Question 1

Which of these elements is most likely to have the highest second ionization energy? Hint: think of Lewis structures.
A)Aluminum (Al)
B)Phosphorus (P)
C)Chlorine (Cl)
D)Magnesium (Mg)
E)Sodium (Na)

Accepted Answer

Sigma vs. Pi Bond

Question 2

One liter of hydrogen gas is placed in a vacuum. The emission spectrum of hydrogen shows a red line of wavelength 650 nm. What was the energy of the photon that released it? A)2)9 * 10^-28 J B)4)1 * 10^-31 J C)2)9 * 10^-19 J D)4)1 * 10^-19 J E)2)9 * 10^-15 J

Accepted Answer

E=energy (J) H=Planck's constant (6.626*10^-34J*s) f=frequency (1/s) C=speed of light (3.0 * 10⁸m/s) l = wavelength (650nm = 6.5 *10^-7m) Equations E=hf f=c/l *this equation applies in a vacuum Therefore E=hc/l E=(6.26*10^-34J*s) * (3.0 *10⁸ m/s)/(6.5 *10^-7 m) = 2.9 *10^-19 J

Question 3

When sodium acetate, NaCH₃COO, is added to water the resulting solution is basic. True or false?

Accepted Answer

The statement is true. In water, NaCH₃COO forms Na⁺ and CH₃COO- ions. Na⁺ is neutral, and does not affect the pH of the solution. CH₃COO- is the conjugate base of acetic acid, and reacts with water to form hydroxide ions. Therefore, the resulting solution will be basic.

Question 4

The following equation is under thermodynamic control. Assuming a temperature of 273K and using the provided information, find the K_eq:A + B --> CDG_f° (A) = -200 kJ/molDG_f° (B) = -100 kJ/molDG_f° (C) = -50 kJ/mol A)K_eq = 1.46 * 10^-14 B)K_eq= 1.46 * 10^-38 C)K_eq = 1.46 * 10^-48 D)K_eq = 0.83 * 10^-27 E)K_eq = 0.83 * 10^-32

Accepted Answer

Under thermodynamic control, the following equation applies: ln (K_eq ) = -DG_rxn °/(R*T) R=ideal gas constant = 8.314 J/mol K DG_rxn°=DG_Gproducts° - DG_Gproducts° DG_rxn° = [-50 kJ/mol * 1mol] - [-100kJ/mol * 1mol - 200kJ/mol * 1 mol] = 250 kJ = 250,000J ln (K_eq ) = -(250,000J)/((8.314J/mol K)*(273K)) solving for K_eq = 1.46 * 10^-48

Question 5

Which of the following compounds contains a double bond? A)C₂H₆ B)C₂H₄ C)C₃H₈ D)CH₄ E)C₄H₁₀

Accepted Answer

Hydrocarbons with the formula C_nH_2n contain double bonds. The only compound with this formula, C₂H₄, must contain a double bond.

Question 6

H₂S + H₂O --> HS^- + H₃O⁺ In the reaction above, what is the conjugate base of H?S? A)H₂O B)HS^- C)H₃O⁺ D)H₂S has no conjugate base E)H₂S acts as its own conjugate base

Accepted Answer

A conjugate acid/base pair is a pair of two compounds that differ only in the presence of a proton. The conjugate acid of a base is that base with one additional proton. The conjugate base of an acid is that acid with one less proton. In the context of the question, the conjugate base of H?S is the species with one less proton, HS-.

Question 7

What term classifies a phase change from a solid directly to a gas?
A)Vaporization
B)Deposition
C)Effervesence
D)Fusion
E)Sublimation

Accepted Answer

Vaporization is a phase change from liquid to gas. Deposition is a phase change from gas to solid. Effervescence does not describe a phase change. Fusion is a phase change from solid to liquid. Therefore, sublimation must be a phase change from solid to gas.

Question 8

Which of the following molecules does not display hydrogen bonding in the liquid phase? A)H₂O B)CH₃CH₂NH₂ C)CH₄ D)NH₃ E)HF

Accepted Answer

Hydrogen bonding occurs when hydrogen is covalently bound to the especially electronegative elements oxygen, nitrogen, and fluorine. The highly polar bond between hydrogen and these elements creates intermolecular attractive forces. The only molecule that does not contain hydrogen bound to one of these elements is CH₄. Thus, CH4 does not display hydrogen bonding.

