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Chapter 2: Problem 37

Write a sentence that describes how to determine the number of moles of a compound in a known mass of the compound if we know its molecular formula.

Short Answer

Expert verified
To determine the number of moles of a compound from a known mass, first calculate the compound's molar mass, then divide the mass of the compound by its molar mass.

Step by step solution

01

Calculate the Molar Mass of the Compound

Determine the atomic mass of each element in the molecular formula from the periodic table. Multiply the atomic mass of each element by the number of times that element occurs in the molecular formula. Add the masses of all elements in the formula to get the molar mass of the compound.
02

Convert Mass to Moles

Use the formula: number of moles = mass of the compound (in grams) divided by the molar mass of the compound (in grams per mole).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Molar Mass
Understanding molar mass is essential for calculating the number of moles from a given mass of a compound. It represents the mass of one mole of a substance, essentially a counting unit representing 6.022 x 10^23 particles—be they atoms, molecules, ions, or other entities.

The molar mass is expressed in units of grams per mole (g/mol) and can be found by summing the atomic masses of all the atoms present in the molecular formula of the compound. For instance, water (H2O) has a molar mass of approximately 18 g/mol because it consists of two hydrogen atoms (1 g/mol each) and one oxygen atom (16 g/mol).
Molecular Formula
The molecular formula provides vital information about the type and number of atoms in a molecule of a substance. For instance, glucose has a molecular formula of C6H12O6, indicating that it comprises six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.

To assist in calculations like finding the molar mass, the molecular formula is crucial as it reflects the exact number of atoms in a single molecule of a compound. You can calculate the molar mass of glucose by adding the atomic masses of its constituent elements—carbon, hydrogen, and oxygen—taking the quantities indicated by the formula into consideration.
Periodic Table
The periodic table is not just a chart but a powerful tool for chemists. It organizes all known chemical elements in a tabular layout where elements with similar properties are in the same column, called a group.

With regard to calculating moles, the periodic table provides atomic masses for each element (usually displayed below the element symbol). The atomic mass reflects the average mass of all the isotopes of that element, weighted by their abundance. When determining the molar mass of compounds, the atomic mass serves as an essential starting point.
Atomic Mass
Atomic mass is marked on the periodic table for each chemical element and is measured in atomic mass units (amu). It approximates the total mass of an atom's protons and neutrons (nucleons). Because electrons have a much smaller mass, they don't significantly affect the atomic mass.

In context, the atomic mass helps us determine the molar mass of a compound by providing the mass contribution of each atom. By understanding that the molar mass of an element in grams per mole is numerically equal to its atomic mass in amu, we bridge the concepts of individual particles and bulk amounts.
Stoichiometry
Stoichiometry is the mathematical relationship between the relative quantities of substances in chemical reactions. The area of stoichiometry that deals with the masses of substances is especially important for tasks such as determining the number of moles from a given mass.

When you express a balanced chemical equation, stoichiometry can tell you the exact proportion of reactants and products involved—information that's essential when scaling reactions up or down. In relation to our initial problem, stoichiometry can guide the proper conversion of mass to moles using the molar mass, ensuring that all calculations adhere to the law of conservation of mass.

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Most popular questions from this chapter

$$\text { A } 55-\mathrm{kg} \text { woman has } 7.5 \times 10^{-3} \mathrm{mol}$$ of hemoglobin (molar mass \(=64,456 \mathrm{g} / \mathrm{mol})\) in her blood. How many hemoglobin molecules is this? What is this quantity in grams?

Determine the number of moles of the compound and determine the number of moles of each type of atom in each of the following: (a) 2.345 mol LiCl (b) 0.0872 mol acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}\) (c) \(3.3 \times 10^{-2} \mathrm{mol} \mathrm{Na}_{2} \mathrm{CO}_{3}\) (d) \(1.23 \times 10^{3}\) mol fructose, \(C_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) (e) 0.5758 mol \(\operatorname{FeSO}_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{7}\)

42\. Calculate the molar mass of each of the following compounds: (a) hydrogen fluoride, HF (b) ammonia, \(\mathrm{NH}_{3}\) (c) nitric acid, \(\mathrm{HNO}_{3}\) (d) silver sulfate, \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) (e) boric acid, \(\mathrm{B}(\mathrm{OH})_{3}\)

How are electrons and protons similar? How are they different?

Determine the mass of each of the following: (a) \(2.345 \mathrm{mol} \mathrm{LiCl}\) (b) 0.0872 mol acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}\) (c) \(3.3 \times 10^{-2} \mathrm{mol} \mathrm{Na}_{2} \mathrm{CO}_{3}\) (d) \(1.23 \times 10^{3}\) mol fructose, \(C_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) (e) 0.5758 mol \(\mathrm{FeSO}_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{7}\)
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