Question

What is the molarity of a solution made by dissolving 25.0 g of sodium thiocyanate (NaSCN) in enough water to make 500 mL of solution? (Chapter 14)

Short answer

The molarity of the solution made by dissolving 25.0 g of sodium thiocyanate (NaSCN) in enough water to make 500 mL of solution is approximately \(0.616 \ mol/L\).

Step-by-step solution

Find the molar mass of NaSCN

Calculate the molar mass of sodium thiocyanate by finding the sum of the atomic masses of each element in the compound. - Sodium (Na): 22.99 g/mol - Sulfur (S): 32.06 g/mol - Carbon (C): 12.01 g/mol - Nitrogen (N): 14.01 g/mol Molar mass of NaSCN = 22.99 + 32.06 + 12.01 + 14.01 = 81.07 g/mol

Convert grams of NaSCN to moles

Use the molar mass of NaSCN to convert the given mass (25.0 g) to moles: moles = 25.0 g / 81.07 g/mol = 0.308 moles (rounded to three decimal points)

Convert the volume of the solution to liters

Given the volume of the solution is 500 mL, convert it to liters: 500 mL = 500/1000 = 0.5 L

Calculate the molarity

Using the formula for molarity (M), we can now calculate the molarity of the solution: M = moles of solute/liters of solution M = 0.308 moles / 0.5 L = 0.616 mol/L The molarity of the solution made by dissolving 25.0 g of sodium thiocyanate (NaSCN) in enough water to make 500 mL of solution is approximately 0.616 mol/L.

Key concepts

Sodium Thiocyanate Solution

Understanding solutions in chemistry is pivotal to grasping various chemical processes, one such solution being a sodium thiocyanate (NaSCN) solution. Sodium thiocyanate is a versatile chemical used in numerous applications, from textile and photography to medical testing. As a reagent, it's particularly known for its roles in titration experiments.

When we talk about a 'sodium thiocyanate solution', we're referring to NaSCN that has been dissolved in a solvent, typically water. The resulting clear, colorless solution exhibits differing properties based on its concentration, and it's crucial for students to understand how to calculate this concentration, as it's essential for experimental success and reproducibility in scientific research.

Converting Grams to Moles

The concept of moles is central to all stoichiometry calculations in chemistry. Converting grams to moles is a fundamental skill necessary for quantifying how much substance is present. To convert grams to moles, you need to know the substance's molar mass, which acts as a conversion factor.

To put it simply, one mole of any substance contains Avogadro's number of particles, which is approximately 6.022 x 10²³. The molar mass, expressed in grams per mole, tells us the mass of one mole of that substance. By dividing the mass of your substance in grams by its molar mass, you can determine how many moles you have—a critical step in preparation for various calculations in laboratory-based courses and professional research.

Molar Mass

Molar mass is a property that links the mass of a substance to its amount in moles and it's measured in grams per mole (g/mol). It is essential for converting between grams of a substance and moles of a substance. Each element on the periodic table has an atomic mass, and the molar mass of a compound like sodium thiocyanate can be found by adding the atomic masses of sodium (Na), sulfur (S), carbon (C), and nitrogen (N).

Having a solid grasp of molar mass is not just about memorizing numbers; it's about understanding that these numbers reflect the mass of Avogadro's number of atoms or molecules, bridging the gap between the macroscopic world we live in and the microscopic world of atoms and molecules.

Solution Concentration

Solution concentration describes how much solute is dissolved in a given amount of solvent. In the context of chemistry, molarity (M) is one of the most common units for concentration, defined as the number of moles of solute per liter of solution. It's calculated with the formula:
\( M = \frac{\text{moles of solute}}{\text{liters of solution}} \).

It is essential to understand that the molarity presents a direct relationship between the quantity of the solute and the volume of the solution. This helps chemists manipulate variables to achieve desired reaction conditions and allows for the standardization of solutions used in titrations, which can be crucial for accurate and repeatable results in both educational laboratories and industry settings.