Question

Determine the formula weights of each of the following compounds: (a) nitric acid, \(\mathrm{HNO}_{3}\); (b) \(\mathrm{KMnO}_{4}\); (c) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) i (d) quartz, \(\mathrm{SiO}_{2}\); (e) gallium sulfide, (f) chromium(III) sulfate, (g) phosphorus trichloride.

Short answer

The formula weights for the compounds are as follows: (a) Nitric Acid, HNO3: 63.01228 g/mol (b) Potassium Permanganate, KMnO4: 158.03404 g/mol (c) Tricalcium Phosphate, Ca3(PO4)2: 310.176 g/mol (d) Quartz, SiO2: 60.0843 g/mol (e) Gallium Sulfide, Ga2S3: 253.567 g/mol (f) Chromium(III) Sulfate, Cr2(SO4)3: 399.8772 g/mol (g) Phosphorus Trichloride, PCl3: 137.332762 g/mol

Step-by-step solution

Identifying the atoms in the compound

The compound nitric acid (HNO3) consists of one hydrogen atom (H), one nitrogen atom (N), and three oxygen atoms (O).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - H (hydrogen) = 1.00784 g/mol - N (nitrogen) = 14.00674 g/mol - O (oxygen) = 15.9994 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of HNO3 by summing up the atomic weights of the components: Formula weight (HNO3) = 1.00784 g/mol (H) + 14.00674 g/mol (N) + 3 * 15.9994 g/mol (O) = 63.01228 g/mol #b) Formula Weight of Potassium Permanganate (KMnO4)#

Identifying the atoms in the compound

The compound potassium permanganate (KMnO4) consists of one potassium atom (K), one manganese atom (Mn), and four oxygen atoms (O).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - K (potassium) = 39.0983 g/mol - Mn (manganese) = 54.938045 g/mol - O (oxygen) = 15.9994 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of KMnO4 by summing up the atomic weights of the components: Formula weight (KMnO4) = 39.0983 g/mol (K) + 54.938045 g/mol (Mn) + 4 * 15.9994 g/mol (O) = 158.03404 g/mol #c) Formula Weight of Tricalcium Phosphate (Ca3(PO4)2)#

Identifying the atoms in the compound

The compound Tricalcium Phosphate (Ca3(PO4)2) consists of three calcium atoms (Ca), two phosphorus atoms (P), and eight oxygen atoms (O).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - Ca (calcium) = 40.078 g/mol - P (phosphorus) = 30.973762 g/mol - O (oxygen) = 15.9994 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of Ca3(PO4)2 by summing up the atomic weights of the components: Formula weight (Ca3(PO4)2) = 3 * 40.078 g/mol (Ca) + 2 * 30.973762 g/mol (P) + 8 * 15.9994 g/mol (O) = 310.176 g/mol #d) Formula Weight of Quartz (SiO2)#

Identifying the atoms in the compound

The compound quartz (SiO2) consists of one silicon atom (Si) and two oxygen atoms (O).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - Si (silicon) = 28.0855 g/mol - O (oxygen) = 15.9994 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of SiO2 by summing up the atomic weights of the components: Formula weight (SiO2) = 28.0855 g/mol (Si) + 2 * 15.9994 g/mol (O) = 60.0843 g/mol #e) Formula Weight of Gallium Sulfide (Ga2S3)#

Identifying the atoms in the compound

The compound gallium sulfide (Ga2S3) consists of two gallium atoms (Ga) and three sulfur atoms (S).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - Ga (gallium) = 69.723 g/mol - S (sulfur) = 32.0605 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of Ga2S3 by summing up the atomic weights of the components: Formula weight (Ga2S3) = 2 * 69.723 g/mol (Ga) + 3 * 32.0605 g/mol (S) = 253.567 g/mol #f) Formula Weight of Chromium(III) Sulfate (Cr2(SO4)3)#

