CHEM 233 Lecture Notes - Lecture 9: Horse Length, Cengage Learning, Benzene

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7 Aug 2016

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Document Summary

Identification of unknown organic compounds by melting point, boiling point and. The purpose of this lab is to determine the unknown solid and liquid samples through different techniques. From the elemental analysis, the molecular and empirical formulas are derived for the unknowns. Infrared (ir) spectroscopy doesn"t provide with chemical composition or quantitative data rather it provides the peaks at certain wavenumber indicating the carbon to carbon double/triple bonds, aromatic rings, carbonyl groups, or hydroxyl groups. Ir uses the wavenumber in cm-1 which provides direct relationship between energy and wavenumber and also proves the hooke"s law. Ir measures the light transmitted by the sample than absorption. The lower % transmittance, the greater is the absorption of light. The device used in this experiment is attenuated total. Reflectance (atr) ft-ir accessory that creates graphs with peaks indicating specific functional groups in unknown. Melting and boiling points techniques are used to figure out the physical properties of the samples.

Related Questions

Identification of an unknown compound

Needed:

Draw the actual structure of the unknown

Explain why this conclusion was reached

Explain how the functional groups were determined based IR

How did you get the exact structure from using NMR

Identify how chemical shifts and peaks areas match hydrogens in the proposed structure

Comment on splitting patterns if they are discernible

Determine the identity of the unknown, explaining why the structure is consistent with NMR and IR

Include melting/boiling points, compare with the literature value of your unknown

Include the reflective index

Include the spectra, including comments

Please give me Post lab questions 2 and 3 at the bottom.

Experiment 7 - Molar Mass of a Volatile Liquid

Introduction. Given the mass of vapor at conditions of known pressure, volume, and temperature, one can determine the molar mass of the vapor. The Ideal Gas Law mathematically relates the quantities of pressure (P in atm), volume (V in liters), and temperature (T in Kelvin) and the quantity of gas (n in moles). Using the expression PV=nRT where R equals the Ideal Gas Constant 0.0821 L*atm/K*mol, one can determine the quantity of gas under given conditions of pressure, volume and temperature. The number of moles of gas is found by

n =

Because the molar mass (MM) is defined as the mass of one mole of substance in units of g/mol, the molar mass of the vapor can be determined by

MM= mass of vapor in grams/moles of vapor

In this experiment, an unknown volatile liquid is heated in a boiling water bath and is vaporized. The vapor forces air from the flask until the pressure within the flask equals the barometric pressure of the lab. As with all gases, the vapor occupies the entire volume of its container. The temperature of the vapor equals the temperature of the boiling water bath. After 8-10 minutes, the vapor is cooled. The mass of the condensed liquid is determined and the molar mass is calculated as described above.

Notes:

Check out unknown from stockroom

Record unknown number

Before weighing your condensed vapor, thoroughly dry the outside of the flask and make sure that no water is trapped under the foil cover

Do not rinse your flask with water between trials

Dispose of waste in appropriate container

Procedure. You will record your data and calculations in your lab notebook.

Obtain an unknown liquid and a 3 inch aluminum foil square. You will need two 600 or 800 mL beakers, and 3 or 4 boiling chips.

Add 3 or 4 boiling chips to the water in an 800 mL beaker and heat the water to the boiling point. Continue heating for 8 to 10 minutes after the water comes to a rolling boil. The temperature of the boiling water is 100.0^oC. This will be the temperature of the vapor. Convert the temperature to Kelvin and record in your lab notebook.

800 mL Beaker

250 mL Flask

11.

Chemical Molar Mass

1-chlorobutane 92.6 g/mol

t-butyl chloride 92.5 g/mol

trichloroethylene 131 g/mol

2-propanol 60.1 g/mol

Ethyl acetate 88.1 g/mol

n-hexane 86.2 g/mol

cyclohexane 84.2 g/mol

2-butanone 72.1 g/mol

Post Lab Questions: Answer the following questions using complete sentences. Include them after your conclusion.

1. If a lab group did not keep the flask submerged in boiling water for a full ten minutes, and some unknown never vaporized, how would that affect the calculated molar mass? In other words, would it make the calculated value too high or too low? Explain why.

2. While performing this experiment, ten lab groups have ten different unknown volatile liquids with a range of molar masses. If all lab groups have exactly the same size of flask (255 mL), and all groups took their unknown vapor to the same temperature (100.0^oC) and pressure (760.0 mmHg), how would the number of molecules within the different flasks compare? Would it vary with molar mass? How? Explain.

3. A student has determined that an unknown liquid is either 1-chlorobutane or t-butyl chloride. What other physical property(s) could be used to determine the identity of the unknown?

Please help me solve for the molar mass of sample 1 and 2 and the molecular formula