In this video, you're going to learn how to use a volumetric flask.
Before watching this video, make sure you've seen the meniscus video.
This is a volumetric flask.
They are easily recognizable by the wide base, and the long thin neck.
Volumetric flasks are used to dilute solutions to very specific and precise volumes.
Each volumetric flask is designed to hold one specific volume.
The volume is indicated by the number at the base of the flask.
The graduation on the neck of the flask indicates where the meniscus should lie when the flask is filled correctly.
As you can see, I have a prepared solution that I wish to dilute to an exact volume
To do this, I'll use a volumetric flask.
Before using it, it's important that you rinse it thoroughly.
To do this, you will use your solvent. In this case, it's deionized water.
Add small aliquots of the solvent
to the flask, and then cap it.
Swirl the solvent around, making sure to coat the entire inner surface
of the flask.
Then drain the solvent into the waste beaker.
When draining, don't shake your volumetric flask because this can damage it.
Do this several times before using it.
Now that your flask is clean, you can begin to transfer your solution.
To do this, place a funnel in the top of your flask
and put your stirring rod down the center of the funnel.
Slowly pour your solution down the stirring rod.
Transferring this way helps to prevent your solution from splashing out of the flask.
It's important not to pour too quickly, and overfill the funnel because that can result in a loss of some of your solution.
Now that you've emptied your solution from the beaker to the flask
there is still some solution remaining on the edges of the glassware.
To make sure this all enters the flask, we continue the process of quantitative transfer.
The first step is rinsing out the beaker throroughly with your solvent.
In my case, it's deionized water.
Rinse the inside of the beaker, and pour the rinsings into the flask, and down the stirring rod, just as before.
Do this three times, to ensure that all of your solution is being removed from the beaker.
Using several small aliquots to rinse is more effective than using one large one.
Now it's important to also rinse down your stirring rod in both the inside and stem of your funnel.
Make sure to watch the amount of solvent you are using when making your rinsings
because you don't want to fill the volumetric flask past the graduation.
Once you've finished with your rinsings,
cap the flask, and invert it several times to mix what you've put in so far.
Let the mixed solution settle, and then fill it up with your solvent.
In this case, it's deionized water.
Fill it up to roughly one centimeter below the top graduation.
At this point, you'll need to be careful not to overfill your flask.
You'll want to begin adding drop wise.
The best way to do this is to decant some of your solvent
and add it to the flask with a dropper or a Pasteur pipette.
Again, you can do this quickly at first, but you'll want to slow down and do more drop wise as you get closer to the graduation.
Try not to touch the inside of the flask
with the tip of your dropper because this can cause contamination.
Fill it slowly until the bottom of the meniscus lines up with the top graduation.
You'll have to do this very carefully because if you go over by even
a small amount, you will have to start again.
Now that you've filled your flask with the correct volume
it's important to mix it just as I've shown before.
This ensures that your solution is properly diluted.
Once your solution has been properly prepared,
you can accurately know the volume.
Knowing this, you can calculate the concentration of the solution inside your volumetric flask.
Doing this properly takes some time
and some practice, but if you follow the instructions that I've told you
You'll be able to master it in no time.