Ch.8 - Basic Concepts of Chemical Bonding

Problem 104a

Chapter 8, Problem 104a

Under special conditions, sulfur reacts with anhydrous liquid ammonia to form a binary compound of sulfur and nitrogen. The compound is found to consist of 69.6% S and 30.4% N. Measurements of its molecular mass yield a value of 184.3 g/mol. The compound occasionally detonates on being struck or when heated rapidly. The sulfur and nitrogen atoms of the molecule are joined in a ring. All the bonds in the ring are of the same length. (a) Calculate the empirical and molecular formulas for the substance.

Verified step by step guidance

Determine the molar mass of sulfur (S) and nitrogen (N). Sulfur has a molar mass of approximately 32.07 g/mol, and nitrogen has a molar mass of approximately 14.01 g/mol.

Calculate the moles of sulfur and nitrogen in 100 g of the compound using the percentage composition. For sulfur, use the formula: moles of S = mass of S / molar mass of S. For nitrogen, use the formula: moles of N = mass of N / molar mass of N.

Find the simplest whole number ratio of moles of sulfur to moles of nitrogen by dividing each by the smallest number of moles calculated in the previous step.

Write the empirical formula using the whole number mole ratios of sulfur and nitrogen obtained. This formula represents the simplest whole-number ratio of atoms in the compound.

Calculate the molecular formula by comparing the empirical formula mass to the given molecular mass (184.3 g/mol). Divide the molecular mass by the mass of the empirical formula to find the number of empirical units per molecule, and multiply the subscripts in the empirical formula by this number.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. To determine it, one must convert the percentage composition of each element into moles, then simplify the ratio of these moles to the smallest whole numbers. In this case, with 69.6% sulfur and 30.4% nitrogen, the empirical formula can be calculated by finding the moles of each element and simplifying their ratio.

Molecular Formula

The molecular formula indicates the actual number of atoms of each element in a molecule of a compound. It can be derived from the empirical formula by comparing the molar mass of the compound to the molar mass of the empirical formula. Given the molecular mass of 184.3 g/mol, one can determine how many times the empirical formula fits into this mass to find the molecular formula.

Chemical Bonding and Structure

Understanding chemical bonding is crucial for analyzing the structure of a compound. In this case, the description of sulfur and nitrogen atoms forming a ring with equal bond lengths suggests a stable cyclic structure, likely involving resonance or delocalized electrons. This concept helps explain the compound's stability and reactivity, particularly its tendency to detonate under certain conditions.

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Related Practice

Textbook Question

The electron affinity of oxygen is -141 kJ/mol, corresponding to the reaction O(g) + e^- → O^-(g). The lattice energy of K₂O(s) is 2238 kJ/mol. Use these data along with data in Appendix C and Figure 7.11 to calculate the 'second electron affinity' of oxygen, corresponding to the reaction O^-(g) + e^-→ O^2-(g)

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Open Question

You and a partner are asked to complete a lab entitled “Carbonates of Group 2 metal” that is scheduled to extend over two lab periods. The first lab, which is to be completed by your partner, is devoted to carrying out compositional analysis and determining the identity of the Group 2 metal (M). In the second lab, you are to determine the melting point of this compound. Upon going to the lab, you find two unlabeled vials containing white powder. You also find the following notes in your partner’s notebook—Compound 1: 40.04% M, 12.00% C, and 47.96% O (by mass); Compound 2: 69.59% M, 6.09% C, and 24.32% O (by mass). (a) What is the empirical formula for Compound 1 and the identity of M? (b) What is the empirical formula for Compound 2 and the identity of M? Upon determining the melting points of these two compounds, you find that both compounds do not melt up to the maximum temperature of your apparatus; instead, the compounds decompose and liberate a colorless gas. (c) What is the identity of the colorless gas?

Open Question

The compound chloral hydrate, known in detective stories as knockout drops, is composed of 14.52% C, 1.83% H, 64.30% Cl, and 13.35% O by mass, and has a molar mass of 165.4 g/mol. (c) Draw the Lewis structure of the molecule, assuming that the Cl atoms bond to a single C atom and that there are a C–C bond and two C–O bonds in the compound.

Textbook Question

A common form of elemental phosphorus is the tetrahedral P₄ molecule, where all four phosphorus atoms are equivalent:

(b) How many P-P bonds are there in the molecule?

764

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Textbook Question

A common form of elemental phosphorus is the tetrahedral P₄ molecule, where all four phosphorus atoms are equivalent:

Draw a Lewis structure for a linear P₄ molecule that satisfies the octet rule. Does this molecule have resonance structures?

1241

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