Chemistry Essay Example about Melting Points

Published: 2022-03-02
Chemistry Essay Example about Melting Points
Type of paper:  Report
Categories:  Chemistry
Pages: 3
Wordcount: 760 words
7 min read

This is a mixture made up of compounds that have the same physical properties but different chemical properties cannot be seen with naked eye and also under a powerful microscope. E.g. air

Heterogeneous Mixture

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This type of mixture is made up of compounds that have different physical and chemical properties and the mixture is always visible and mostly it is separated by layers e.g. Mixture of oil and water.

Separation of mixtures into a pure components is an important process in chemistry. The mixtures can be separated in the basis of physical and chemical properties e.g. solubility, Effects on heat, base and acidity. Different methods can be used to separate mixtures including: Fractional Distillation, Decantation, Filtration, Chromatography, crystallization and Evaporation.


Name of the Compound Molar Mass/gmol-1 Density/gmL-1 Litearature Hazardeous Properties

Benzoic Acid 122.12 0 122.0 Irritant

1,2 diphenylethanedione 214.26 0 137-139 Toxic

Dichloromethane 84.93 1.325 41 Toxic


Diethyl ethane 74.12 0.708 34.6 Flammable


Dichloromethane 84.93 1.325 41 Toxic




Two layers is formed with a boundary. 1,2 diphenyl ethaniode was formed at the base and aqueous sodium hydroxide at the top because the former is less dense than the latter. Dichloromethane forms at the bottom because it has a higher density (d= 1.33 g/cm3) than water which has a lower density (1.00 g/cm3).


Benzoate Solution + Hydrochloric Acid = Benzoic Acid + Sodium Chloride



When dilute aqueous solution of sodium Hydroxide (NaOH) is added to a mixture of Benzyl and Benzoic acid in a flask that is fitted with stopcock, then the flask is shaken and allowed to settle thereafter two layers will form where one is a layer of dichloromethane and the other aqueous layer will be at the top.


Dichloromethane forms at the bottom because it has a higher density (d= 1.33 g/cm3) than water which has a lower density (1.00 g/cm3).



Benzoic Acid + 1,2 diphenyl ethanedioneDissolved in Dichloromethane

Use of separatory funnel

Aqueous Phase

Sodium Benzoate

1,2 diphenyl ethanedione Organic Phase

Precipitate of benzoic acid

Crude solid 1,2 diphenyl ethanedione Evaporate the solvent Acidify Section

Crystals of 1,2 diphenyl ethanedione Recrystallize


The two solvent were allowed to separate back into two layers because after shaking, one compound ends up in the dichloromethane layer and the other component ends up in the water layer resulting in the neutral organic compound benzyl remaining in the organic dichloromethane layer and benzoic acid being extracted in the aqueous sodium hydroxide layer as its conjugate base. Later the stopcock was opened and then drained the lower organic layer that contains benzyl into a beaker.


In this way the two organic components was successfully separated.


Heat to Standard Temperature

Benzoic Acid Solution Pure colourless Crystal

Of 122 degrees centigrade Solid dry benzoic acid




When a small quantity of dichloromethane was added to the impure solid of benzyl and heated then cooled a crystal product of benzyl was formed with impurities upon using vacuum filtration, the impurities were removed a pure dry solid of benzyl was found.


The Purification of benzyl through recrystallization was possible because of the fact that benzyl has different solubility in different solvent at different temperatures thus making it possible to remove impurities using this properties.



Mass of Benzoic acid

Mass of weigh boat = 2.2053g

Mass of weigh + Benzoic acid = 2.6053g

Mass of Benzoic Acid = 0.4g

Calculation of % recovery of Benzoic Acid

= (0.4/0.5) * 100%

= 80 %

Melting Point Determination of Benzoic Acid

Temperature 1 slow = 108 degrees centigrade

Temperature 2 slow = 120 degrees centigrade

Melting Point Range of Benzoic acid = 121-123 degrees centigrade

Melting Point of Benzoic acid= 122 degrees centigrade

Appearance of Benzoic acid crystals = Solid colourless dry Crystals

Mass of recrystallized 1,2 diphenyl ethandione

Mass of weigh boat = 2.2053g

Mass of weigh boat + 1,2 diphenyl ethandione = 3.1053g

Mass of 1,2 diphenyl ethandione = 0.9 g

Appearance of 1,2 diphenyl ethandione

Crystals = Yellow Crystals

Calculation of % mass recovery of 1,2 diphenyl ethandione

Remember that the maximum recovery possible is 1.00 grams because you combined two samples (yours and your partners)

= (0.9/1) * 100

= 90%


Melting points are usually expressed as a range between when materials begin to melt and when it has completely melted. Pure compounds characteristically have a sharp melting range while most mixed or impure compounds have a broad melting range. Another characteristic of melting points is their depression upon introduction of impurities or mixing. In our case the lower melting point of the impurity lowered the melting point of the benzoic acid from the standard as the temperature increases until it reached the standard i.e. 121-123 degrees centigrade impurities got separated hence producing pure colourless solid of benzoic acid.

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