Identifying the atoms in the compound

The compound chromium(III) sulfate (Cr2(SO4)3) consists of two chromium atoms (Cr), three sulfur atoms (S), and 12 oxygen atoms (O).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - Cr (chromium) = 51.9961 g/mol - S (sulfur) = 32.0605 g/mol - O (oxygen) = 15.9994 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of Cr2(SO4)3 by summing up the atomic weights of the components: Formula weight (Cr2(SO4)3) = 2 * 51.9961 g/mol (Cr) + 3 * 32.0605 g/mol (S) + 12 * 15.9994 g/mol (O) = 399.8772 g/mol #g) Formula Weight of Phosphorus Trichloride (PCl3)#

Identifying the atoms in the compound

The compound phosphorus trichloride (PCl3) consists of one phosphorus atom (P) and three chlorine atoms (Cl).

Determine atomic weights

Refer to the periodic table to find the atomic weights for each element: - P (phosphorus) = 30.973762 g/mol - Cl (chlorine) = 35.453 g/mol

Calculate the formula weight

Using the atomic weights, we'll calculate the formula weight of PCl3 by summing up the atomic weights of the components: Formula weight (PCl3) = 30.973762 g/mol (P) + 3 * 35.453 g/mol (Cl) = 137.332762 g/mol

Key concepts

Atomic Weights

The concept of atomic weights is crucial when calculating the formula weight of a compound. Atomic weight is the average mass of atoms of an element, measured in atomic mass units (or g/mol when expressed scientifically). This weight reflects the average weight of naturally occurring isotopes of the element. For example, hydrogen has an atomic weight of approximately 1.00784 g/mol. When finding the atomic weight of elements like hydrogen, nitrogen, or oxygen, the periodic table is an invaluable tool for quick reference and accuracy.
Understanding atomic weights allows us to make precise calculations in chemistry. They provide the basic metrics needed to determine how heavy or light a compound is at the molecular level, enabling scientists and students to discern the makeup of chemical substances.

Periodic Table

The periodic table is an organized chart of all chemical elements, which is arranged based on ascending atomic number, electronic configurations, and recurring chemical properties. Dmitri Mendeleev first created it to predict elements that were yet to be discovered. Each element on the table is represented by a unique symbol along with its atomic number and atomic weight.
The periodic table is not just an organizational tool – it is a comprehensive source of information about elements. It lists their atomic weights, which are fundamental to calculations for formula weights of chemical compounds. By simply referencing it, chemists and students can find out the composition and reactions expected from particular elements.

• Atomic number tells us the number of protons in an element.
• Atomic weight gives the average mass of the atoms of the element.

The layout of the table helps you quickly locate trends and relationships among different elements, such as how atomic weights tend to increase from left to right across a period.

Chemical Compounds

Chemical compounds are a combination of two or more different elements bonded together. These compounds have distinct properties and compositions that are different from the individual elements that form them. They can be broken down into two main types: ionic and covalent.

• Ionic Compounds: Formed by the transfer of electrons between atoms, these compounds often consist of metals and nonmetals.
• Covalent Compounds: Formed by the sharing of electrons between atoms, usually consisting of nonmetals.

The properties of chemical compounds depend significantly on the types of elements involved and their arrangement within the molecule. Understanding the makeup of these compounds, using their molecular formula, allows us to calculate their formula weight. This leads to insights into their potential reactions and interactions with other compounds.

Molecular Formula Analysis

Molecular formula analysis involves decomposing a chemical compound into its individual elements to understand its composition. A molecular formula provides the exact number of each type of atom in a molecule, giving insights into its molecular structure.
For instance, nitric acid has the molecular formula \(\mathrm{HNO}_3\). This reveals each molecule contains one hydrogen atom, one nitrogen atom, and three oxygen atoms. Through analysis, we recognize that molecular formulas are crucial for calculating the formula weight of compounds.

• Identify individual element symbols and their quantity in the compound.
• Use the atomic weights of these elements to calculate the compound's formula weight.

This simple analysis informs everything from the energetic potentials of the compound, how it will react under certain conditions, and even its physical properties like boiling and melting points.