Diffusion and Osmosis Lab Notes

Diffusion in Liquids and Colloids

• Water Medium:

  • Potassium permanganate ($\text{KMnO}_4$) diffuses faster in distilled water ($1\text{: }06\text{: }38$) than in tap water ($1\text{: }30\text{: }27$), yielding a $23\text{-minute and }49\text{-second}$ difference.

• Colloid Medium (Gelatin):

  • Rate and distance of diffusion correlate inversely with molecular size.

  • $\text{KMnO}_4$ (smallest molecular size): Diffused the furthest ($1.5\,\text{cm}$), with movement continuing until approximately $85\,\text{min}$.

  • Methylene Blue (intermediate molecular size): Diffused to $1.2\,\text{cm}$, leveling off after $75\,\text{min}$.

  • Congo Red (largest molecular size): Diffused the least ($0.9\,\text{cm}$), with measurable movement stopping after $20\,\text{min}$.

Dialysis and Membrane Permeability

• Dry Longganisa Skin Membrane:

  • Methylene Blue diffuses into the beaker $2.5\,\text{min}$ after placement.

  • Chloride test shows precipitate after resting for $18\,\text{min}$.

  • Calcium test remains negative (no precipitation).

• Soaked Longganisa Skin Membrane:

  • Methylene Blue diffusion is delayed, appearing at $5.5\,\text{min}$.

  • Hydration/soaking of the membrane hinders and slows down the diffusion rate of Methylene Blue compared to the dry membrane.

Osmosis in Membranes

• Liquid Transfer and Volume Changes:

  • Osmosis causes net water movement from the beaker into the test tube across the skin membrane.

  • Beaker weight decreases while test tube weight increases across both dry and soaked setups.

  • Dry Skin Setup: Beaker weight drops from $79.04\,\text{g}$ to $77.30\,\text{g}$, test tube weight increases from $17.13\,\text{g}$ to $18.44\,\text{g}$, and column height decreases from $3.5\,\text{cm}$ to $3.3\,\text{cm}$.

  • Soaked Skin Setup: Beaker weight drops from $77.49\,\text{g}$ to $76.17\,\text{g}$, test tube weight increases from $15.32\,\text{g}$ to $16.13\,\text{g}$, and column height increases from $3.5\,\text{cm}$ to $3.7\,\text{cm}$.

  • The initial hydration state of the membrane influences both the rate of water movement and volume height changes.

Osmosis in Red Blood Cells

• Hypotonic Solution ($0.07\,\text{M}\,\text{NaCl}$):

  • Water enters the cell via osmosis due to higher solute concentration inside.

  • Cell expands from $7.5\,\mu\text{m}$ to $10\,\mu\text{m}$ (approx. $33\%$ increase) starting at $35\,\text{min}$.

• Solution Behavior ($0.15\,\text{M}\,\text{NaCl}$):

  • Cell size decreases from $7.5\,\mu\text{m}$ to $5\,\mu\text{m}$ at $45\,\text{min}$.

• Hypertonic Solution ($0.30\,\text{M}\,\text{NaCl}$):

  • Water leaves the cell via osmosis.

  • Cell shrinks from $7.5\,\mu\text{m}$ to $5\,\mu\text{m}$ (approx. $34\%$ reduction) starting at $50\,\text{min}$.