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Computers in Introductory Chemistry Laboratories

A Proposal Submitted to NSF in June 2000
funded May 2001-April 2003


In June 2000 we submitted to NSF a proposal to purchase computers and laboratory interfacing for the introductory chemistry laboratories. This document is an attempt to show the logic of that request.


edited: January 21, 2001 (This is being revised, August 2004)
comments to: Paul Endres
file: nsf/nsf5_HPC.htm

Introduction:

For some time we have been trying to find a way to bring computerized data collection to the general chemistry course. There are some serious problems that need to be resolved.
  • cost (purchasing computers, but also developing software and maintenance)
  • space (including where computers are placed)
  • security (from theft, but also from laboratory chemicals which are tough on electronics)
  • accessories (30-50% of the cost of a typical installation is devoted to sensors and interfacing with the computer.)
  • actual experiments designed to intelligently use computers
One approach is to have computers around the perimeter of the lab
  • students take experimental materials to the computer work site
  • we have up to 60 students in these labs
    • 60 computers is unrealistic
  • working individually on alternate weeks would require 30 computers
  • basic cost-- about $2500 for computer and lab interfaces (about $75,000)
  • each standard computer needs about 4 ft of table top
    • we'd need about 120 feet of space around the room
    • there isn't that kind of space available in the general chemistry lab
Another approach is to place a computer at the lab bench
  • we still need about 4 ft of bench space
  • that's over half of the area for one student work station
  • we might build a stand to keep most of the computer off the table top
  • however, we need to keep the computer safe (from water, reagents, ring stands)
It's difficult to see a way to use conventional desktop computers in this environment.

We could, of course, use fewer computers

  • have students work in groups of two or four
  • to have computer use limited to 20 minutes/lab so same machine can be shared by 2-3 groups
  • This can be done, but it severely limits the role of the computer in experiments
We then examined the prospects for lap tops or similar units
  • space needed per unit is much smaller
  • cost is generally higher than for standard PC's
    • ($1500-2000 for computer; $250 accessories)
  • laptops are generally easier to damage, harder to get repaired
  • laptops are harder to keep secure (easier to steal)
  • laptops might be harder to keep safe (easier to move into a region of chemical danger)
At the other extreme, there are calculator based labs developed and a company called Vernier Software In March 2000 we got local funds for one of the Vernier / TI systems to evaluate the system.

We were not satisfied with this approach:

  • programming is extremely awkward
  • dumping data to a PC is possible, but not convenient
  • data display is tiny
  • computational options are surprisingly limited
  • students familiar with computers would see this as a very backwards technology
One other option is the use of smaller computer devices
  • PDA-- Personal Data Assistant like the Palm (TM) devices
  • HPC-- Handheld Personal Computers
    • Obviously these are smaller and fit our space well
    • They are portable and could be kept relatively secure when not in use
    • They are generally designed for a somewhat more rugged environment than PC's and laptops
    • They are considerable less expensive than PC's ($100-500)
    • They have communication features that we could use effectively
Most of the PDA's pose serious problems
  • They have no commercial software that can handle laboratory situations
  • They are programmed using a specialized programming language
  • We could expect a steep learning curve and a long preparation time before we could use such devices in the lab.
  • Most students would be unfamiliar with the specific device and would have to learn its operation
  • Most PDA's actually have a tiny screen with modest capability
However, a few of the HPC units operate under Microsoft Windows-CE
  • this means the screen has the look and feel of conventional computing activity
  • a programmer can develop software using standard computing languages like Visual Basic
  • the screens generally have larger size and better resolution than most PDA's
In particular, we evaluated a unit made additional feature has to do with funding All of these factors led us to write a proposal for computer based experiments in the introductory chemistry labs based on the HPC approach.

Let's look at some typical applications. Let us also ask some very specific questions.

  • 1. What are the (chemistry) concepts that the experiment develops?
  • 2. In what way does the computer change the experiment?
  • 3. How do you focus on the chemistry rather than the computing?
  • 4. What other factors (pro and con) enter the picture?

Calorimetry

  • Dissolve a metal (Ca, Mg, Zn, Fe) in acid
  • Measure the temperature rise
    • store temperature vs.. time data
    • display temperature vs.. time graph
  • Compute the Enthalpy change in the reaction.
The calculation depends only on the overall temperature rise. It would be cheaper and easier to use a thermometer to make that measurement. What advantages are there to using the computer?
  • The real time graph shows additional information
  • student gets experience extracting information from graph
  • actually see the rate of the reaction
  • could examine the effect of surface area
    • compare time for large pieces vs granualar metal samples
  • can see heat loss
  • can see cooling after the reaction
    • due to both heat losses (insulation) and to evaporative cooling
    • this would probably not be noticed with thermometer
Process is rapid (5 minutes)
  • time to focus on interpretation and calculations
  • time to include a calibration run
  • time to make several runs and comparisons

Titrations

Acid-Base Titration Curves

We do this now with conventional glassware and pH meter.

  • typically make 10-20 additions of titrant
  • read and record pH
  • then plot graph
  • finally interpret graph
  • each run typically takes 30 minutes
  • students likely to get 2-3 runs in a period.
using computer to log and plot pH
  • allows many more data points to be collected, leading to smoother and well defined graphs
  • minimizes tedium and transcription errors
  • data appears in real time
  • experiment provides data initially as a visual image
  • student is free to focus on data, to try to predict remainder of the curve
run is much faster
  • could be a 2-4 minute run
  • it would be realistic to do 5 (or even 10) different runs for comparison
    • strong and weak acids, strong and weak bases
      • with good graphics, endpoints of weak acid-weak base can be determined
    • polyprotic acids
    • mixtures (bicarbonate, carbonate), (HCl and acetic acid)
  • Again, comparison of runs begins with a visual image (curve) with clear qualitative differences

Titrations

Other than Acid/Base by pH

Could monitor temperature during an acid base titration curve

  • can actually use both temperature and pH probes and plot both
  • this is rapid process
  • results show up immediately as visual image
Not likely to do with conventional equipment
  • would be too tedious to collect many data points
  • would need to do more slowly and heat loss is more of a factor then
Could monitor electrical conductivity during a titration
  • complexing reagents, precipitates, neutralization

Kinetics

Can expect to monitor concentration of one species throughout a reaction

  • typically be colorimetry or spectrophotometry
  • could also use a species selective electrode
  • can monitor heat produced by reaction
Again, the history of the reaction is displayed in real time as an image

Vapor Pressure of a Liquid

  • Simple pressure sensor can record pressure vs.. time.
  • Small amount of liquid added to a closed flask connected to the probe
  • As liquid evaporates, pressure rises
  • Pressure levels off when the equilibrium vapor pressure is reached
  • Again, process produces a real time visual image (graph)
  • Process is rapid (2-5 minutes)
    • Could be one part of a larger experiment on gases
    • Could be run at several temperature to determine enthalpy of evaporation
  • Could be done with conventional equipment
    • pressure measurement is more difficult and slower
      • of course, same probe could be set up for a voltmeter
    • would only get a few data points
    • would rely on initial and final values, not on curve

Important concepts to be examined: