pH Sensor - Tech Tips with Vernier

Uploaded by verniervideo on 25.06.2012

Measure. Analyze. Learn.
This is the pH sensor.
It's used in quite a few of our books.
It's used in the chemistry , the physical science,
middle school, biology, so, it's used across the curriculum.
And, it's used to measure the pH of a solution.
To use this, you need to take it out of this storage solution.
And, this is a pH 4 buffer solution
that keeps from damaging the sensor.
So, you to make sure that you always
store it in the solution.
It's good to make sure you have clean solution in there.
And, the sensor booklet that comes with the sensor
talks about what it is, and how can get more of that,
and/or make your own.
To use this, we need to take it out.
So, I'm going to unscrew this cap
and as I do this, it loosens this gasket.
I'm going to pull it out and I would be ready to use it.
Now, the active part of this sensor
is this glass globe down here.
And so, that must be in contact with the solution
that you're trying to measure the pH.
You need to be careful with this, because it's glass
and it actually has a protective cage around there,
But, sometimes students will put this down, or
maybe you're using this in a stream and
they plunge it down in the stream and
hit it on a rock and break it.
So, that is why it has the cage.
So, you want to be a little bit careful with that.
To use it, your going to take it, and just make sure that's
immersed in a solution.
We'll make some measurements here.
So, the first thing I need to do is to
plug this into my LabQuest.
It's an analog sensor, so it goes into
one of the analog ports here.
And, when I plug it in, I end up getting my meter reading here.
And it is close to the 4; where I had it in the solution before.
So, it's reading right there close.
And, now I'm ready to make a measurement.
So, I have a solution here.
And, we're interested to know what kind of solution that is.
So, maybe I plunge it down in there.
And, we look at what happens to our meter value there.
So, it is climbing, so it must be a base.
And so, it has stabilized about there, so 11.2 something.
So, it's obviously a base.
Now, to put this away, I need to make sure I clean it,
So, I have some distilled water here.
So, I just going to kind of rinse that off, to clean that up.
And then, I will put this back into my storage solution.
So, I put it back into the storage solution,
And then, I tighten up on this gasket to keep it from leaking out.
We have some common questions about this.
People ask about, "Do I have to calibrate this sensor?"
And the answer we like to say is, "No".
In general you don't.
Your often interested in the change in the pH value,
or you want a measurement,
but you're not worried about it out to the hundredths place,
or something like that.
So, you can use the stored calibration on there.
You can calibrate it, if you want to.
And, to do this, you put it into known conditions.
So, you might put it into a pH 4 buffer solution,
and tell it that's what it is;
and then move it into, say, a 10, and tell it that's what it is;
and then, you can actually store that to sensor.
This is a smart sensor that has built in storage capacity.
And so, you can tell it that's what it was,
and actually save that calibration.
Sometimes as these age, the values can shift a little bit.
And so, maybe once a year you do calibrate,
and be able to do that.
Another common question that we get,
and it 's kind of interesting, is that people will say,
"What's the pH of distilled water?"
And, they think, oh, it's going to be 7,
because that is what the book says.
And, what happens is, is that they try it out in distilled water
and they find it's not actually 7.
What's happening is, there is not enough ions in solution
for the device even to work in distilled water.
And so, without the ions it doesn't work.
Or, sometimes they put it into a solution
and they find that it's actually slightly acidic,
because it turns out that maybe the distilled water has been
sitting around for a while and
you have some carbon dioxide dissolved in that,
so you have a weak carbonic acid.
So, that is what you might discover there.
If you actually wanted to use this in a
very soft solution, or something without a lot of ions,
there is actually some things that you can add to your solution.
It doesn't change the pH,
but provides some ion to make it work there.
So again, it's a very useful sensor.
It's used across the curriculum.
And so, it's definitely one that you should have.
All of our sensors come with a booklet.
And, this is the pH sensor booklet.
And, a lot of the common questions that people will have
about this particular sensor will be answered in here.
Things about the storage solution;
cleaning of the device, how you can do that.
And so, it's definitely a good reference.
If you have one of these, you might want to refer to it,
if you have further questions about this particular sensor.