Problem 51 - Chemistry and Chemical Reactivity

Question

Give the formula for each of the following ionic compounds: (a) ammonium carbonate (b) calcium iodide (c) copper(II) bromide (d) aluminum phosphate (e) silver(I) acetate

Step-by-Step Solution

Answer

(a) \( \text{(NH}_4\text{)}_2\text{CO}_3 \); (b) \( \text{CaI}_2 \); (c) \( \text{CuBr}_2 \); (d) \( \text{AlPO}_4 \); (e) \( \text{AgC}_2\text{H}_3\text{O}_2 \).

Step 1: Identify ions in ammonium carbonate

Ammonium carbonate is composed of ammonium ions and carbonate ions. The ammonium ion is \( \text{NH}_4^+ \) and the carbonate ion is \( \text{CO}_3^{2-} \). Balance their charges by using 2 ammonium ions for one carbonate ion, giving \( \text{(NH}_4\text{)}_2\text{CO}_3 \).

Step 2: Identify ions in calcium iodide

Calcium iodide is made up of calcium ions and iodide ions. Calcium ion is \( \text{Ca}^{2+} \) and iodide ion is \( \text{I}^- \). To balance the charges, two iodide ions are required for one calcium ion, resulting in \( \text{CaI}_2 \).

Step 3: Identify ions in copper(II) bromide

Copper(II) bromide includes copper(II) ions and bromide ions. The copper(II) ion is \( \text{Cu}^{2+} \) and the bromide ion is \( \text{Br}^- \). Two bromide ions are needed to balance one copper(II) ion, forming \( \text{CuBr}_2 \).

Step 4: Identify ions in aluminum phosphate

Aluminum phosphate is formed from aluminum ions and phosphate ions. The aluminum ion is \( \text{Al}^{3+} \) and the phosphate ion is \( \text{PO}_4^{3-} \). Their charges are already balanced, so the formula is simply \( \text{AlPO}_4 \).

Step 5: Identify ions in silver(I) acetate

Silver(I) acetate consists of silver ions and acetate ions. The silver(I) ion is \( \text{Ag}^+ \) and the acetate ion is \( \text{C}_2\text{H}_3\text{O}_2^- \). Their charges directly balance, resulting in \( \text{AgC}_2\text{H}_3\text{O}_2 \).

Key Concepts

Chemical Formulas

Understanding chemical formulas is crucial in identifying the composition of ionic compounds. A chemical formula represents the types and numbers of atoms in a substance. For ionic compounds, it reflects the smallest whole number ratio of ions necessary to balance positive and negative charges. For example, in ammonium carbonate, the formula

• \( \text{(NH}_4\text{)}_2\text{CO}_3 \)
• is derived by using two ammonium ions (\(\text{NH}_4^+\)) for every carbonate ion (\(\text{CO}_3^{2-}\)).

In each formula, the subscript numbers indicate how many of each type of ion are in the compound. These subscripts are essential for ensuring that the compound's overall charge is zero. Making sense of chemical formulas helps chemists understand the composition and structure of substances. Formulas like \( \text{CaI}_2 \) for calcium iodide and \( \text{AlPO}_4 \) for aluminum phosphate show balanced ratios derived from the charges of their respective ions.

Ion Charges

Ion charges result from atoms losing or gaining electrons to achieve a stable electron configuration. Cations are positively charged ions formed by losing electrons, while anions are negatively charged, formed by gaining electrons. Understanding these charges is key to forming ionic compounds.

• For example, the ammonium ion \( \text{NH}_4^+\) has an overall positive charge due to the loss of an electron.
• Similarly, the carbonate ion \( \text{CO}_3^{2-}\) gains electrons, resulting in a negative charge.

Recognizing the charges helps in predicting how ions will combine. In copper(II) bromide, the copper(II) ion \( \text{Cu}^{2+} \) indicates a loss of two electrons, while the bromide ion \( \text{Br}^- \) gains one electron, necessitating two bromide ions for every copper(II) ion. Understanding ion charges leads to correctly writing and interpreting chemical formulas, which is essential for discussing chemical compounds.

Balancing Charges

One of the key concepts in forming ionic compounds is balancing charges. Ionic compounds must be electrically neutral, which means the total positive charge must equal the total negative charge. To do this, the number of each type of ion is adjusted. To balance charges, consider the ions involved:

• For calcium iodide, \( \text{Ca}^{2+} \) and \( \text{I}^- \), you need two iodide ions to balance one calcium ion, resulting in the formula \( \text{CaI}_2 \).
• In the case of aluminum phosphate, both the aluminum ion \( \text{Al}^{3+} \) and phosphate ion \( \text{PO}_4^{3-} \) have balanced charges, so only one of each is needed, giving \( \text{AlPO}_4 \).

This concept simplifies the process of writing the correct chemical formula. When ions come together to form compounds, adjusting their quantities ensures that the resulting compound is neither positively nor negatively charged, but neutral.

Naming Compounds

Naming ionic compounds correctly requires knowing the ions involved and their charges. Typically, the name of a compound reflects its constituting ions with the cation named first, followed by the anion.

• Take silver(I) acetate as an example: "silver(I)" indicates the charge on the silver ion \( \text{Ag}^+ \), while "acetate" refers to the \( \text{C}_2\text{H}_3\text{O}_2^- \) ion.
• Another example is copper(II) bromide, where "copper(II)" specifies the \( \text{Cu}^{2+} \) ion, indicating a +2 charge, paired with bromide ions, \( \text{Br}^- \).

Proper naming helps in identifying the compound's composition and structure. The Roman numeral in names like copper(II) is essential because many transition metals can have more than one possible charge. By carefully naming compounds, chemists and students can accurately communicate about chemical substances and predict their behavior.