Practice Questions Non-covalent interactions/water

11. Amphiphilic molecules A) have both oxidizing and reducing groups. B) are micelles. C) have chromophores in two different wavelength regions. D) have both acidic and basic groups. E) have both hydrophilic and hydrophobic groups

E

2. Hydrogen bonds within liquid water A) are attractions between protons and oxygen nuclei. B) are attractions between two hydrogen atoms. C) are attractions between protons and hydroxide ions. D) are ion-induced dipole attractions. E) are dipole-dipole attractions.

E

4. Which of the following compounds are capable of hydrogen bonding with alike molecules? A) CH3CH2CH2CH2CH3 B) CH3CH2OCH2CH3 C) CH3NH2 D) HOCH2CH2OH E) Both C and D are correct

E

5. Which of the following is not an example of noncovalent interactions between molecules? A) Salt bridges B) Hydrogen bonds C) Hydrophobic interactions D) Ionic bonds E) Disulfide bonds

E

17. Calculate the ratio of dihydrogen phosphate to hydrogen phosphate in blood at pH 7.4. The Ka is 6.3 x10-8.

[H2PO4-]/[HPO42-] = 0.63

18. You prepare a solution by mixing 60 mL 0.10 M sodium acetate and 40 mL 1.0 M acetic acid (pKa 4.76). a. Calculate the pH of this solution. b. Calculate the pH after 5.0 mL of 1 M NaOH is added to 100 mL of the buffer (assume the total volume will be 105 mL).

18a pH = 3.94, 18b pH = 4.26

1. Rank the following interactions in order of increasing strength (start with the weakest interaction). A) ionic interactions, hydrogen bonds, London dispersion forces, covalent bonds B) London dispersion forces, hydrogen bonds, ionic interactions, covalent bonds C) London dispersion forces, ionic interactions, hydrogen bonds, covalent bonds D) covalent bonds, London dispersion forces, ionic interactions, hydrogen bonds E) hydrogen bonds, London dispersion forces, ionic interactions, covalent bonds

B

14. Salt bridges in proteins are an example of _________. A) Hydrogen bonds B) Ionic interactions C) Hydrophobic interactions D) van der Waals forces E) London dispersion forces

B

15. Which of the following species would form a buffer with HPO42-? A) H3PO4 B) H2PO4- C) CO32- D) All would form buffers with HPO4-2 E) Both A and B

B

16. Phosphoric acid is a polyprotic acid, with pK values of 2.14, 6.86, and 12.38. Which ionic form predominates at pH 9.3? A) H3PO4 B) H2PO41− C) HPO42− D) PO43− E) none of the above

C

3. A hydrogen bond is best defined as: A) A strong chemical bond between hydrogen and another element B) A weak chemical bond between hydrogen and another element C) A relatively strong electrostatic bond between hydrogen and oxygen or nitrogen D) A weak electrostatic bond between hydrogen and oxygen or nitrogen E) A bond between two hydrogens

C

6. Which of the following factors is responsible for the fact that water is a liquid at room temperature? A) Covalent O-H bonds B) Ionic bonds C) Hydrogen bonds D) Hydrophobic bonding between water molecules E) The molecular weight of water

C

8. Which of the following statements is true of weak acids dissolved in water? A) They are completely ionized in water B) They are totally unionized in water C) They are partially ionized in water D) The dissociation constant is a function of pH E) The dissociation constant is a function of solute concentration

C

9. Which of the following statements about water is not true? A) The electron-rich oxygen atom of one water molecule can interact with the electron-poor proton on another water molecule to form a hydrogen bond. B) Liquid water is only 15% less hydrogen bonded than ice. C) Water is a nonpolar molecule with a bent molecular geometry. D) Water can form highly ordered, cage-like, structures around nonpolar molecules. E) Water is a key player in the energetics of hydrophobic interactions.

C

10. _____ is exceptionally soluble in water due to the formation of hydrogen bonds. A) NaCl B) Benzene C) Sodium palmitate D) Ethanol E) Oxygen

D

12. Which of the following is the best explanation for the hydrophobic effect? A) It is caused by an affinity of hydrophobic groups for each other. B) It is caused by the affinity of water for hydrophobic groups. C) It is an entropic effect, caused by the desire of water molecules to decrease their entropy by forming highly ordered structures around the hydrophobic groups. D) It is an entropic effect, caused by the desire of water molecules to increase their entropy by excluding hydrophobic groups, which they must otherwise surround with highly ordered structures. E) It is an entropic effect caused by the desire of hydrophobic groups to increase their entropy by associating with other hydrophobic groups

D

13. A solution is made by mixing 1.0 mL of 1.0 M acetic acid (pK = 4.76, Ka = 1.74 x 10-5 ) with one 999 mL of pure water. Calculate the pH of the resulting solution (assume the total volume is 1.0 L). A) 10.1 B) 3.0 C) 1.0 D) 3.9 E) 1.32

D

7. Acetic acid can act both as a H-bond donor and as a H-bond acceptor. What is the maximal number of H-bonds a single molecule of acetic acid can form with surrounding water molecules. A) 2 B) 3 C) 4 D) 5 E) 6

D