A chemist wants to make \(2.5 \mathrm{~L}\) of a \(0.100 \mathrm{M} \mathrm{KCl}\) solution. How much \(\mathrm{KCl}\) in grams should the chemist use?

Molarity is a term used to describe the concentration of a solution, indicating how many moles of solute are present in one liter of solution. It's a vital concept in chemistry that facilitates the standardization of solutions for use in experiments and reactions. To calculate molarity, you can use the formula:

Moles to Molarity

The formula is expressed as Molarity (M) = Moles of Solute / Volume of Solution in Liters (L). For example, if a chemist needs a 0.100 M KCl solution, and they have 2.5 L of solution, the moles of KCl required would be 0.100 M multiplied by 2.5 L, yielding 0.25 moles of KCl.

Molar mass is the weight of one mole of a chemical compound, often measured in grams per mole (g/mol). It is a crucial factor in converting between the mass of a substance and the number of moles. Each element's molar mass is found on the periodic table and it corresponds to the element's atomic weight. For compounds like KCl, the molar mass is the sum of the molar masses of the individual elements.

Calculating Molar Mass of KCl

In the case of potassium chloride (KCl), the molar mass is found by adding the atomic mass of potassium (approximately 39.10 g/mol) and chlorine (approximately 35.45 g/mol), giving us a molar mass of approximately 74.55 g/mol for KCl.

When working with chemical reactions, it's often necessary to convert moles to grams. This conversion helps scientists accurately measure out substances for experiments. The conversion is done by multiplying the number of moles by the substance's molar mass.

Converting Moles of KCl to Grams

Following our ongoing example, to convert 0.25 moles of KCl to grams, we use KCl's molar mass (74.55 g/mol). So, 0.25 moles multiplied by 74.55 g/mol results in approximately 18.64 grams of KCl.

Preparing a chemical solution of a desired molarity involves dissolving the correct amount of solute into a solvent, usually water, to achieve a specified total volume. Accuracy is key, as the concentration impacts the outcome of chemical reactions.

Steps to Prepare a KCl Solution

Using our example to create a 0.100 M solution of KCl in 2.5 L of water, the chemist would weigh out approximately 18.64 grams of solid KCl on a balance. This solid is then dissolved in less than 2.5 L of water, ensuring complete dissolution, and the solution is diluted with water to reach the final volume of 2.5 L. By measuring carefully and adjusting the volume after dissolving, the chemist can ensure the final molarity is accurate.