Question

Explain how you determine the molar mass of a compound.

Short answer

To determine the molar mass of a compound, follow these steps: 1) Identify the elements in the compound and their proportions. 2) Determine the atomic mass of each element using a periodic table. 3) Multiply the atomic mass of each element by the number of atoms of that element in the compound. 4) Add up the individual element masses to find the total molar mass. For example, for water (H2O), we have two hydrogen atoms with an atomic mass of 1.01 g/mol and one oxygen atom with an atomic mass of 16.00 g/mol. Thus, the molar mass of water is 2.02 g/mol (hydrogen) + 16.00 g/mol (oxygen) = 18.02 g/mol.

Step-by-step solution

Identify the elements present in the compound and their proportions

To determine the molar mass of a compound, first identify the elements present in the compound along with their proportions. Write down the chemical formula of the compound to help visualize the elements and their proportions. For example, let's find the molar mass of water (H2O). The chemical formula tells us that water contains two hydrogen atoms (H) and one oxygen atom (O).

Determine the atomic mass of each element in the compound

Find the atomic mass of each element present in the compound. You can find atomic masses on a periodic table (usually listed below the element symbol). Use the mass numbers rounded to one decimal place. For example, in water (H2O): - The atomic mass of hydrogen (H) is 1.01 g/mol. - The atomic mass of oxygen (O) is 16.00 g/mol.

Multiply the atomic mass of each element by the number of atoms of that element

Multiply the atomic mass of each element by the number of atoms of the same element present in the compound. For example, in water (H2O): - There are 2 hydrogen atoms. 2 x 1.01 g/mol = 2.02 g/mol - There is 1 oxygen atom. 1 x 16.00 g/mol = 16.00 g/mol

Add up the individual element masses

Add up the masses obtained in the previous step to determine the molar mass of the compound. For example, in water (H2O): Molar mass of water = 2.02 g/mol (hydrogen) + 16.00 g/mol (oxygen) = 18.02 g/mol Thus, the molar mass of water (H2O) is approximately 18.02 g/mol.

Key concepts

Atomic Mass

Understanding atomic mass is crucial when it comes to calculating the molar mass of a compound. Atomic mass refers to the weight of a single atom of an element and is usually expressed in atomic mass units (amu). However, for the purpose of determining the molar mass of a compound, we use the value in grams per mole (g/mol), which usually corresponds to the atomic weight of an element as indicated on the periodic table.

To illustrate, each hydrogen atom has an atomic mass of approximately 1.01 g/mol, whereas each oxygen atom has an atomic mass of about 16.00 g/mol. These values are averages that take into account the distribution of isotopes and their respective abundances in a naturally occurring sample of the element. When calculating molar mass, the atomic mass of each element, multiplied by the number of atoms of that element in the molecule, will provide the contribution of that element to the total molar mass of the compound.

Chemical Formula

The chemical formula of a compound is similar to a recipe; it tells you which elements are present and in what proportions. It is vital to not only list the elements but also to understand the subscripts in the formula, which indicate how many atoms of each element are in one molecule of the compound.

For example, in the chemical formula for water, H₂O, the subscripts tell us that there are two hydrogen atoms and one oxygen atom. To find the molar mass, you must consider these proportions; each hydrogen atom contributes 1.01 g/mol, so two of them contribute 2.02 g/mol, and the single oxygen atom contributes 16.00 g/mol. By using the chemical formula and knowing how to interpret it, you can calculate the molar mass accurately. Remember, the absence of a visible subscript implies that there is one atom of that element present in the molecule.

Periodic Table

The periodic table is an indispensable tool for chemists. It not only offers a way to visualize all known elements, but it also provides essential data, such as atomic mass which is pivotal in computing the molar mass of compounds. Each element's atomic mass is displayed under its symbol on the periodic table, and it represents the average mass of atoms of an element, measured in atomic mass units (amu).

When you're tasked with finding the molar mass of a compound, refer to the periodic table to find the atomic mass of each element involved. These values are standardized, accounting for variability due to isotopic distribution. It's noteworthy that while the atomic masses on the periodic table might be shown in amu for atomic scale calculations, they can be applied directly in grams for mole-scale calculations, simplifying stoichiometric computations in chemistry.