CHEM 212 Lecture Notes - Fractional Distillation, Distillation, Methanol

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21 Nov 2012

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Distillation and vapour phase chromatography are different methods of separating two or more liquids. During distillation, the liquid is vaporized, condensed then collected in a different container. It is ideal to use distillation when the boiling point between the compounds differ by. Preparative gas chromatography or high pressure liquid chromatography may be more successful if the boiling point difference is less than 30 c. 1. Volume distilled (ml) temp. ( c) volume distilled (ml) temp. ( c) *for fractional distillation, measurements stopped at 8. 5ml because the temperature was remaining constant. The volume composition of the mixture from the graph is 19. 2% methanol, and 80. 8% butanol. The molar composition of the mixture from the graph is 35. 0% methanol, and 65. 0% butanol. From the graph there is 2. 5ml of methanol, therefore there are 10. 5ml of butanol (13-2. 5=10. 5). % volume of butanol= (100%) = 80. 8% nmethanol= nbutanol= mole % methanol= (100%) = (100%) = 35. 0% mole % butanol= (100%) = (100%) = 65. 0%

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WORD BANK:

Atomic solids

Body-centered cubic

Boiling point

Condensation

Covalent atomic solids

Crystal lattice

Crystalline solids

Distillate

Distillation

Dynamic equilibrium

Evaporation

Face-centered cubic

Freezing

Freezing point

Ionic solids

Intramolecular

Interionic forces

Intermolecular forces

Liquid State

Macromolecule

Melting

Melting point

Metallic atomic solids

Molar heat of fusion

Molar heat of vaporization

Molecular solids

Non-bonding atomic solids

Non-crystalline (amorphous) solids

Properties of Liquids

Properties of Solids

Simple cubic

Solid State

Sublimation

Surface tension

Surfactants

Vapor pressure

Vaporization

Viscosity

Wetting action

Use the Vocabulary words above to complete the following sentences words can be used more than once, some words are not be used.

d. The molecules of a ________ are in constant motion. e. The __________ of a liquid is related to the shape of the molecules that make up the liquid. f. The force of attraction that causes the surface of a liquid to contract and form a âbeadâ or spherical drop is called? _________ _______ g. Chemical that reduce surface tension are called? __________ h. A liquids ability to spread out evenly over a surface as a thin film is called itâs? _________ _______ i. ____________ is the process by which molecules of a liquid break away and go into the gas phase. j. When the molecules of a volatile liquid jump to gas phase it is called _________. k. The reverse of evaporation (the conversion of a vapor to a liquid) is called? _________ l. When the rate at which the water is evaporating is equal to the rate at which the water vapor is condensing, you have established a __________ _________. m. ________ _______ is the partial pressure of a gas in dynamic equilibrium with its liquid. n. ________ _______ is when the vapor pressure equals the atmospheric pressure. o. Boiling point can be used to purify a solution of two or more substances by ________. p. The condensed vapor sample is called the? ________ q. The exact quantity of heat required to vaporize 1 mole of a liquid at constant pressure and temperature is called the ________ ________ ___ __________. r. In ________________ __________ the particles do not have a definite or regular order (there is no repeating pattern throughout the solid). s. In ____________ __________, the particles are arranged in regular, systematic patterns called a ________ _________. t. The three different types of crystal lattices based on the cube are? ________ ______, _____________ ______, and ___________, ________. u. The three types of atomic solids include _________ _____, ___________ ______, and __________ ________.

Please help me with the following problem. It has many parts to it, but it is one question. Thank you in advance

Synthesis of 1-Bromobutane

Reaction Scheme

NaBr, H2SO4

CH3CH2CH2CH2OH---------------------> CH3CH2CH2CH2Br + NaHSO4 + H2O

H2O

Possible by-products:

1-butene (bp â6.3 ^oC), di-n-butyl ether, C₄H₉OC₄H₉, (bp 141 ^oC)

Properties of reagents and product:

Substance	Mol Wt. (g/mol)	Density (g/ml)	bp, ^oC	Solubility	Hazards
1-butanol	74.12	.81	117-118	Sol water, Miscible alc, ether, and more	Flammable, irritant
H₂SO₄ (con)	98.07	1.84	280	X	corrosive material
sodium bromide	102.89	X	X	X	X
1-bromobutane	137.03	1.27	101.6	Insol in water; sol in alcohol, ether	Flammable, irritant

Quantities used in the reaction and yield data:

Substance	g or mL	Calculated moles	Theoretical Yield moles grams		Actual Yield, grams
1-butanol	mLs		x	x	x
H₂SO₄ (con)	11.5 mL		x	x	x
sodium bromide	13.3 g		x	x	x
Water	15.0 mL	x	x	x	x
1-bromobutane	x	x			Want 7.5 g

A. Assume the above synthesis of 1-bromobutane is known to proceed in 75% yield and you would like to prepare 7.5 g of material. Back calculate how many mLs of 1-butanol you will need for the reaction to synthesize the 7.5 g of product, assuming that the 1-butanol is the limiting reagent. Place this number in the table. Also, calculate all the remaining missing data to fill the table.

Experimental Procedure: The NaBr, 1-butanol, and water are combined in a round-bottomed flask containing a stir bar and cooled to 0 ^oC. Concentrated sulfuric acid is slowly added with stirring. The reaction flask is then prepared for a 50-minute âbriskâ reflux using a heating mantle. After reflux, two layers will be present. The condenser is removed and replaced with a distillation apparatus. Distill the mixture, recording the temperature range, until no more water- insoluble droplets are collected and the temperatures reaches around 115 ^oC. (The boiling point is elevated due to azeotropic distillation of the water with the 1-bromobutane and increasing amounts of sulfuric acid).

B. Propose a way that you could test if the droplets coming over are âwater-insolubleâ.

Be specific with the manipulations, glassware, and what observation you would see.

The collected liquid is transferred to a separatory funnel and 10 mL of water is added. Two layers form, the bottom being the 1-bromobutane layer. The layers are separated, one through the bottom and one through the top, and the separatory funnel is cleaned and dried. The bromobutane layer is returned to the separatory funnel and washed with ice-cold sulfuric acid to remove traces of the starting material, butene and ethereal by-products.

C. Will the top or bottom layer be the bromobutane layer when washing with concentrated sulfuric acid? Why?

The sulfuric acid layer is removed and the 1-bromobutane is washed with 10 mL 3 M NaOH followed by 10 mL aqueous sodium chloride (brine).

D. What is the purpose of each of these washes?

NaOH â

Brine -

Care should be taken to save the correct layer. The 1-bromobutane is then dried over anhydrous CaCl₂.

E. How will you decide how much drying agent to use? How will you know that the 1-bromobutane is dry.

The product is distilled to obtain a clear, colorless liquid.

F. TLC â Suppose you wanted to follow the above reaction by TLC.

a. Describe how you would go about finding a good solvent or solvent pair to use.

b. Suggest a specific solvent system you would try.

c. Draw below what you would want the TLC plate to look like and show the expected relative R_f values for the 1-butanol and 1-bromobutane. Label the spots, baseline, and solvent front.

CHEM 212 Lecture Notes - Fractional Distillation, Distillation, Methanol

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