 Okay, the next example on that lab sheet is parts and parts are less frequently used terms of making solutions, but they are, and so I gave an example here of a solution that is a three to two to one of ethylene, chloroform, and isoamyl alcohol. So this would be three parts of ethylene plus two parts chloroform plus one part isoamyl alcohol. So you have three parts plus two parts plus one part, so you're going to have a total of six parts, but they'll be in that ratio of three to two to one. So if you're doing it, you could say three parts, if you're doing it, you could do 30 mils of ethylene, 20 mils of chloroform, and 10 mils of isoamyl alcohol. So you'd have a total of 60 mils. You know, if you could do it 60 mils, 40 mils, and 20 mils, you can do it in any final volume that you want, but at the end of the addition, they're going to be at that ratio of three to two to one. So in this case, if our total is six, three out of six would be ethylene, two of the six would be chloroform, and one of the six would be the isoamyl alcohol. So if it's parts, it'll be written like this, and it's just like three parts plus two parts plus one part. The next topic that we'll put here is what we'll call multiple solutes. So this is kind of a different topic. It's not just about concentration of one thing because many, many times in the laboratory, we work with a lot of buffer solution that are made up of multiple solutes. So if not just like salt and water or sodium hydroxide and water, it's actually a mixture of things. In water. So even when you're making a solution of multiple solutes, that you have some protocol of your phone, some recipe, some recipe that you're following. And I won't give you just three examples, and there can be a lot of examples, but I'll give you kind of three examples of kind of recipe that you may come upon. So here's your recipe. One molar, magnesium chloride, 0.4 percent thymidine, and 20 percent glucose. Now to make this solution, you would have to have three individual solutions made up that you're going to add together. So you'll have your one molar magnesium chloride. So you'd have to make that up. You'd have to make up 0.4 percent thymidine and a solution of 20 percent glucose. So those would be kind of your stocks. Then you would have to mix them. So you'd have five mils of the one molar magnesium chloride, 10 mils of thymidine, and 25 mils of that. So you just add those together. Ultimately you'd have 40 mils of solution. So this recipe just tells you what you're going to mix together, but it requires that you make up the individual components there. I have here a recipe for phosphate buffered saline. Now if you were to Google phosphate buffered saline, you could find a lot of different recipes for phosphate buffered saline because there are different variations on that. But this is kind of a simple recipe and we're going to say that it has sodium chloride because if it needs to be saline we're going to have some sodium phosphate and some potassium phosphate and it's going to say 0.2 grams. Let me try to not have two decimal points here. 1.15 grams and 0.2, my bad is 7.5 grams of sodium chloride. 1.15 grams of sodium phosphate and 0.2 grams of potassium phosphate and it says bring to volume 1 liter. So to make this solution you would find these materials and weigh out those individual components and dissolve them and then bring them to volume 1 liter. Now quite often when you make up a biological solution it will specify a pH. So as part of the before you're bringing it to your volume, your final volume you'll have to adjust the pH to the desired pH. So there's an additional step. Say for instance you may request that this pH be pH say 7.4. So after you dissolve these in your less than one liter you would take them to the pH meter adjust your pH to 7.4 and finish bringing them to volume of one liter because either the acid or base that you need to add to adjust your pH is going to add to your volume somewhat. So another recipe, try this again. So this recipe tells you what your final concentration of each of the components is in your final solution. So you decide what volume that you're going to make, find the masses of your tris or your EDTA. So you say if I were wanting to make say liter this tris EDTA SDS buffer I would say okay I'd have to find the weight, the molecular weight of tris and decide what a tenth of a mole of that was to make it a molar. I'd have to find the weight of EDTA and figure out the how much that was for a hundredths of a mole of that in a liter and for SDS at 1% there'd be a gram for a hundred mils so far we're doing a liter it'd be 10 grams. So once you sort out what volume you desire then you weigh out the appropriate weights of the individual components to give you that concentration. That is a bit more work than if the recipe just says go get this and weigh it out. This recipe you're going to have to you know individual so it's you know if I were just making point one molar tris then I would have to figure the amount of weight that gives me a tenth of a mole. The point is I'm making this multiple solute solution then I have to do that for each of the components and then again what I've always remember that ultimately the final with the bring them to your final volume dissolve them because something particularly even like EDTA can often be very slow to go in solution so you have to make sure you give them time to dissolve in less than the final volume and then bring them to the final volume. Okay a last little example I'm going to talk about in this video is down on toward the close bottom of your page three of your solutions lab and it's talking about stock solutions and it says that biologists often use highly concentrated stock solutions as a way of making up solutions pretty frequently so that's something that you're using a lot and it's something that you can make up as a concentrate and then just dilute it from your stock when you're ready to use it then it's a kind of a time saver and so we talk about the stock and we talk about the working solution or the working strength in the stock solution to concentrate right and so an equation that we use that you've probably seen before is our v1 c1 v2 time c2 where the volume times the concentration of one solution is equal to the volume and concentration of the other so we substitute for these ones with assets of the volume of the stock time the concentration of stock equal to the volume of the diluted working strength times the concentration of the diluted working strength so an example here which says how would you make 400 ml of a 1 point molar nacl solution and again we're gonna assume this is aqueous so that we're gonna be using water as the solvent and that that's where our stock is made oh I didn't solution from a 5.0 molar stock okay how would you make 400 ml of 1.5 molar sodium chloride solution from a 0.50 molar sodium chloride stock solution so so this is the question that we're looking for what is the volume of the stock that we need we know the concentration of the stock if 5 molar is equal to you know the volume 400 ml of our let's say this is our vd times concentration d is 1.5 molar so right so your volume of your stock is equal to 400 ml times 1.5 molar over 9.0 molar the molar units cancel out so you have 400 ml times 1.5 divided by 5 okay so that is equal to 400 ml time 0.3 so that's equal to 120 ml of stock right then brought the volume of 400 ml right so v1 c1 it was v2 c2 in this case the unknown that we were asking was what volume of the stock and that's usually with the stock the question that you're going to be asking is what is the volume of the stock that you're going to need right and in this case I say we had a 5 molar stock and we're wanting to make 400 ml of a 1.5 molar okay so this is like those proportions you've been working but in this case you just go under both sides about a 5 molar 400 ml times 0.3 it's 120 ml of your stock okay and then it told you you're wanting to make 400 ml so that's the final bring to the end so thanks for watching the solution video going through these problems there are a number of sample problems intact and on the lab sheet and you know work on those and the in the actual in the lab exercise you're going to be actually making up you'll be giving recipes and you'll be actually making up some solutions and unless they don't take this lightly this you know making solutions and as I said in the previous video making delusions are a foundational basic skill that the employers are going to expect you to know you know kind of as part of you know so that have become part of your DNA you know by the time you leave the program you know you will hesitate when someone starts talking about recipes or concentrations or molerities and percent solutions and and what not so yeah just keep saying that we know work problems do examples until you feel comfortable with it because it's a key skill so once again thanks for listening and until next time