What molarity of ZnCl2 forms when 25.0 g of zinc completely reacts with CuCl2 according to the following reaction? Assume a final volume of 275 mL. Zn(s) + CuCl2(aq)-ZnCl2(aq) + Cu(s)

Understanding the molar mass of a substance is a foundational concept in chemistry, particularly when it comes to molarity calculations. The molar mass represents the weight of one mole of a substance and is expressed in grams per mole (g/mol). This value can easily be found on the periodic table as the atomic mass of the element. For compounds like ZnCl2 in our exercise, you calculate the molar mass by adding together the atomic masses of all atoms within the molecule.

For example, for ZnCl2, the molar mass would be the sum of the molar mass of Zn and twice the molar mass of Cl, since there are two chloride ions for every zinc ion in the compound. It's essential to accurately calculate the molar mass as it directly affects the subsequent steps in the stoichiometry of the reaction.

The next key theme here is converting grams to moles, which allows chemists to use the mole as a bridge between the mass of a substance and the number of particles it contains. Using the molar mass, the number of moles can be calculated as follows: \[\begin{equation}moles = \frac{mass \text{ (in grams)}}{molar \text{ mass (g/mol)}}\end{equation}\]This simple conversion is crucial when working with reactions because reactions occur on a per-mole basis, not per-gram. Thus, by knowing the number of moles of a reactant, you can directly relate it to the product's moles via the stoichiometry of the balanced chemical equation.

Stoichiometry is at the heart of most chemical calculations. It involves using the ratios of moles of reactants and products in a balanced chemical equation to figure out the amounts of substances involved in the reaction. As seen in the given exercise, the stoichiometry is straightforward because the mole ratio between Zn and ZnCl2 is 1:1. This means that for every mole of Zn that reacts, one mole of ZnCl2 is produced.

Understanding this relationship allows us to predict outcomes of chemical reactions and calculates the quantities needed or produced. Often, stoichiometry is not so simple and understanding how to set up and use mole ratios becomes crucial in solving more complex problems.

After understanding the molar mass and the moles conversion, and determining the stoichiometry of the reaction, the next step is to determine the solution concentration. The concentration of solutions in chemistry is often expressed as molarity, which is the number of moles of solute per liter of solution (mol/L).

To calculate molarity, you take the number of moles of your solute — in this case, ZnCl2 — and divide it by the volume of the solution in liters. It's important to note that the solution's volume is not necessarily the summed volumes of the individual components before mixing; reactions can lead to volume changes. For accurate molarity calculations, one must always use the final volume of the prepared solution.