Question 9

Which of the following elements is the most electronegative?
A)Boron
B)Lithium
C)Potassium
D)Oxygen
E)Cesium

Accepted Answer

Electronegativity describes the tendency of an atom to attract electrons in a covalent bond. In general, electronegativity increases going across periods and up groups. Thus, the elements in the top right corner of the periodic table are the most electronegative. In the context of the question, oxygen is the only element in this area of the periodic table, and it is the most electronegative.

Question 10

Which of the following molecules acts as a Lewis acid? A)HCl B)SO₄^2- C)CCl₄ D)H₃PO₄ E)BH₃

Accepted Answer

A Lewis acid is an electron pair receiver. In the context of the question, the only molecule that readily receives electron pairs is BH₃. Therefore, BH3 is a Lewis acid.

Question 11

Which of the following elements exists as a liquid at 25 degrees Celsius?
A)Silicon
B)Chlorine
C)Boron
D)Arsenic
E)Mercury

Accepted Answer

At 25 degrees Celsius, the only two elements that exist as liquids are bromine and mercury. In the context of the question, mercury is the only element that exists as a liquid at 25 degrees Celsius.

Question 12

How many molecules are in .275 grams of SO₃? A)3)22x10²⁰ B)4)50x10²¹ C)2)07x10²¹ D)1)12x10²⁰ E)4)56x10²²

Accepted Answer

Begin this problem by converting grams of SO₃ to moles of SO₃ using the molar mass of SO₃. Once you have obtained this value, use Avogadro's number to convert moles of SO3 to molecules of SO₃. The final expression is (.275 grams SO₃) x (1 mol / 80.057 grams) x (6.022x10²³molecules / 1 mol), indicating that the correct answer is 2.07x10²¹.

Question 13

Which of the following molecules displays planar geometry? A)NH₃ B)BH₃ C)XeO₄ D)CH₄ E)SiF₆

Accepted Answer

NH3 has three bonding hydrogens and a lone pair of electrons, giving it trigonal pyramidal geometry. XeO₄ has four bonding oxygens and thus tetrahedral geometry. Similarly, CH₄ has four bonding hydrogens and tetrahedral geometry. SiF₆ has six bonding flourines, and octahedral geometry. BH₃ has just three bonding hydrogens and no lone pairs of electrons, therefore displaying trigonal planar geometry.

Question 14

What volume of .250 M potassium hydroxide is needed to neutralize 1.25 liters of .500 M hydrochloric acid?
A)2)50 liters
B)1)25 liters
C))625 liters
D))375 liters
E)5)0 liters

Accepted Answer

Hydrochloric acid (HCl) is a strong, monoprotic acid. Potassium hydroxide (KOH) is a strong base that contains one hydroxide anion per molecule. The concentrations and volumes of these solutions are related by the formula (Molarity₁)(Volume₁) = (Molarity₂)(Volume₂). Entering the variables into this equation gives (.250 M)(Volume₁) = (.500 M)(1.25 liters). Solve for Volume1 to find the correct answer, 2.5 liters.

Question 15

Which of the following conditions guarantees that a reaction will occur spontaneously in the forward direction?
A)The temperature is negative
B)Change in enthalpy is positive
C)Change in entropy is negative
D)Change in Gibbs free energy is negative
E)Change in temperature is positive

Accepted Answer

A spontaneous process always moves from higher energy reactants to lower energy products. Therefore, the difference in energy between the products and the reactants is negative. Thus, a negative change in Gibbs free energy guarantees a spontaneous reaction in the forward direction.

Question 16

What is the concentration of H⁺ ions in a solution that has an OH^- concentration of 1x10^-4molar? A)1x10^-10 molar B)1x10^-9 molar C)1x10^-8 molar D)1x10^-5 molar E)1x10^-4 molar

Accepted Answer

Solutions that contain hydronium and hydroxide ions obey the equation [H⁺ ] [OH^-] = 1x10^-14 Plugging the values from the problem into this equation gives [H+] (1x10^-4) = 1x^-14 14. Solving for the concentration of H⁺ions gives the correct answer, 1x10^-10 molar.

