Pre Lab 2- Simple & Fractional Distillation; GC Analysis PDF

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2 NAME: Rachel Totos

COURSE-SECTION: CHEM 233- MW12pm

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Pre-Lab & Reaction Table

3 pts: The pre-lab is well written, organized, and neat. It contains all required elements: title, introduction, equations/reactions, calculations and pre-lab questions. Every element is thorough and correct.

2 pts: All elements are present, but there are minor errors, misinformation, or slight omissions in one or two of these elements. Some mistakes are present in calculation of rxn table.

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2 pts: The procedure is thorough and contains details that are specific to the experiment. Procedure is original and authentic, and a diagram of the setup is included.

1 pt: Generally, the procedure is well written and thorough, but may be missing some key steps that should have been performed in the laboratory.

Pre-Lab Questions

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Pre-Lab Report 2 Simple & Fractional Distillation with Gas Chromatography Analysis Rachel Totos TA: Xuan Duong 20 June 2021

Simple & Fractional Distillation with Gas Chromatography Analysis Introduction Simple distillation is the process of separation of a volatile mixture in which the difference in temperature of each pure substance is more than 50°C. Fractional distillation is carried out in similar steps that are taken during simple distillation process; however, it is ideally used for separating two volatile components with similar boiling points and a Hempel Column is used in the apparatus to create a temperature gradient. The purpose of the temperature gradient is so that the fractional distillation process can carry out separation at a lower boiling point. The purpose of the experiments was to successfully separate a 1:1 v/v mixture of acetone and 2-propanol into three fractions based on temperature by simple and fractional distillation, and utilize gas-liquid chromatography (GLC) analysis to determine the success of the separation. After completing the gas chromatography analysis for each three fractions, record the area, mole percent and retention time for acetone and 2-propanol. More volatile solutes will have a lower boiling point, higher equilibrium vapor pressure, larger amount of solute in mobile phase, a smaller partition coefficient and a shorter retention time. The main difference in boiling points is due to alcohol group on the 2-propanol and the ketone on the acetone. Equations Boiling point (mixture):

Ptot =Patm

Dalton’s Law:

Ptot =P A + P B + PC …

Raoult’s Law:

Px =N x∗P °

Mole fraction:

N x=

nx ( n x +n y ) [ solute ∈stationary phase ] [ A ] s = [ A]m [ solute∈mobile phase ]

Partition coefficient:

K c=

Ideal % composition:

total ¿ mol of component mol∈a mixture ¿ x 100 % mol %= ¿

Procedure Before beginning any experiment, safety comes first, so it is important to wear proper lab attire, goggles and gloves. For the simple distillation experiment, a round bottom flask, or “stillpot”, is clamped to a ring stand where 30mL of the 1:1 acetone/2-propanol mixture is added using a graduated cylinder. The stillhead along with a West Condenser attached to the arm of the stillhead followed by a vacuum adapter, is placed on top of the stillpot and held together using Keck clips to prevent separation and vapors from escaping. Then, the thermometer adapter is placed on top of the stillhead with the thermometer placed so that the bulb reaches the entrance of the condenser. The water source is attached to the bottom of the condenser using one hose, and a secondary hose is placed at the top opening of the condenser and is emptied into the drain in order to maximize surface area for condensation. Next, the water is turned on slowly to create a small stream to prevent splashing and graduated cylinder is placed under the vacuum adapter to collect the distillate. The temperature is recorded at every 1mL added. A total of three graduated cylinders are obtained to represent a total of three fractions. The first fraction is collected when there is a steady temperature, the second fraction is collected once there is a dramatic change in temperature and the third fraction is collected the temperature levels off again and remains

steady. Each fraction is then analyzed using the GLC instrument, followed by recording of observations and calculations. Fractional distillation is carried out in the same process with slight changes in the setup of the apparatus. Instead of the stillhead being connected to the stillpot—a Hempel Column with coil copper wire at the bottom and filled with Raschig rings, is attached to the stillpot with the same stillhead + thermometer adapter + West Condenser apparatus on top. Two pipette bulbs are also attached to the Hempel Column to help maintain the temperature gradient. The rest of the fractional distillation procedure are the same steps carried out in the simple distillation experiment. Pre-Lab Questions 1. Under what conditions can a good separation be achieved with a simple distillation? In an ideal case of simple distillation, only one of the components in the mixture will be volatile, therefore the distillate will be a pure compound. More commonly, there are several volatile components present in a mixture with a difference in boiling point greater than 40°C-50°C. 2. How does the composition of the liquid at the top of a fractional distillation column compare with the composition of the liquid at the bottom of a column? Answer in terms of the relative amounts of lower-boiling and higher-boiling components. The liquid at the top of the fractional distillation column has a low boiling point component than the liquid at the bottom of the column. 3. Using the figure below, calculate the mole % composition of the vapor from a solution containing 6 moles of toluene and 14 moles of benzene? Show all your work! mol% composition= (#moles of component / total #moles in mixture) x 100% 6 =0.3 x 100 %=30 % Toluene mol% composition = 6 +14 14 =0. 7 x 100 %=7 0 % Benzene mol% composition = 6 +14 Composition Diagram For a Binary Mixture of Benzene and Toluene

383.3 Temperature (K)

378.3 373.3 368.3 363.3 358.3 353.3 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

mol Fraction of Benzene 4. At 25°C, the vapor pressure of toluene is 36.7 torr and the vapor pressure of benzene is 118.2 torr. A solution contains a molar ratio of 4:1 toluene to benzene. What is the vapor pressure of the solution? Given: P°(toluene)= 36.7 torr mole of toluene= 4mol P°(benzene)= 118.2 torr

mole of benzene= 1mol

Ptotal= Pt + Pb Psolution= Pt + Pb Nx= # mol / total # mol of mixture Px= (P°t * Nxt) + (P°b * Nxb)

(

)(

P x = 36.7 torr∗4 + 118.2 torr∗1 5 5 P x = ( 29.36 torr) +( 23.64 torr )

)

Px= 53 torr *the vapor pressure of the solution is 53 torr.

5. Using letters A-E, arrange the following compounds in order of decreasing boiling point. Which compound has the highest vapor pressure and which the lowest? Explain your answer!

A

B

C

D

E

Boiling point rank: A > B > E > D > C Many factors can affect boiling point, such as dipole moment, intermolecular forces, branching and molecular weight. As dipole moment increases, intermolecular forces increase and boiling point increases. Branching decreases the boiling point. An increase in molecular weight or increasing number of carbons increases the boiling point. Vapor pressure is the inverse of boiling point. So, if a compound has the highest boiling point, it has the lowest vapor pressure, and those with the lowest boiling point have the highest vapor pressure.  Compound A: straight chain (no branching) and contains an alcohol group, hydrogen bonding. * alcohols have a higher boiling point than ethers and alkanes. This compound has the lowest vapor pressure.  Compound B & E: compound B is an alkane with minor branching in which has a slightly higher boiling point than compound E where more branching takes place. The boiling point of alkanes are higher than the boiling point of ethers.  Compound D & C: both ethers are very similar; however, compound D has 7 carbons (higher molecular weight) compared to compound C with 6 carbons. Recall that the increase number of carbons increases boiling point. In this case, compound C has the highest vapor pressure....