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Calculate the molality of each of the following solutions: (a) $14.3 \mathrm{g}$ of sucrose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ in $676 \mathrm{g}$ of water, (b) 7.20 moles of ethylene glycol $\left(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{2}\right)$ in $3546 \mathrm{g}$ of water.

a) $0.0618 \mathrm{m}$b) $2.03 \mathrm{m}$

Chemistry 102

Chapter 12

Physical Properties of Solutions

Solutions

Rice University

Drexel University

University of Maryland - University College

Lectures

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.

07:18

Calculate the molality of …

01:59

06:53

Okay, so in this question, we want to calculate morality. Okay, so they formula for that, we're gonna write it right here in the symbol M. It's the number off malls of your Salyut I'm going to represent with n divided by. Well, let me just highlight here. This is the number of moles, okay? And that is divided by the more, um, sorry. The maths off the solution. Okay, But normally that is kilograms, so follow the convention. Okay, So obviously define oh, masses mold per kilograms. But sometimes it can also represent just with this lower case M So for, um, a we have, um, 14 0.3 grams of sucrose gates. I'm gonna right here s u C sucrose king and that IHS dissolved in 676 grams. Oh, water. Okay, okay. So if you perform this calculation, you're not gonna arrive, Um, and what we expect, right? So there's a few conversions we gotta do before, so here I'm just laying down the data. So the first thing you're gonna need the molar mass off sucrose. Okay, So recall, um, this is given in the problem. The form of the sucrose is C 12 age 22. 0 11 And you can compute the molar mass of that. And you should arrive at something 342.3 grams per mole. Okay, so this factor here will be used to convert the grams of sucrose and two malls of sucrose because that's what we need on the top, right? Malls of sucrose. So that's our first conversion factor. That I'm going apply here is a fraction. Okay, so it iss So what we want, we won most. So we put that on the top. I know there. One mole off sucrose. So I'm going to represent this the symbol soup cruise. This is equivalent according to this 2 342.3 grams of sucrose king. So by applying this conversion factor here, you're gonna get, um, this amount of sucrose in number of moles, so the top is correct. Now we look at the bottom, so we do have the mass of water here. However, we need kilograms. Okay, So all you have to do is to convert grams two kilograms. You could do that like, automatically and just plug in the correct one. But I'm gonna put a another conversion factor here to take care of that. And that is a well known relationship, right? Are conversions. So we know them. 1000 grams. I'm going to ride 1000 grams off anything. In fact, I'm just gonna put water, so we be consistent. Um, 1000 grams of water will be one kilogram. Okay, that's well known. So now this is all the factors you need, so you just finish it up. Um, And the cool thing about laying down or your data like this that now you can check if things make sense by canceling the units. So, first of all, grams of sucrose, we can cancel that out, and we can also cancel grams of water. Okay, so we are left with malls of sucrose right here in kilograms of water. So that's exactly what we wanted, right? Number of most off, um, this valued by the mass off the solvent. Okay, so there you go. So you do this little calculation here, you should arrive zero point 06 one a most for a kilogram. Okay. No, let me make this better. Okay, That's terrible. Um, what's important here about Sig Figs? Okay. The conversion factor will not really affect the six weeks. So the six eggs, you will look at your data. Okay, so here, three sig figs, three sig figs at the end. Okay, No, the second case, the second problem be easier, because now you have already, um the ethylene like, Oh, you are given the information in malls I came. So that's 70.2 moles of ethylene glycol menace E E C oh, you see? And that IHS dissolved in 3546 grams of water. So again, we we would follow the same procedure with. Since the data is in malls already for the ethylene glycol, we can skip that. So we just really convert grams of water. So 1000 grams of water, It's equivalent one kilogram game so you can go ahead and cancel the units to see if you your solution makes sense. All right. Most per kilograms. That's exactly what we want. So you do this calculation and you should get 2.3 no per kilogram. Okay, so that's it.

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