Problem 37 - Chemistry and Chemical Reactivity

Question

Name two insoluble salts of each of the following ions. (a) \(\mathrm{Cl}^{-}\) (b) \(\mathrm{Zn}^{2+}\) (c) \(\mathrm{Fe}^{2+}\)

Step-by-Step Solution

Answer

(a) \( \mathrm{AgCl} \), \( \mathrm{PbCl_2} \); (b) \( \mathrm{ZnS} \), \( \mathrm{Zn(OH)_2} \); (c) \( \mathrm{FeS} \), \( \mathrm{Fe(OH)_2} \).

Step 1: Identifying Insoluble Salts for Chloride Ion

To find insoluble salts containing \( \mathrm{Cl}^{-} \), we look for cations that form insoluble chlorides. Common examples are \( \mathrm{AgCl} \) (silver chloride) and \( \mathrm{PbCl_2} \) (lead(II) chloride). These are known to be sparingly soluble or insoluble in water.

Step 2: Identifying Insoluble Salts for Zinc Ion

Next, we find insoluble salts for \( \mathrm{Zn}^{2+} \). Compounds like \( \mathrm{ZnS} \) (zinc sulfide) and \( \mathrm{Zn(OH)_2} \) (zinc hydroxide) are generally considered insoluble in water, making them good examples for \( \mathrm{Zn}^{2+} \) insoluble salts.

Step 3: Identifying Insoluble Salts for Iron(II) Ion

Finally, for \( \mathrm{Fe}^{2+} \), consider salts like \( \mathrm{FeS} \) (iron(II) sulfide) and \( \mathrm{Fe(OH)_2} \) (iron(II) hydroxide), which are typically insoluble, fitting our criteria for insoluble salts of \( \mathrm{Fe}^{2+} \).

Key Concepts

Understanding Chloride Ion: Insoluble Salts

Chloride ions (\( \mathrm{Cl}^{-} \)) form various compounds, but not all of them are soluble in water. Insoluble salts are those that do not easily dissolve in water. This mostly depends on the type of cation paired with the chloride ion. Let's explore some common examples:

• **Silver Chloride (\( \mathrm{AgCl} \))**: Silver chloride is notoriously insoluble in water. In fact, it is one of the most well-known insoluble salts. When chloride ions bind with silver ions, they form a white precipitate of \( \mathrm{AgCl} \) which remains undissolved in water.
• **Lead(II) Chloride (\( \mathrm{PbCl_2} \))**: Lead chloride is slightly more soluble than silver chloride in hot water but is still considered insoluble at room temperature. It makes a white precipitate that is barely dissolved, especially in cold water.

Knowing these is useful in various applications, such as in precipitation reactions where identifying insoluble salts helps in determining chemical compositions.

Exploring Zinc Ion: Creation of Insoluble Compounds

When it comes to zinc ions (\( \mathrm{Zn}^{2+} \)), they can form insoluble salts with specific anions. Two notable examples include zinc sulfide (\( \mathrm{ZnS} \)) and zinc hydroxide (\( \mathrm{Zn(OH)_2} \)). These compounds are essential in both industrial and laboratory settings.

• **Zinc Sulfide (\( \mathrm{ZnS} \))**: This compound is mostly insoluble in water and appears as a white or sometimes yellowish powder. It is used widely in luminescent materials such as those in paints and x-ray screens.
• **Zinc Hydroxide (\( \mathrm{Zn(OH)_2} \))**: Though not widely utilized in common household products, zinc hydroxide is important in creating other zinc compounds. It’s insoluble, meaning it doesn’t easily dissolve in waters, such as acids and bases.

These insoluble salts are also significant in separation techniques used during the extraction of different metals.

Iron(II) Ion: Formation of Insoluble Salts

Iron(II) ions (\( \mathrm{Fe}^{2+} \)) often create insoluble compounds when paired with specific anions. Two iconic examples are iron(II) sulfide (\( \mathrm{FeS} \)) and iron(II) hydroxide (\( \mathrm{Fe(OH)_2} \)), which have distinct characteristics and uses.

• **Iron(II) Sulfide (\( \mathrm{FeS} \))**: This is a black compound that's a favorite in demonstrating insolubility in chemistry labs. It plays a significant role in geochemical processes where sulfide ions are abundant.
• **Iron(II) Hydroxide (\( \mathrm{Fe(OH)_2} \))**: It's a compound that is weakly soluble in water, notable for its pale green color. It can form naturally and is sometimes seen as precipitate under reducing conditions in water systems.

Understanding these compounds can be important in fields such as environmental chemistry and mineralogy.