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Integration and Practice of All Three Lab Tasks

Figures (8)

Figure 3.4 Scientists classify monosaccharides based on the position of their carbonyl group and the number of carbons in the backbone. Aldoses have a carbonyl group (indicated in green) at the end of the carbon chain, and ketoses have a carbonyl group in the middle of the carbon chain. Trioses, pentoses, and hexoses have three-, five-, and six- carbon backbones, respectively.
Figure 3.5 Glucose, galactose, and fructose are all hexoses. They are structural isomers, meaning they have the same chemical formula (C6H12O6) but a different atom arrangement.
Figure 3.6 Five and six carbon monosaccharides exist in equilibrium between linear and ring forms. When the ring forms, the side chain it closes on locks into an α or β position. Fructose and ribose also form rings, although they form five-membered rings as opposed to the six-membered ring of glucose.
Figure 3.7 Sucrose forms when a glucose monomer and a fructose monomer join in a dehydration reaction to form a glycosidic bond. In the process, a water molecule is lost. By convention, the carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group. In sucrose, a glycosidic linkage forms between carbon 1 in glucose and carbon 2 in fructose.
Figure 3.8 Common disaccharides include maltose (grain sugar), lactose (milk sugar), and sucrose (table sugar).
Figure 3.9 Amylose and amylopectin are two different starch forms. Unbranched glucose monomer chains comprise amylose by α 1-4 glycosidic linkages. Branched glucose monomer chains comprise amylopectin by α 1-4 and α 1-6 glycosidic linkages. Because of the way the subunits are joined, the glucose chains have a helical structure. Glycogen (not shown) is similar in structure to amylopectin but more highly branched.
Figure 3.10 Cellulose is an organic compound composed of linear chains of hundreds to thousands of linked glucose molecules. The glucose monomers form hydrogen bonds, holding the chains firmly together side-by-side and form strong microfibrils. This rigidity is an important structural component of the cell walls found in plants. Credit: Ryan, K. Rao, A. and Hawkins, A. Department of Biology, Texas A&M University.
Figure 3.11 Insects have a hard outer exoskeleton made of chitin, a type of polysaccharide. (credit: Louise Docker)

Colligative properties depend on the total number of solute particles in a solution, not their identities. These properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. The presence of nonvolatile solute particles reduces the surface area available for solvent molecules to escape into the vapor phase, lowering the solution's vapor pressure.

This effect is described by Raoult’s law, which states that the partial pressure of a solvent in a solution is equal to its mole fraction multiplied by its pure vapor pressure. The mole fraction is the ratio of the moles of solvent to the total moles of all solution components. The vapor pressure lowering leads to an increase in the boiling point and a decrease in the freezing point.

The boiling point elevation is directly proportional to the molal concentration of solute particles and the boiling point elevation constant of the solvent. Similarly, the freezing point depression is directly proportional to the molal concentration of solute and the freezing point depression constant. These relationships are crucial for practical applications like de-icing roads and purifying water through distillation.

Osmotic pressure, another colligative property, depends on the molarity of solute particles and the temperature. It is the pressure required to stop the net movement of solvent through a semipermeable membrane. Osmotic pressure is used in reverse osmosis to purify water by applying pressure greater than the osmotic pressure, forcing solvent from a more concentrated solution to a less concentrated one.

These properties are essential in both natural processes and industrial applications, demonstrating the importance of solute concentration in determining solution behavior.

Key Points

  • Casein is a family of related phosphoproteins commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in human milk.
  • Freezing point depression is the decrease in freezing point of a dilute solution compared to that of the pure solvent, directly proportional to the molal concentration of the solute.
  • Colligative properties are solution properties that depend only upon the total concentration of solute species, regardless of their identities, and include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.
  • An emulsion is a mixture of two immiscible liquids, where one liquid is dispersed in the form of small droplets throughout the other liquid, often stabilized by an emulsifier such as casein.
  • Curd is the solid mass formed when milk is coagulated, typically through the action of rennet or acid, and is a key component in the production of cheese.

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