13. Helium effuses through a small opening at a rate of 1×10⁻⁹ mol s⁻¹. An unknown gas at the same temperature and pressure is found to effuse through the same opening at a rate of 3.78×10⁻¹⁰ mol s⁻¹. What is the molecular mass of the unknown gas? (A) 4 g mol⁻¹ (B) 14 g mol⁻¹ (C) 18 g mol⁻¹ (D) 28 g mol⁻¹ (E) 40 g mol⁻¹

13. Helium effuses through a small opening at a rate of 1×10⁻⁹ mol s⁻¹. An unknown gas at the same temperature and pressure is found to effuse through the same opening at a rate of 3.78×10⁻¹⁰ mol s⁻¹. What is the molecular mass of the unknown gas?
(A) 4 g mol⁻¹
(B) 14 g mol⁻¹
(C) 18 g mol⁻¹
(D) 28 g mol⁻¹
(E) 40 g mol⁻¹

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統計： A(2), B(0), C(0), D(4), E(0) #3340058

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6. A strip of copper is placed in a 1 M solution of copper nitrate, and a strip of silver is placed in a 1 M solution of silver nitrate. The two metal strips are connected to a voltmeter by wires, and a salt bridge connects the solutions. The following standard reduction potentials apply: Ag⁺(aq) + e⁻ → Ag(s) E° = +0.80 V Cu²⁺(aq) + 2e⁻ → Cu(s) E° = +0.34 V When the voltmeter is removed and the two electrodes are connected by a wire, which of the following does not take place? (A) Electrons flow in the external circuit from the copper electrode to the silver electrode. (B) The silver electrode increases in mass as the cell operates. (C) There is a net general movement of silver ions through the salt bridge to the copper half-cell. (D) Negative ions pass through the salt bridge from the silver half-cell to the copper half-cell. (E) Some positive copper ions pass through the salt bridge from the copper half-cell to the silver half-cell.

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