Organic Chemistry- Lab

True or False:

Nonpolar molecules dissolve polar molecules

False

The substance being dissolved

Solute

The substance that is doing the dissolving

Solvent

Forces within a molecule

Intramolecular forces

Forces between molecules

Intermolecular forces

Intramolecular forces influence ________ properties

Chemical

Intermolecular forces influence ________ properties

Physical

Identify the intermolecular force:

• result from temporary dipoles

• present in all molecules

• induces a temporary dipole in surrounding molecules

• the only intermolecular force present in alkanes

Dispersion forces

Identify the intermolecular force:

• present in all polar molecules

Dipole-Dipole

Identify the intermolecular force:

• Only capable with O, N, and F bonded to H

Hydrogen bonding

Identify the intermolecular force:

• strongest intermolecular attraction

• ions from an ionic compound are attracted to the dipole of polar solvent molecules

Ion-Dipole

Almost all organic compounds in their ionic form are _______ in water and _________ in organic solvents

Soluble; insoluble

Rank the following in order of increasing strength:

1. Dipole-Dipole

2. Ion-Dipole

3. Dispersion forces

4. Hydrogen bonding

3,1,4,2

Hydrophillic

Polar

Hydrophobic

Nonpolar

C-C bonds are:

Nonpolar

C-H bonds are:

Nonpolar

What ratio of carbon-oxygen+nitrogen is required to be considered soluble in water?

3.5:1

Do acid and acid (or base and base) reactions take place? Why or why not?

No, because there is no proton donor/acceptor present.

True or False:

Solubility limits do not vary in temperature

False

A solution that has the maximum amount of solute that a solvent can dissolve; if you add more solute, it will not dissolve

Saturated solution

A solution that has more solvent than saturation; more solute will dissolve if added

Unsaturated solution

Slow and selective crystal growth

Crystallization

Rapid and nonselective crystal growth; impurities are trapped in the lattice

Precipitation

A good solvent is ________ soluble at room temperature and ____ soluble at elevated temperatures

Slightly; very

Describe how to make the first melting point determination

Start 30 C below literature value and increase at a rate of 10 C/min

Describe how to make the second (official) melting point determination

Start 5 C below the first m.p. determination and increase at a rate of 2 C/min

True or False:

Melting point is always recorded in a range

True

List the two qualifications that must be met in order for a sample to be considered pure

The m.p. must be within 5 C of literature value; the m.p. must have a range of or below 2 C

Impurities cause a ________ and a ____ range in the m.p.

Decrease; wide

% recovery=

(g of substance isolated/g of original material) X 100

Why should the crystal solution be cooled slowly after the hot solvent is added?

The crystals should be cooled slowly so that a precipitate does not form instead of crystals.

Why is the crystal solution chilled?

Chilling the solution brings more solvent out of solution

If a higher temperature increases a substance’s solubility in a solvent, then a lower temperature _________ that substance’s solubility in the solvent

Decreases

Why are the crystals washed with cold solvent prior to filtration?

This rinses off any remaining impurities

List two sources of loss in a solubility lab

If a sample is soluble in a solvent at room temperature, some amount will always remain in solution, resulting in less crystals forming. Adding too much hot solvent = more “room” for solute to dissolve = less crystals come out of solution

List the two factors that make a solvent good for an extraction

1. Dissolves the compound that will be extracted (the organic salt)

2. Should be immiscible with the original solution so that two distinct layers can form

What is the equation for the distribution coefficient?

K=C2/C1

C1=

The concentration at equilibrium of the solute in solvent 1

Is one 1.5 mL extraction with solvent more efficient than 3 .50 mL extractions with solvent?

No

An extraction that uses immiscible solvents where one solvent makes up the aqueous layer and the other makes up the organic layer

Liquid-liquid extraction

A technique used to separate components of a mixture

Chromatography

TLC consists of two phases, name them

Mobile phase and stationary phase

The mobile phase of TLC is

Liquid

The stationary phase of TLC is

Solid

How does chromatography separate components of a mixture?

Polarity

True or False:

Molecules are constantly adsorbing from solvent and desorbing back into it

True

Equilibrium depends on the molecule’s ________ for the solvent and solid

Affinity

What is the polarity of the solid stationary phase in TLC? What gives it it’s polarity?

Polar; it can hydrogen bond

Nonpolar molecules spend ____ time adsorbed to the polar solid phase and ____ time in the mobile phase

Less; more

True or False:

Less polar molecules travel up the plate slower than more polar molecules, regardless of the solvent used

False

How many spots does a pure sample give?

One

How is the retention factor calculated?

Distance travelled by the spot/distance travelled by the solvent front

What does a larger Rf value indicate?

The spot travelled farther than a spot with a smaller Rf value

A good TLC solvent is

Not too polar or nonpolar

What are three factors that influence the Rf value of a spot?

1. The polarity of the TLC plate

2. The polarity of the solvent

3. The polarity of the compound

Thin-layer chromatography is ___ dimensional and column chromatography is _____ dimensional

Two; three

In thin-layer chromatography, the mobile phase travels __ due to _________ ______

Up; capillary action

In column chromatography, the mobile phase travels ____ due to _______

Down; gravity

True or False:

Thin-layer chromatography is used for samples of larger quantities and column chromatography is used for samples of smaller quantities

False

Are the samples used in thin-layer chromatography recovered?

No

Are the samples used in column chromatography recovered?

Yes

List two reasons why the horizontal bands in column chromatography may be distorted

Nonlevel surface when packing the solvent; irregular surface

What is the proper diameter to height ratio for a column?

8:1

How much alumina should be added to a column?

20-30 times the weight of the sample

Why is the solvent often changed halfway through column chromatography?

The solvent is often changed halfway through the run in order to remove the more polar compound from the stationary alumina