CHE 1302 Lecture Notes - Lecture 1: Freezing-Point Depression

14 views2 pages

greyduck910

20 Dec 2017

School

Department

Course

Professor

For unlimited access to Class Notes, a Class+ subscription is required.

Document Summary

Colligative properties of electrolytes (assume kno3 completely dissociates in solution. : estimate the freezing point of a 0. 20m solution of kno3(aq). The freezing point of pure water is 0 c and kf for water is 1. 86 c/m. The assumption means that i equals the number of moles of ions that can be formed per mole of kno3. One mole of kno3 forms two moles of ions when it dissolves in water: Hence, i = 2; and then the freezing point depression of the solution is. Remember that this is just the change in freezing point ( tf). For h2o solutions, the magnitudes of tf(solution) and tf(solution) are numerically the same because tf(solvent) is 0 c. The freezing point tf(solvent) for pure water is 0 c and kf for water is. Tf = tf(solvent) tf(solution) = 0 c ( 0. 796 c) = 0. 796 c. 0. 796 c = i 0. 21m (1. 86 c/m) i =

Related Questions

Please help me solve for the molar mass of sample 1 and 2 and the molecular formula

Experiment 1084-03: Determination of M.M. by Freezing Point Depres sion Measure the freezing-point depressions solute whose empirical formula is known Pool the class hat occur with solutions containing mass of the solute and its Background Information However, as soon as the solution begins to freeze, Adding a solute to a pure, non-volatile lquid ature will remain constant untl all the (solvent) lowers the vapor pressure of the solvent raises its boiling point, and lowers (depresses) its freezing point. The extent to which these are aftected depends on the relative number of solute particlos in the solution. Properties of solutions that depend only on the number of solute molecules in a given quantity of solvent are called colligative properties. Such cyclohexane turns into solid. Once the substance again. The freezing point is the temperature where it stays constant, Le. the liquld phase and the sold phase of the cyclohexane coexists (Figure 3-1) boiling point elevation and osmotic pressure. They do NOT dopend on the nature of the solute, but DO depend on the nature of the solvent. As a consequence, colligative properties can be used to determine an unknown molar mass for a solute. In this experiment, we will be using cyclohexane (d " 0.779 gmL, K, . 20.5 oC/m) as the solvent to determine the molar mass of a white solid with an empirical formula of C,HC. The freezing point depression, Î7, is the difference between the freezing point of the pure solvent, TP, and the freezing point of the solution (solvent and solute). T As mentioned above, thits quantity is proportional only to the molal concentration of the solute, m Figure 3-1. Cooling Curves The proportionality constant, K, is called the freezing-point-depression constant. The K value of 20.5 C/m for Cyclohexane is one of the largest values one can find. Molal concentration is defined as the number of moles of substance in 1 kg of solvent. Now we can calculate the molar mass of a solute from ATã K,, the mass of the The freezing point of a solution in cyclohexane can be obtained in a similar way. Cooling results in an initial rapid decrease in the temperature until freezing begins as seen in the cooling curve of the pure solvent. However, the temperature of the solution does not remain constant while being frozen. As the cyclohexane in the solution treezes, cyclohexane is taken away from the solution and the concentration of the solute becomes higher In the liquid portion. Thus the molal concentration of the solute increases and the freezing point of the solute and the mass of the solvent. remaining liquid becomes lower. The result is a steadily decreasing freezing temperature until the solution is completely frozen. When all the solution In order to determine ATP, we will measure the freezing point of pure cyclohexane and the freezing point of a solution of the solute in is frozen, the temperature decreases more rapidly To evaluate the freezing point of pure cyclohexame, you will cool a sample of this substance, and measure the temperature as a The freezing point of the solution is the temperature at which the solution starts to freeze. portion represents the concentration of the starting function of time. As cooling begins, theOnly at this point, the concentration of the liquid temperature of the cyclohexane decreases rapidly.

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

CHE 1302 Lecture Notes - Lecture 1: Freezing-Point Depression

Document Summary

Get access

Related Documents

CHE 1302 Study Guide - Quiz Guide: Formula Unit, Colloid, Freezing-Point Depression

CHE 1302 Study Guide - Midterm Guide: Formula Unit, Sodium Chloride, Intermolecular Force

CHE 1302 Lecture Notes - Lecture 4: Freezing-Point Depression, Semipermeable Membrane, Molar Mass

Related Questions