluble because neither zinc nor carbonate fit the soluble-ion criteria.

• Alkali metal carbonates, such as sodium carbonate, are soluble.
• Ammonium carbonate is also soluble.

Learning these exceptions helps in accurately predicting solubility and the outcome of different reactions.

Understanding Lead Salts and Solubility

Lead salts pose an interesting case due to unique solubility rules. Most lead compounds are considered insoluble except when paired with particular ions, such as acetates and nitrates.
Lead(II) acetate ($\mathrm{Pb}{\left({\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_2\right)}_2$) stands out as one of these exceptions and is soluble in water.

• General rule: lead salts are not soluble.
• Exceptions exist when dealing with specific anions like acetate.

Understanding these exceptions is important for anticipating the behavior of lead salts in different chemical settings.