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What are the normal freezing points and boiling points of the following solutions? (a) $21.2 \mathrm{g} \mathrm{NaCl}$ in $135 \mathrm{mL}$ of water and (b) $15.4 \mathrm{g}$ of urea in $66.7 \mathrm{mL}$ of water

$-10.0^{\circ} \mathrm{C}$, $102.8^{\circ} \mathrm{C}$, $-7.14^{\circ} \mathrm{C}$, $102.0^{\circ} \mathrm{C}$

Chemistry 102

Chapter 12

Physical Properties of Solutions

Solutions

Drexel University

University of Kentucky

Brown University

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.

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35.What are the normal fre…

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Calculate the freezing poi…

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What is the freezing point…

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the first solution on this problem has 21.2 grams off sodium chloride. So to calculate the variation in the boiling point in the Prison point because of collective properties, we have to first compute the morality off these solutions. So first up is to compute the number of malls, the number of malls, sodium chloride. Okay, so we have 21.2 grams of sodium chloride, and the more massive sodium chloride is 50 a 0.4 Gramps. Okay, Doing this calculation, you should find that the number of malls off sodium chloride in the solution points 0.363 mo. Okay, so now we can compute the morality. So morality all represent with his leader AM will be the number of months divided by the mass off the solvent, the water in kilograms. We were actually given 13 five milliliters. So we have to do some conversions here. So first we can assume that it didn't see off. The water is one Demings that we have one militar per one gram and then we gonna just convert units. We gonna say 1000 Grimm's is equivalent to one kilogram. Okay, so now we should have all the pieces we need. So, militar skins of here grams cancer here in the final, we have most per kilogram, which is what we want. And there would be 2.69 Melo, I'm just abbreviating more per kilometre. Um Okay, so now we have the morality. Just one less thing. We will need the ven um the vent off factor the little I in the former. So just recall the sodium chloride. So as a solid it dissolves in water to produce soldier in and clo right? Okay, that means I Z equals two. Okay, so let's compute the boiling point So the variation in the boiling point will be equal The constant Let me write a former first K b times The morality times I So we have everything. Let's just plug in. The constant is 0.5 one to sell shoes for Malala t times The morality would just computer is 2.69 and I is equals to Okay, so that's cancels and we are left with computing this you should find 2.75 sources So that's how much the boiling point will be raised. So remember the boiling point of water is 100. So the new boiling point for dissolution is 100 Plus this. So it's 100 to so rounding 100 2.8. Okay, um, a better answer could be 103 because three sig figs we were given an, um the data with 366 So that's how I would write the answer right here. No, let's do the same for the freezing point. So, the prison point, we also have all the data. Let me write a former first. It's gonna be negative because the prison point go down the constant prison point depression, constant times, Malala gee, times higher. We have everything. So mine is 1.86 So that's the constant that you've gotta look up and the Malala t is 2.69 again with computer. That and I it's too. So doing this calculation, you should find something minus 10 houses. So the prison point will go down by 10 cells is since the freezing point of water is zero. Then we can say that the prison point of this solution will be, um oops, will be minus themselves. Okay, that's it for the first, um, solution. Now we have to repeat this The same procedure for a re Yuria. So Okay, so that would be be. And the first thing again, Let's compute the number of moles of Yuria. That will be the fourth, the 15.4 grams that was given. And you use the more mats. The molar mass of Yuria is 60 grams. So you arrive a 0.257 molt. Cool. Now we go ahead and compute Malala Gee, just like we did Morality Number of moles over the mass, off the solvent. So we have right there the number of most of Sawyer already. Now again, the mass off the solving wasn't given. What we have is the We have 66.7 milliliters of water. So we're gonna again assume that the densities just once a one militar Z equals one gram and we're going to convert us too Kilograms, because it has to be the number down here has to be in kilograms. So we just apply some converging factors. Uh, cancel some units, militarised, trams, and we're laughter mole per kilogram. So all right, computing, there's You should find 3.85 Melo. Okay. What now? Now we have the Muladi. What? What's gonna be I for your area? So you re It's a molecule. And it doesn't really break down into anything when you're putting solution. OK, so actually, I for Yuria is one and any molecule that is not an acid. This is what you expect. Okay, in general. Okay, so let's compute the changing the boiling point without the TV. I'm not gonna write the former. I'm just gonna play in the numbers. The constant again is the same one from the first item off this problem, because it's still the same solvent, right? This constant is specific for the solvent. Then we move, supplied by the morality, and I is just one. So the variation here will be 1.97 Celsius. Okay, So that means that the final boiling point is 100 which is the normal plus this. So just rounding this +236 things we have 100 to see Houses. Okay. Same thing for prison point. Plugging in the numbers the same constant as before. Times the mill outing times the vent off fact factor, which is one computing this You should find minus 7.16 cells is and since the freezing point is normally zero, that the freezing point of the solution will be zero plus this so minus 7.16 cells.

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