Question

Describe how you would prepare \(250 \mathrm{~mL}\) of a \(0.707 M\) \(\mathrm{NaNO}_{3}\) solution.

Short answer

Dissolve 15.024 g of \( \text{NaNO}_3 \) in water to make 250 mL of solution.

Step-by-step solution

Understanding the Molarity Formula

The molarity (M) formula is given by \( M = \frac{n}{V} \), where \( M \) is the molarity, \( n \) is the number of moles of solute, and \( V \) is the volume of the solution in liters. In this problem, we need to determine how many moles of \( \text{NaNO}_3 \) are required for a 0.707 M solution with a volume of 0.250 L.

Calculate the Moles of \( \text{NaNO}_3 \) Needed

Rearrange the molarity formula to solve for moles: \( n = M \times V \). Substitute the known values into the equation: \( n = 0.707 \text{ M} \times 0.250 \text{ L} \). This results in \( n = 0.17675 \text{ moles} \) of \( \text{NaNO}_3 \).

Convert Moles to Grams

To find out how many grams are needed, we use the molar mass of \( \text{NaNO}_3 \). The molar mass of \( \text{NaNO}_3 \) is approximately 85 g/mol. Using the equation: \( \text{mass} = \text{moles} \times \text{molar mass} \), we calculate the mass: \( 0.17675 \text{ moles} \times 85 \text{ g/mol} = 15.02375 \text{ grams} \).

Measuring and Mixing the Solution

Weigh 15.024 grams of \( \text{NaNO}_3 \) (rounded appropriately for practical lab measurement) using a balance. Dissolve this amount in a small quantity of distilled water, then transfer the solution to a 250 mL volumetric flask. Fill the flask with distilled water up to the 250 mL mark and mix thoroughly to ensure homogeneity.

Key concepts

Preparation of Solutions

When preparing a solution, the key goal is to dissolve the desired amount of solute into a solvent, achieving a specific concentration. To do this accurately and effectively:

• Determine the amount of solute needed, based on the desired molarity and volume of the solution.
• Use precise measuring equipment, such as balances for solids and volumetric flasks for liquids, to ensure accuracy.
• Dissolve the solute first in a portion of the solvent before transferring it to a container where you will make the final volume adjustment.
• Mix thoroughly to achieve a homogenous solution, which helps ensure that the concentration is uniform throughout.
• Always use distilled or deionized water when preparing chemical solutions, as impurities in regular tap water can affect the chemical reaction or the accuracy of the concentration.

By following these steps, you can effectively prepare a solution with the desired concentration.

Sodium Nitrate

Sodium nitrate, or NaNO₃, is a common ionic compound that appears as a white crystalline solid. It is often used in agriculture, in fertilizers due to its high nitrogen content, and in chemistry labs for various experiments:

• It is highly soluble in water, making it an ideal candidate for solution preparation in volumetric analysis and other chemical applications.
• Due to its ionic nature, NaNO₃ dissociates fully in water to give sodium ions (Na⁺) and nitrate ions (NO₃⁻), which can partake in various reactions.
• Because of these properties, it is critical to measure it accurately and to ensure that it is completely dissolved when preparing solutions for experiments or analyses.

When using sodium nitrate, safety precautions should always be followed, including wearing protective equipment and storing it properly to avoid moisture, which could alter its composition.

Molar Mass

The molar mass of a compound is the mass of one mole of its entities (atoms, molecules, ions, etc.) and is crucial in converting between grams and moles in stoichiometric calculations. This value is usually expressed in grams per mole (g/mol):

• For sodium nitrate (NaNO₃), the approximate molar mass is 85 g/mol.
• The molar mass is found by adding together the atomic masses of all the atoms that make up the molecule. For NaNO₃, this includes sodium (Na), nitrogen (N), and three oxygen atoms (O).
• This value is vital when calculating how much of a substance you need to weigh out to get a specific number of moles for a solution, as shown in the calculation converting 0.17675 moles to approximately 15.024 grams of NaNO₃.

Understanding and using molar mass effectively allows you to accurately prepare solutions with specific molarities.

Volumetric Analysis

Volumetric analysis is a core method used in analytical chemistry to determine the concentration of an analyte by measuring the volume of a reactant needed for a complete reaction. This technique often involves titrations:

• It requires precise volume measurements, usually carried out using a burette or a volumetric flask.
• In preparation of solutions for volumetric analysis, the concentration (molarity) must be accurate since it affects the validity of the titration results.
• Sodium nitrate solutions can be used in volumetric analysis when there is a need to supply nitrate ions in reactions, making the preparation of its solution a common practice.
• Titration, a common volumetric method, measures the amount of one solution required to react completely with a volume of another solution, aiding in finding unknown concentrations.

Precision in volumetric analysis ensures the accuracy and reliability of experimental results, which is vital in both educational and professional laboratory settings.