CHM135H1 Lecture Notes - Lecture 12: Freezing-Point Depression, Boiling-Point Elevation, Vapor Pressure

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CHM135H1 Full Course Notes

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Chm135h1 f - lecture 12 - chapter 12 (2) 1. 0 m nacl solution has higher boiling point. Solution always has higher boiling point than its solvent in the pure form. Solution always has lower freezing point than its solvent in the pure form. Svap: boiling = more disorder therefore s > 0. Sfr: freezing = less disorder therefore s < 0. Sgas is above sliquid as it is more disordered. Entropy for gas and solid phase of pure solvent and solution are identical, since the solute does not evaporate / not incorporated into lattice structure of solid (that"s why glaciers that form from seawater are pure water) Only thing that changes is entropy of solution in liquid form. Therefore svap solution < svap pure, and sfr solution > sfr pure. This is what leads to boiling point elevation and freezing point depression. Intuitively, we think that gibbs should be negative for boiling and positive for freezing.

Related Questions

When a solute is added to a liquid, the boiling point of the resulting solution is __________ than the freezing point of the pure liquid.

A. no different

B. higher

C. lower

When a solute is added to a liquid, the boiling point of the resulting solution is __________ than the freezing point of the pure liquid.

A. higher

B. no different

C. lower

Solution properties are defined as _______________ if the property depends solely on the number of particles of solute and solvent in the solution, not the identity of the solute.

A. vapor pressure

V.colligative

chemical

hydrogen bonding

The advantage of using ________________ rather than the more commonly used unit of ___________________ is that it is independent of temperature effects on density (and thus, volume) of the solution

A. molarity, ppb

B. molarity, % mass

C. molality, molarity

D. molarity, ppm

If a 6.75 g sample of NaCl were dissolved in 8.41 kg of methanol, the molality would be ___________________ m.

A. 0.0137

B. 1.602

C. 0.803

D. 0.0445

The only information needed to determine the freezing point depression of a non-electrolyte is ______________________________ and _________________________________. f

A. the freezing point constant for the solvent, the temperature

B. the boiling point constant, the boiling point elevation

C. the delta T, the color of the most concentrated sample

D. the molality of the solute, the Kf of the solvent

An aqueous solution boils at 100.50oC. What is the freezing point of the solution? Kb(H2O) = 0.51 oC/m; Kf(H2O) = 1.86 oC/m

A. 0.50 oC

B. -0.50 oC

C. -1.82 oC

D. -5.50 oC

Bromoform has a normal freezing point of 7.80 oC and its Kf = 14.4 oC/m. A solution of 2.58 g of an unknown in 100 g of bromoform freezes at 5.43 oC. What is the molecular weight of the unknown?

A. 18.02 g / mol

B. 0.165 g / mol

C. 156 g / mol

D. 44.01 g / mol

Calculate the freezing point of 0.200 m solution of fructose, C6H12O6, a) in water (boiling point, 0 oC), and b) in acetic acid (boiling point, 16.6 oC). Kf(water) = 1.86 oC/m and Kf(acetic acid) = 3.9 oC.

A. -0.372 oC and 15.8 oC

B. -0.958 oC and 12.3 oC

C. 3.221 oC and 0.875 oC

D. -4.124 oC and 0.0035 oC

10.

Calculate the boiling point, in Celsius, at 1atm of a solution containing 30.0 of cane sugar (molecular weight = 342 g / mol) and 150 g of water.

A. 100.30

B. 103.00

C. 99.7

D. 301.00

Experiment 10 Colligative Properties Introduction A pinch of wa make boiling water hotter. A handful will clear the snow from your steps. Every day we the physical properties of materials around us, but often don't know why we use these particular s or what chemistry is involved. Modifying the temperature of phase changes, by adding a second chemical to the pure solvent are examples of manipulating the Colligative Properties of a solution. this lab, we will study how varying the concentration and type of a salt affects the point of a solution. Colligative properties are properties of a solution containing 2 or more components. Typically, the primary is the solvent and the other called the such as color or hardness, properties depend on the number of particles of astute in the not the identity of the In many cases, the rokute will determine the number of solute particles (degree of ionization, solubility, etc,) in the solvent, but a colligative property does not depend upon the nature of the particles. Two colligative properties commonly encountered are boiling point elevation and freezing point depression (the temperature of of a is lower than of pure solvent). We will be studying boiling point elevation in this Most of the previous work that you have done with solutions has involved units of molarity, M, or moles of solute per liter of solution. Boiling point elevation calculations (as well as those for freezing point depression) or moles of solute per kilogram of solvent. boili change of temperature. When the temperature of a solution changes, the volume of the solution also changes. Since molarity depends on a change in wil the solution's molarity. Molality depends on the mass of the solvent. and thus is independent of temperature. n't Hoff Factor salt into and the of moles inorganic salts in an aque the based on the addition of the number dissociates, the total number of particles in the solution will be of cations and anions produced from the dissociation. Thus; Nacion Na Choaa (2moles of particles) Cacbrs Ca +2ch (3moles of particles) The quantity of particles produced per mole of solute is called the van'tHoff factor and is given the symbol, i, If 1 mole of sodium chloride were completely dissociated, iwould be 2. This theory works very well for dilute solutions and non-electrolytes (i 1, no dissociation at all since nonelectrolytes not ionize), For does not always apply to more concentrated solutions. Thus, when there are a large number of particles in a solution, they have a tendency to recombine as the salt and you don't get 100% dissociation. example, at a NaCl concentration of 0.1M, iwill be 1.81 (90% dissociation) rather than 2 (100%). Boiling Point Elevation solute causes the solution to boil at a higher When a solution is heated, the presence of a non-volatile point of the pure liquid and the temperature than the pure The difference between the boiling boiling point of the solution is: 169

CHM135H1 Lecture Notes - Lecture 12: Freezing-Point Depression, Boiling-Point Elevation, Vapor Pressure

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