Question

For each compound, list the correct formula and calculate the formula mass. (a) barium bromide (b) dinitrogen trioxide (c) copper(I) sulfate (d) hydrobromic acid

Short answer

The correct formulas and formula masses are: (a) BaBr2, 297.13 u; (b) N2O3, 76.02 u; (c) Cu2SO4, 223.17 u; (d) HBr, 80.91 u.

Step-by-step solution

Determine the chemical formula for barium bromide

Barium bromide consists of barium (Ba) and bromine (Br). The valency of barium is +2 and bromine is -1. Thus, to balance the charges, we need two bromine atoms for each barium atom resulting in the chemical formula BaBr2.

Calculate the formula mass for barium bromide

The atomic mass of barium (Ba) is 137.33 u and that of bromine (Br) is 79.90 u. The formula mass is calculated as follows: \(1 \times 137.33 u + 2 \times 79.90 u = 137.33 u + 159.80 u = 297.13 u\).

Determine the chemical formula for dinitrogen trioxide

Dinitrogen trioxide consists of nitrogen (N) and oxygen (O), with nitrogen having a valency of +3 and oxygen having a valency of -2. Using these valencies, for every two nitrogen atoms, three oxygen atoms are needed, resulting in the chemical formula N2O3.

Calculate the formula mass for dinitrogen trioxide

The atomic mass of nitrogen (N) is 14.01 u and that of oxygen (O) is 16.00 u. The formula mass is calculated as follows: \(2 \times 14.01 u + 3 \times 16.00 u = 28.02 u + 48.00 u = 76.02 u\).

Determine the chemical formula for copper(I) sulfate

Copper(I) sulfate consists of copper (Cu) with a +1 charge and the sulfate (SO4) with a -2 charge. To balance the charges, we need two copper atoms for every sulfate ion, resulting in the chemical formula Cu2SO4.

Calculate the formula mass for copper(I) sulfate

The atomic mass of copper (Cu) is 63.55 u, sulfur (S) is 32.07 u, and oxygen (O) is 16.00 u. The formula mass is calculated as follows: \(2 \times 63.55 u + 1 \times 32.07 u + 4 \times 16.00 u = 127.10 u + 32.07 u + 64.00 u = 223.17 u\).

Determine the chemical formula for hydrobromic acid

Hydrobromic acid is composed of hydrogen (H) with a +1 charge and bromine (Br) with a -1 charge. Since the charges are already balanced, the chemical formula is HBr.

Calculate the formula mass for hydrobromic acid

The atomic mass of hydrogen (H) is 1.01 u and that of bromine (Br) is 79.90 u. The formula mass is calculated as follows: \(1 \times 1.01 u + 1 \times 79.90 u = 1.01 u + 79.90 u = 80.91 u\).

Key concepts

Formula Mass

Understanding the formula mass is essential in chemistry for comprehending the composition of compounds. It is the sum of the atomic masses of all atoms in a chemical formula. This mass is commonly measured in unified atomic mass units (u), also known as daltons (Da).

To calculate the formula mass of a compound, we simply multiply the atomic mass of each element by the number of times it appears in the chemical formula, then sum these values for all elements involved. For example, the formula mass of water (H2O) involves 2 hydrogen atoms each with an atomic mass of approximately 1 u, and 1 oxygen atom with an atomic mass of approximately 16 u. So, the formula mass is calculated as: \(2 \times 1 u + 1 \times 16 u = 18 u\).

This concept is vital for a variety of applications like determining how much of a chemical is needed for a reaction or understanding the molar relationships in stoichiometry. Moreover, by honing skills in calculating formula mass, students develop a firmer grasp of molecular compositions and stoichiometric calculations in chemistry.

Chemical Formula

A chemical formula represents the types and numbers of atoms in a molecule of a chemical substance. It is a concise way of expressing information about the atoms that constitute a particular chemical compound. Chemical formulas can be simple or empirical, displaying the simplest integer ratio of atoms, or they can be molecular, showing the exact number of atoms of each type in the compound.

Take, for instance, glucose, which has a molecular formula of C6H12O6. This tells us that a single molecule of glucose contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. To write chemical formulas, the valency of elements—indicating their ability to combine with other elements—is taken into account to ensure that the resulting compound is electrically neutral unless it's an ion. Understanding the principles of writing chemical formulas is foundational for making sense of chemical reactions and processes.

Valency

Valency is the combining power of an element, especially as measured by the number of hydrogen atoms it can replace or combine with. This is a fundamental concept in chemistry because it helps scientists understand and predict how elements will react with one another.

For example, the valency of hydrogen is 1, while oxygen is 2. This means that it takes two hydrogen atoms to combine with one oxygen atom to form water. Valency plays a central role in determining the proportions of elements that come together to form compounds. Having a clear understanding of valency is crucial for correctly writing chemical formulas, predicting the products of chemical reactions, and balancing chemical equations. In many cases, studying an element's position in the periodic table can provide clues to its valency, aiding in the prediction of its chemical behavior.

Atomic Mass

Atomic mass, or atomic weight, is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. It is expressed in unified atomic mass units, where one atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom, approximately equal to the mass of a proton or a neutron.

The atomic masses of elements are often listed in the periodic table and are vital for chemistry calculations like formula mass and molar mass. For instance, when calculating the formula mass of copper(I) sulfate, the atomic mass of copper, sulfur, and oxygen are used in conjunction with their respective quantities from the chemical formula. This concept ties in closely with Avogadro's number when considering the mass of a mole of substances, a cornerstone of quantitative chemistry. An accurate understanding of atomic masses is essential for students as they progress into more advanced topics such as reaction stoichiometry and thermodynamics.