Investigation: Make your predictions in the spaces provided on your lab report.
ID: 257069 • Letter: I
Question
Investigation:
Make your predictions in the spaces provided on your lab report.
Mark the eggs with pencil, and the four bowls, with the following labels:
Water, Vinegar, Vinegar and Salt, Vinegar and Sugar
In the mixing bowl, combine 2 teaspoons of food coloring with 2 cups of water and mix well. Pour ½ cup of this solution into each of the four bowls.
Add 1 tablespoon of vinegar to each of the three "vinegar" bowls.
Add 1 tablespoon of salt to the "salt" bowl, and add 1 tablespoon of sugar to the "sugar" bowl.
Stir each of the solution bowls until they are thoroughly mixed.
Use the spoons to lower each egg into its respective solution. Wait 10 minutes, then remove the eggs with the spoons.
Rinse each egg three times in the tub of water, then set the eggs someplace safe to dry. A paper towel or egg carton would do just fine.
Answer the set of summary questions on your lab report, and turn in the completed lab to your instructor.
Observations
Conditions
Observations
Water
The egg showed little or no change in color.
Vinegar
The egg changed to the color of the food coloring.
Vinegar and Salt
There was little or no change in the color of the egg.
Vinegar and Sugar
The egg changed to the color of the food coloring.
1. Which conditions caused the food coloring to form a compound on the surface of the egg? How could you tell?
2. When salt is added to the solution, it dissolves into its component ions. How did this seem to affect the compound formed on the egg shell?
3. In the vinegar and salt solution, is it possible there was some other compound that formed on the egg shell instead of the food coloring? Based on what you know about the charge on the egg shell and the ions in the solution, what might have reacted to form a compound on the shell instead of the food coloring?
4. What affect did the sugar have on the reaction of the food coloring with the egg shell, if any? Does this indicate anything to you about the charge of the sugar in the solution?
Conditions
Observations
Water
The egg showed little or no change in color.
Vinegar
The egg changed to the color of the food coloring.
Vinegar and Salt
There was little or no change in the color of the egg.
Vinegar and Sugar
The egg changed to the color of the food coloring.
Explanation / Answer
1.Most food dyes are acid dyes, so called because they only work in acidic conditions. The vinegar—a solution of 5 percent acetic acid in water—is there to bring the pH low enough that the dye will actually bind.
The colored molecules (dye) themselves are sodium salts of a phenolic acid. Once those dyes get thrown into water, the sodium ions fall off, leaving behind the negatively-charged part of the molecule. Add vinegar, and you're adding lots of free protons—positively charged hydrogen ions—which fly in to take the place of those missing sodiums. The hydrogens, now associated with the dye molecules, are important because they allow hydrogen bonding. Their slightly positive charge acts like a magnet, attracting it (and the dye, in tow) to slightly negative atoms in the protein molecules and calcium carbonate (CaCO3) in the eggshell.
2.
The membrane of a cell (in this case, the egg) is semipermeable, meaning that small particles can go in and out of the cell while large particles stay out. Water and other nutrients (and food coloring) are small enough to travel in and out of the cell. When the concentration of water in the cell is different than the concentration of water outside of the cell, the water will move either in or out of the cell to balance the concentration inside and out. This is called osmosis.
Osmosis explains why the egg in the corn syrup shriveled up. Corn syrup has a very low concentration of water in it so some of the water from the inside of the egg traveled through the membrane into the corn syrup, making the egg cell shrink, there by releasing the dye into water and hence decolourising the egg.
3.
nsoluble calcium carbonate (CaCO3) that makes up the outer layer of the shell eggs reacted with vinegar - an aqueous acetic acid solution (CH3COOH). As a result, soluble calcium acetate (Ca(CH3 COO)2) was formed. The gas bubbles evolved in the process is carbon dioxide (CO2), excluded from the carbonate by the acid. So, what happened with the egg shell can be expressed by the reaction equation:
CaCO3 + 2CH3COOH ? Ca(CH3COO)2 + CO2? + H2O
The result is an egg without a hard shell. Only the inner shell membranes, which are similar to parchment (the same matte film, which can be seen when cleaning boiled eggs) remain intact. They are strong enough to hold the liquid contents inside, but are still quite fragile.
4. when sugar is added, the cocentration of dye is more as compared to that in the eggs. hence the dye molecules move from higher concentration i.e from the solution to the egg causing the colouration of the egg surface.
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