Practical 4 (SA/V)

[original Word template] 

 Purpose: Determine affect of SA/V ratio on diffusion out of “cells”

Criteria:  none (introductory, formative practical)

Length:   0.5 hour (max)

Date (time): August 18-19, 2010 (?)

Cohort: 2012 exams

Objective:

Measure leaching of ions by conductance-meter (Vernier) from different size agar shapes (cubes or cylinders) as an indirect measurement of affect of SA/V ratio on diffusion rate out of “cells”

Material:

• agar (23 g agar, 50 g NaCl, 1000 mL deionized H20) in rectangular dishes and square petri dishes
• Vernier conductance probes & Logger Pro (v 3.8) software
• deionized water
• miscellaneous glassware (beakers, graduated cylinders, etc.)
  

Method:

1. Students are provided with agar (23 g agar, 50 g NaCl, 1000 mL deionized H20) in rectangular dishes. See http://www.sciencestuff.com/playground/agar_powder.shtmlfor agar prep method. 
2. Students separately determinewhat “regular” shape (cube? cylinder? sphere?) they will use in their experiment. 
3. Students makedifferentsizesof sameshape
4.   Recorddimensions of each piece (later this data is needed to determine SA/V ratio. 
5. Place400 mL deionized water in clean 600 mL beaker on stir plate, addclean stir bar and measurebaseline conductance.
6. Notestarting time, place agar shape into beaker and record conductance.
7. Recordconductance until conductance measurements make clear pattern on graph; (this may take some trial and error.)
8. Recorddata into appropriate tables; you can use Logger Pro tables for data at this point.
9. Collectdata for conductance of 4 samples:
1. pure, deionized water
2. 3 similar shapes, ie. all cubes or all spheres or all cylinders (this ideas credited to Sunny Suh). 
10. Collectyour own 4 readings and at least 2 readings from 2 different students. Total data would be 8 conductances.
11. Appropriately processdata.
12. Makerelevant graphs.
13. Submitas single Word document (with data and tables inside of it) to Turnitin.com