18. The mass of a sample of calcium carbonate powder is measured using weight by difference. If a vial containing calcium carbonate powder has an initial mass of 87.36 ± 0.03 g and a final mass of 76.99 ± 0.03 g, what mass of calcium carbonate was taken?
(A) 10.37±0.04 g
(B) 10.37±0.03 g
(C) 10.370±0.042 g
(D) 10.370 ± 0.004 g
(E) 10.370 ± 0.005 g

14. X-rays are a commonly used electromagnetic wave in medical imaging technology. Using an X-ray tube to generate X-rays, the shortest wavelength Amin that can be produced is inversely proportional to the voltage V of the tube. This relationship can be expressed by the following equation. = Q/V. What is the value of the constant Q in the equation? Planck constant, an electric charge, and the speed of light are denoted as h, e, and c, respectively. (A) hc (B) e/h (C) e/(hc) (D) hc/e (E) e²/h

15. The dimensions of stress are _____.(A) [M/TL] (B) [M/T2L] (C) [MT/L] (D) [M/L] (E) [MTL]

16. For the Arrhenius equation, k = exp, which of the following statement is CORRECT? (A) The effect of an enzyme is to increase the magnitude of A. (B) The exp (-Ea/RT) term represents the fraction of molecules with a kinetic energy larger than Ea. (C) The reaction rate k is linearly proportional to temperature T. (D) The activation energy Ea is associated with the collision frequency of the reactants. (E) The steric factor of reaction affects the magnitude of Ea.

17. Which of the following are state functions? (A) work, heat, enthalpy (B) heat, enthalpy, energy (C) enthalpy, energy (D) work, heat, enthalpy, energy (E) work, heat

19. Which of the following ionic compounds has (in absolute values) the largest lattice energy; that is, which has the lattice energy most favorable to a stable lattice? (A) LiF (B) Lil (C) CsF (D) MgO (E) CsI

20. What is the key step in the Heck reaction? (A) radical generation (B) carbocation formation (C) palladium-catalyzed oxidative addition and reductive elimination (D) nucleophilic substitution (E) decarboxylation

21. _____is the upward force exerted on an object in a gaseous or liquid fluid. The mass measured by an analytical balance in air is _____ its actual mass. (A) Buoyancy; heavier than (B) Buoyancy; lighter than (C) Electromagnetic force; heavier than (D) Electromagnetic force; lighter than (E) Tare; equal to

22. How many electrons in an atom can have the quantum numbers n = 4, 1 = 2? (A) 18 (B) 32 (C) 2 (D) 6 (E) 10

23. Which of the following options shows the molecules in the order from most polar to least polar? ("=" indicates that two molecules are similarly polar) (A) CF2Cl2 ＞ CF2H2 ＞ CCl2H2 ＞ CH4 = CCl4 (B) CF2H2 ＞ CCl2H2 ＞ CF2Cl2 ＞ CH4 = CCl4 (C) CH4＞ CF2Cl2 ＞ CF2H2 ＞ CCl4 ＞ CCl2H2 (D) CF2Cl2 ＞ CF2H2 ＞ CCl4 ＞ CCl2H2 ＞ CH4 (E) CH4 ＞ CF2H2 ＞ CF2Cl2 ＞ CCl4 ＞ CCl2H2

24. Lead(II) nitrate reacts with sodium chloride in aqueous solution to form a precipitate. What is the net ionic equation for the precipitation process? (A)(B)(C) (D)(E)