Measure. Analyze. Learn.
This is the conductivity sensor.
It's used in quite a few of our lab manuals.
It shows up in the chemistry manual, the biology manual,
water quality for say total dissolved solids.
So, it's a real useful sensor across the board there.
We want to cover a little bit of how you use this sensor.
What it does is, it's measuring the conductivity in solution.
So, It's actually using electricity to be able to do that.
And, the important thing to be able to do,
is to place your probe down into the liquid, deep enough that
you're actually covering the lower part here where the sensor is.
So, you need to be able to put that in there.
This is a multi-range sensor.
And, it has a switch here on the end.
And, this allows you to adjust it
for what you expect you values to be.
And so, it's a sensitivity switch.
And so, it's important to have that
where you think you ranges are going to be.
So, if you're doing a particular lab from one of our manuals,
they usually will tell you to have it in one or the other ranges.
Now, if you're doing something on your own,
and you're not quite sure; you could just test your solution
in maybe different ranges to see if it works out there.
And so, its got a 0 to 200, 0 to 2000,
and 0 to 20,000 microsiemens is the unit there.
So, let's collect some data.
So, to do this, I need to immerse this in my distilled water.
And, I have this attached to the Vernier Stir Station.
And, I'm just going to have it drop some salt water into there,
and change the conductivity of this.
The first thing I need to do is
put this on the electrode support bracket here.
And, I'm going to put it here.
And, I need to attach this magnetic stirrer to it.
And, so in order to do this, I'm just going to
slide it up the side there; bring it around;
lower it down into my solution; there we go;
let it slide down to there.
So, I have the tip submerged, at this point.
And, maybe I'll turn this up a little bit,
so that it's starting to stir.
So now, I'm ready to attach my sensor to the LabQuest.
It is an analog sensor, so I'm going to plug it in here.
When I do this, it's going to default to finding the sensor, there.
And so, It knows that I have plugged this in,
And so, it's giving me the meter screen there,
and the current reading on the sensor.
And, it's actually fairly close to 0 here.
This was distilled water;
my beaker may have been a little bit dirty,
and so, it may be reading slightly above 0 there.
I'm going to adjust my range, before I actually get started here.
Right now, I have it on 0 to 200,
And, I suspect that given what I've done here,
is that as I start to add the salt water,
that the conductivity may increase fairly rapidly.
So, I may do 0 to 2000.
And, we see our meter screen here,
and it's giving me a reading there close to 0,
for my distilled water. So, that's nice.
The collection parameters up here,
in the upper right corner, are time based.
Meaning, that we're are looking at conductivity
as a function of time.
The rate is 1 sample per second, is the default;
for 3 minutes, or 180 seconds.
And so, that's perfect for what we want to do.
We're going to start adding salt water,
and see what happens to the conductivity.
So, I'm ready to begin collection.
So, I'm going to press the start button down here.
And, let it start collection.
And then, I will open the valve,
and let the salt water start to drip into the beaker.
And as we do this, we see that the conductivity
of the solution begins to rise.
We've collected data, probably, long enough now.
We could let it run out to the 180 seconds,
but I think we have enough data to be able to do our analysis.
Maybe we're interested in the rate of increase
of the conductivity as we drop the water into there.
After we hit stop, the graph auto-scales.
And, it's making it as large as possible
given the data we've collected.
It looks like a nice increase in conductivity.
It's fairly straight there. There's a little bit of bumpiness,
and that's caused by the stirring action.
If we don't stir it fast enough, or it's not quite mixed,
you may get a little bit of bumpiness there on the graph.
But, it looks like a fairly steady increase,
after I started adding the saltwater, at that point.
So, we would like to do the analysis,
and maybe we want to fit this part of the graph here
with some kind of mathematical equation.
So it looks like it's a line to me.
So, what I want to do is highlight the region of the graph;
maybe go all the way over there.
So, that’s a nice section of the linear portion of the graph.
And, to do the curve fit, I want to go to 'Analyze'.
And, I will do curve fit, and check the box next to conductivity.
And, in the upper right corner there,
it says, "Choose Fit", so it wants me to find an equation there.
So, I'm going to go up and we'll try 'Linear'.
It looks like it fits fairly nicely there.
And, I'll hit 'OK'.
And so now, it has fit that section with a line.
I end up with the slope/intercept form of the equation there,
and my slope is 13.53.
So, that would be the increase in conductivity
as a function of time for this graph.
So again, this is the Vernier Conductivity Probe.
It's used widely across a lot of our different labs.
Labs from all of the chemistry manuals,
all of the biology manuals, environmental science,
water quality. So, labs such as: watershed testing,
conductometric titration, total dissolved solids,
and maybe diffusion through membranes.
So, it's definitely a very versatile probe.