Question

A chemistry student needs \(125 \mathrm{mL}\) of \(0.150 \mathrm{M} \mathrm{NaOH}\) solution for her experiment, but the only solution available in the laboratory is \(3.02 \mathrm{M}\). Describe how the student could prepare the solution she needs.

Short answer

To prepare 125 mL of 0.150 M NaOH solution from a 3.02 M stock solution, the student should measure out approximately 6.21 mL of the 3.02 M NaOH stock solution using a graduated cylinder or a pipette. Then, pour the measured 6.21 mL of 3.02 M NaOH solution into a 125 mL volumetric flask and add distilled water up to the 125 mL mark on the flask. Gently swirl the solution to mix the NaOH from the concentrated solution into the water until the solution is homogeneous. The final 0.150 M NaOH solution is now prepared and ready for the experiment.

Step-by-step solution

Identify given information

Initial Concentration (M1) = 3.02 M Final Concentration (M2) = 0.150 M Final Volume (V2) = 125 mL

Use the dilution formula to find the initial volume (V1)

Using the formula, M1V1 = M2V2, fill in the given information and solve for V1: \(3.02 \mathrm{M} \times V1 = 0.150 \mathrm{M} \times 125 \mathrm{mL}\) To find V1, divide both sides by 3.02 M: \(V1 = \cfrac{0.150 \mathrm{M} \times 125 \mathrm{mL}}{3.02 \mathrm{M}}\) Calculate V1: \(V1 \approx 6.21 \mathrm{mL}\)

Prepare the 0.150 M NaOH solution

1. Firstly, the student should put on proper safety equipment, such as gloves, goggles, and a lab coat to protect themselves from any accidents while working with the chemicals. 2. Measure out approximately 6.21 mL of the 3.02 M NaOH stock solution using a graduated cylinder or a pipette for more accurate measurements. 3. Pour the measured 6.21 mL of 3.02 M NaOH solution into a 125 mL volumetric flask. 4. Slowly add distilled water to the volumetric flask, up to the 125 mL mark on the flask. Swirl the solution gently to mix the NaOH from the concentrated solution into the water, until the solution is homogeneous. 5. The final 0.150 M NaOH solution is now prepared and ready to be used in the experiment. Note: It's important to handle NaOH solutions carefully and to ensure proper safety measures are taken, as this compound is known to be caustic and can cause burns if not handled correctly.

Key concepts

Dilution Formula

When working with solutions, knowing how to dilute a concentrated solution to achieve a desired concentration is crucial. The dilution formula is a simple equation that helps us determine the volume of the concentrated solution needed:\[ M_1V_1 = M_2V_2 \] Where:

• \(M_1\) is the initial concentration of the solution (the concentrated stock solution).
• \(V_1\) is the volume of the concentrated solution you need to find.
• \(M_2\) is the desired concentration of the final solution.
• \(V_2\) is the volume of the final diluted solution.

In this exercise, our task was to dilute a 3.02 M \( ext{NaOH}\) solution to make 125 mL of a 0.150 M \( ext{NaOH}\) solution. By plugging in the known values into the dilution formula, we can easily calculate that approximately 6.21 mL of the concentrated solution is needed. Simple multiplication and division can perform these calculations. Knowing this formula saves time and effort in preparing solutions accurately.Using the dilution formula ensures precision in experiments, where concentrations are vital for the reactions. Always carefully measure and mix the solutions to achieve the desired outcomes in a laboratory setting.

Safety Precautions in Chemistry

Safety is an essential concern in any chemical lab activity. Proper safety measures can prevent accidents and injuries. Working with chemicals involves risks, so always prepare by wearing:

• Gloves to protect your hands from harmful substances.
• Goggles to guard your eyes against splashes or fumes.
• A lab coat or apron to protect your skin and clothing.

Beyond personal protective gear, ensure your workspace is clean and well-ventilated. Familiarize yourself with the chemicals before beginning, as some may be caustic or emit toxic fumes. In this exercise, we worked with \( ext{NaOH}\), a caustic chemical that can cause burns upon contact with skin. Handle such substances carefully, following all safety protocols. Always have a clear safety protocol in place and know how to use safety equipment, such as fire extinguishers and eyewash stations. Proper disposal of chemicals is also crucial to prevent environmental harm. Remember, understanding and knowing these precautions can drastically reduce the risk of accidents, ensuring a safer and more productive laboratory experience.

Volumetric Flask

A volumetric flask is a piece of glassware that is critical for preparing precise solution volumes. It is designed with a narrow neck and a single calibrated mark to denote a specific volume. A volumetric flask is essential because it offers a high degree of accuracy when making solutions. In this exercise, a 125 mL volumetric flask was used to ensure the proper dilution and mixing of the \( ext{NaOH}\) solution. To use a volumetric flask correctly, pour the solution into the flask, and then add distilled water little by little until you are close to the calibrated mark. As you approach the mark, add water more slowly, using a pipette or dropper if necessary, to avoid surpassing the line. Always remember to mix the solution by swirling gently after adding water, ensuring the solute distributes evenly throughout the solution. This mixing is crucial in achieving a homogeneous solution, which means that the concentration is consistent throughout the solution.Volumetric flasks come in various sizes, typically ranging from 5 mL to 2 L, and are indispensable in experiments requiring accurate solution concentrations. This precise measurement ensures the reliability and repeatability of experimental results.