Ep 30 Memorizing Dilution Solutions

Memorizing Dilution Solutions 

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Solving a stock solution problem in calculations. Want to check out the book, you can go here:

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Auto Generated Transcript:

All right, I wanted to talk about dilution and solutions. I saw this on social media and I thought it’d be good to review how to do it and show you how I do things. I teach introductory chemistry as well as pharmacology, so it’s really a lot easier to do this kind of math if you’ve already had chemistry because it’s so similar to the stuff that we’re doing.

Here was the question that was presented or something like this: How many mLs of a four percent stock solution do you need to compound 100 mL of a 0.04 dilution in distilled water? What I usually see is some kind of ratio proportion or something like that where they just start scribbling numbers in. What I want to give you is a much more regimented way that you can do it every time so it always works.

The first thing I like to do before I even mess with any equations is just to write down the variables in a way that’s clear. The first concentration is four percent. The first volume, well, it’s how many mL so we don’t even know. The second concentration is 0.04 and the second volume is 100 mL.

Now that I have my variables, it just makes it a lot easier for me to say okay, what kind of equation would have this kind of stuff in it? The equation would be concentration of one times the volume of one is the concentration of two times the volume of two. We do this in chemistry all the time where we take the molarity times the volume equals the molarity times the volume.

Somebody who’s taking introductory chemistry is just going to have a lot easier time with this because they’ve worked through this type of equation. It’s just a matter of putting your head together that oh, the M is a concentration would be the same thing.

Now this is where it gets a little bit tricky. It’s a lot easier here because we have this horizontal equation. We don’t have something over something equals something over something. We don’t have to get something from the numerator or denominator. So numerator is on top, denominators on bottom and we don’t have to get something from the denominator.

All we have to do is move this C1 to the right and the way that you do that is you multiply both sides by one over C1. So this would cross this one out and then the C1 would be under here. This is what it would look like, the isolated variable equation. So this is isolated, the V1 is on the left and C2 times V2 over C1.

Now this may be a little difficult for some because they prefer to have the number on the right side. You’ve always multiplied two plus two equals four not something equals two plus two oh that’s four. So it may or may not be difficult, I can do it either way but again I just prefer to just leave the isolated variable where it lay and just kind of work with that.

But this is the equation that we’re actually using: V1 equals C2 times V2 over C1 and then this is where you plug in the numbers: V1 equals 0.04 times 100 mL divided by four; V1 equals four mLs over four; and then V1 equals one mL.

Again if you have questions like this feel free to put it in either the YouTube video in the comments. I’m on Tony PharmD, sorry I couldn’t think of anything more clever or you can always send me something at tonythepharmacist@gmail.com.

But what I want to do is I want to show you how to do this in five seconds or less and this is how I would have done it. I wouldn’t have even gone through all of this, I’m just doing it so you can see how it’s done.

I would have just looked at this and said okay, I’ve got this concentration of four percent and this concentration is one one hundredth of that okay so in some way my answer is gonna have to do one to a hundred okay so if this is 100 mLs then this is probably just going to be 1 mL and that would have been it, I would have been done.

So if you’re wondering like ‘I don’t understand how does that person finish the test so fast?’ They’re not actually going through all those steps, they’re just intuiting it because they’ve done so many of them before like ‘Oh, it’s a solution problem or a dilution problem.’

So how can we make this so this actually sticks in our head because I think it’s really tough to visualize this if you have some stock solution you don’t actually have a name of anything and even if you did have the name of a medicine, have you had experience with that medicine to know what it looks like color it is?

What I did was I did this with milk which is something that everybody probably recognizes and what I do is I just change the question from how many mLs of a two percent milk do you need to compound 100 mLs of one percent milk. So it’s the same thing, I’m taking a higher percentage to a lower percentage, same number of mLs in distilled water.

Our variables are two percent, don’t know, one percent and 100 mLs. Our equation is the same: C1 times V1 equals C2 times V2. We isolate the variable same way: V1 equals C2 times V2 divided by C1 and now we plug in the numbers and we see V1 equals 0.01 times 100 mL divided by 0.02 that’s 1ml divided by 0.02 which is 50mls.

Now let’s look at this one more time and say, ‘Oh well, if I’m going from 2 to 1 percent and gonna go half, then what I expect is this number will be halved.’ Okay, so just like we did one hundredth before, you know we went from four to .04. We went from 100 to one. We’re going from two to one and one is half of two and 50 mLs. Our answer is one half of 100.

If you want to see some questions like this, I did a book memorizing pharmacy technician mnemonics. Again, I know I’ve talked about in the last couple episodes but what I did was instead of doing the math by the type of math, I did it by body system. So I did a GI problem in the GI section and a musculoskeletal problem in the musculoskeletal section.

But if you’ve got specific types of problems that are really bugging you and you’re like, ‘Okay well, I want to know how Tony would do this,’ then you know just give me an email or just throw it in the comments on Tony PharmD on YouTube and then just let me know.

But again, this kind of math is really all about this process. Let’s go to soccer because in soccer there’s an expression that you want to get there fast and arrive slow. Okay so when I say get there fast, what I mean is the first thing I do is I’m very quick about this. I just okay first variable, second variable, third variable, fourth variable.

Okay what’s my equation? Okay let’s isolate the variable. Now I go slow because I want to make sure okay concentration two, concentration two. Let’s not actually gently mix up C1 and C2. Okay, I put that one there V2 100 mLs okay C1 4 okay that’s going to be there.

So when we say you know get there fast arrive slow, we’re saying you know you can write down the variables very quickly because you know that that’s right in front of you. The equation maybe it takes a minute or two to kind of just like okay which one do I need to use but it’s so much easier when you have the C1 V1 C2 V2 like oh yeah yeah I remember this one I know what I’m doing.

And then isolating the variable requires just a little bit of math and then plugging in the numbers is the easiest part but the easiest to mess up because you know we’re a little too fast with it.

So again, you know I want you to succeed in these kinds of problems so make sure you take the time to give me a couple problems that you might be struggling with and I’m happy to solve them for you.

Like to learn more?

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or here: https://www.audible.com/pd/B01FSR7HLE/?source_code=AUDFPWS0223189MWT-BK-ACX0-059486&ref=acx_bty_BK_ACX0_059486_rh_us

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