Agar Cube Diffusion Lab

Summary

In this lab video, agarose gel cubes of different sizes (1 cm, 2 cm, and 3 cm) are soaked in a sodium hydroxide (NaOH) solution, turning pink due to phenolphthalein, a base indicator. The cubes are then immersed in hydrochloric acid (HCl), causing the pink color to fade as the acid neutralizes the base. Over time, the color dissipates, and the surface of the cubes clears. Measurements are taken to track the diffusion process, and students are tasked with recording the data, calculating volumes, and analyzing surface area-to-volume ratios to accept or reject their hypotheses.

Takeaways

• 🔬 The instructor set up a diffusion lab with different sizes of agarose gel cubes (1 cm, 2 cm, and 3 cm).
• 📏 Each group in the lab will receive three cubes of each size to conduct the experiment.
• 💡 Students are instructed to write a hypothesis and provide a rationale before starting the experiment.
• 🧪 The instructor uses a 0.1 molar sodium hydroxide (NaOH) solution to immerse the cubes, starting with the largest (3 cm) cubes to avoid crushing the smaller ones.
• 🟣 The cubes contain phenolphthalein, a base indicator that turns pinkish-purple in the presence of a base like NaOH.
• ⌛ The cubes are left in the NaOH solution for about 10 minutes to allow full diffusion, making them translucent as the base permeates the entire cube.
• ⚗️ After soaking in NaOH, the cubes are transferred to beakers containing 1 molar hydrochloric acid (HCl), causing the pink color to fade as the base is neutralized by the acid.
• 🔍 The cubes are observed for diffusion progress, with the outer layers clearing up before the inner parts, showing different diffusion rates based on size.
• 📊 The instructor takes measurements (length, width, height) of the cubes and calculates their volumes to complete the data table.
• 📏 Students are encouraged to use the calculated volume and surface area-to-volume ratio to accept or reject their hypothesis based on the experiment's results.

Q & A

What are the three different sizes of agarose gel cubes used in the experiment?

The three different sizes of agarose gel cubes used are 1 cm, 2 cm, and 3 cm cubes.

What solution is used to submerge the agarose gel cubes in the first part of the experiment?

The agarose gel cubes are submerged in a 0.1 molar sodium hydroxide (NaOH) solution.

Why did the agarose gel cubes turn pink when submerged in sodium hydroxide?

The agarose gel cubes contain phenolphthalein, a pH indicator that turns pink in the presence of a base such as sodium hydroxide.

What observation can be made about the color of the cubes after soaking in sodium hydroxide?

The outside of the cubes turns pink while the inside remains less pink or translucent, indicating that the sodium hydroxide has not fully diffused to the center.

How long were the cubes left to soak in the sodium hydroxide solution?

The cubes were left to soak for about 10 minutes, though additional time was given to ensure the middle of the cubes became translucent.

What solution were the cubes transferred to after soaking in sodium hydroxide?

The cubes were transferred to a 1 molar hydrochloric acid (HCl) solution.

What was the purpose of submerging the cubes in hydrochloric acid?

The hydrochloric acid neutralizes the base (sodium hydroxide) within the cubes, causing the pink color from the phenolphthalein to disappear.

What was observed in the cubes after being placed in hydrochloric acid?

The pink color started to fade, first on the outer edges and then moving inward, as the hydrochloric acid neutralized the sodium hydroxide.

What measurements were taken from the cubes after the experiment?

The length, width, and height of each cube were measured to calculate their volume in cubic centimeters.

Why were multiple trials performed for the volume measurements?

Multiple trials were performed to ensure accuracy and consistency in the data. If the results are close, it indicates reliable data. Large discrepancies would suggest an error.