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CHEM 210 Module 2 Exam Newest
- a higher melting or boiling point indicates the molecule has: stronger inter- molecular forces.
- What is the shape of water?: Bent. The bond angle is 104.5 degrees.
- What is autoionization, and how is it important for water?: Autoionization is the ability of a compound to react with itself to form ions. One water molecule reactswith a second molecule to form two ions: H3O+ and OH-. These ions exist in smallamounts in pure water and influence the chemistry of water.
- Name the three non-covalent forces discussed in this module.: 1. Dipole-di-pole forces, 2. Hydrogen bonding, and 3. London dispersion forces
- What type of non-covalent interaction is known as the strongest dipole-di- pole force?: hydrogen bonds
- How does the strength of London forces change with increasing molecularweight?
Explain briefly.: As molecular weight increase, the strength of London forces also increase. This is due to the increased number of electrons in larger mol-ecules. The larger number of electrons creates the potential of stronger temporarydipoles.
- What is the concentration, in M, of water as a pure liquid?: 55.5 M
- Define Keq and Kw.: Keq is the equilibrium constant. Numerically, it is equal to the concentrations of equilibrium products (in M) multiplied together over the concentration of equilibrium reactants multiplied together.
Kw is called the ion product. It is, essentially, the Keq for water that is equal to 1.0 x10-14; the formula is:
9. Identify the acid, conjugate base, and proton in the following reaction.
HCOOH --> H+ + HCOO-: HCOOH weak acid H+ proton HCOO- conjugate base
- A buffer system has a pKa of 8.5. What is its effective buffering range?: 7.5to 9.
- Weak acid A has a pKa of 3.2, while weak acid B has a pKa of 5.6. Is Weak acid A or B the stronger of the two?: Weak acid A is stronger because a smaller pKa indicates a
What is the sign (+ or -) of ” G, H ” , and ” S in this reaction?: G(-) happens as written, H” is (-) gives off heat, and ”S is (+) because more disordered gases are produced.
- What is the role of ATP in helping a non-spontaneous reaction occur?: It provides a source of energy to assist the reaction. ATP breakdown has a significantnegative G” value.
- Which attribute contributes to water's unusual properties?: -geometry of molecule -polarity of O-H bonds -ability of water molecules to H bond -the bond angle of water
- What factor contributes to the bent shape of a water molecule?: The un- shared electron pairs on the oxygen atom
- List the acids in DECREASING order of strength (strongest to weakest): Nitrous acid (Ka = 4.0 x 10-4); acetic acid (Ka = 1.7 x 10-5); phosphoric acid(Ka = 7.3 x 10-3): Phosphoric acid, nitrous acid, acetic acid
- Elemental iodine (I2) is a solid at room temperature. What is the dominant attractive force that exists between I2 molecules in the solid?: london forces
19. Which one of the following molecules can form a hydrogen bond?
A. HIB. HClC. N2D. CH4E. H2O: E
- A hydrogen bond can form between a hydrogen atom bonded to nitrogen,N-H, and .: O 21. The following reaction occurs in glues purchased from hardware stores. Customers use this product to glue plastic together.
Epoxy (l) + hardener (l) ö Glue (s) + heat given off What is the sign (+ or -) of the change in ” G and H? A) ” G is (+) and ” H is (-) B) G ” is (-) and ” H is (-) C) ” G is (-) and ” H is (+) D) ” G is (+) and ” H is (+) E) None of the above: B
22. Which of the following is the free-energy change of a reaction? A) ” G B) ” S C) ” H
D. 5.6 X 10-
E. None of the above: A
- In equilibrium constant expressions, the concentration is expressed inunits of as indicated by the brackets [ ].: molarity 29. Which of the following compounds would not be soluble in water? A. NaCl B. OH- C. Glucose D. Wax E. All of the above would be soluble: D 30. The hybridization of the central atom in water is.
A. s B. sp C. sp D. sp E. None of the above: D
31. Three identical molecules dissolve in water. Each molecule contains both a polar portion and nonpolar portion of structure. The three molecules interact in such a way that the nonpolar sections align. This is an example of the .: hydrophobic effect
- (Short Response) How does the strength of a hydrogen bond compare tothe strength of a London Force? Also, how about the strength of a hydrogenbond compared to a dipole-dipole force? Briefly comment on these differ- ences.: A hydrogen bond is much stronger than the strength of a London Force and it is the strongest dipole dipole force. A hydrogen compared to a dipole dipole force is still stronger, however a dipole force is the strongest intermolecular force. Ahydrogen bond's strength is the strongest out of these three.
- What is the hydrophobic effect and how does a clathrate help explain this phenomenon?: The hydrophobic effect helps scientists explain how biologicalmolecules form and interact. For instance, when molecules with both a nonpolar andpolar regions dissolve in water, the nonpolar regions pack together. The packing of the nonpolar regions minimizes the interaction with water and the polar region interact with water, which in total is called the hydrophobic effect. The driving forcebehind this effect is the spontaneous drive of water to bind to itself through hydrogenbonds. To maximize the hydrogen bonds, water orders itself around the hydrophobicportion of the nonpolar regions in a cage structure also called a clathrate. In so doing, water can form bonds with itself and also permit the nonpolar regions to be dissolved.
- what makes water unique: has high heat of vaporization, boiliing point, andmelting point
- dipole dipole interactions common in what molecules: polar molecules ex)HCl
- london forces characteristics: weakest forces and can only occur betweenany 2 molecules
- aqueous system that resists changes in pH when small amounts of acid or base
