Hi. This is Tom Loschiavo, Chemistry Education Manager at PASCO scientific,
and I'm here today to talk about titrations.
Titrations are a valuable analytical tool in chemistry.
If you can measure the property of a solution as you add some reactant to it,
then when you see a change in that measurable property then you know the reaction is complete.
Most titrations involve pH and a buret to monitor the volume of titrant added.
In this case, we're going to do it a little differently.
We're going to measure pH and temperature using our Chemistry Sensor,
and we're going to use our Drop Counter and our drop dispenser
to measure the volume of titrant added.
Let's get this set up so we can see how it works.
I'm going to build a graph, build a page of pH versus fluid volume.
Now, with any titration, you want to do some calibrations beforehand.
You want to calibrate the pH meter.
To calibrate in SPARK, you go to the Tools and you can calibrate your sensor.
In this case, I can calibrate my Chemistry Sensor and my pH.
Now, I already pre-calibrated this with my buffers 4 and 10.
And I need to calibrate my Drop Counter so that it knows what the fluid volume is.
I'm going to calibrate my Drop Counter fluid volume.
The way to do this is use a graduated cylinder, and drop the titrant through the Drop Counter
into the graduated cylinder until a certain volume that you want.
I know that when I did this, in 10 mL of volume the Drop Counter counted 327 drops.
I'm going to use that as my calibration.
Now that my measurements are set up, I now need to set up my probes.
I'm going to put in my pH sensor.
I'm going to put it in far enough so that it doesn't hit the stirrer.
And in this case, I'm also going to put in my temperature sensor.
I'm taking advantage of the Drop Counter's multiple sensor ports.
There are three ports on here.
The other nice thing about the Drop Counter is it tells me when drops are added,
and I'm going to use my drop dispenser to add those drops.
Let's start the data collection, and I'll show you how the drop dispenser works.
Now it's going to record a drop in SPARKvue when I turn this on.
Notice the two stopcocks. One is for setting the flow rate,
and the other one is for turning it on and off.
There's a little tip at the end to ensure very small drop size.
I'm going to turn this on.
As a drop goes through, the LED light in here blinks
so that you know that a drop is being collected.
I'm going to rescale my graph a little bit.
Here's my initial pH -- very high, because I'm titrating sodium hydroxide with hydrochloric acid.
We'll let this go and we'll see how the titration curve looks.
We can see after a couple of minutes of data collection,
the pH is starting to gradually go down.
And now it's going down steeper.
Now we see those big drops in pH
that are indicative of the equivalence point being reached.
We'll let this go for a little bit longer to round out that pH curve.
OK. I'm going to turn off the drop dispenser.
And I'll stop data collection.
Now we have a textbook example of a pH titration curve of a strong base with a strong acid.
We can go further with that.
We can use the SPARKvue tools and our extra measurements to really analyze
what's going on in the system.
One great way to analyze a titration is to look at the second derivative.
I'm actually going to build a new graph that includes the second derivative of the pH.
I'm going to build a page, go to calculated data, and I'm going to do my first derivative
with one of the Math functions.
This is going to be a derivative of my measurement of pH versus fluid volume.
Now I'm going to do my second derivative.
This is going to be a derivative of that first derivative ... versus fluid volume.
Those calculations are complete, so we'll hit Done.
Now I'm going to take advantage of SPARKvue's multiple y-axis.
I'm going to plot pH and the second derivative, both on the same graph, versus the fluid volume.
Here's my multiple y-axis feature.
Now we have both of those graphs coming in and showing you the equivalence point.
The pH's equivalence point should be right around 7,
because it was a strong acid-strong base.
The second derivative shows that by showing you where the plot crosses the zero.
We see a nice indication of the equivalence point using that second derivative.
Now I can go even further with this because I did have
the stainless steel temperature probe in there.
In this case, I'm going to plot my pH and temperature versus fluid volume,
and just see what the data shows me.
Again using the multiple Y-axis feature.
Here we have the temperature steadily increasing as the reaction happened.
Then once the reaction stopped happening, because the equivalence point was reached,
then the temperature leveled off
and it would eventually start to cool back down to room temperature.
We can see that that point where the temperature started leveling off is approximately
the same point as the pH equivalence point.
We can really get an idea of understanding the system that's happening in the beaker
with the reactants and the products.
Titrations are a great analytical tool.
By taking advantage of multiple measures and multiple displays,
we can really get rich datasets to explore.
Thank you very much. This has been Tom Loschiavo.
If you have any questions or comments, please feel free to reach me at chemistry@pasco.com.
Thank you.