Biology homework help

3 Solubility in Water

 Background

Organisms are made up of mostly water. The human body, for example, may be up to 70% water. This is because water is used for numerous functions such as digestion, absorption, transport, insulation, temperature buffer and medium for metabolic reactions. However, it will not be able to perform these tasks unless molecules dissolve in it. Hence, most of the molecules that are inside the body of organisms are water soluble (can dissolve in water).

These water soluble molecules mix well with water because they are alike; they have a charge and are said to be polar. The charges on polar molecules like water and the molecules of the soluble substances attract each other, making these soluble substances hydrophilic (waterloving). In contrast, the lipids of the cell membrane are nonpolar or hydrophobic (water-hating) and serve as a barrier to the passage of polar molecules across the membrane.

Lipid substances such as vegetable oil and steroids are nonpolar. They are soluble in other lipids but not in water. Such nonpolar molecules are, therefore, able to diffuse into the cells by passing through the lipid layers of the membrane.

Detergents have a special property. They can literally act as a bridge between the polar and nonpolar worlds.  One end of the detergent molecule is polar and dissolves in water; the other end is nonpolar and can dissolve in fats and oils.  Molecules such as detergent that have both polar and nonpolar regions are called amphipathic. Biology homework help

 

 

Hypotheses and predictions

  • If a substance is polar, then it will dissolve in polar substances such as water.
  • If a substance is nonpolar, then it will not dissolve in water, but instead will dissolve in nonpolar substances such as oil.

Purpose

  • To demonstrate solubility of different substances in water.
  • To determine the effect of adding detergent to a mixture of water and a nonpolar substance.

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Materials for DIY (Do-it-yourself) experiment

  • Water
  • Oil (ie. vegetable or olive oil)
  • Food coloring (liquid or powder such as Kool-Aide or Jello mix)
  • Dish soap or detergent
  • Jar with lid
  • Spoon to stir

 

Procedure for DIY experiment

(*if your group does not have above materials, please see alternative assignment at end of lab)

  1. Half-fill a jar with water.
  2. Add a few drops of food coloring into water & stir using spoon. Record your observations in the table. Take a picture.
  3. Add oil into the jar with water & food coloring until it is about ¾ full, cover with lid tightly & shake. Wait about 1 min & record your observations in the table. Take a picture.
  4. Add dish soap or detergent into the same jar & cover tightly again. Shake the jar gently and immediately record your observations in the table. Take a picture.
  5. Wash out the jar & return all materials to their proper place. Biology homework help

Results

 

Table 1. Results of combining various substances with water

Solvent 

 

Substance added

 

Observations (number of layers. color of layer/s)

 

Is the substance added soluble in water?   Yes or No

 

Water

 

Food coloring

 

   
Water + Food coloring

 

Oil    
Water+Food coloring+Oil

 

Dish soap

 

   

 

 

Submit a picture of your jar at the end of the experiment with this assignment.

 

Alternative Procedure if group does not have above materials

Materials

  • Water
  • Vegetable oil
  • Potassium permanganate (KMnO4)
  • Detergent
  • Capped Test tube
  • Scoops for detergent & potassium permanganate (KMnO4)

Procedure

  1. Pour 5 ml of water into a test tube.
  2. Add 5 mL of vegetable oil into a test tube. Cap the test tube. Shake the tube gently. Let rest for one minute. Record your observations in the table.
  3. Using forceps, add 2crystals of KMnO4 into the same tube. Be careful not to add too many. Cap and shake the tube Record your observations in the table.
  4. Add a pinch of detergent to the same tube. Shake the tube gently and immediatelyrecord your observations in the table.
  5. Wash out the test tube & return to proper place. Biology homework help

 

Solvent 

 

Substance added

 

Observations (number of layers. color of layer/s)

 

Is the substance added soluble in water?   Yes or No

 

Water

 

Oil    
Water + oil KMnO4

 

   
Water + Oil + KMnO4

 

Detergent

 

   

 

 

 

Submit a picture of your jar at the end of the experiment with this assignment.

Discussion/Conclusion

    1. Did the food coloring (or KMnO4if you did not perform the experiment) dissolve in water? _______ (Y/N)
    2. Explain the observation/s that support/s your answer in 1a.
    3. Is food coloring (or KMnO4) polar, nonpolar or both? ________________

 

    1. Did oil dissolve in the water? ________ (Y/N)
    2. Explain the observation/s that support/s your answers in 2a.
    3. Is oil polar, nonpolar or both? ________________

 

    1. Soaps & detergents are said to be   What does this term mean?

 

    1. Did the dish soap (or detergent) dissolve in the water? ________ In the oil? _______
    2. Explain the observation/s that support/s your answer in 4a.
    3. Is detergent polar, nonpolar or both? ________________

 

    1. Using your knowledge of dish soap’s polarity, explain how dish soap or detergent “cleans” our greasy, dirty dishes?

 

 

*Alternative procedure used in “Solubility in Water Lab” Video if your group does not have necessary materials:

Materials

(used in already performed experiment)

  • Water                                        
  • Vegetable oil
  • Potassium permanganate (KMnO4)
  • Detergent
  • Capped Test tube
  • Scoops for detergent & potassium permanganate (KMnO4)

Procedure (read through)

  1. Pour 5 ml of water into a test tube.
  2. Add 5 mL of vegetable oil into a test tube. Cap the test tube. Shake the tube gently. Let rest for one minute. Record your observations in the table.
  3. Using forceps, add 2crystals of KMnO4 into the same tube. Be careful not to add too many. Cap and shake the tube Record your observations in the table.
  4. Add a pinch of detergent to the same tube. Shake the tube gently and immediatelyrecord your observations in the table.
  5. Wash out the test tube & return to proper place. Biology homework help

 

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