Problem 61 - Chemistry The Central Science

Question

Predict the chemical formula for the ionic compound formed by (a) \(\mathrm{Ca}^{2+}\) and \(\mathrm{Br}^{-},(\mathbf{b}) \mathrm{K}^{+}\) and \(\mathrm{CO}_{3}^{2-},(\mathbf{c}) \mathrm{Al}^{3+}\) and \(\mathrm{CH}_{3} \mathrm{COO}^{-},(\mathbf{d}) \mathrm{NH}_{4}^{+}\) and \(\mathrm{SO}_{4}^{2-},(\mathbf{e}) \mathrm{Mg}^{2+}\) and \(\mathrm{PO}_{4}^{3-}\) .

Step-by-Step Solution

Answer

The chemical formulas for the ionic compounds formed are: (a) CaBr2, (b) K2CO3, (c) Al(CH3COO)3, (d) (NH4)2SO4, and (e) Mg3(PO4)2.

Step 1: (a) Ca2+ and Br-

For a net zero charge, simply balance the charges of the ions involved in the compound. In this case, one Ca2+ ion has a charge of +2, and one Br- ion has a charge of -1. Therefore, we would need two Br- ions to balance one Ca2+ ion. Chemical formula: CaBr2

Step 2: (b) K+ and CO3 2-

In this case, one K+ ion has a charge of +1, and one CO3 2- ion has a charge of -2. Therefore, we would need two K+ ions to balance one CO3 2- ion. Chemical formula: K2CO3

Step 3: (c) Al3+ and CH3COO-

In this case, one Al3+ ion has a charge of +3, and one CH3COO- ion has a charge of -1. Therefore, we would need three CH3COO- ions to balance one Al3+ ion. Chemical formula: Al(CH3COO)3

Step 4: (d) NH4+ and SO4 2-

In this case, one NH4+ ion has a charge of +1, and one SO4 2- ion has a charge of -2. Therefore, we would need two NH4+ ions to balance one SO4 2- ion. Chemical formula: (NH4)2SO4

Step 5: (e) Mg2+ and PO4 3-

In this case, one Mg2+ ion has a charge of +2, and one PO4 3- ion has a charge of -3. Therefore, we would need three Mg2+ ions to balance two PO4 3- ions. Chemical formula: Mg3(PO4)2

Key Concepts

Ionic Compounds

Ionic compounds are formed when positive and negative ions come together to create a neutral compound. This happens through the transfer of electrons between atoms.
These compounds are typically composed of metals and non-metals. When the metal loses electrons, it becomes a cation with a positive charge. The non-metal gains these electrons, turning it into an anion with a negative charge.

• Ionic bonds are strong due to the electrostatic attraction between oppositely charged ions.
• They often form crystalline solids with high melting points.
• Examples in this exercise include compounds like CaBr e/2/, formed from calcium and bromide ions.

Understanding ionic compounds is crucial for predicting the formulas of compounds created by different ions.

Balancing Charges

Balancing charges is essential to achieve a neutral ionic compound. Every compound must have a net charge of zero, meaning all positive charges must equal all negative charges.

For example, if you have a cation with a charge of +2 and an anion with a charge of -1, you will need two of the anions to balance one of the cations.

• Example: For CaBr e/2/, calcium has a +2 charge, and bromide has a -1 charge. Therefore, two bromide ions are needed per calcium ion.
• In correction with KCO e/3/ vs2, potassium has a +1 charge and carbonate has a -2 charge, requiring two potassium ions for each carbonate.

Balancing charges ensures the stability and neutrality of ionic compounds.

Cation and Anion Pairing

Cation and anion pairing involves the combination of positively charged and negatively charged ions. The cation, usually a metal, pairs up with an anion, often a non-metal or polyatomic ion.
This pairing is driven by the difference in charges, allowing them to "stick" together in a stable configuration.

• In pairs like Al(CH e/3/COO) e/3/, one aluminum cation pairs with three acetate anions.
• For compounds like (NH e/4/) e/2/SO e/4/, two ammonium cations balance one sulfate anion.

Understanding how cations and anions pair is key to determining the correct chemical formula of an ionic compound.

Ion Charge

An ion charge is the electrical charge an ion carries, which can be either positive or negative.
The charge is a result of losing or gaining electrons. Metals usually lose electrons to become positively charged cations, while non-metals gain electrons to become negatively charged anions.

• Charges are crucial for predicting how ions will combine. For instance, Mg e/2/+ has a +2 charge, and PO e/4/) vs3- carries a -3 charge.
• These charges determine how many of each ion are needed to balance and form a neutral compound.

By knowing the charges of ions, you can predict the number and ratio of ions required to create ionic compounds.