Shrimp and Grits

One thing that most new science students have trouble doing is keeping proper track of units.  Beginning students will write down numbers, assured that they and everyone else will just know what units the number has.

Ten minutes later they’ve forgotten what the units of their numbers were and completely mess up their calculations.

Well, here’s yet another bad thing that can happen when you don’t pay attention to units.

OPP said the U.S. woman’s Mercedes Benz was clocked at a speed of 140 km/h heading west on Highway 401 just before 10:30 p.m. Sunday.

[...]

The total fine amounted to $405.

According to police, the Californian’s explanation for speeding was that the speedometer in her Benz only gave readings in miles per hour and she wasn’t familiar with the metric system.

She was driving in a 100 km/hr zone.  If we’re to believe this woman’s excuse, she saw the “100 km/hr” sign and thought “Whoo!  100!  That means I can drive 100 miles per hour here!  Floor it!”

(Now if she really didn’t understand the system, she might have considered using a little common sense.  Her speedometer at the time would have been reading about 87 miles per hour, which is enough to get a ticket most places in the US.)

So here we have a case of mistaken units costing a woman a lot of money.  Something to think about if you’re a new student feeling a little lazy in the lab …

OpenOffice.org recently released the 2.4.0 version of its free office software. I’m a Linux user, so I’ve used OpenOffice for years on my own machines.

There’s a Windows version, but I’ve always been hesitant about replacing Excel on our lab machines with OpenOffice Calc. Why the hesitation? Excel had one feature that OpenOffice Calc did not. A small feature, but one that saved my students a lot of time.

We don’t have anything in our lab that requires Excel, and our students usually use Excel for simple plotting of calibration curves. Excel could do simple regression analysis on the data and with one or two additional clicks, print a chart that included the regression line and its equation.

OpenOffice.org could print a chart that included a regression line, too. The problem was the equation. To get the equation of the regression line, you had to redo the regression somewhere else in the spreadsheet. If you wanted the equation of the line displayed on the chart, you had to manually type the equation onto the chart as a subtitle. This added a lot of extra steps to what should have been a simple one-click process. I teach chemistry, not computers. Wrestling with software to get it to do something that should be simple is a waste of my time.

That’s finally changed with OpenOffice 2.4.0. it’s now easy to display the equation on a chart, as you can see below.

… so now I should be able to use OpenOffice in my student labs. And if you haven’t looked at OpenOffice for data workup in student labs, check it out. It’s one less piece of software for your school and your students to buy.

There’s a simple relationship that we use quite a bit in analytical chemistry: the relationship between how concentrated a solution is and how much light it absorbs. It’s called Beer’s Law, and in simplified form, it looks something like this:

… where A = Absorbance (measured by a spectrometer), c = concentration, and k = a constant***. Even if you’re not familiar with Beer’s Law or the instrument it’s used with, you can see that this is a simple linear relationship. If you know the value of the constant k, then you can measure the absorbance of a solution on the spectrometer, then use the equation to find out how concentrated the solution is.

So how do you get the constant? Just make some solutions where you already know the concentration, and measure the absorbance of each one with a spectrometer. The raw data looks something like this.

Test Tube	Concentration (M)	Absorbance
1	0.0100	0.25
2	0.0150	0.38
3	0.0250	0.63
4	0.0450	1.13
5	0.0600	1.50

Now, what would you do to find that constant, k, that relates the absorbance and the concentration? Here’s a hint - you’ll need to plot the data and perform a linear regression analysis to find out the value of k. This might sound hard, but a modern spreadsheet can make a nice looking plot and perform the linear regression. All you have to do is enter the data, tell the spreadsheet what things to plot, and let the spreadsheet do the grunt work.

Some of my students had to plot absorbance and concentration data as part of a recent laboratory experiment. A depressingly high percentage of these students produced this plot.

Quick! What’s wrong with this plot? (And no fair peeking below to see the answer!)

After making the plot, these students used the value for k that the spreadsheet calculated to find the concentrations of their unknown samples … and failed miserably - reporting concentrations that were several orders of magnitude too high. Impossibly high.

So where did the students go wrong? Their plots should have looked like this.

Beer’s Law, after all, is a relationship between absorbance and concentration, not between absorbance and the numbers arbitrarily assigned to each test tube for identification! To further the problem, many of these students did not even notice that the concentration numbers they reported were ridiculously wrong.

I’ve been teaching freshman chemistry full-time for more than seven years, and this sort of mistake is much more common now than it was seven years ago.

