Chromatography lab

What are the two main components of chromatography?

Adsorbent & eluent

Where do you put the eluent and carry out the separation?

Erlenmeyer flask

If the mobile phase did not work as expected what mobile phase would you choose instead?

The mobile phase that we choose must be more polar so that its intermolecular attractions to the sample are stronger and the sample is less attracted to the paper meaning it will travel farther and separate more.

What is the rate of flow and what else is it called?

The rate of flow is the distance a sample moves along a paper in comparison to the overall distance the solvent travels; also called the Rf value.

What do all approved food dyes share in common?

They are charged, water-soluble organic compounds that bind to natural ionic and polar sites in large food molecules.

How is the rate of flow calculated?

Distance sample travels/ overall distance solvent travels

What is capillary action?

The ability of a liquid to flow against gravity up a narrow tube or porous material.

What is chromatography used for?

To separate organic compounds for identification or purification.

Predict the relative color intensity that would be produced by methyl orange on cotton, nylon, and wood.

(Least polar sites) nylon<cotton<wood (cis- most polar)

Why were almost all of the original food color additives phased out?

Most were not safe for consumption and were being added to foods with no health testing.

What is another name for the adsorbent?

Stationary phase (chromatography paper)

Of the original 695 color additives how many are still used today?

2

What is another name for the solvent or eluent?

Mobile phase

What factors determine whether the separation by an eluent will be successful?

The affinity of a substance for the eluent versus the adsorbent allows molecules to be separated by chromatography. (Depends on polarity)

What are the experiments safety hazards?

- Isopropyl alcohol: moderate fire risk/slightly toxic - FD&C dye: slightly hazardous/irritant

Argue scientifically which dyes were present in the unknown mixture.

- The blue dye was blue No. 1 because the blue traveled the furthest meaning it was the most attracted to the eluent and therefore the most polar. Between the two blue dyes, No. 1 one is polar while No. 2 is trans meaning it is much less polar, if at all. - The red dye was red No. 3 because the red barely travels at all meaning of polarity is very low (reflected in its low RF value) and Red No. 40 is very polar so it can't be right. - The yellow dye is No. 5 because although it traveled less than blue, it had to be somewhat polar to make it halfway and No.6 is less polar than No.5

How many color additives total are used today?

7

What is the difference between absorption and adsorption

Absorption is a physical and chemical event occurring during contact between materials that have an attraction for each other. Adsorption is different from absorption in that the molecules of the material physically adhere to the adsorbent rather than being absorbed into the interspaces of the absorbent material.

Based on the Rf values of samples A and B (A was higher - see picture) what can you conclude about the intermolecular attractions both samples have for the eluent and the paper?

Because Sample a traveled further on the chromatography paper (higher Rf), it has a stronger attraction to the eluent, but a weaker attraction to the paper, in comparison to sample B. This means that sample A is more polar than sample B.

Which dye was most compatible with the mobile phase and which was the least?

Blue was most compatible because it traveled farthest up the paper, meaning that it has the strongest intermolecular attraction to the eluent where as red barely traveled at all because it was more attracted to the paper than the eluent so had a little compatibility with the eluent.

Based on the diagrams and intermolecular attractions, predict and rank the strength of the attractions experienced by red, blue, and yellow dyes.

Blue>yellow>red for IPA and NACl because blue always travel the farthest, and was the only one that showed up for IPA meaning it had the strongest intermolecular attraction/highest polarity with the eluent.

How would isopropyl alcohol interact with water and what intermolecular attraction takes place?

CH3CH2—CH3 The hydroxide connects to a carbon atom and the water molecule (don't forget the four extra electrons around the oxygen); dispersion

Why does changing the polarity of the eluent affect the separation of a mixture so much?

Changing the polarity of the eluent will only slightly affect the solubility of the molecules but may greatly change the relative attraction for the adsorbent.

What is the most difficult task in chromatography?

Choosing the eluent is the most difficult task because the polarity determines the level of separation that will be achieved; different samples will spend varying amount of time interacting with the paper and solvent.

What are the main parts of this experiment?

Compare the separation of a dye in two solvents. Using the more effective solvent, observe it's effect on an unknown dye.

What concept does chromatography work on?

Compounds to be separated are slightly soluble in the eluent and will spend some of the time in the eluent and some of the time in the adsorbent.

Predict and explain the types of intermolecular forces that would occur between paper and water. How do these interactions account for the hydrophilic nature of the water?

Hydrogen bonding occurs between paper and water because of the OH from the chromatography paper and the H from the water; this strong intermolecular force accounts for the tendency of the water to travel in a capillary action opposite of gravity.

How can you judge whether a mixture was separated properly by chromatography?

If you can clearly see all of the separate colors of a mixture and they have practically stopped moving as the eluent continues to make its way up the paper.

Argue which mobile phase was better for dye separation. Do your experimental results support the predictions made by intermolecular force analysis?

NaCl was better because it fully separated the sample into a three components, red, yellow, and blue, whereas IPA only showed blue. We predicted that NaCl would be a better mobile phase, which supports our results, because it is more polar than IPA meaning that it stronger attraction to the individual dyes in the sample and will carry them further allowing them to separate.

Explain the types of intermolecular interactions that would occur between red No. 40, blue No. 1, and yellow No. 5 food dyes and the paper.

Red/yellow & paper: h-bond because there is an OH in the dye and an OH in the glucose from the paper Blue & paper: ion-dipole because there is an N+ that can bond with the OH-

Replacement for labeling and drawing the chart (#26) - what is the difference between stationary phase, mobile phase, and solvent front?

Stationary phase is the chromatography paper, mobile phase is the eluent as it moves, and the solvent front represents the distance the solvent has traveled up the paper.

If a fabric contains more ionic and polar groups in its structure, then the intensity of the dye color due to methyl orange should increase, because...

The affinity of the methyl orange for the fabric will increase, therefore adding more color to the fabric (more likely to form dipoles).

How do the the attractive forces between molecules change in the transition from gas to liquid to solid?

The attractive forces between molecules becomes stronger as a substance transitions from a gas to a solid, because the molecules are pulled closer together.

Write a general statement describing how the size of a molecule influences the strength of London dispersion forces between the molecules.

The bigger the molecule is, the stronger London dispersion forces are because the valence electrons are farther from the nuclei, meaning they are not held as tightly as they are in smaller molecules and can therefore form dipoles more easily.

What could have been done to determine whether a color additive was harmful before it was used in the food industry?

They could have used chromatography to determine the purity of each additive.

What is the experiments objective?

To investigate the factors that influence the separation of food dye using paper chromatography.

What were food color additives initially used for?

To make food more visually appealing to the consumer and mask poor quality.

How would sodium chloride interact in water and what intermolecular attraction takes place?

Water molecules around sodium and chloride ions; ion-dipole