Lab 1: Diffusion of Molecules in a Gas and a Liquid Flashcards
Explain how the thermal (kinetic) motion of molecules influences the distribution of molecules in a gas or a liquid.
All molecules have their own kinetic energy, which is the energy of movement. This causes them to randomly diffuse. Due to this random movement, there are collisions between molecules that will send them in random directions.
Define diffusion and net diffusion.
Diffusion is the random, continual movement of a substance due to its intrinsic, kinetic energy.
Net diffusion is the passive movement of a substance from high to low concentration.
List the factors that affect the rate of diffusion of molecules. Explain how they affect diffusion.
- Concentration gradient (greater concentration = greater rate of diffusion)
- Temperature (greater temperature = more KE = more collisions = greater rate of diffusion)
- Molecular weight (higher molecular weight = slower rate of diffusion)
- Medium through which the molecule is diffusing
Explain how a pH indicator allows us to observe diffusion of OH- ions.
When OH- ions diffuse, they increase the pH. Phenolphthalein produces a color change when the pH is within 8.2-10.0. This allows us to measure how far the OH- ions move over time to learn about the rate of diffusion.
Describe the relationship between distance and time with respect to diffusion of a solute in a liquid. Explain how the collisions of OH- ions in the tube can explain this relationship.
As time progresses, the diffusion rate of OH- ions ions decreases because the concentration gradient gets smaller, leading to a smaller probability that OH- ions will experiences collisions in the pink portion compared to the clear portion of the tube.
What was the equation derived from the data? Use it to compare how far net diffusion of OH- ions will get in 10 msec vs. 100 msec. (msec = 0.001 sec)
Does it matter which experimental condition you choose (i.e. 1.0M vs. 0.05M NaOH)?
slope = (d^2)/t
Compare the rate of diffusion in a gas vs. a liquid. Explain what is happening at the molecular level that accounts for this difference (think about density/collisions)
The rate of diffusion in a gas is much faster than in a liquid because the space between constituent particles is higher in a gas than in a liquid. Liquids are more dense and have more particles, which slows down the diffusion rate.
Explain the advantages and disadvantages of diffusion as a means of moving molecules in the body. Describe where and over what sort of distance scale it is a useful means of moving molecules in the body.
Diffusion can be used to move small distance but should not be used to move longer distances. This is because as time goes on, the diffusion rate decreases, so long distances would take a very long time. Diffusion is typically good for up to 50-100 microns, but no larger. For longer distances, the body uses blood.
