How to Establish the Temperature Range of Crystalline Substances Precisely - Paper Example

There experiment seek to fulfill are range of objectives. The first objective is to figure out how to establish the temperature range of crystalline substances precisely. When a solid substance is manufactured its melting point is typically established to facilitate its identification and to ascertain its purity. The second purpose is to assess the impact of the purity of solid substances on its melting pattern. Pure substances typically have melting point range but the temperature range for impure substances is extremely wide. Along these lines, a sharp MP is used as a proof of purity, whereas a widely ranging temperature is evidence that the substance is impure. It is regularly, although not generally, hold that an adulterated substance will have a lower MP than a similar substance when it is unadulterated. In this manner, unadulterated benzoic acid has a MP of between 122o C and 123o C, while a sullied sample may have a MP of between 115o C and 120o C. The other application of a physical constant of an obscure substance is to distinguish it from a range of possibilities. By and large, the melting point is just one of the many parameters that enable the identification of compounds. A huge number of organic compounds in their solid states have known melting points. Maybe ten thousand of these will have an indistinguishable MP from the unknown compound. Although the compound is no known, the field has been narrowed using the MP of the compounds. In this investigation, the objective is to determine the melting point of N-phenyacetamide and its identity from a range of compounds.

Melting Points

First, the expression melting point is a contradiction because it refers to a temperature range rather than a point when most of the crystals of a solid substance liquefy. When determining the MP of a substance, the focus should be on the melting range rather than melting point. The reasons for computation of MP are purity estimation and compound identification. Melting points are typically established by setting a couple milligrams of the material for testing into a MP capillary, and subsequently heated together with a thermometer to record temperature range. The MP capillary is heat tolerant, thin-walled glass tube around 100 mm long and not more than 2 mm in diameter.

Procedure

50-100 mg of N-phenyacetamide pulverized through smashing using a mortar and pestle. The melting point tube is filled by N-phenyacetamide through thrusting the open end into the crushed substance several times.

The sealed end of the capillary is tapped vigorously against the table to work the solid materials plug towards the end of tube. Alternatively, a file was drawn across the loosely held tube on the hand.

The procedure was repeated until the tube contained at least two-millimeter column of the packed powered of N-phenyacetamide at the sealed end. The amount of the chemical settled at the bottom of the tube is recorded.

The white coloring at the top part of the tube is rather the reflected light and not N-phenyacetamide crystals. The tube is inserted into the MP device and heating commenced. Temperature was allowed to increase at a relatively rapid rate to within twenty and twenty-five below the expected MP of the compound.

During the process of determining the actual MP, however, the temperature was not allowed to increase more rapidly than between one and two degree Celsius per minute.

Hence, the rate of heating was decreased when the temperature was above fifteen degree Celsius beneath the expected MP. The melting point of the subject substance, N-phenyacetamide, was recorded on the report sheet.

Boiling Point

In the same way, point ranges of other salicylic and benzoic acids, as well as other compounds were determined and recorded. The compound additionally boiled at around 1130C. To exhibit the impact of contaminations on the boiling point of an unadulterated substance, the melting point of a 50-50 blend by weight (fifty milligram of each compound) of urea and N-phenyacetamide are used. The process is repeated with 75-25 and 25-75 blends. Using boiling point midpoints, the data is plotted on the report sheet.

Procedure

A small measure of the finely salicylic acid is introduced into a thin-walled and sealed capillary. The narrow tube is partially immersed into a porcelain pot.

The temperature range is noted, the point crystallization starts and the point the substance is completely liquefied.

The noted temperature range is the temperature interval between the upper and lower value. The Boiling point (BP) is a typical property of an unadulterated chemical substance.

The resulting BP range can be affected by the virtue of the material as well as by the volume of the substance, the quantity of the material, density, and the intensity of heating.

A limited time is required to exchange heat through the capillary walls and all through the samples mass.

When block or bath is heated rapidly, it results in a rise in temperature a few degrees amid the time the boiling is expected to happen. It brings about an observed temperature range that is above the true one.

When the bath or block temperature approaches the Boiling Point of the Salicylic acid, for accurate result it is critical that temperature is raise gradually, as a rule around 20C per minute. The quantity of the substance needs to be sufficiently small and tightly packed in the capillary tube. The section of solid in the tube ought to be sufficiently high to be seen as it melts (around 2 mm). The materials behavior on melting should be recorded and watched carefully.

Crystallization

When the determining the point of crystallization of an unknown substance, time can be save by first obtaining the estimate MP through the use of the rapid heating approach, roughly between fifteen and twenty degree.

Procedure

The bath is allowed to cool to about fifteen degree Celsius just beneath the estimate CP.

The second portion of the sample is then used in determining the melting range more accurately through the slow heating approach.

The unknown sample is collected and its melting point determined and its data filled in the report sheet.

The identity of the mixture is ascertained through the CP approach.

The data collected is used in making preliminary identification. Fifty milligram of the unknown substance \is mixed with known of equal weight for the determination of the melting point.

The procedure is repeated to determine with accuracy the identity of the peculiar substance.

The findings were recorded in the data sheet and graphs plotted for analysis.

Analysis

Results

Compound Molar Mass Density Literature MP Hazardous properties

N-phenyacetamide 135.17 - 114.3 Toxic, irritant

Salicylic acid 138.12 - 159.0 Toxic, irritant

Charcoal 12.0 - - Toxic, irritant

Celite- - - Irritant

Organic Compound Melting Point

Benzophenone 48.0

Naphthalene 80.5

N-phenylacetamide 114.3

Benzoic acid 122.0

Urea 135.0

Salicylic acid 159.0

Experimental Melting Point = (T1 + T2)/2 = (114.3 +118.9)/2 = 116.6

Interval Volume of collected liquid/ml Observed temperature / Co

1 1 ml 55 Co

2 5 ml 55 Co

3 10 ml 57 Co

4 5 Discussion

Although melting points tend generally to be directly proportional to molecular weights of substances, compound that differ by simply CH2 (homologous series) often depict melting points that are significantly distinct from the expected pattern for the substances of higher homology. In a number of homologous series of aliphatic compounds, their MPs tend to alternate. The MPs of successive members of the substances in the homologous series is lower or higher than those of previous members, contingent to whether the constituent carbon atom are odd or even.

In the study, the melting and boiling ranges were recorded for each compound instead of melting and boiling ranges. The reasoning behind the decision is that impure substances and polymers tend to boil or melt over a range of degrees. In the view of the substances melting and boiling points, it was extremely difficult to differentiate between two substances based on the data generated from the study alone. The temperature ranges of the compounds do no vary significantly such that experimental error could be used as an excuse to disputing the results and as the only identifying property. Considering these conclusion, I believe that Salicylic acid is an impure substance because it boiled over a range of degree Celsius. When both compounds were a mixture of the said acid, their boiling points would be identical theoretically to those of other compounds. As it is the case with typical alkanes, the boiling and melting points of successive members always increase although in smaller or larger amounts dependent whether the carbon atoms are even or odd. As far as boiling points are concerned, substances with functional groups tend to have relatively higher boiling points as compared to nonpolar functional groups. Unlike the case of boiling points, cyclic or highly branched molecules, often symmetrical, seem to have a high point compared to the strain-chained isomers. The combined impact of branching or the existence of rings is the reduction in temperature range over which liquids make take to vapourize at pressure lower than 760 Torr. For unique cases, the liquid range is not present in pressue below 760 Torr and hence the substance sublimes withoiut necessarily melting.