Problem 92 - Chemistry: An Atoms-Focused Approach

Question

How many moles of \(\mathrm{NaCl}\) are there in a crystal of halite that has a mass of \(6.82 \mathrm{g} ?\)

Step-by-Step Solution

Answer

Answer: Approximately 0.1167 moles of NaCl are present in a 6.82 g halite crystal.

Step 1: Calculate the molar mass of NaCl.

Using the periodic table, find the atomic weight of sodium (Na) and chlorine (Cl). Sodium's atomic weight is approximately 22.99 u and chlorine's atomic weight is approximately 35.45 u. Now, add the atomic weights of both elements to find the molar mass of NaCl: M(NaCl) = 22.99 + 35.45 = 58.44 g/mol.

Step 2: Convert the mass of the halite crystal to moles.

In order to convert mass to moles, we will use the following formula: moles = mass (g) / molar mass (g/mol). Plug in the given mass of the halite crystal (6.82 g) and the calculated molar mass of NaCl (58.44 g/mol) into the formula: moles = 6.82 g / 58.44 g/mol.

Step 3: Calculate the number of moles of NaCl.

Divide the mass of the halite crystal by the molar mass of NaCl to find the number of moles: moles = 6.82 g / 58.44 g/mol = 0.1167 moles. Hence, there are approximately 0.1167 moles of NaCl in the given halite crystal.

Key Concepts

Molar Mass

Molar mass is a fundamental concept in chemistry that helps us understand the weight of one mole of a compound. A mole is a standard unit to quantify large numbers of atoms, and molar mass makes it easier to work with these large quantities. It is expressed in grams per mole (g/mol).
To determine the molar mass of a compound, like sodium chloride (NaCl), we need the atomic masses of its constituent elements. Using a periodic table, we find that sodium (Na) has an atomic mass of approximately 22.99 u (atomic mass units) and chlorine (Cl) has an atomic mass of about 35.45 u.
Adding these atomic masses gives us the molar mass of NaCl:

• Sodium (Na): 22.99 u
• Chlorine (Cl): 35.45 u

Therefore, the molar mass of NaCl is 58.44 g/mol. Understanding molar mass is key when performing calculations involving moles and mass.

Moles

Moles are a crucial concept in chemistry for quantifying substances. One mole equals Avogadro's number, which is approximately 6.022 x 10^23 particles. These particles could be atoms, molecules, or ions depending on the substance being measured.
This concept is similar to everyday units of measurement, like a dozen, which always represents 12 items. Moles allow chemists to calculate chemical quantities and converts between mass, volume, and number of particles using the mole concept.
In the context of sodium chloride (NaCl) with a given mass of 6.82 g, we can calculate the number of moles using its molar mass:

• Formula: moles = mass (g) / molar mass (g/mol)
• Given: mass = 6.82 g and molar mass of NaCl = 58.44 g/mol

When we perform this calculation, we find that the sample contains approximately 0.1167 moles of sodium chloride. This use of moles makes it straightforward to relate the mass of a substance to the number of chemical entities present.

Sodium Chloride (NaCl)

Sodium chloride, commonly known as table salt, is represented by the chemical formula NaCl. This compound is composed of equal parts sodium (Na) and chlorine (Cl).
In its crystalline form, which is known as halite, NaCl plays an essential role in various industries and biological processes. It is crucial for flavoring and preserving food, as well as maintaining proper electrolyte balance within the human body.
The interaction between sodium and chlorine occurs when a sodium atom donates an electron to a chlorine atom, forming an ionic bond. This transfer leads to the creation of positively charged sodium ions (Na⁺) and negatively charged chloride ions (Cl⁻), which maintains the compound's overall charge neutrality.
Given its molar mass of 58.44 g/mol, sodium chloride is frequently used in stoichiometric calculations. Whether you are calculating the number of moles in a certain mass, as shown in the original exercise, or producing chemical reactions, understanding NaCl's properties and composition is integral to mastering chemical problem-solving.