Problem 43 - Chemistry The Molecular Science

Question

Write the chemical formulas for these compounds. (a) Iron(III) nitrate (b) Potassium carbonate (c) Sodium phosphate (d) Calcium chlorite (e) Sodium sulfate

Step-by-Step Solution

Answer

(a) Fe(NO_{3})_{3}, (b) K_{2}CO_{3}, (c) Na_{3}PO_{4}, (d) Ca(ClO_{2})_{2}, (e) Na_{2}SO_{4}.

Step 1: Understanding the Chemical Names

First, we need to understand the names given. Each name consists of two parts: the cation (positively charged ion) and the anion (negatively charged ion). The chemical formula combines these two types of ions.

Step 2: Identifying Cations and Their Charges

For each compound, identify the cation and its charge: (a) Iron(III) has a charge of +3, denoted as Fe^{3+}. (b) Potassium has a charge of +1, denoted as K^{+}. (c) Sodium has a charge of +1, denoted as Na^{+}. (d) Calcium has a charge of +2, denoted as Ca^{2+}. (e) Sodium, again, has a charge of +1, denoted as Na^{+}.

Step 3: Identifying Anions and Their Charges

Next, identify the anion and its charge: (a) Nitrate has a charge of -1, denoted as NO_{3}^{-}. (b) Carbonate has a charge of -2, denoted as CO_{3}^{2-}. (c) Phosphate has a charge of -3, denoted as PO_{4}^{3-}. (d) Chlorite has a charge of -1, denoted as ClO_{2}^{-}. (e) Sulfate has a charge of -2, denoted as SO_{4}^{2-}.

Step 4: Balancing Charges to Determine Formula

We balance the total positive and negative charges to find the chemical formula. (a) To balance Fe^{3+} and NO_{3}^{-}: Fe(NO_{3})_{3}. (b) To balance K^{+} and CO_{3}^{2-}: K_{2}CO_{3}. (c) To balance Na^{+} and PO_{4}^{3-}: Na_{3}PO_{4}. (d) To balance Ca^{2+} and ClO_{2}^{-}: Ca(ClO_{2})_{2}. (e) To balance Na^{+} and SO_{4}^{2-}: Na_{2}SO_{4}.

Step 5: Writing Final Formulas

Using the balanced charges from the previous step, we write the final chemical formulas: (a) Iron(III) nitrate: Fe(NO_{3})_{3} (b) Potassium carbonate: K_{2}CO_{3} (c) Sodium phosphate: Na_{3}PO_{4} (d) Calcium chlorite: Ca(ClO_{2})_{2} (e) Sodium sulfate: Na_{2}SO_{4}

Key Concepts

Cations and Anions

In chemistry, understanding cations and anions is essential to forming correct chemical formulas. Cations are positively charged ions, which means they have lost one or more electrons. Anions, on the other hand, are negatively charged ions, having gained electrons.
When writing chemical formulas, it's crucial to identify which element serves as the cation and which one is the anion. The position of these ions in the periodic table helps us determine their charges.
For example:

• Iron(III) is a common cation with a charge of +3, noted as \( \text{Fe}^{3+} \).
• Calcium is another common cation with a charge of +2, represented as \( \text{Ca}^{2+} \).
• On the anion side, nitrate carries a charge of -1, \( \text{NO}_3^{-} \).
• Phosphate is an anion with a charge of -3, written as \( \text{PO}_4^{3-} \).

Recognizing these charges helps to predict and balance the formula of compounds they form.

Balancing Charges

Balancing charges is a critical skill when constructing ionic compound formulas. To ensure the compound is neutral, the total positive charge from the cations must equal the total negative charge from the anions.
For instance:

• Consider iron(III) nitrate: \( \text{Fe(NO}_3)_3 \). Here, each iron cation has a charge of +3, while each nitrate anion carries -1.
• To achieve a neutral compound, we need three nitrate ions to balance one iron ion, hence the formula \( \text{Fe(NO}_3)_3 \).
• For potassium carbonate, \( \text{K}_2\text{CO}_3 \), potassium (\( \text{K}^+ \)) pairs with carbonate (\( \text{CO}_3^{2-} \)). Two potassium ions are needed to counteract the -2 charge of a single carbonate ion, resulting in \( \text{K}_2\text{CO}_3 \).

Balancing these charges is all about finding the lowest ratio of ions that produces an overall charge of zero, ensuring the compound's stability.

Ionic Compounds

Ionic compounds are made from cations and anions, bonding together to achieve a stable, neutral compound. These compounds usually form crystalline structures and have high melting and boiling points due to the strong forces holding the ions together.
Let's examine some common ionic compounds:

• Potassium carbonate, \( \text{K}_2\text{CO}_3 \), is a salt used in agriculture and food production. It forms when potassium ions bond with carbonate ions.
• Sodium sulfate, \( \text{Na}_2\text{SO}_4 \), utilized in detergents, consists of sodium cations bonding with sulfate anions.
• Calcium chlorite, \( \text{Ca(ClO}_2)_2 \), often used as a bleaching agent, results from calcium ions interacting with chlorite ions.

Understanding ionic compounds requires a comprehensive grasp of how cations and anions come together, adhering firmly due to electrostatic forces. Recognizing examples and applications of these compounds helps elucidate their importance in everyday chemistry.