Problem 74 - Chemistry The Central Science In Si Units

Question

Give the chemical formula for each of the following ionic compounds: (a) sodium phosphate, (b) zinc nitrate, (c) barium bromate, \((\mathbf{d})\) iron(II) perchlorate, \((\mathbf{e})\) cobalt(II) hydrogen carbonate, (f) chromium(III) acetate, \((\mathbf{g})\) potassium dichromate.

Step-by-Step Solution

Answer

(a) \( \text{Na}_3\text{PO}_4 \), (b) \( \text{Zn(NO}_3\text{)}_2 \), (c) \( \text{Ba(BrO}_3\text{)}_2 \), (d) \( \text{Fe(ClO}_4\text{)}_2 \), (e) \( \text{Co(HCO}_3\text{)}_2 \), (f) \( \text{Cr(C}_2\text{H}_3\text{O}_2\text{)}_3 \), (g) \( \text{K}_2\text{Cr}_2\text{O}_7 \).

Step 1: Determine the Formula for Sodium Phosphate

Sodium has a charge of +1, represented by Na. Phosphate is a polyatomic ion with the formula \( \text{PO}_4^{3-} \). To balance the charges, we need three sodium ions for each phosphate ion. Thus, the formula is \( \text{Na}_3\text{PO}_4 \).

Step 2: Determine the Formula for Zinc Nitrate

Zinc has a charge of +2, represented by Zn. Nitrate is a polyatomic ion with the formula \( \text{NO}_3^- \). To neutralize the charge of +2 from one zinc ion, we need two nitrate ions. Therefore, the formula is \( \text{Zn(NO}_3\text{)}_2 \).

Step 3: Determine the Formula for Barium Bromate

Barium has a charge of +2, represented by Ba. Bromate is a polyatomic ion with the formula \( \text{BrO}_3^- \). We need two bromate ions to balance the charge from one barium ion, leading to the formula \( \text{Ba(BrO}_3\text{)}_2 \).

Step 4: Determine the Formula for Iron(II) Perchlorate

Iron(II) refers to the Fe ion with a +2 charge. Perchlorate is a polyatomic ion with the formula \( \text{ClO}_4^- \). To balance the charge, two perchlorate ions are needed for one iron ion, giving the formula \( \text{Fe(ClO}_4\text{)}_2 \).

Step 5: Determine the Formula for Cobalt(II) Hydrogen Carbonate

Cobalt(II) indicates Co with a +2 charge. Hydrogen carbonate is a polyatomic ion, \( \text{HCO}_3^- \). Two hydrogen carbonate ions are required to balance one cobalt ion, resulting in the formula \( \text{Co(HCO}_3\text{)}_2 \).

Step 6: Determine the Formula for Chromium(III) Acetate

Chromium(III) means Cr with a +3 charge. Acetate is a polyatomic ion with the formula \( \text{C}_2\text{H}_3\text{O}_2^- \). Three acetate ions are required to balance one chromium ion, giving the formula \( \text{Cr(C}_2\text{H}_3\text{O}_2\text{)}_3 \).

Step 7: Determine the Formula for Potassium Dichromate

Potassium has a charge of +1, represented by K. Dichromate is a polyatomic ion with the formula \( \text{Cr}_2\text{O}_7^{2-} \). Two potassium ions are needed to neutralize the charge of one dichromate ion, so the formula is \( \text{K}_2\text{Cr}_2\text{O}_7 \).

Key Concepts

Understanding Chemical Formulas

Chemical formulas are the building blocks of understanding ionic compounds. They express the types and numbers of atoms in a compound. Each element in a chemical formula is represented by a symbol (like Na for sodium or Zn for zinc). These symbols are often followed by a subscript number indicating the number of atoms of that element in the compound.
Another crucial aspect is the charge balance, ensuring the overall neutrality of the compound.

• An ionic compound results from the combination of a positive ion (cation) and a negative ion (anion).
• To determine the correct formula, the total positive charges must balance the total negative charges.

For example, in sodium phosphate, knowing that sodium (Na) has a +1 charge and phosphate (\(\text{PO}_4^{3-}\)) has a -3 charge, three sodium ions balance one phosphate ion, resulting in \(\text{Na}_3\text{PO}_4\). Understanding these relationships helps in predicting the chemical formula of any ionic compound.

The Role of Polyatomic Ions

Polyatomic ions are ions composed of more than one atom. They can be considered as a single ion because they behave as a unit, carrying a specific charge that affects chemical formulas.
Here are key points about polyatomic ions:

• They often consist of multiple elements that form a complex ion, bound together with an overall charge.
• Common polyatomic ions include nitrate (\(\text{NO}_3^-\)), sulfate (\(\text{SO}_4^{2-}\)), and phosphate (\(\text{PO}_4^{3-}\)), among others.

When forming compounds with polyatomic ions, it's important to treat the ion as a single unit. For example, in zinc nitrate, you need two nitrate ions (\(\text{NO}_3^-\)) to balance the +2 charge of one zinc ion, resulting in \(\text{Zn(NO}_3\text{)}_2\). Polyatomic ions add complexity but also demonstrate the beautiful intricacies of chemistry, highlighting how atoms join forces to form stable structures.

The Essential Concept of Charge Balancing

Charge balancing is a fundamental concept in creating chemical formulas for ionic compounds. It ensures that the overall compound has no net electrical charge. This neutrality is key to the compound's stability and existence.
To achieve charge balance:

• The total positive charge from the cations must equal the total negative charge from the anions.
• Identify the charge of each ion and determine how many of each are needed to balance out the charges.

Consider chromium(III) acetate: chromium has a +3 charge while acetate has a \(\text{C}_2\text{H}_3\text{O}_2^-\) charge. It takes three acetate ions to balance one chromium ion, giving \(\text{Cr(C}_2\text{H}_3\text{O}_2\text{)}_3\). In every ionic compound, charge balancing is the guiding principle for determining the chemical formula. It requires careful consideration of each element's charge and cooperation between ions to maintain harmony and neutrality.