Point Depression

Obtain a pair of solids whose melting points are within 1 °C of one another and determine whether they indeed depress one another s melting points. Some possible examples are 3-furoic acid and benzoic acid, 1-naphthylacetic acid and 2,5-dimethyl benzoic acid, frans-cinnamic acid and 2-furoic acid, 2-methoxybenzoic acid and malic acid, or dimethyl fumarate, 9-fluorenone, and methyl 4-bromobenzoate. Consult with your instructor regarding these and other possibilities. 

Return any unused samples to your instructor or dispose of them in the appropriate container for nonhazardous organic solids. Discard the used capillary tubes in a container for broken glass do not leave them in the area of the melting-point apparatus or throw them in wastepaper baskets. 

Describe errors in procedure that may cause an observed capillary melting point of a pure compoimd 

Describe on a molecular level the difference between the two physical changes melting and dissolving.  

Answer the following questions about melting points. 

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Beckmann thermometer A very sensitive mercury thermometer with a small temperature range which can be changed by transferring mercury between the capillary and a bulb reservoir. Used for accurate temperature measurements in the determination of molecular weights by freezing point depression or boiling point elevation. 

The problem is similar to the case of lubricating oils polyalkylnaphthalenes or alkyl polymethacrylates called pour point depressants have been commercialized to lower the pour point. 

Examples of pour point depressants for lubricating oils. 

Damin, B., A. Faure, J. Denis, B. Sillion, P. Claudy and J.M. Letoffe (1986), New additives for diesel fuels cloud point depressents . SAE paper No. 86-1527, International fuels and lubricants meeting and exposition, Philadelphia, PA. 

This is an expression of Raoult s law which we have used previously. Freezing point depression. A solute which does not form solid solutions with the solvent and is therefore excluded from the solid phase lowers the freezing point of the solvent. It is the chemical potential of the solvent which is lowered by the solute, so the pure solvent reaches the same (lower) value at a lower temperature. At equilibrium... 

Pourpoint additives Pour-point depressants Pour un Homme... 

Long-chain esters of pentaerythritol have been used as pour-point depressants for lubricant products, ranging from fuel oils or diesel fuels to the high performance lubricating oils requited for demanding outiets such as aviation, power turbines, and automobiles. These materials requite superior temperature, viscosity, and aging resistance, and must be compatible with the wide variety of metallic surfaces commonly used in the outiets (79—81). 

Anhydrous calcium chloride absorbs water to a capacity of 3.5 kg/kg of calcium chloride and forms a nonreuseable brine. This technique is best suited for remote appHcations where modest dew point depressions are required and gas processing volumes are small. 

Physical properties of glycerol are shown in Table 1. Glycerol is completely soluble in water and alcohol, slightly soluble in diethyl ether, ethyl acetate, and dioxane, and insoluble in hydrocarbons (1). Glycerol is seldom seen in the crystallised state because of its tendency to supercool and its pronounced freesing point depression when mixed with water. A mixture of 66.7% glycerol, 33.3% water forms a eutectic mixture with a freesing point of —46.5°C. 

Practically all lubricating oils contain at least one additive some oils contain several. The amount of additive that is used varies from < 0.01 to 30% or more. Additives can have detrimental side effects, especially if the dosage is excessive or if interactions with other additives occur. Some additives are multifimctional, eg, certain VI improvers also function as pour-point depressants or dispersants. The additives most commonly used in hydrautic fluids include pour-point depressants, viscosity index improvers, defoamers, oxidation inhibitors, mst and corrosion inhibitors, and antiwear compounds. 

Garbodiimide Formation. Carbodiimide formation has commercial significance in the manufacture of Hquid MDI. Heating of MDI in the presence of catalytic amounts of phosphine oxides or alkyl phosphates leads to partial conversion of isocyanate into carbodiimide (95). The carbodiimide (39) species reacts with excess isocyanate to form a 2 + 2cycloaddition product. The presence of this product in MDI leads to a melting point depression and thus a mixture which is Hquid at room temperature. 

R, mst inhibitor O, oxidation inhibitor D, detergent—dispersant VI, viscosity-index improver P, pour-point depressant W, antiwear EP, extreme pressure F, antifoam and M, friction modifier. 

Pour-Point Depressants. The pour point of alow viscosity paraffinic oil may be lowered by as much as 30—40°C by adding 1.0% or less of polymethacrylates, polymers formed by Eriedel-Crafts condensation of wax with alkylnaphthalene or phenols, or styrene esters (22). As wax crystallizes out of solution from the Hquid oil as it cools below its normal pour point, the additive molecules appear to adsorb on crystal faces so as to prevent growth of an interlocking wax network which would otherwise immobilize the oil. Pour-point depressants become less effective with nonparaffinic and higher viscosity petroleum oils where high viscosity plays a dominant role in immobilizing the oil in a pour-point test. 

Viscosity (Viscosity-Index) Improvers. Oils of high viscosity index (VI) can be attained by adding a few percent of ahnear polymer similar to those used for pour-point depressants. The most common are polyisobutylenes, polymethacrylates, and polyalkylstyrenes they are used in the molecular weight range of about 10,000 to 100,000 (18). A convenient measure for the viscosity-increasing efficiency of various polymers is the intrinsic viscosity Tj, as given by the function... 

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