Problem 120 - Chemistry An Atoms First Approach

Question

Write the formula for each of the following compounds: a. ammonium hydrogen phosphate b. mercury(I) sulfide c. silicon dioxide d. sodium sulfite e. aluminum hydrogen sulfate f. nitrogen trichloride g. hydrobromic acid h. bromous acid I. perbromic acid J. potassium hydrogen sulfide k. calcium iodide 1\. cesium perchlorate

Step-by-Step Solution

Answer

The formula for each compound is as follows: a. NH4H2PO4 b. Hg2S c. SiO2 d. Na2SO3 e. AlH3(SO4)2 f. NCl3 g. HBr h. HBrO2 i. HBrO4 j. KHS k. CaI2 1. CsClO4

Step 1: a. ammonium hydrogen phosphate

First, identify the formulas and charges of each component: - ammonium (NH4+) - hydrogen (H+) - phosphate (PO4^3-) Now use the cross-method to combine the ions: - NH4(+1) + H(+1) + PO4(-3) - NH4H2PO4 The formula for ammonium hydrogen phosphate is NH4H2PO4.

Step 2: b. mercury(I) sulfide

First, identify the formulas and charges of each component: - mercury(I) (Hg2^2+) - sulfide (S^2-) Now use the cross-method to combine the ions: - Hg2(+2) + S(-2) - Hg2S2 - Simplify: Hg2S (since the 2's cancel out) The formula for mercury(I) sulfide is Hg2S.

Step 3: c. silicon dioxide

First, identify the formuals and charges of each component: - silicon (Si^4+) - dioxide (O^2-) Now use the cross-method to combine the ions: - Si(+4) + O2(-2) - SiO2 The formula for silicon dioxide is SiO2.

Step 4: d. sodium sulfite

First, identify the formulas and charges of each component: - sodium (Na+) - sulfite (SO3^2-) Now use the cross-method to combine the ions: - Na(+1) + SO3(-2) - Na2SO3 The formula for sodium sulfite is Na2SO3.

Step 5: e. aluminum hydrogen sulfate

First, identify the formulas and charges of each component: - aluminum (Al^3+) - hydrogen (H+) - sulfate (SO4^2-) Now use the cross-method to combine the ions: - Al(+3) + H(+1) + SO4(-2) - AlH3(SO4)2 The formula for aluminum hydrogen sulfate is AlH3(SO4)2.

Step 6: f. nitrogen trichloride

As a molecular compound, nitrogen trichloride uses prefixes to indicate stoichiometry: - nitrogen (N) - trichloride (3 chlorine atoms, Cl3) The formula for nitrogen trichloride is NCl3.

Step 7: g. hydrobromic acid

Hydrobromic acid is formed by hydrogen and bromine ions in aqueous solution: - hydrogen (H+) - bromide (Br-) Now use the cross-method to combine the ions: - H(+1) + Br(-1) - HBr The formula for hydrobromic acid is HBr.

Step 8: h. bromous acid

Bromous acid is also in aqueous solution and has a bromite ion: - hydrogen (H+) - bromite (BrO2-) Now use the cross-method to combine the ions: - H(+1) + BrO2(-1) - HBrO2 The formula for bromous acid is HBrO2.

Step 9: i. perbromic acid

Perbromic acid is in aqueous solution and has a perbromate ion: - hydrogen (H+) - perbromate (BrO4-) Now use the cross-method to combine the ions: - H(+1) + BrO4(-1) - HBrO4 The formula for perbromic acid is HBrO4.

Step 10: j. potassium hydrogen sulfide

First, identify the formulas and charges of each component: - potassium (K+) - hydrogen (H+) - sulfide (S^2-) Now use the cross-method to combine the ions: - K(+1) + H(+1) + S(-2) - KHS The formula for potassium hydrogen sulfide is KHS.

Step 11: k. calcium iodide

First, identify the formulas and charges of each component: - calcium (Ca^2+) - iodide (I-) Now use the cross-method to combine the ions: - Ca(+2) + I(-1) - CaI2 The formula for calcium iodide is CaI2.

Step 12: 1. cesium perchlorate

First, identify the formulas and charges of each component: - cesium (Cs+) - perchlorate (ClO4-) Now use the cross-method to combine the ions: - Cs(+1) + ClO4(-1) - CsClO4 The formula for cesium perchlorate is CsClO4.

Key Concepts

Ionic Compounds

Ionic compounds are essential in chemistry. They form when metals lose electrons to form cations and non-metals gain those electrons to become anions. This electron transfer creates a strong electrostatic attraction between the oppositely charged ions, forming what we know as an ionic bond.
An important characteristic of ionic compounds is that they are electrically neutral. This is because the total positive charge from the cations and the total negative charge from the anions must balance out. Here are a few examples:

• Ammonium Hydrogen Phosphate (NH₄H₂PO₄): This compound is composed of ammonium (NH₄⁺), a hydrogen ion (H⁺), and the phosphate ion (PO₄³⁻).
• Calcium Iodide (CaI₂): Consists of calcium (Ca²⁺) and iodide ions (I⁻).
• Cesium Perchlorate (CsClO₄): Made up of cesium (Cs⁺) and perchlorate ions (ClO₄⁻).

Though ionic compounds are often formed from simple ions, some like ammonium and perchlorate are polyatomic, involving multiple atoms covalently bonded with a charge.

Cross Method

The cross method is an efficient technique used to write the formulas of ionic compounds. This method is particularly useful for ensuring that the charges between the cations and anions balance correctly and the compound is neutral.
Here's how the cross method works:

• Identify the cation and its charge, as well as the anion and its charge.
• Cross the charges (ignore the signs) to become subscripts of the opposite ion.
• Simplify the subscripts to the smallest ratio that maintains charge neutrality.

Take, for example, the compound mercury(I) sulfide. You'll start with mercury(I), Hg₂²⁺, and sulfide, S²⁻. Crossing the charges involves making the subscript of Hg₂ equal to 2 and S equal to 2. Upon simplification, you get Hg₂S. This method ensures that ionic compounds are written correctly.

Molecular Compounds

Molecular compounds are formed when atoms share electrons through covalent bonds. Unlike ionic compounds that form through electron transfer, molecular compounds result from electron sharing between non-metals.
They are characterized by a distinct use of prefixes in their naming, which indicates the number of atoms involved.

• Nitrogen Trichloride (NCl₃): Here, the prefix 'tri-' indicates there are three chlorine atoms bonded to a single nitrogen atom.
• Silicon Dioxide (SiO₂): Known as SiO₂, it doesn't use a prefix because one silicon atom bonds with two oxygen atoms by default.

Thus, understanding the naming conventions of molecular compounds greatly helps in clearly representing their formulas.

Acids and Bases

Acids and bases play crucial roles in chemistry, each having distinct properties and behaviors. Acids are substances that release hydrogen ions (H⁺) in solutions, whereas bases release hydroxide ions (OH⁻).
Acids are categorized by the anion with which they combine:

• Hydrobromic Acid (HBr): Formed by hydrogen ions (H⁺) and bromide (Br⁻).
• Bromous Acid (HBrO₂) and Perbromic Acid (HBrO₄): Both involve the bromine atom bonded with oxygen, differing in the number of oxygen atoms.

Bases, on the other hand, often arise from metal hydroxides. For instance, sodium hydroxide is a classic base releasing OH⁻ ions upon dissolution. Understanding these compounds cooks up many reactions in the world of chemistry.