Boiling points molecular elevation

When 8.8 g of a mystery compound is added to 42.1 g of benzene, the boiling point is elevated to 81.9°C. What is the molecular mass of this mystery compound ... 

Molecular Depression of the Freezing Point Molecular Elevation of the Boiling Point Nomenclature of Inorganic Chemistry Nomenclature of Organic Compounds Nomograph and Table for Doppler Linewidths Optical Properties of Metals... 

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. 

Raoult s law When a solute is dissolved in a solvent, the vapour pressure of the latter is lowered proportionally to the mole fraction of solute present. Since the lowering of vapour pressure causes an elevation of the boiling point and a depression of the freezing point, Raoult s law also applies and leads to the conclusion that the elevation of boiling point or depression of freezing point is proportional to the weight of the solute and inversely proportional to its molecular weight. Raoult s law is strictly only applicable to ideal solutions since it assumes that there is no chemical interaction between the solute and solvent molecules. 

Molecular weight determinations by depression of the freezrng-point are more accurate and far less troublesome than those by the elevation of the boiling-point (p. 440), and the former method should always be preferentially employed if the solubility of the organic compound in the soh ent is sufficiently high. 

The use of water as a solvent should be avoided whenever possible, as its Molecular Elevation Constant is so low that only a small elevation of the boiling-point is obtained. 

Where M is the molecular weight of the solute, Dt is the elevation of boiling point in °C, c is the concentration of solute in grams for lOOOgm of solvent, and K is the Ebullioscopic Constant (molecular elevation of the boiling point) for the solvent. K is a fixed property (constant) for the particular solvent. This has been very useful for the determination of the molecular weights of organic substances in solution. 

M depends not on the molecular sizes of the particles but on the number of particles. Measuring colligative properties such as boiling point elevation, freezing point depression, and vapor pressure lowering can determine the number of particles in a sample. 

Corollary.—The molecular elevation of boiling-point is independent of the nature of the solute. 

With the aid of elaborate refinements, including a 20-junction thermocouple. Pay was able to measure boiling point elevations with a precision of 0.0002°C and molecular weights of polyethylene up to 35,000 with an error not exceeding 10 percent. 

TABLE 11.9 Molecular Elevation of the Boiling Point (Continued)... 

Methods for the determination of Molecular weight based on colligative property are vapour-pressure lowering, boiling point elevation (ebulliometry), freezing-point depression (cryoscopy), and the Osmotic pressure (osmometry). 

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