Question

Give the number of atoms of the specified element in a formula unit of each of the following compounds, and calculate the molecular (formula) mass: (a) Hydrogen in ammonium benzoate, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COONH}_{4}\) (b) Nitrogen in hydrazinium sulfate, \(\mathrm{N}_{2} \mathrm{H}_{6} \mathrm{SO}_{4}\) (c) Oxygen in the mineral leadhillite, \(\mathrm{Pb}_{4} \mathrm{SO}_{4}\left(\mathrm{CO}_{3}\right)_{2}(\mathrm{OH})_{2}\)

Short answer

Follow these steps: (a) 9 H, molecular mass = 139.16 g/mol. (b) 2 N, molecular mass = 132.12 g/mol. (c) 10 O, molecular mass = 809.84 g/mol.

Step-by-step solution

Identify the element in the compound

For each compound given, identify where the specified element is located in its chemical formula.

Count the number of specified atoms

Count the total number of atoms of the specified element in the chemical formula of each compound.

Calculate the atomic mass for the element

Find the atomic mass of the specified element using the periodic table.

Break down the formula into individual elements

List all the elements in the compound and their respective counts.

Calculate the molecular mass

Using the atomic masses obtained from the periodic table, multiply the number of each type of atom by its atomic mass and sum these individual masses to get the total molecular mass.

Key concepts

Atomic Structure

Atomic structure is the fundamental concept in understanding chemistry. An atom consists of a nucleus made up of protons and neutrons, surrounded by electrons. The number of protons in an atom determines the element and is called the atomic number. Electrons orbit the nucleus in various energy levels or shells.
Each electron has a negative charge, protons have a positive charge, and neutrons are neutral. The balance of these charges makes an atom neutral overall. Understanding atomic structure is essential when calculating the molecular mass since the atomic mass of an element is mainly due to the protons and neutrons in the nucleus. Atomic structure helps us comprehend how atoms bond and form compounds.

Stoichiometry

Stoichiometry is the area of chemistry that involves the calculation of reactants and products in chemical reactions. It's vital for understanding how substances combine and react according to specific ratios.
Using stoichiometry, we can calculate the quantities of reactants needed or products formed in a given reaction. This involves using balanced chemical equations, which provide the molar ratios of reactants and products.
In the context of our exercise, stoichiometry helps us understand the relationships between the atoms in a molecule and their respective masses. When we calculate the molecular mass, we use the stoichiometric coefficients to ensure that each element's contribution is accurately represented.

Chemical Formula

A chemical formula is a representation of a substance using element symbols and numerical subscripts. It shows the elements present in a compound and the number of atoms of each element.
For instance, in the formula \(\text{C}_{6} \text{H}_{5} \text{COONH}_{4}\), it represents ammonium benzoate, where each molecule contains 6 carbon atoms, 5 hydrogen atoms, 1 oxygen atom, and 1 nitrogen atom within the \(\text{COONH}_{4}\) group.
Understanding chemical formulas allows us to identify the types and numbers of atoms in a molecule. This information is crucial for calculating the molecular mass, as it tells us how many atoms of each element are present, allowing us to sum their respective atomic masses.

Periodic Table

The periodic table is a tabular arrangement of elements, ordered by their atomic number, electronic configuration, and recurring chemical properties. It provides critical information about each element, such as its atomic mass, symbol, and atomic number.
For example, the atomic mass of carbon (C) is approximately 12.01, hydrogen (H) is about 1.01, and oxygen (O) is around 16.00. By using the periodic table, we can find these values and use them for calculating the molecular mass of a compound.
The periodic table is a vital tool for chemists. It helps to quickly reference the properties of elements and understand their interactions in forming compounds. When working on problems involving molecular mass, the periodic table is indispensable for providing the atomic masses required for calculations.