James Cameron was wrong. The machines will take over eventually, but not via squads of semi-indestructible Schwarzeneggers. They will simply rob us of our ability to think.

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*** This constant depends on several things, including the identity of the substance you’re analyzing and the size of the spectrometer’s sample holder.

PZ Myers describes a study published in Science correlating courses in high school with success in college-level biology, chemistry, and physics courses. As you might expect, success in college chemistry increases when you take high school chemistry, success in college biology increases when you take high school biology, and success in college physics increases when you take high school physics.

However, a high school course in one science doesn’t translate to better grades in a different science. That’s unfortunate, but didn’t really surprise me. Many high school level science courses cover a lot of topics in a small amount of detail and don’t focus on connections between the sciences or the overall scientific method.

However, there appears to be one high school subject that increases success in all three of the studied college sciences, and that’s … math! This is unsurprising to me. As someone who’s taught freshman chemistry full-time for seven years (has it really been that long?), I’ve noticed that students who are proficient with math almost always succeed in freshman chemistry, and those who really struggle with math rarely succeed. As I’ve said to other teachers:

Give me a student who knows basic math, and I can teach her chemistry. But don’t expect me to teach her basic math and chemistry in one semester.

That said, I think this study isn’t all that useful unless the researchers had some way to control for the effects of self-selection bias on the results. In our state, at least, these high school science and advanced math courses examined are optional, and only students who demonstrate high aptitude in math and science already (which would probably translate to success in college science) and who are on the college prep track take them.

My introductory chemistry class is geared primarily towards students who are getting their associate’s degree in a medical field - mainly nursing. Because of this, we use drug dosage calculations for math practice when we discuss metric unit conversions.

Some students think I’m harsh when I don’t give credit for botched drug calculations. I, of course, disagree - and Abel Pharmboy’s found a news item that illustrates why:

A pharmacy erroneously made a drug 10 times more potent than intended, which killed three people who received it at an Oregon clinic, the state medical examiner said Friday.

if any of my students are reading this, take note. Stupid math mistakes are sometimes amusing, but never when someone’s life is at stake!

Here’s a little public service announcement to all of you budding science teachers. If you’re a new biology teacher in a public high school, it’ll do you good to stick to teaching science.

If the article above is correct, Kris Helphinstine couldn’t last longer than eight days as a biology teacher before unleashing the crazy:

Kris Helphinstine included Biblical references in material he provided to students and gave a PowerPoint presentation that made links between evolution, Nazi Germany and Planned Parenthood.

The Biblical references were probably merely inappropriate in a high school biology class. But “links between evolution, Nazi Germany, and Planned Parenthood”? Do we really need the tinfoil-hat conspiracy crowd teaching our high schoolers? No, we don’t. The local school board felt that way, too. They fired Helphinstine:

“I think his performance was not just a little bit over the line,” board member Jeff Smith said. “It was a severe contradiction of what we trust teachers to do in our classrooms.”

In his defense, Helphinstine said that he was merely trying to teach “critical thinking”. He must have neglected to inform the students of his objectives, since they were apparently more confused by his materials than anything.

As for me, I’m not buying Helphinstine’s excuse. There is plenty of material you can use to teach “critical thinking” in science classes without loading up on the Bible, Planned Parenthood, or Nazi conspiracies. Even if his intentions were honorable^***, he led his class into an educational minefield. He shouldn’t have been surprised when one of those mines went off.

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^***It’d be nice to see the materials used in the class. That’d help us judge his intentions.

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Update: It doesn’t look so good for Helphinstine. More here

I have often joked that, in addition to fume hoods, chemistry laboratories come equipped with giant invisible brain vacuums mounted above the door. These giant vacuums suck the common sense right out of students’ heads as they walk into the laboratory.

How else can we account for the fact that many students lose all common sense while they’re in the lab?

Here’s an example. We’re performing a specific heat lab in my introductory chemistry lab. Students heat up a metal sample by placing it into a test tube suspended in boiling water. Since the water is boiling, the metal evnetually reaches the same temperature as the boiling water: 100^oC. The metal is then put into a cup which contains a known amount of room temperature water. The students then measure how much heat goes from the metal sample to the room temperature water.

The lab manual asks students a queston: Why is the metal sample placed into a test tube and then lowered into the boiling water rather than being placed directly in the boiling water?

Putting the metal sample directly into the water - obviously - gets it wet. Transferring hot water along with the metal sample to the cup will make the temperature inside the cup go up more than expected, and the energy calculated will be too large.

