Chem Lab Exam 1 - Chromotography

Front 1

A technique that is used by chemists to separate components of a mixture originally by color.

Back 1

Chromotography

Front 2

T/F Chromotography is from the Greek word "chroma," for color, and "graphein," to write.

Back 2

T

Front 3

Although Chromotography is a technique used to separate components of a mixture originally by color, color is NOT a required property to achieve separation of compounds by this procedure. T/F?

Back 3

T

Front 4

The basis of chromatography is the _______ (defined as separation based on differences in affinity for two separate phases) of compounds between a _____ phase and a _____ phase.

Back 4

partitioning; stationary phase, mobile phase

Front 5

What are the stationary phases used in this experiment?

Back 5

The cellulose chromatography sheet and TLC chromatography sheet

Front 6

In paper chromatography, which stationary phase is used?

Back 6

Cellulose chromatography sheet

Front 7

During the experiment, the solvent is only allowed contact with the spot by migrating up the sheet through the spot by _______

Back 7

Capillary action

Front 8

The ratio of the distance traveled by a compound to the distance traveled by the solvent is defined as?

Back 8

Rf value

Front 9

When calculating Rf value, in both the numerator and the denominator, the distance traveled is measured from?

Back 9

The center of each spot

Front 10

Does chromatography provide reliable quantitive values of the relative amounts of each of the constituents? Why/why not?

Back 10

No; the relative intensities of color as well as the relative sizes of the various solitude bands in a chromatogram may only be used as a visual estimate of the relative amounts of each of the constituents. Sophisticated instruments are required to determine reliable quantitative values.

Front 11

Explain the procedure for the thin layer chromatography experiment.

Back 11

First, we make our developing chamber for the TLC sheet. In a beaker, place filter paper at the bottom to act as a wick, and pour no more than 25 mL of the developing solvent (5:3:2 ethyl acetate:ethanol: water). Then, we take our TLC chromatography sheet and gently draw a line approximately 2 cm from the bottom and evenly spaced X marks on this line where we will place a dot for each of the different types of permanent markers, leaving the last X mark for an unknown marker that will be determined at the end of the experiment. Then, lean the TLC plate up against the side of the beaker opposite to the filter paper, with the sample side of the sheet facing the solvent. Cover the chamber with foil and watch until the solvent front is no less than 1 cm from the top of the sheet. When you take the sheet out, immediately make a trace of the exact line across the top of the sheet at the solvent had reached at the precise time you removed it.

Front 12

Explain the procedure for separation of cations by paper chromatography.

Back 12

In this experiment, paper chromatography Will be used to separating a mixture of cations Cu^2+, Ni^2+, and Fe^3+. First, fill a 1000 mL beaker with no more than 25 mL of developing solvent (1:9 hCl: acetone). Prepare a wick with filter paper and place it in the chamber, covering it with aluminum foil while we prepare the chromatographic paper. Draw a line across the bottom of the chromatography graphic sheet about 2 cm from the bottom of the paper, evenly spacing 5 X marks on the line. On the two outside X's, spot you're given an unknown mixture of copper, nickel, and iron twice. On the 3 inside X marks, spot your known solutions of iron chloride, nickel chloride, and copper sulfate once. Staple the paper into a circle and place in the chamber, recovering with an aluminum foil. Let develop for 15 to 30 minutes or until the solvent is no less than 1 cm from the top of the sheet. Then remove from the chamber and using a pencil immediately make a tracing of the exact line across the top of the sheet that the solvent has reached, and quickly outline the yellow iron spots with a pencil before they fade. Allow all of the solvent to evaporate from the sheet call mom and use a hair dryer to thoroughly dry the paper to ensure that all of the residual HCl is removed. To see the spots of nickel ion, spread sheet evenly with the dimethylglyoxime solution and circle them. To make the copper and nickel ions visible, place the sheet over a beaker that contains a few milliliters of concentrated ammonia (NH3). Once the copper can be seen it should be circled lightly with a pencil. Identify your unknown cat ions based on a comparison of spot colors and calculate Rf values.

Front 13

What was the mobile phase used for the TLC chromatography experiment?

Back 13

The developing solvent containing a 5:3:2: ratio of ethyl acetate: ethanol: water

Front 14

What was the mobile phase used for the paper chromatography experiment?

Back 14

The developing solvent containing a 1:9 ratio of hCl: acetone.

Front 15

T/F: chromatography is a technique that is used to combine components into a mixture.

Back 15

False

Front 16

True/false: Color is not required to perform chromatography correctly

Back 16

True

Front 17

True/false: alumina, silica, and paper are all examples of stationary phases

Back 17

True

Front 18

True/false: in this experiment, we will perform thin layer chromatography

Back 18

True

Front 19

True/false: Rf values have units of g/J.

Back 19

False

Front 20

True/false: the Rf value is measured from the starting line to the beginning of the spots

Back 20

False

Front 21

True/false: is the stationary phase and the mobile phase stay the same, then the Rf values of the constituents will remain the same between trails

Back 21

True

Front 22

What does TOC stand for?

Back 22

thin layer chromatography

Front 23

Why do certain components move further on the stationary phase than others?

Back 23

Since different solutes have different affinities for the stationary phase and also different affinities for the mobile phase, a separation of components occurs. This happens because the speed of flow of one solute is retarded by these affinities more than that of another solute as a solvent passes through the stationary phase.

Front 24

Why was it important to have a wick and to keep the beaker covered with foil why the samples were developing

Back 24

The wick serves as an aid to saturate the chamber with solvent vapors, and the foil is necessary to keep those vapors inside the chamber.