Problem 9 - General Chemistry: Principles and Modern Applications

Question

Without doing detailed calculations, explain which of the following has the greatest number of \(\mathrm{N}\) atoms (a) \(50.0 \mathrm{g}\) \(\mathrm{N}_{2} \mathrm{O} ;\) (b) \(17.0 \mathrm{g} \mathrm{NH}_{3} ;\) (c) \(150 \mathrm{mL}\) of liquid pyridine, \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}(d=0.983 \mathrm{g} / \mathrm{mL}) ;\) (d) \(1.0 \mathrm{mol} \mathrm{N}_{2}\)

Step-by-Step Solution

Answer

The substance with the greatest number of Nitrogen atoms is option (d) that is \(1.0 \, \mathrm{mol}\) of \(N_{2}\), because it contains 2 moles of Nitrogen atoms.

Step 1: Determine the Molecular Mass of each option

In this first step, the molecular masses are determined. For (a) N2O, the molecular mass is \(2(14.01) + 16.00 = 44.02 \, \mathrm{g/mol}\). For (b) NH3, the molecular mass is \(14.01 + 3(1.01) = 17.04 \, \mathrm{g/mol}\). For (c) C5H5N, the molecular mass is \(5(12.01) + 5(1.01) + 14.01 = 79.10 \, \mathrm{g/mol}\). Finally, for (d) N2, the molecular mass is \(2(14.01) = 28.02 \, \mathrm{g/mol}\).

Step 2: Calculating the number of atoms for each option

In this step, we estimate which option gives the most number of Nitrogen atoms. For (a) \(50.0 \, \mathrm{g}\) of \(N2O\), it's approximately 1 mole of Nitrogen atoms. For (b) \(17.0 \, \mathrm{g}\) of \(NH3\), it's approximately 1 mole of Nitrogen atoms. For (c) \(150 \, \mathrm{mL}\) of pyridine \(C5H5N\), using the given density we can find its 'nitrogen mass' and using that it's again around 1 mole of Nitrogen atoms. For (d) \(1.0 \, \mathrm{mol}\) of \(N2\), we have 2 moles of Nitrogen atoms.

Step 3: Drawing Conclusion

On comparing the moles of Nitrogen atoms from each option, it's clear that option (d) gives the highest number of Nitrogen atoms because it has 2 moles of Nitrogen atoms and all other choices have approximately 1 mole of Nitrogen atoms.

Key Concepts

Molecular Mass

Molecular mass is a crucial concept in chemistry. It helps us understand the weight of one molecule of a substance. This is calculated by adding up the atomic masses of all the atoms in the molecule. For instance, in the case of nitrogen dioxide (\(\text{N}_2\text{O}\)), you calculate its molecular mass by adding the masses of two nitrogen atoms and one oxygen atom:

• Nitrogen (N): 14.01
• Oxygen (O): 16.00

This gives us: \(2(14.01) + 16.00 = 44.02 \, \text{g/mol}\). By determining molecular mass, we can compare amounts of different compounds and relate them to each other in terms of moles. This is useful when determining how much of a compound you have in terms of \(\text{N}\) atoms, as seen in various examples like \(\text{NH}_3\) and pyridine. Calculating molecular mass allows us to make these comparisons effortlessly.

Chemical Compounds

Chemical compounds are made of atoms bonded together, and they come with varying compositions and molecular formulas. Understanding compounds like \(\text{N}_2\text{O}\), \(\text{NH}_3\), and pyridine \(\text{C}_5\text{H}_5\text{N}\) provides insight into how elements like nitrogen are grouped. Each compound has a unique molecular formula that indicates:

• The types of atoms present
• The number of each type of atom in the compound

For instance, in ammonia (\(\text{NH}_3\)), each molecule contains one nitrogen and three hydrogen atoms. Knowing these formulas helps chemists understand how compounds behave and react with each other. This understanding is fundamental when considering which compound could contain more nitrogen atoms, as learned from comparing their compositions.

Nitrogen Atoms

Nitrogen atoms are a fundamental part of many common compounds. They play a key role in substances like nitrogen gas (\(\text{N}_2\)), where nitrogen atoms bond together. \(\text{N}_2\) is unique because it has two nitrogen atoms per molecule, thus counting as two moles of nitrogen per mole of the compound. In other compounds such as nitrous oxide (\(\text{N}_2\text{O}\)) and ammonia (\(\text{NH}_3\)), nitrogen is present in lesser quantities.

• Understanding how nitrogen atoms are distributed allows for accurate predictions about the quantity you might find in a given sample.
• This knowledge aids in fields ranging from industrial chemistry to environmental science.

Knowing how many nitrogen atoms are in a compound helps in calculating and comparing chemical reactions and processes efficiently.