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Calculate the molalities of the following aqueous solutions: (a) $1.22 M$ sugar $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ solution (density of solution $=1.12 \mathrm{g} / \mathrm{mL}$ ), (b) $0.87 \mathrm{M}$ NaOH solution (density of solution $=1.04 \mathrm{g} / \mathrm{mL}$ ), (c) $5.24 \mathrm{M} \mathrm{NaHCO}_{3}$ solution (density of solution $=$ $1.19 \mathrm{g} / \mathrm{mL})$.

Moles of solute $=5.24 \mathrm{mol} \mathrm{NaHCO} 3$Mass of solvent $=0.74984 \mathrm{Kg}$Molality $=\frac{5.24 \mathrm{mol} \mathrm{NaHCO}_{3}}{0.749894 \mathrm{Kg}}=6.988 \mathrm{m}$

Chemistry 102

Chapter 12

Physical Properties of Solutions

Solutions

University of Central Florida

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03:58

In chemistry, a solution is a homogeneous mixture composed of two or more substances. The term "solution" is also used to refer to the resultant mixture. The solution is usually a fluid. The particles of a solute are dispersed or dissolved in the solvent. The resulting solution is also called the solvent. The solvent is the continuous phase.

05:06

In physics and thermodynamics, the natural tendency of a system to change its state is its tendency to increase the entropy of the system. It is a measure of the disorder in a system.

15:07

Calculate the molalities o…

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05:26

04:29

Calculate the molarity of …

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When 13.62 g (about one ta…

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Two aqueous solutions of s…

Hello, everyone. And welcome to this such session by Miss Hallstrom on morality calculations given polarity and density. And again, we're looking at polarity to help us calculate morality quickly. Let's review what malaria morality is. Morality is bowls of Salyut per kilogram of solvent and orders to solve these problems. We're going to make an assumption we're going to assume since polarity, which is abbreviated with a cop capital AM is moles of Salyut per leader of solution. Our sample size is one leader. We're gonna make the assumption that we have one leader. Okay, let's go ahead and immediately get started on trying to solve our first problem 1st 1st problem. We're going to be looking at a 1.22 Moller sucrose solution and sucrose for those Don't remember a seat 12 age 22 11. I'm also going to make a note right now that the molar mass of sucrose is 242 0.34 grams per mole because we will be using that. I'm also told that my density of this solution is 1.12 grams per mil. A leader um, morality is molds of Salyut per kilogram of solvent since we're working with. I don't really want a color wheel here, but what I've got since we're working with this number, there we go. We know that we have 1.22 moles of Salyut and one leader. Oh, solution. These two values are the same. When I'm ready to solve the problem, my numerator is going to be 1.22 moles. What we need to figure out is how many kilograms kilograms of solvent do we have? I'm going to, for the first problem, go through this whole calculation. If I have one leader of solution, I know that one leader is 1000 milliliters and I know that I have 1.12 grams per mil leader. And if I look at this, I can see I have 1000 120 grams of solution and I'm going to do this calculation this type of calculation for all three of the problems today. If I'm ever given the density and mill arat e, I can figure out the grams of my solution. Now, this would be a little easier is if I just because I need to use kilograms if I switch this right away. To say that one leader and 1.12 kilograms per leader is the density. And you can go through the mass and math and verify that. But this is a true statement. 1.12 kilograms. This is the mass of the entire solution of the solution in its entirety, which is not the same as kilograms of solvent defying the kilograms of solvent. I'm going to have to subtract from the massive solution the massive my Salyut, which I don't have. I do know that my mass of my solution is 1.12 kilograms. But what about this value? Well, in order to find the value that goes here, let me switch colors again. Let's go with this. I need to take my, um number of moles 1.22 moles of sucrose times 342 0.43 grams per mole. And that is going to give me see if I can find right down this 400 18 when I round grams of Salyut, which equals 0.418 kilograms. So I've got all the numbers I need now to solve to substitute into this equation. My kilograms would we don't hear. My kilograms of solvent is equal to 1.12 kilograms of solution minus 0.418 kilograms of solve it, which equals with correct number of significant figures 0.70 kilograms. Morality. You have to sort of go back here. 1.22 moles divided by 0.70 kilograms equals 1.74 Well, well, which is the answer. And don't forget that the abbreviation for morality is lower. Case M. Okay, so I'm going to run through this problem quickly and do a little bit of cheating morality, given polarity and density we found by taking the moles of Salyut which is taken from our moles of Salyut in our Moeller arm Bowler solution times it's gonna be one leader times the density which will be in kilograms per leader minus our moles times. The Moller may us and this is for our salyut. Now this one needs to be converted. Teoh Um kilograms. This will be in kilograms to convert this two kilograms. It's just going to be already down here. Bowles Times Bowler Mass will be some number in grams per mole, and that will be 1000 grams for one kilogram. So from a math standpoint, we're going to take this quantity divided by 1000 to get kilograms. And that's how we solve it. So I'm going to use this equation for our next problem for problem number two. Let me find it for problem number two. We're going to start with a 0.87 moller solution of sodium hydroxide. Sodium hydroxide has a bowler mass 40.0 grams per mole. You can verify that if you'd like and a look. Its density is very close. Sorry about all those things popping up okay by somebody so big unmasks here today. Now I'm going to write this equation down again. The morality is going to be equal to the moles of Salyut. I'm gonna put that down here and substitute it right away. This case is 0.87 and we're going to take for this part one leader times one point times the density. So I have one leader times 1.0 for grams per mil leader, kilograms per leader. And then I'll go into this color and here I'm going to take bulls a Salyut times the bowler massive the Salyut divided by 1000. And I'll set that up. Nicer, if you will. Over here. 0.87 moles times 40 grams per mole times 1000 grams per kilogram. So if I do this problem, I get an answer of 0.87 Mullah Al And that is indeed the correct answer. This isn't too unusual because this is this density is very close to one. So with rounding to only two significant figures, that one works pretty well. And let's do one more problem for good measure and this one problem. Three. Let me get back to Black. We're going to be working with a sodium bicarbonate. Excuse me. A 5.24 Moller solution of sodium bicarbonate and sodium bicarbonate has a molar mass of 84 0.1 grams per mole, and our density is given as 1.19 grams per mil a leader, which is equal to 1.19 kilograms per leader. Okay, so I'm going to just because it's only our second time doing this right down our general format. Not gonna color code at this time. Bulls of Salyut It's gonna be one times density Minus moles of Salyut times the molar mass divided by 1000. Okay, show me some been solved. We get 5.24 malls. I've Salyut divided by one leader times 1.19 kilograms per leader Cross cross minus 5.24 balls times 84.1 grams per mole and divide that quantity by 1000 grams per kilogram. Plug those numbers into your trusty calculator and I got 6.99 mole l So you can think through these. This is just dimensional analysis remembering that morality is molds of Salyut per kilogram Absolve int If I'm given polarity all I really need to do is assume I have one leader solution. Subtract from the corrected for density mass of solution. Subtract the massive Salyut and you are set to go. These take a little bit of practice, but they're not too hard. Good luck. Thanks for joining

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