One student had some trouble with the answer, and asked for a hint. But the problematic part of the answer might not be what you think …

Me: So, how is the metal sample going to be affected if you put it directly into the boiling water instead of the dry test tube?

Student: I don’t know.

Me: Okay. Hmm … Let’s say you’re riding in a boat and you fall overboard. What do you get?

Student: You get … tired? From swimming?

Me: How about this? You jump into the pool. How are you different after you jump into the pool from the way you were before you jump in?

Student: You’re … wet?

Me: Good. So now all you need to think about now is how that metal sample being wet with hot water before you put it into the cup would affect your results.

Good news, everyone!

A new study shows that Americans of 2005 (28%) are much more likely to understand science articles in the news than Americans of 1988 (10%). The study’s author says that the major reason is that more colleges have basic science courses as an entry requirement.

I’ll buy that line of argument. Put more people through basic science courses early, and at least some of it will stick. More people with some scientific knowledge is certainly a good thing. But there’s one little problem - there’s also the issue

that people are giving increasing credence to pseudoscience such as the visits of space aliens, lucky numbers and horoscopes.

Why?

One problem, [Carol Susan Losh of FSU] said, is that pseudoscience can speak to the meaning of life in ways that science does not.

What, does no one read Carl Sagan anymore?

I’m not sure I buy that belief in pseudoscience is up because of some sort of search for the meaning of life. Wasn’t that need just as real in the past as it is today? I might be inclined to buy into the idea that, since pseudoscience is all over the web, people are more exposed to nonsense than they ever were previously.

As silly as I think astrologers and people who claim to talk to the dead are, I don’t worry about them that much. Why? Mainly because most practitioners of pseudosciences like astrology aren’t seeding school boards with candidates to try to sneak astrology into the science classroom.

But there’s one pseudoscience out there whose practitioners can’t keep their mitts off the science curriculum. Creationism.

Back to the article …

[...] there also has been a drop in the number of people who believe evolution correctly explains the development of life on Earth and an increase in those who believe mankind was created about 10,000 years ago.

(emphasis mine)

To believe that the world / mankind was “created” six to ten thousand years ago, you have to throw away the foundations of almost all the sciences. Fundamental facts and theories in chemistry, physics, geology, biology, etc. are simply incompatible with the young Earth viewpoint.

And the numbers of these people are growing? That’s a frightening thought!

A post over at Pooflingers Anonymous reminded me of a little rant I’ve been meaning to post for a while.

Consider this lovely Pasteur pipet.

The Pasteur pipet is truly a small wonder. It’s cheap, disposable, and can be used to transfer small amounts of liquid from one place to another with almost no mess. The suction from the bulb keeps the liquid inside from dripping. There’s also very little risk of contamination of sample, since the glass part is disposable - and is only used to transfer one solution.

What irritates me to no end in introductory labs, though, is one simple error that students will just keep on making over and over again - no matter how many times I point out the error and correct it. That error is …

… holding the pipet with the tip up.

Holding the pipet this way causes the liquid inside the pipet to run down into the rubber bulb. While the glass body of the pipet is essentially chemically inert, the rubber bulb is not. Strong acids attack the bulb, as do many solvents - and the products of these reactions get into the dispensed liquid. Any contaminant that’s present in the rubber bulb - usually caused by some other student holding the pipet with the tip up - will also get washed into the dispensed liquid.

All of these contaminants will screw up results. For students, that translates into bad grades. That, at least, is something that students should understand!

Well, it’s official. Anti-science candidate Karen Floyd has been defeated by Jim Rex for the post of SC Superintendent of Education.

This, of course, assumes that there aren’t legal challenges to the vote. We shall see.

Updated on 11/21/06: Floyd has conceded.

Why only a little happy? Well, the margin of victory was only 455 votes! Rex’s opponent was not only unqualified for the office but also said such mind-bogglingly foolish things as

More and more scientists are publicly coming out in favor of an Intelligent Design Theory because that is what the evidence is telling them is true.

Long gone are the days when God was excluded from scientific circles. If we ignore that reality, we will only limit our children’s scientific knowledge.

Clearly, the theory of the politically-correct minority has been allowed to dominate our classrooms to the point where not only is evolution being taught as a scientific truth, but the public address system cannot be used to say a prayer for the safety of athletes before a football game - this is wrong.

(Source: SC PIE)

455 votes … out of a million. We’ve got a long way to go in South Carolina.