Mixed Melting Points PDF

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Mixed Melting Points

Olivia pizzella 31st August 2020 Organic Chemistry Dr. D’Amelia

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Purpose A Mixed Melting Point experiment is to understand the most important physical property of the compound. Doing a Mixed Melting Point to any compound can identify the compound if it is unknown and it can identify its indication of purity. Introduction Melting points can be used to identify as well as establish purity. This can be identified in two ways, One the purper the substance the higher the melting point and two the purper the substance the narrower the melting point range. In this experiment a DigiMelt will be used to find the melting points of the compounds. Some organic compounds melting points can range from three to five degree celsius change. While heating up chemicals ite very important to be wearing all lab safety equipment. Experimental log Experimental Log -

Observations

The chemical was heated to melting point All chemicals took over 5 degrees to melt

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1:1 Urea/ t-cinnamic acid took 5 degrees celsius to melt 1:9 Urea/ t-cinnamic acid took 24 degrees celsius to melt 9:1 Urea/ t-cinnamic acid took 8 degrees celsius to melt - physical change

Data

Solid

Starting melting temperature (oC

Final melting temperature (oC)

1:1 Urea/ t-cinnamic acid

95

100

3

1:9 Urea/ t-cinnamic acid

102

126

9:1 Urea/ t-cinnamic acid

112

130

Discussion questions 1.

 Definition of Melting Point

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“Temperature    at which the solid   and liquid   forms of a pure substance can exist in equilibrium (Encyclopedia Britannica).”

2. Description of the melting process (what happens when a compound melts?) and your observations -

A melting process is the melting or fusion of a compound's physical process that results in a phase transition from solid to liquid.

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When a compound melts it changes its state. By adding energy to molecules that begin to move quicker and that can break away from other molecules. This happens slowly and every molecule in the substance has to get energy to move quicker.

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- physical changes to compound start from solid to liquid

3.  Analysis of the melting ranges of the pure substances and the mixtures Starting melting temperature (o C

Final melting temperature (o C)

1:1 Urea/ t-cinnamic acid

95

100

1:9 Urea/ t-cinnamic acid

102

126

9:1 Urea/ t-cinnamic acid

112

130

- One way to test is a substance is pure is by determining the melting point of that compound. A pure substance has a melting range between three to five degrees. Impurities depress and then broaden the melting range. This means that the purified sample would have a higher and smaller melting range than the original; it would not be an exact, impure sample. All compounds were melted over more than 3-5 degrees so The greater variation in intermolecular forces causes the wider range of temperatures.

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4.  Discuss melting ranges of the 1:9 and 9:1 mixture of dimethylaminobenzaldehyde or acetamide and acetanilide ranges of pure substances and compare them with those reported in the literature (not  the hand-written value listed on the bottle’s label) -

The experimental melting range of trans-cinnamic acid (1.1) was  in the range of 133.0°C-133.4°C. The theoretical melting range was 134°C-136°C (Pubchem) The experimental melting range of urea (9.1) was determined 132.5°C–133°C and the theoretical melting range 133°C-134°C (Pubchem) The experimental melting range of trans-cinnamic acid (1.1) was  in the range of 133.0°C-133.4°C. The theoretical melting range was 134°C-136°C (chemical book, 2019)

5. Explain  what factors contribute to the melting ranges observed for the three mixtures of Aspirin/Benzoin or trans-Cinnamic Acid/Urea; does the melting range of the 1:1 mixture differ from the other mixtures? Account for factors that may influence the differences in melting ranges observed in the 1:1 mixture versus the 1:9 and 9:1 mixture. -The 9:1 urea to trans-cinnamic acid mixture had a melting range of 132.5°C–133° . The 1:1 urea to trans-cinnamic acid mixture had a melting range of 1 33.0°C-133.4°C. The 1:9 urea to trans-cinnamic acid mixture had a melting range of 1 33°C-134°C  Because of the impurities the melting range of these three mixtures is lower than the urea and transcinnamic acid. The 1:1 urea to trans-cinnamic acid mixture had the largest melting range, it was melting at the lowest temperature Because The mixture's high amount of impurity. The 9:1 and 1:9 urea to trans-cinnamic acid mixture had similar melting ranges, and began melting at a higher temperature. This can be explained because when a solid is impure its structure is disrupted, meaning a greater variation of intermolecular forces occurs in different areas of the solid. The more impure a solid is the more this occurs and there is less energy required. 6. Draw  conclusions regarding mixed melting point -The results of this experiment shows that as the amount of impurity increases the melting range this also increases the compound begins melting at a lower temperature. The melting points of the compounds were lower than the pure substances they were composed of. This is again due to the variation of intermolecular forces of different areas of the impure solid causing less energy to be required.

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References "Matter | Definition, Characteristics, States, Examples, & Facts". Encyclopedia Britannica , 2020, https://www.britannica.com/science/matter National Center for Biotechnology Information. "PubChem Compound Summary for CID 444539, Cinnamic acid" PubChem , https://pubchem.ncbi.nlm.nih.gov/compound/Cinnamic-acid. Accessed 1 September, 2020....