Biology, Answering the Big Questions of Life/Organic Chemistry

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Lab 3 - Organic Chemistry Lab[edit]

Organic molecules are chemicals which contain carbon. The structure of a molecule and its charge determine whether or not it will dissolve in water.

Chemicals which can dissolve in water are said to be 'hydrophilic'(water loving) while those which do not dissolve in water are said to be 'hydrophobic' (water fearing).

In the cell, hydrophilic molecules are found in the cytoplasm, while hydrophobic molecules are found in the phospholipid membranes.

Some molecules have both hydrophilic and hydrophobic parts. These molecules are said to be 'amphipathic'.

Phospholipids, the molecules which make up the plasma membrane are amphipathic, they have a charged phosphate group which is hydrophilic as well as a hydrocarbon chain which is hydrophobic. This allows cells to remain dissolved in water.

Amphipathic chemicals will form 'emulsions'. Solutions where oil droplets stay suspended in the water. Hydrophobic molecules will separate into the oil layer, while hydrophilic molecules will dissolve in the water fraction of the cell.

In this lab we will determine if molecules are hydrophilic, hydrophobic or amphipathic.


Instructions:[edit]

1. Place four test tubes with lids in a test tube rack. Fill each tube to about 1/4 full with corn oil, then Add water until tube is about 2/3 full.

2. Add the following to each tube.

  • Tube 1 - Control (do not add anything to this tube)
  • Tube 2 - Sudan IV dye ( about 10 to 12 drops)
  • Tube 3 - Methylene blue (about 5 drops)
  • Tube 4 - Dishwashing detergent (about 1/2 dropper)


3. Seal each test tube and mix it well.


4. Let the tubes sit for several minutes in the test tube rack as the solutions separate out.


5. Sketch each tube showing whether the substance dissolved in the oil or water fraction. If the tube does not separate out after several minutes, and the control has separated, list the chemical as amphipathic.


6.Fill the table.

Tube number
Description of tube
hydrophilic/hydrophobic/amphipathic