A saline solution contains \(1.1 \% \mathrm{NaCl}\) by mass. How much \(\mathrm{NaCl}\) is present in \(96.3 \mathrm{~g}\) of this solution?

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It is like a set of mathematical tools that allows chemists to calculate the amounts of substances consumed and produced in a given reaction. In the context of your homework problem, stoichiometry allows you to determine the amount of sodium chloride (NaCl) in a saline solution based on its percentage composition by mass.

When a problem states that a solution contains 1.1% NaCl by mass, this is actually providing you with a stoichiometric ratio. It tells you that for every 100 grams of saline solution, 1.1 grams is NaCl. Thus, when you have a different mass of the solution, as in your example with 96.3 grams, stoichiometry techniques let you calculate the corresponding mass of NaCl through simple proportional reasoning.

Molarity is a measure of the concentration of a solution. It is defined as the number of moles of a solute present in one liter of solution. The unit for molarity is moles per liter ((\text{M})), which is often abbreviated as 'M'.

Determining the molarity of a solution requires knowing the exact amount of solute (in moles) and the volume of the solution (in liters). Using the stoichiometry of a compound, like the saline solution in your exercise, you would first need to convert the mass of NaCl to moles. After that, if the volume of the solution were provided, you could calculate the molarity with the formula: \[ M = \frac{\text{moles of solute}}{\text{liters of solution}} \].

However, molarity does not necessarily directly relate to the percentage composition by mass unless you also have the density of the solution to convert between mass and volume.

The concentration of a solution can be expressed in various ways, with percent composition by mass being one of them. It is a measure of how much solute is present in a certain amount of solution or solvent and is often used because it's a simple and direct expression.

Percent composition is crucial in preparing solutions in the lab or in industry, as it directly relates to how much substance you'll need to add to a specific amount of solvent to achieve the desired concentration. For instance, when you're given that a saline solution is 1.1% NaCl by mass, that immediately gives you the ratio needed to calculate the mass of solute in any given mass of solution.

The beauty of percent composition by mass is its simplicity: To find the mass of the solute, you multiply the percent (in decimal form) by the total mass of the solution, as brilliantly showcased in the step-by-step solution to your exercise. Understanding the concept of solution concentration is essential in fields such as pharmacy, medicine, biochemistry, and environmental science, where precise solution preparations are a daily necessity.