CHEM 204 Lecture Notes - Lecture 6: Phase Diagram, Fractional Distillation, Benzene

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25 Jan 2018

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=(cid:4666)(cid:1875)(cid:1857)(cid:1859) (cid:1872) (cid:1867)(cid:1858) (cid:1871)(cid:1867)(cid:1864)(cid:1873)(cid:1872)(cid:1857)(cid:4667) (cid:1849)(cid:1857)(cid:1859) (cid:1872) (cid:1867)(cid:1858) (cid:1871)(cid:1867)(cid:1864)(cid:1873)(cid:1872)(cid:1867)(cid:1866) (cid:883)(cid:882)(cid:882: do not need to know the molar mass of the solute (therefore good for, mole fraction biochemists) It is easy to measure the volume of the solutes rather than the weight (in the case of molality: disadvantages, volume is temperature dependent, since the volume of a solution is dependent on temperature. It is independent on temperature because it is the ratio of weights- it does(cid:374)"t (cid:448)a(cid:396)y like volume does with temperature. 7. 2 partial molar quantities: volume is innately an extensive property: the amount of substance determines the amount of water. If the volume is expressed as a partial molar quantity (l/mol) however, it is intensive. If we take half of each (cid:449)e"d e(cid:454)pe(cid:272)t it to (cid:271)e 0. 038l/(cid:373)ol but we actually only get 0. 036l/mol. Why is this: this is because the interaction between water molecules and the interaction between ethanol molecules are both weaker than the interactions between ethanol and water molecules.

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DETERMINATION oF MOLAR EXPERIMENT 23 MASS FROM FREEZING POINT DEPRESSION EQUIPMENT AND CHEMICALS: Equipment 600 mL beaker Chemicals Cyclohexane (C Stir plate 100 ml. graduated cylinder Clamp Nonvolatile Unknowns Freezing point apparatus Spin vane 0.1 C Thermometer INTRODUCTION: When a solute is introduced into a pure solvent the newly formed solution will have certain physical properties that are from the solvent. As a of the presence of the the pressure of the solution will be lower than that of the pure solvent. As the vapor pressure is lowered there is a resulting increase in the amount of energy required to reach the boiling point of the solution. Conversely, the solution must cool to a lower temperature before a state change from liquid to solid occurs. These changes in physical properties vapor pressure lowering, boiling point elevation and freezing point depression are collectively referred to as colligative properties. These colligative properties, which also include osmotic pressure, do not depend on the nature of the nonvolatile solute in the solution but rather on the concentration of solute present. Because the properties are independent of the nature of the solute, they may be used to determine other properties of the solute such as molecular weight. The effect of a nonvolatile, nonelectrolyte solute on a pure solvent will be examined by finding the freezing point depression of a cyclohexane unknown so solution. The freezing point of a pure sample of cyclohexane will be determined. Introducing a nonelectrolyte solute should in solution formed to freeze at a lower temperature. This temperature will then be experimentally determined As stated the The molality of the solution dependent on the quantity of solute particles present in solution. (moles solute particles per kilogram of solvent) is directly proportional to the change in temperature between the freezing point of the pure solvent and that of the ATfss Kim The molal freezing point depression constant, K for cyclohexane is equal to 20.00 cfmolal By experimentally determining the freezing point depression of a ohexanel unknown solution, the molal concentration is easily calculated. In turn the molar mass of the unknown olute can be calculated as well Chemistry 132 EXPERIMENT23

Chemists often use molarity, M, in moles/liter, to measure the concentration of solutions. Molarity is a common unit of concentration because the volume of a liquid is very easy to measure. However, the drawback of using molarity is that volume is a temperature-dependent quality. As temperature changes, density changes, which affects volume. Volume markings for most laboratory glassware are calibrated for room temperature, about 20°C. Fortunately, there are several other ways of expressing concentration that do not involve volume and are therefore temperature independent.

A mass of 0.630 g of NaCl is dissolved in 525 g of water.

1. Calculate the morality of the solution.

2. Calculate the mole fraction of salt in the solution.

3. Calculate the concentration of the salt solution in percent by mass.

4. Calculate the concentration of the salt solution in parts per million.

Include units for each.

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CHEM 204 Lecture Notes - Lecture 6: Phase Diagram, Fractional Distillation, Benzene

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