PERTEMUAN-8 : MEMBUAT LARUTAN DENGAN KONSENTRASI TERTENTU

Summary

This educational video provides a detailed guide on how to prepare solutions with specific concentrations. It covers the steps for creating solutions from solid substances like NaOH and liquid concentrates like sulfuric acid. The process involves precise measurement techniques such as weighing, using volumetric flasks, and applying dilution formulas. The video emphasizes accuracy in measurements and proper use of laboratory equipment to ensure the successful preparation of solutions, making it ideal for students and individuals in scientific fields. Key concepts include molarity, dilution, and the importance of using the correct tools.

Takeaways

• 😀 First step in making a solution is to carefully weigh the solid substance that will be dissolved.
• 😀 An analytical balance should be used to ensure precise measurement of the solid substance.
• 😀 A volumetric flask (also known as a lab flask) is needed for creating solutions with a specific concentration.
• 😀 A volumetric flask measures a single type of volume, e.g., a 1000 mL flask is used for a 1000 mL solution.
• 😀 A beaker can be used for dissolving substances but is less precise compared to a volumetric flask.
• 😀 Additional tools like a spray bottle and dropper pipette may be needed during the solution preparation process.
• 😀 For example, to make a 0.2 M NaOH solution of 500 mL, you need to calculate the molar mass and the amount of NaOH required.
• 😀 To make 0.1 mol of NaOH for the solution, the mass of NaOH needed is 4 grams, based on the molar mass of NaOH (40 g/mol).
• 😀 After weighing the NaOH, it should be added to the volumetric flask and dissolved in water until half of the final volume.
• 😀 Finally, water should be carefully added until the solution reaches the mark on the flask, ensuring precise volume measurement.

Q & A

What is the first step in preparing a solution from a solid or crystal?

The first step is to carefully weigh the solid substance to be dissolved, and calculate how many grams of the solid are required for the solution.

What is the purpose of using an analytical balance in preparing a solution?

An analytical balance is used to weigh the solid substance accurately, ensuring the correct amount of material is used for the solution.

Why is a volumetric flask preferred over a beaker when preparing solutions?

A volumetric flask provides more accurate measurements for preparing solutions to a specific volume, whereas a beaker is less precise.

What is the disadvantage of using a beaker to prepare solutions?

The disadvantage of using a beaker is that it offers less precision in measuring the volume compared to a volumetric flask.

What equipment is needed for making a 0.2 M NaOH solution of 500 mL?

You will need an analytical balance, a 500 mL volumetric flask, distilled water, and a pipette to add water carefully to the desired level.

How do you calculate the amount of NaOH needed to make a 0.2 M solution of 500 mL?

First, use the formula: mol = molarity × volume (in liters). For this example: 0.2 M × 0.5 L = 0.1 mol. Then, multiply by the molar mass of NaOH (40 g/mol) to get the mass: 0.1 mol × 40 g/mol = 4 grams.

What should be done after measuring 4 grams of NaOH crystals?

The 4 grams of NaOH should be placed into the volumetric flask, and distilled water should be added until it is roughly halfway filled. Then, the flask is gently shaken to dissolve the NaOH.

What is the final step in preparing the NaOH solution?

The final step is to carefully add distilled water to the flask until the solution reaches the mark on the flask. This ensures the solution has the correct volume.

What is dilution, and how is it applied in the preparation of solutions?

Dilution is the process of reducing the concentration of a solution by adding solvent. This is used when making a solution from a concentrated stock, like making a 2 M H2SO4 solution from an 18 M stock.

How do you calculate the volume of a concentrated solution needed for dilution?

Use the dilution equation: C1 × V1 = C2 × V2, where C1 is the concentration of the stock solution, V1 is the volume of the stock solution needed, C2 is the desired concentration, and V2 is the final volume. For example, to make 500 mL of 2 M H2SO4 from 18 M, you calculate: V1 = (C2 × V2) / C1 = (2 M × 500 mL) / 18 M = 55.56 mL.