Problem 14 - Chemistry and Chemical Reactivity

Question

For each of the following compounds, give the formula, charge, and the number of each ion that makes up the compound: (a) \(\mathrm{Mg}\left(\mathrm{CH}_{3} \mathrm{CO}_{2}\right)_{2}\) (d) \(\operatorname{Ti}\left(\mathrm{SO}_{4}\right)_{2}\) (b) \(\mathrm{Al}(\mathrm{OH})_{3}\) (c) \(\mathrm{KH}_{2} \mathrm{PO}_{4}\) (e) \(\mathrm{CuCO}_{3}\)

Step-by-Step Solution

Answer

(a) Mg(CH3CO2)2: Mg2+ and 2 CH3CO2-. (d) Ti(SO4)2: Ti4+ and 2 SO4 2-. (b) Al(OH)3: Al3+ and 3 OH-. (c) KH2PO4: K+ and H2PO4-. (e) CuCO3: Cu2+ and CO3 2-.

Step 1: Understand Compound (a)

The compound given is \( \mathrm{Mg}\left(\mathrm{CH}_{3} \mathrm{CO}_{2}\right)_{2} \). Magnesium is \( \mathrm{Mg}^{2+} \) and the acetate ion is \( \mathrm{CH}_{3} \mathrm{CO}_{2}^{-} \). The formula indicates there are two acetate ions to balance the charge of one magnesium ion.

Step 2: Analyze Compound (d)

For \( \operatorname{Ti}\left(\mathrm{SO}_{4}\right)_{2} \), the sulfate ion \( \mathrm{SO}_{4}^{2-} \) has a -2 charge. Since there are two sulfate ions, the total negative charge is -4. Titanium must have a \( \mathrm{Ti}^{4+} \) charge to balance it, with one titanium ion paired with two sulfate ions.

Step 3: Identify Components of Compound (b)

\( \mathrm{Al}(\mathrm{OH})_{3} \) contains aluminum, \( \mathrm{Al}^{3+} \), and hydroxide, \( \mathrm{OH}^{-} \). Three hydroxide ions are needed to balance the +3 charge of the aluminum ion, resulting in the formula being \( \mathrm{Al}(\mathrm{OH})_{3} \).

Step 4: Determine Ions in Compound (c)

In \( \mathrm{KH}_{2} \mathrm{PO}_{4} \), potassium (\( \mathrm{K}^{+} \)) and dihydrogen phosphate (\( \mathrm{H}_{2} \mathrm{PO}_{4}^{-} \)) each have one ion, with the charges balancing as both are +1 and -1 respectively.

Step 5: Explain Compound (e)

For \( \mathrm{CuCO}_{3} \), copper is \( \mathrm{Cu}^{2+} \) and carbonate is \( \mathrm{CO}_{3}^{2-} \). One copper ion balances out one carbonate ion, resulting in the neutral compound \( \mathrm{CuCO}_{3} \).

Key Concepts

Ionic Compounds

Ionic compounds are fascinating entities that are formed when cations (positively charged ions) and anions (negatively charged ions) come together. This process of formation is based on the electrostatic attraction between oppositely charged ions. Consider

• aluminum hydroxide (\( \mathrm{Al}(\mathrm{OH})_{3} \))
• magnesium acetate (\( \mathrm{Mg}(\mathrm{CH}_{3} \mathrm{CO}_{2})_{2} \))
• and other compounds.

Each compound listed involves a precise combination of these ions to achieve a balanced and electrically neutral compound overall.
In their simplest form, an ionic compound is often represented by the formula unit, which is the smallest electrically neutral collective of ions that reflects the entire compound's chemical composition. Understanding the intrinsic nature of ionic compounds helps us comprehend how matter interacts and forms varied chemical entities.

Balancing Charges

Balancing charges in ionic compounds is essential for ensuring stability. This involves ensuring that the total positive charge from the cations equals the total negative charge from the anions. Let's consider the titanium sulfate (\( \operatorname{Ti}\left(\mathrm{SO}_{4}\right)_{2} \)) compound. Here, two sulfate ions (each \( \mathrm{SO}_{4}^{2-} \) with -2 charge) pair with titanium to neutralize the compound.
To achieve balance:

• Titanium contributes a \( \mathrm{Ti}^{4+} \) charge, resulting in a perfect counterbalance with two sulfate ions producing the total -4 charge.

Learning to balance charges effectively is crucial in predicting the formation of compounds and understanding how they maintain neutrality.

Cation and Anion Identification

Identifying cations and anions within a compound is foundational to chemical understanding. Cations are positively charged ions, while anions hold a negative charge. For example, in aluminum hydroxide (\( \mathrm{Al}(\mathrm{OH})_{3} \)),

• the cation is aluminum (\( \mathrm{Al}^{3+} \))
• and the anion is hydroxide (\( \mathrm{OH}^{-} \)).

In copper carbonate (\( \mathrm{CuCO}_{3} \)),

• copper provides the cation (\( \mathrm{Cu}^{2+} \))
• and carbonate comments the anion (\( \mathrm{CO}_{3}^{2-} \)).

Cation and anion identification requires an understanding of typical charges for elements and common polyatomic ions. With practice, the recognition of these ions aids in deducing the chemical behaviors and reactions they undergo.

Compound Composition Analysis

Analyzing a compound’s composition involves understanding how various ions interrelate within a chemical structure. Looking at these compounds, such as potassium dihydrogen phosphate (\( \mathrm{KH}_{2} \mathrm{PO}_{4} \)), informs us about ion ratios and bonding.Each molecule includes

• one potassium ion (\( \mathrm{K}^{+} \))
• and one dihydrogen phosphate ion (\( \mathrm{H}_{2} \mathrm{PO}_{4}^{-} \)).

These ions align perfectly with each charge canceling out, helping us to reach a thorough understanding of compound formation.
Other examples, like copper carbonate (\( \mathrm{CuCO}_{3} \)), reveal the simplicity or complexity of ionic pairs. Conducting a compound composition analysis helps us to unravel how different atoms and ions come together to form stable entities through defined ratios and interactions.