3210 Experiment 2 (Online) - Melting Point wqrg zdfh rtjh stjsfgj srytj sf PDF

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SUMMER 2021 CHEM 3210 Experiment 2: Melting Point (Online)

University of North Texas

Melting Point Technique: Determining the Unknown Compound Using Melting Point Data 6th Edition(pp) Reading from the manual 48-55 3.2 Melting Point (mp) of Pure Urea and Cinnamic Acid 3.3 MP of Mixtures of Urea–Cinnamic Acid 3.4 Identification of Unknown and Mixed Melting Point

7th Edition(pp) 48-55

Please read the notes before proceeding further. This is an “ONLINE LAB”. Please write the actual procedure for the lab report from the demonstration video, use the below information as a reference source only. Prelab is not required for online labs. Prepare a “FULL REPORT” (procedure, observations, and data) from the video demo. Write a scientific conclusion based on your observations from the video. The FINAL LAB REPORT IS DUE THE SAME WEEK EK”” . More details about the theory, technical information, and prelab/postlab questions can be found in the PowerPoint slides. Materials (Chemicals) List: Urea, trans-cinnamic acid, unknown (check the list below), capillary tubes, Mel-Temp apparatus. The reference table should contain molecular formula, melting point values and molar mass values for above chemicals. Experiment: Packing the solid in a melting point capillary t ube 1.

2. 3. 4. 5.

Take a small amount of urea and trans-cinnamic acid in two separately labeled watch glasses. Make sure that the samples are finely powdered (with the use of a metal spatula if required). Samples must be dry and finely powdered. Capillary tubes are thin-walled, fragile, sealed at one end: about 100 mm x 2 mm Gently tap in some of the solid into the open end of a thin-walled capillary tube, careful not to break the tube. Use a spatula if needed Invert the capillary tube (open end facing upward) and tap, repeat the process several times, until solid are tightly packed, drop the tube down a long glass tube. Repeat the procedure several times till solid is packed tightly at the closed end of the thin-walled capillary tube. (2-3 mm of solid should do it)

Determining the mp using MEL-TEMP apparatus

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SUMMER 2021 CHEM 3210 Experiment 2: Melting Point (Online)

University of North Texas

A. Known compounds 7. Load the thermometer and the melting point capillary tubes (loaded with samples) into the apparatus (MEL-TEMP). Turn on the apparatus. 8. Adjust the heating knob so that heating is rapid within 10 oC of known mp (heat setting differs, ask your TA). 9. Continue heating slowly, adjust the knob carefully so that the heating rate is slow during the melting of the solid, about 1-2 oC per minute. 10. Report the melting range (i.e. the temperature at which the solid just begins to melt and the temperature at which all the solid has melted) for both pure urea and pure trans-cinnamic acid. 11. Softening or shrinking of the sample is NOT to be considered melting- you must be able to see liquid! Record all observations: maybe decomposition, darkening, etc. 12. Cool the MEL-TEM to room temperature by blowing air before starting the new experiment. ▪ Repeat the experiment with urea and trans-cinnamic acid, record data in the data table. Two readings for known compounds. Record all observations: maybe decomposition, darkening, etc. B. Mixture of compounds Using the same technique/protocol described above determines the mixture of compounds. 14. Collect the mixtures of trans-cinnamic acid and urea (1:4; 1:1; 4:1) into the mp capillary tubes 15. Determine the melting points of prepared mixtures – record data in the table. Observe for lowering and broadening of the melting point range. ▪ the second reading for mixtures will be determined by the TA based on a time constrain ▪ Record all observations: maybe decomposition, darkening, etc. 13.

C. Unknown compounds Using the same technique/protocol described above, determine the mp of the given unknown Do the unknown twice: First reading: heat rapidly, determine approximate mp range Cooldown the apparatus to at least 10oC below the approximate mp Second reading: heat slowly (about 1oC per minute): use a new sample, in a new tube! Confirm the identity of the unknown by doing a mix melting point (unknown +identified) Make sure to identify the unknown and confirm the unknown before stepping out of the lab. The lab report is incomplete without unknown identification details. 16.

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SUMMER 2021 CHEM 3210 Experiment 2: Melting Point (Online)

University of North Texas

List of substances with mp values that will help to determine the unknown Compound

Melting Point (Literature)

Naphthalene

79-82 oC

Benzophenone

49-51 oC

Salicylic acid

158-160 oC

Benzoic acid

120-122 oC

Urea

133-135 oC

Trans-Cinnamic acid

133-135 oC

Acetanilide

113-115 oC

Sulfanilamide

165-166 oC

Phenylacetic acid

76-77 oC

Table for recording the data. Include all the data acquired in the lab or available from the demo video Sample

Theoretical melting range (if known) (°C)

1st reading (melting begins) (°C)

transcinnamic acid

urea 1:4 mixture 1:1 mixture 4:1 mixture Unknown sample

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1st reading (melting ends) (°C)

*2nd *2nd reading reading (melting ends) (melting (°C) begins) (°C)

SUMMER 2021 CHEM 3210 Experiment 2: Melting Point (Online)

University of North Texas

Unknown sample + Identified known (1:1) FINAL Report Should Include: Objective, Procedure, Observations (changes during the experiment from the video demo.), Data (melting point values from video demo), prelab/post lab questions, and conclusions. Reach out to your TA if you have any questions. CLEANING (in-person labs): Note: Students will lose 2 points for not cleaning their working areas after the experiment. Dispose of the extra solids carefully into solid waste. Dispose of the capillary tubes carefully into the broken glass or solid waste depending on instructions from your TA. Follow TA’s instructions carefully. HAZARDS/SAFETY (only for in-person labs): Start your experiments only after TA’s approval Strictly follow social distancing protocols, reach out to your TA if you are concerned about social distancing or other health concerns. Please avoid crowding at wash stations and waste disposal hood or other common areas. Do not touch any hot objects directly, let them cool to RT first. Work carefully with capillary tubes and the instrument. Ask your TA if you have any questions regarding the procedure before starting the experiment. Follow your TA instructions strictly for the handling of the apparatus/chemicals/ disposal of the chemicals Do not remove your safety goggles during any time in the lab Wash your hands thoroughly with soap before stepping out of the labs Do not taste or smell the samples The extra solids are disposed of in the solid waste container. As TA for HELP! Do not hesitate.

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