Question

introduction:
in this lab, we will investigate the relationship between surface area - to - volume ratio and diffusion efficiency using agar cubes. the cubes contain phenolphthalein, a ph indicator that is colorless in neutral or acidic conditions but turns pink when exposed to a base. we will immerse the agar cubes in a solution of sodium hydroxide (naoh), a basic substance. as the naoh diffuses into the cubes, the pink color will appear in regions where the base has diffused.
the size of the agar cubes affects the surface area - to - volume ratio, which in turn influences how fast and how far the naoh can diffuse into the cube. you will observe how cube size affects the rate of diffusion and the depth to which the naoh penetrates.
pre - lab questions:

1. what is diffusion? how does diffusion occur in living cells?
2. what is phenolphthalein, and how does it work in this experiment? what color will it change to?
3. what is sodium hydroxide (naoh), and why is it used in this experiment?
4. surface area - to - volume ratio: how do you think this ratio will affect the diffusion of naoh?
5. predicting the results: predict which size of agar cube (small, medium, or large) will have the greatest diffusion. explain your reasoning.
6. hypotheses: your hypothesis should state how you expect the size of the agar cubes to affect the rate and extent of naoh diffusion. use an if, then statement for the alt. hypothesis. write complete sentences.

alternative hypothesis:
null hypothesis:

1. variables:

• independent variable:
• dependent variable:
• control variables:

safety considerations:

Explanation:

1. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. In living cells, it occurs across the cell - membrane for small, non - polar molecules like oxygen and carbon dioxide.
2. Phenolphthalein is a pH indicator. In this experiment, it is colorless in neutral or acidic conditions and turns pink in basic conditions. When NaOH diffuses into the agar cube, the areas with NaOH will turn pink.
3. Sodium hydroxide (NaOH) is a strong base. It is used in this experiment to create a concentration gradient for diffusion and to react with the phenolphthalein to show the extent of diffusion.
4. A higher surface - area to volume ratio will allow for faster diffusion of NaOH as there is more surface area available for the NaOH to enter the cube relative to the volume that needs to be filled.
5. The small agar cube is likely to have the greatest diffusion as it has the highest surface - area to volume ratio, allowing NaOH to penetrate more quickly and thoroughly.
6. Alternative hypothesis: If the size of the agar cube is smaller, then the rate and extent of NaOH diffusion will be greater. Null hypothesis: The size of the agar cube has no effect on the rate and extent of NaOH diffusion.
7. Independent variable: Size of the agar cube. Dependent variable: Rate and extent of NaOH diffusion. Control variables: Concentration of NaOH solution, temperature, time of diffusion.

Answer:

1. Diffusion is the movement of molecules from high to low concentration. In cells, it occurs across the membrane for small non - polar molecules.
2. Phenolphthalein is a pH indicator, colorless in neutral/acidic, pink in basic. Turns pink in this experiment with NaOH.
3. NaOH is a strong base, used to create diffusion gradient and react with phenolphthalein.
4. Higher ratio allows faster diffusion due to more surface area for entry.
5. Small cube, because it has the highest surface - area to volume ratio.
6. Alternative: If cube size is smaller, then diffusion rate/extent is greater. Null: Cube size has no effect on diffusion rate/extent.
7. Independent: Size of agar cube. Dependent: Rate/extent of NaOH diffusion. Control: NaOH concentration, temperature, time.