• Like
Diffusion prac
Upcoming SlideShare
Loading in...5

Thanks for flagging this SlideShare!

Oops! An error has occurred.

Diffusion prac



Published in Technology , Business
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads


Total Views
On SlideShare
From Embeds
Number of Embeds



Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

    No notes for slide


  • 1. Diffusion experimentIntroductionThe atoms of various elements are not all equal in size, but for the purposes of this practical, we willconsider them to be so. So we will compare the relative sizes of the substances with which we aredealing via the number of atoms within each molecule. Please complete the following table to ascertainthe relative sizes: Substance Molecular formula No. of atoms per molecule Potassium iodide KI Water H2O Glucose C6H12O6 Starch (C6H10O5)500In this experiment we will be observing the movement of the aforementioned substances over a semi-permeable membrane. Dialysis tubing is essentially a very tightly woven mesh, with gaps of a fairlyregular size.Diffusion in the process by which a substance will cross a membrane in a singular direction, based onthe concentration gradient, until equilibrium is reached.Osmosis is a special form of diffusion. In this case the substance is unable to pass through themembrane so, instead, water will cross the membrane until equilibrium is reached.MaterialsRetort stand and clamp Stop watchThistle funnel Marker penGas jar Sugar testape100ml beaker Soluble starch solution (5%)Rubber band Glucose solution (5%)Dialysis tubing Potassium iodide solutionMethodGroup A will be using a 5% glucose solution. Group B will be using a 5% soluble starch solution.A. B.
  • 2. 1. Prepare your retort stand and clamp. Fill gas jar ¾ full with water. If you are in a group that will be using the starch solution, add a few drops of potassium iodide to the water in the gas jar, just enough to permanently discolour the water. 2. Half fill a 100ml beaker with your allocated solution 3. Wet a length of dialysis tubing under a tap for 1 minute, massaging it until soft and pliable 4. Tie a knot in one end of the tubing. Massage open the other end of the tubing and insert the narrow end of the thistle funnel. Secure the bag by repeatedly wrapping a rubber band until very tight. Make sure the dialysis tubing stays moist the entire time. 5. Tilt the funnel on an angle and very slowly fill the tubing with your solution, you must avoid any air bubbles. If any appear, immediately squeeze them out the top of the tubing. 6. Hold funnel upright and top up with solution until it comes half way up the stem of the funnel. 7. Once the tubing is full of solution, attach it to the clamp and immerse in to the gas jar full of water. Make sure the entire tubing is covered by water. Mark the point on the thistle funnel to which the solution reaches. 8. Start the stop watch and every 10 minutes record your observations. - Obs. 1: Has the solution height changed since your last reading - Obs. 2a: Has the constitution of the water in the gas jar changed (testape can be used to check for the presence of glucose). - Obs 2b: Has the constitution of the solution in the tubing changes (stach stains blue/black in the presence of iodine).Write-upPlease complete a full prac write-up including AIM, HYPOTHESIS, RESULTS and CONCLUSION.You may cut out the materials and method and paste in to your write-up.You will also need to obtain results from another group that did the alternate experiment to youPlease include the following questions in your conclusion:Q1. Based on the results of the experiment, can you make an estimation of the size of molecules thatare able to pass through the dialysis tubing? What evidence do you have for this assumption?Q2. In the case of the glucose solution, which direction did substances diffuse and what evidence wasthere for this?Q3. In the case of the starch solution, which direction did substances diffuse and what evidence wasthere for this?Q4. Explain the difference in structure between an actual plasma membrane and the dialysis tubing.Q5. Did your experiment create any results that cannot be explained by the processes of diffusion orosmosis?Q6. If you listed any anomalous results in answer to the above question, what does this indicate aboutthis experiment as a model for action across a plasma membrane? How could it have been improved?