Question 17

Ag⁺(aq) + e- --> Ag(s)In an electrolytic cell, where could this chemical reaction occur? A)Anode B)Cathode C)Salt bridge D)In solution E)This reaction could not occur in an electrolytic cell

Accepted Answer

This reaction shows a silver cation gaining an electron. Thus, silver is undergoing reduction. In electrolytic cells, reduction occurs at the cathode, so this reaction occurs at the cathode.

Question 18

Electrolysis requires energy input to force a non-spontaneous reaction to occur. True or false?

Accepted Answer

The statement is true. Electrolysis occurs when electrical current causes a non-spontaneous reaction to proceed.

Question 19

Which of the following elements has the largest atomic radius?
A)Lithium
B)Boron
C)Fluorine
D)Potassium
E)Rubidium

Accepted Answer

Atomic radius decreases across a period and increases down a group. Elements in the first group will be the largest in their period. Of these elements, the bottom most element (the element with the highest atomic number) will have the largest atomic radius. Therefore, rubidium has the largest atomic radius of the elements listed.

Question 20

Which pair of elements and/or ions is isoelectronic? A)F^- and Cl^- B)O and Na C)K⁺ and Ar D)Mg²⁺ and S E)Br and Kr

Accepted Answer

Two species are isoelectronic if they have the same number of electrons. Two neutral elements cannot be isoelectronic, so the correct pair must be either an element and an ion, or two ions. The correct pair, with 18 electrons each, is K⁺ and Ar.

Quiz 2: Chemistry

Which of these elements is most likely to have the highest second ionization energy? Hint: think of Lewis structures. A)Aluminum (Al) B)Phosphorus (P) C)Chlorine (Cl) D)Magnesium (Mg) E)Sodium (Na)

One liter of hydrogen gas is placed in a vacuum. The emission spectrum of hydrogen shows a red line of wavelength 650 nm. What was the energy of the photon that released it? A)2)9 * 10-28 J B)4)1 * 10-31 J C)2)9 * 10-19 J D)4)1 * 10-19 J E)2)9 * 10-15 J

When sodium acetate, NaCH3COO, is added to water the resulting solution is basic. True or false?

Which of the following compounds contains a double bond? A)C2H6 B)C2H4 C)C3H8 D)CH4 E)C4H10

H2S + H2O --> HS- + H3O+ In the reaction above, what is the conjugate base of H?S? A)H2O B)HS- C)H3O+ D)H2S has no conjugate base E)H2S acts as its own conjugate base

What term classifies a phase change from a solid directly to a gas? A)Vaporization B)Deposition C)Effervesence D)Fusion E)Sublimation

Which of the following molecules does not display hydrogen bonding in the liquid phase? A)H2O B)CH3CH2NH2 C)CH4 D)NH3 E)HF

Which of the following elements is the most electronegative? A)Boron B)Lithium C)Potassium D)Oxygen E)Cesium

Which of the following molecules acts as a Lewis acid? A)HCl B)SO42- C)CCl4 D)H3PO4 E)BH3

Which of the following elements exists as a liquid at 25 degrees Celsius? A)Silicon B)Chlorine C)Boron D)Arsenic E)Mercury

How many molecules are in .275 grams of SO3? A)3)22x1020 B)4)50x1021 C)2)07x1021 D)1)12x1020 E)4)56x1022

Which of the following molecules displays planar geometry? A)NH3 B)BH3 C)XeO4 D)CH4 E)SiF6

What volume of .250 M potassium hydroxide is needed to neutralize 1.25 liters of .500 M hydrochloric acid? A)2)50 liters B)1)25 liters C))625 liters D))375 liters E)5)0 liters

Which of the following conditions guarantees that a reaction will occur spontaneously in the forward direction? A)The temperature is negative B)Change in enthalpy is positive C)Change in entropy is negative D)Change in Gibbs free energy is negative E)Change in temperature is positive

What is the concentration of H+ ions in a solution that has an OH- concentration of 1x10-4molar? A)1x10-10 molar B)1x10-9 molar C)1x10-8 molar D)1x10-5 molar E)1x10-4 molar

Ag+(aq) + e- --> Ag(s)In an electrolytic cell, where could this chemical reaction occur? A)Anode B)Cathode C)Salt bridge D)In solution E)This reaction could not occur in an electrolytic cell