Consider this question: What is the mass of solute in 200.0 L of a 1.556-M solution of KBr? (a) Outline the steps necessary to answer the question. (b) Answer the question.

Understanding the molar mass of a substance is essential when dealing with chemical solutions and reactions. It represents the weight of one mole of a chemical compound expressed in grams. The molar mass can be found by adding the atomic masses of all the elements in the compound, which are listed in the periodic table of elements. For example, potassium bromide (KBr) consists of potassium (K) and bromine (Br). The molar mass of KBr is the sum of the atomic mass of K (approximately 39.10 g/mol) and Br (approximately 79.90 g/mol), which equals 119.00 g/mol. This value is critical in converting between moles of KBr and mass of KBr, a frequent requirement in chemistry problems.

The concept of moles of solute is fundamental in solution chemistry. A mole is a standard unit of measurement in chemistry that quantifies the amount of a substance. One mole is defined as the quantity containing as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in 12 grams of carbon-12. This number is Avogadro’s number, which is approximately \(6.022 \times 10^{23}\). To determine the moles of solute in a solution, one can use the molarity, which tells us the moles of solute per liter of solution (mol/L). The formula to find the moles of solute is given by multiplying the molarity by the volume of the solution in liters. In our exercise, 1.556 mol/L of KBr multiplied by 200.0 L gives us the total moles of solute present.

The mass of the solute can be calculated once the moles of solute are known. This is achieved by multiplying the moles of solute by its molar mass. Remember, the mass will be in grams if the molar mass is in grams per mole. This step is a crucial link between the abstract concept of moles and the practical, tangible concept of mass. For the given problem, to find the mass of solute in KBr, you multiply the moles of KBr calculated from the molarity by the molar mass of KBr (119.00 g/mol). It translates the amount of substance from a molecular level to a level that can be physically measured on a scale.

Solution concentration, particularly expressed as molarity, is extremely important in chemistry. Molarity is defined as moles of solute per liter of solution, and it is expressed as mol/L or M. It provides a straightforward way to understand the strength of a solution. In the context of the problem, a 1.556 M solution of KBr means there are 1.556 moles of KBr in every liter of the solution. To prepare or dilute solutions with precision, understanding and performing molarity calculations is vital. Whether you are a chemist formulating a reaction or a student in a lab class, being able to correctly determine solution concentration is a key skill.