Problem 35 - Chemistry Matter and Change

Question

Outline the laboratory procedure for preparing a specific volume of a dilute solution from a concentrated stock solution.

Step-by-Step Solution

Answer

To prepare a specific volume of a dilute solution from a concentrated stock solution, follow these steps: (1) Gather necessary materials, such as a pipette, volumetric flask, and distilled water. (2) Use the dilution equation \(C_1V_1 = C_2V_2\) and given concentrations to calculate the volume of stock solution required. (3) Measure the calculated volume of stock solution. (4) Transfer the stock solution to a volumetric flask, rinsing the pipette with distilled water. (5) Slowly add distilled water to the flask, mixing the solution well. (6) Fill the volumetric flask to the desired final volume. (7) Mix the solution thoroughly by inverting and shaking the flask. (8) Label the volumetric flask with the prepared dilute solution's concentration and volume, then store or use it as required.

Step 1: Gather necessary materials

Before starting the procedure, gather all the necessary materials, including the concentrated stock solution, a volumetric flask of the desired size, a pipette or a graduated cylinder for accurate measurement, and distilled water.

Step 2: Determine the volume of stock solution required

Use the dilution equation \(C_1V_1 = C_2V_2\), where \(C_1\) is the concentration of the stock solution, \(V_1\) is the volume of the stock solution required, \(C_2\) is the desired concentration of the final dilute solution, and \(V_2\) is the desired final volume of the dilute solution. Solve for \(V_1\): \[V_1 = \frac{C_2V_2}{C_1}\] Using the given concentrations and desired volume, calculate the volume of the stock solution required to prepare the dilute solution.

Step 3: Measure the calculated volume of stock solution

Using a pipette or graduated cylinder, carefully measure the calculated volume of stock solution.

Step 4: Transfer the stock solution to a volumetric flask

Transfer the measured volume of the stock solution to the volumetric flask. Ensure that all the solution is transferred by rinsing the pipette or graduated cylinder with a small amount of distilled water and adding this to the flask as well. Do not exceed the desired final volume.

Step 5: Add distilled water to the volumetric flask

Slowly add distilled water to the volumetric flask containing the stock solution. It is crucial to add the water gently and mix the solution well as you add it.

Step 6: Fill the flask to the desired final volume

Continue to add distilled water until the volumetric flask reaches the desired final volume. In most cases, the volumetric flask will have a mark indicating the final volume.

Step 7: Mix the solution thoroughly

Seal the volumetric flask with a stopper and gently invert and shake the flask several times to ensure that the stock solution and water are mixed well, making sure no air bubbles are trapped.

Step 8: Store or use the prepared dilute solution

Label the volumetric flask with the prepared dilute solution's concentration and volume. Store the prepared dilute solution appropriately or use it for the intended experiment as required.

Key Concepts

Dilution Equation

The dilution equation is a fundamental tool used in preparing solutions, making it easy to work with different concentrations. This mathematical formula, expressed as \( C_1V_1 = C_2V_2 \), allows you to determine the required amount of a concentrated stock solution to achieve a desired dilute solution.

• \( C_1 \): Concentration of the stock solution (initial concentration).
• \( V_1 \): Volume of the stock solution needed.
• \( C_2 \): Desired concentration of the final solution.
• \( V_2 \): Desired final volume of the dilute solution.

This equation helps ensure the right balance between concentration and volume, making sure your prepared solution meets the experimental requirements. To use it, rearrange the equation to solve for \( V_1 \) and plug in your known values.

Volumetric Flask

A volumetric flask is a type of laboratory glassware that measures and holds precise volumes of liquid. This flask is essential for preparing solutions because of its accuracy.
Volumetric flasks are distinguishable by their round body, flat bottom, and long neck. Usually, there's a single graduation mark on the neck that indicates the exact volume capacity. The flask should be filled just to this mark to ensure precision.
Using a volumetric flask is a way to guarantee that your solution has the precise volume you aim for, making it a crucial tool in laboratories where accuracy is of the utmost importance.

Pipette Usage

Pipettes are essential tools in the lab for measuring and transferring exact volumes of liquid. When preparing diluted solutions, a pipette's precision ensures the accurate amount of stock solution is used.
Here are some tips for effective pipette usage:

• Aim for a pipette that best matches the volume you need to measure.
• Use a pipette bulb or automatic pipette to draw liquid into the pipette.
• Ensure the pipette tip is submerged slightly in the liquid to accurately draw the required volume.

Transferring liquids precisely with a pipette supports the accurate preparation of solutions, which underscores the importance of mastering this tool in laboratory settings.

Distilled Water

Distilled water is used in dilution because it's free from impurities that could interfere with chemical reactions or experiments. It is a form of purified water, often used in scientific experiments for this reason.
Its purity means it won't add unwanted ions or compounds to the solution, maintaining the integrity of your dilution. When working with volatile or sensitive compounds, using distilled water ensures that only the intended substances are present.
Always make sure to add distilled water slowly and mix well to prevent the formation of concentrated layers in the volumetric flask.

Stock Solution

A stock solution is a large volume of a concentrated solution, from which smaller dilutions can be made. This allows for resource savings and efficient workspace management.
Stock solutions are used routinely in laboratories to make working solutions of lower concentrations. By preparing a single solution and diluting it as needed, labs can quickly and efficiently produce the desired concentrations for different experiments.
The preparation and dilution of stock solutions using a volumetric flask and pipette are standard procedures, emphasizing the versatility and importance of stock solutions in chemical laboratories.