Lab techniques

extraction components

Separation funnel Stop clock flask

TLC shows a mixture after

Distillation

Distillation

Distillation is a technique used to separate liquid molecules based on their boiling points, and there are three common types: simple, fractional, and vacuum. In each, a liquid mixture is heated, and the molecule with the lowest boiling point distills first. The mixture must be heated slowly so that the molecule with the lowest boiling point can evaporate before the molecules with the higher boiling points.

Which of the following characterize gas-liquid chromatography? Gas mobile phase Liquid stationary phase Separation based on polarity Room-temperature column conditions A.I only B.I and II only C.I and III only D.I, II, and IV only

Gas-liquid chromatography is a technique used to separate molecules in a mixture based on their boiling points. The mobile phase is an inert gas such as helium or nitrogen (Number I), and the stationary phase is a liquid that coats a solid support on the inside of the column (Number II).

The (R)-enantiomer of the antiasthma drug albuterol is the active isomer. If a researcher wants to separate a racemic mixture of albuterol, which of the following methods will most likely separate the enantiomers?

A 50:50 mixture of enantiomers is known as a racemic mixture. Enantiomers have many of the same chemical and physical properties, including melting and boiling points, solubility, and polarity, although they differ in the way that they interact with plane-polarized (linear) light. Therefore, separation of enantiomers relies on changing the physical properties of the molecules The separation of enantiomers, such as those in the racemic mixture of albuterol, requires the addition of a resolving agent (a chiral molecule). When a resolving agent is added to a racemic mixture, it reacts with each enantiomer, forming a covalent bond or an ionic salt. Because the resolving agent is chiral, it incorporates a new chiral center into each enantiomer, creating a pair of diastereomers. Diastereomers can be separated from each other because, unlike enantiomers, they have different physical properties.

Researchers separate a mixture by both simple distillation and vacuum distillation. Which expression accurately describes the relationship of the mixture components' boiling points (bp) in each distillation? A. Simple distillation bp = vacuum distillation bp B. Simple distillation bp < vacuum distillation bp C. Simple distillation bp > vacuum distillation bp D. Simple distillation bp = 2(vacuum distillation bp

Because vacuum distillations are performed under reduced pressure, the boiling point of a compound under vacuum will decrease relative to its boiling point at atmospheric pressure. Therefore, the simple distillation boiling point of a molecule is greater than the boiling point of that molecule under vacuum (ie, simple distillation bp > vacuum distillation bp).

Vacuum distillation

Liquids that boil above 150C separates different components of a liquid in pressures under 1 atm

Simple distillation

Liquids that boil below 150 C and have at least 25C difference in boiling temperature.

Fractional distillation

Liquids that boil below 150 C and have more than 25C difference in boiling temperature.

Which of the following statements correctly describes the peaks displayed in a mass spectrum? A.The tallest peak is the molecular ion. B.The peaks are uncharged molecules. C.The height of each peak is dependent on molecular weight. D.The peaks represent ionized fragments of the sample

Mass spectrometry is a technique that measures the molecular weight of a molecule. Molecules in a sample are injected into a mass spectrometer, where they are bombarded with a beam. This beam removes electrons from the molecule and forms a positively charged ion known as the molecular ion The molecular ion can also fragment during bombardment to form smaller ions. the peaks observed in the mass spectrum represent ionized fragments of the sample.

How do separate the organic phase from the aqueous phase in extractions?

Open the stop clock, the aqueous phase will pour into the flask and the organic phase will be left in the separation funnel

What are the two layers present in extractions

Organic phase (less dense)------ on top of Aqueous phase (more dense)----- water and ions

True or False Because vacuum distillations are performed under reduced pressure, the boiling point of a compound under vacuum will decrease relative to its boiling point at atmospheric pressure.

True

True or False Simple and vacuum distillations are set up in the same way, except that simple distillations are done at atmospheric pressure, whereas vacuum distillations are connected to a vacuum pump and performed at reduced pressure.

True

Gas-liquid chromatography (GLC)

a technique used to separate molecules in a mixture on the basis of boiling point. Relative boiling points of molecules can be determined based on intermolecular forces, molecular weight (MW), and branching. Volatile molecules (low boiling points) spend more time in the gas phase rather than interacting with the liquid stationary phase of a GC column and travel quickly to the detector. Molecules with higher boiling points, however, condense and spend more time interacting with the liquid stationary phase and slowly make their way through the column as the temperature increases.

In general, the perceived color of a substance is?

complementary to the color of the wavelength that is maximally absorbed by that substance a color's complement is the color directly across from it on the wheel.

Thin Layer Chromatography (TLC)

is a technique used to separate compounds based on polarity. In normal-phase thin-layer chromatography, the stationary phase is made up of a polar, adsorbent material, typically silica and the mobile phase is a nonpolar solvent The rate at which a compound travels up the plate is a function of the relative polarities of the compound and the solvent. If a mixture remains near the plate's origin, a more polar solvent is needed to increase the compound's affinity for the mobile phase relative to its affinity for the stationary phase. Conversely, if a mixture travels with the solvent front, a more nonpolar solvent is needed to decrease the compounds' affinity for the mobile phase relative to its affinity for the stationary phase.

mass spectrometry

technique based of the detection of vaporized molecules and their ionized (charged) fragments; detection and display of the spectra are based on the mass-to-charge ratio (m/z) of the ions

If thin-layer chromatography shows that the distillate is not pure, then what most likely happened?

the distillation was not successful at separating the compounds in a mixture. Because a mixture should be heated at a slow rate for separation, a possible error in the distillation is heating the mixture too quickly, causing the molecules to evaporate together.

The color of a substance is determined by

the wavelength of light it absorbs, which is, in turn, determined by the electronic structure of the molecule of interest