Determine the chemical formula of each compound and refer to the formula to calculate the mass percent composition of each constituent element. (a) copper(II) iodide (b) sodium nitrate (c) lead(II) sulfate (d) calcium fluoride

Understanding the chemical formula of a compound is a fundamental step in chemistry, akin to knowing a person's name. It provides information about the types and numbers of atoms in the smallest unit of a substance. For instance, copper(II) iodide's formula is CuI2. This tells us that each unit of this compound contains one copper atom and two iodide ions. If the charges aren't balanced, as in calcium fluoride, the formula reflects the necessary ratio to balance the charges, resulting in CaF2.

To determine a chemical formula, you must know the charges on the ions making up the compound. The subscripts in the formula are essentially the simplest whole numbers that balance the overall charge of the compound.

The molar mass of a substance is the weight of 1 mole (6.022 x 10²³ particles) of that substance. Molar mass is expressed in grams per mole (g/mol) and is calculated by summing the atomic masses of all atoms in a molecule. For example, to find the molar mass of sodium nitrate (NaNO3), you would add the atomic mass of one sodium atom (22.99 g/mol), one nitrogen atom (14.01 g/mol), and three oxygen atoms (16.00 g/mol each).

Understanding Atomic Mass

Each element's atomic mass is listed on the periodic table and reflects the average mass of all isotopes of that element, proportionate to their occurrence. Molar mass calculation thus requires you to multiply the atomic mass of each element by the number of times that element appears in the formula, and then sum all these values.

Atomic mass, often listed as atomic weight on the periodic table, represents the average mass of atoms of an element, measured in atomic mass units (amu). Each isotope of an element has its own mass, and the atomic mass reflects the weighted average of these isotopes as they occur naturally.

When computing mass percent composition, it is necessary to use the atomic mass of each element involved. In calculating the molar mass of lead(II) sulfate (PbSO4), for example, atomic masses from the periodic table are used: lead (Pb) 207.2 amu, sulfur (S) 32.06 amu, and oxygen (O) 16.00 amu.

While a chemical formula provides the exact number of each type of atom in a compound, an empirical formula presents these numbers in the simplest whole-number ratio. To find this, divide the number of atoms of each element by the greatest common divisor for all elements in the compound. For instance, if a molecule has the formula C6H12O6, its empirical formula is CH2O, as the numbers 6, 12, and 6 can all be divided by 6.

The empirical formula doesn't generally indicate the actual number of atoms in a molecule but rather the simplest ratio between them. However, for ionic compounds like sodium chloride (NaCl) or calcium fluoride (CaF2), the empirical formula also represents the chemical formula because these compounds exist as networks of ions rather than discrete molecules.

Stoichiometry is the branch of chemistry that deals with the quantities of substances involved in chemical reactions. It extends beyond just knowing the formulas—it's the calculation of reactants and products in a chemical equation. It involves using the coefficients from a balanced chemical equation to determine the relative amounts of reactants needed and products formed.

In stoichiometry, understanding the concept of the mole is crucial because it allows chemists to count particles by weighing them. This counting by weighing is fundamental when converting grams to moles or vice versa, facilitating the calculation of how much of each substance is required or produced in a reaction.