Chapter 8: Problem 25
The ______ of a substance is the mass (in grams) of 1 mol of the substance.
Short Answer
Expert verified
The molar mass of a substance is found by identifying the chemical formula, locating the atomic masses of each element on the periodic table, multiplying the atomic masses by their subscripts in the chemical formula, and finally adding the multiplied atomic masses together. For example, the molar mass of H₂O is \(18 \,\text{g/mol}\).
Step by step solution
01
Verifying our understanding of the given concept: Molar Mass
Molar mass is the mass of one mole of a substance. A mole, as you may know, is a basic unit of measure in chemistry and represents \(6.022 \times 10^{23}\) entities of a substance, where entities can be atoms, molecules, ions, or other chemical units. Molar mass is usually expressed in units of grams per mole (g/mol), and it can be determined by adding the atomic masses of all the elements in a compound.
02
Identifying the substance and its chemical formula
First, we identify the substance for which we want to find the molar mass. This includes knowing the chemical formula of the substance, representing its constituent elements and their proportions.
For example, let's find the molar mass of water (H₂O).
03
Finding atomic masses of each element using the periodic table
Now, locate each element in the substance's chemical formula on the periodic table and find their atomic masses. These masses are usually listed beneath the element symbol on the periodic table. It's important to use atomic mass, not atomic number.
For H₂O, the atomic mass of Hydrogen (H) is approximately 1 g/mol, and the atomic mass of Oxygen (O) is approximately 16 g/mol.
04
Multiplying the atomic mass of each element by its subscript in the chemical formula
Next, multiply the atomic mass of each element by the number of atoms of that element in the substance (indicated by the subscript in the chemical formula). If there is no subscript, assume it is 1.
For H₂O, we have:
- 2 Hydrogen atoms: \(2 \times 1 \,\text{g/mol}\) = 2 g/mol
- 1 Oxygen atom: \(1 \times 16 \,\text{g/mol}\) = 16 g/mol
05
Adding the multiplied atomic masses to find the molar mass
Finally, add the results from step 3 to find the molar mass of the substance.
For H₂O:
Molar mass = (2 g/mol) + (16 g/mol) = \(18 \,\text{g/mol}\)
Thus, the molar mass of water (H₂O) is \(18 \,\text{g/mol}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Mole Concept
The mole concept is fundamental to understanding chemistry and involves a specific number of particles, similar to how a dozen refers to twelve items. In chemistry, one mole is exactly equal to Avogadro's number, which is approximately \(6.022 \times 10^{23}\) entities. These entities could be atoms, molecules, ions, electrons, or other microscopic particles. This concept allows chemists to count substances at the atomic scale by weighing them. A mole's mass, expressed in grams, corresponds to the substance's molar mass, bridging the gap between microscopic particles and macroscopic measurements.
For instance, if you have a mole of carbon atoms, you would have \(6.022 \times 10^{23}\) carbon atoms, which would weigh about 12 grams, since the atomic mass of carbon is 12 atomic mass units (amu). This leads to practical applications such as determining how many atoms are in a sample or how much of a chemical is needed for a reaction.
For instance, if you have a mole of carbon atoms, you would have \(6.022 \times 10^{23}\) carbon atoms, which would weigh about 12 grams, since the atomic mass of carbon is 12 atomic mass units (amu). This leads to practical applications such as determining how many atoms are in a sample or how much of a chemical is needed for a reaction.
Atomic Mass
Atomic mass is at the core of calculating molar mass and understanding chemical compositions. It refers to the mass of an individual atom, usually expressed in atomic mass units (amu) or unified atomic mass units (u). These units are based on a standard scale where 1 amu is defined as one-twelfth of the mass of a carbon-12 atom.
Importance of Atomic Mass in Calculations
When computing molar mass, it's essential to use the average atomic mass of each element as it naturally occurs, which includes all its isotopes and their relative abundance. This average can be found on any standard periodic table, typically under the symbol of the element. Knowing the atomic mass allows us to convert between the number of atoms and the measurable mass of a sample for practical laboratory applications.Chemical Formula
A chemical formula represents the types and number of atoms in the smallest unit of a substance. For compounds, this smallest unit is the molecule. The formula provides significant information - it reveals the elements present, their proportions, and can imply the structure of the compound.
Understanding the chemical formula is crucial when calculating the molar mass because it gives the exact proportions to multiply by each element's atomic mass. This calculation tells us how much one mole of a compound weighs, which is important for many experimental and industrial chemical processes.
- Subscripts in a formula indicate the number of atoms of each element.
- For example, in water (H₂O), 2 hydrogen atoms (H) and 1 oxygen atom (O) are present in each molecule.
Understanding the chemical formula is crucial when calculating the molar mass because it gives the exact proportions to multiply by each element's atomic mass. This calculation tells us how much one mole of a compound weighs, which is important for many experimental and industrial chemical processes.
Periodic Table
The periodic table is an organized arrangement of all known elements, providing comprehensive information that is essential in chemistry. Each element is listed by its atomic number and chemical symbol, and the table is structured so that elements with similar chemical behaviors fall into the same columns (groups).