20. Which of the following statements is correct?
(A) In volatilization gravimetry, the analyte is separated from other constituents of a sample by converting it to a precipitate of known chemical composition.
(B) In precipitation gravimetry, the product should be of sufficiently low solubility and reactive with constituents of the atmosphere.
(C) A colloid consists of solid particles from 10-2 to 10-6 m in diameter that are visible to the naked eyes.
(D) Nucleation is a process in which a maximum number of atoms, ions, or molecules join together to give a small number of larger particles.

(E) When a precipitate is formed at high relative supersaturation, nucleation is the major precipitation mechanism.

16. Analysis of a bottle of 100 mg aspirin tablets yields an average aspirin content of 99.8 mg, with a standard deviation of ±0.3 mg. Assuming Gaussian statistics, which of the following statements is true?(A) None of the tablets contains less than 99.5 mg of aspirin.(B) 68% of tablets contain between 99.5 and 100.1 mg of aspirin.(C) 97% of tablets contain between 99.5 and 100.1 mg of aspirin.(D) All of the tablets contain less than 100 mg of aspirin.(E) The average value is incorrect.

17. The ionic strength of a solution depends on which of the following? I. The size of ions II. The charges on ions III. The concentration of the ions(A) I and II only.(B) I and III only(C) I, II and III only(D) II and III only(E) None of them.

18. A voltaic cell is constructed by immersing a strip of copper metal in 1.0 MCuSO4 solution and a strip of aluminum in 0.50 M Al2(SO4)3 solution. A wire and a salt bridge complete the circuit. The aluminum strip loses mass, and the concentration of aluminum ions in the solution increases. The copper electrode gains mass and the concentration of copper ions decreases. Which of the following are applicable to the copper electrode? I. The anode   II. The cathode   III. The positive electrode   IV. The electrode at which electrons are produced V. The negative electrode    VI. The electrode at which electrons are used up(A) I, III, and V(B) I, IV, and V(C) II, III, and VI(D) II, IV, and VI(E) None of the first four responses contains all the correct choices and no others

19. Which of the following statements is incorrect?(A) A buffered solution is one that resists a change in pH when either hydroxide ions or protons are added.(B) The ability of a buffer system to resist pH changes is its buffer capacity, indicated by ẞ value.(C) The Henderson-Hasselbalch equation enables to approximate the pH of a buffer solution.(D) The hydronium ion concentration of a solution containing a weak acid and its conjugate base is independent of the ratio of the molar concentrations of these two solutes as well as dilution.(E) The composition of buffer solutions can be visualized by plotting the relative equilibrium concentrations of the two components of a conjugate acid/base as a function of the pH of the solution.

1. While recent snow storms have closed many schools in the U.S., some are choosing to hold classes__________， turning snow days into 'cyber' days.(A) realistically (B) virtually(C)optimistically(D)conceptually

2. The __________ for Tommy combined sadness and humor on Saturday, with his friends paying their final respects to this acclaimed actor.(A) fantasy (B) federal(C)funeral(D)fictional

3. Hit-and-run statistics plainly show that this form of vehicular __________ has become distressingly common in Taiwan.(A) admission (B) license(C)training(D)wrongdoing

4. The ____ of the Internet somehow empowers users to make harsh comments they would likely never say to a person's face.(A) anonymity (B) antonym(C)autopsy(D)automobile

5. Up to 50 students at Stingy Elementary School had their school lunches thrown out because of outstanding ____ on their account.(A) bankruptcy (B) balances(C)benefits(D)benevolence

6. None of its coral islands is more than 1.8 meters above sea level, making Maldives ____ to a rise in sea level associated with climate change.(A) vindictive (B) vagrant(C)vulnerable(D)veracious