Question 1

According to Grahm's law, which of the following gases would effuse through a small hole in a closed container the fastest?

Accepted Answer

According to Grahm's law, a gas effuses at a rate inversely proportional to the square root of its mass. Thus, the lightest gas, H₂, will effuse the fastest.

Question 2

Compound X donates a pair of electrons in a chemical reaction. This compound is best classified as a(n)

Accepted Answer

A Lewis base donates a pair of electrons in a chemical reaction. The compound caN_Not be a halogen because halogens receive electrons to form a full octet.

Question 3

CH₃COOH + H₂O --> CH₃COO^- + H₃O⁺ Which of the following descriptions best characterizes CH₃COO^- in the reaction above?

Accepted Answer

In the reaction above, CH₃COOH acts as a weak acid. Therefore, CH₃COO^- is best characterized as a conjugate base.

Question 4

Using the ideal gas equation, find the pressure of 22.4L of helium at 273K when n=1.00 mol. Adjust this calculation using the real gas equation to find the actual pressure. What are the ideal and real pressures?

Accepted Answer

Solution is as follows: PV=nRT P=pressure (atm) V=volume (22.4L) n=amount (1 mol) R = constant (0.08206 L*atm/mol*K) T = temperature (273K) Ideal gas equaion gives P=1.0atm a=0.03412 (L²*atm/moL²) b= 0.02370 (L/mol) (P+(an²/V²))(V-nb)=nRT By substituting in the known values of V, n, R, and T, you solve for P=1.001atm, or 1.00atm with significant figures.

Question 5

Find the pH of the a 0.500M solution of the weak base Ammonia (NH₃). The k_b = 1.78*10^-5 NH₃ +H₂O --> NH₄⁺ + OH^-

Accepted Answer

The solution is as follows: The equilibrium equation is k_b=[NH₄][OH^-]/[NH₃] Since NH₃ will not fully dissociate, the concentrations of OH^- and HN ₃are unknown (x) and the concentration of NH₃ at equilibrium will be 0.5 - x. k_b = [x][x]/[0.500-x] Assuming x is so small it's negligible, that yields; k_b = x²/[0.500] (1.78 * 10^-5) = x²/[0.500] (1.78 * 10^-5) * 0.500 = x² x= .003M which is the concentration of OH^- Using the equilibrium equation for water, we have H₂O? H⁺ + OH^- The equilbrium value, Kw is 10^-14 Kw = [H⁺][OH^-] * 10^-14 = [H⁺][0.003] [H⁺] = 3.33*10^-12 pH = -log [H⁺] = -log (3.33 * 10^-12) = 11.48

Question 6

In the following titration reaction: I ₂+ 2 s₂O₃- --> S₄O₆-2 + 2I^- Starch is used as an indicator. When starch is exposed to iodine (I₂) it is a deep blue color. When the iodine is reduced to iodide (I^-), the solution will turn clear. Assume that it takes 100mL of 0.500M s₂O₃^- to neutralize 50mL of I ₂(indicated by the solution turning clear). What was the original concentration of iodine?

Accepted Answer

Solution is as follows: V_s2O3 = 100mL = 0.1 L [s₂O₃] = 0.500M V_{I 2}= 50mL = 0.05L [I₂] = ?? moles of s₂O₃ = 0.500M * 0.1L = 0.05mol s₂O₃ from the mole ratio in the balanced chemical equation, 1mol I ₂= 2mol s₂O₃ 0.05mol s₂O₃ * 1mol I₂/2mol s₂O₃ = 0.025mol I₂ M=n/V which means the concentration of iodine is 0.025mol/0.05L = .5M

Question 7

Which of the following isn't true about electrostatic force?

Accepted Answer

F=k_e * (q₁)(q₂)/(r²) where F is force, ke is Coulomb's constant, q₁ and q₂ are the magnitudes of the charges and r is the distance between the charges (meaning B is true because distance is a factor). As r decreases, F increases because dividing by a smaller number always yields a larger result. Thus C is false and D is true.

Question 8

Calculate the change in entropy of the following equation: FeCl₃(s) + 3Na(s) --> Fe(s) + 3NaCl(s)

Accepted Answer

Solution is as follows: DS_rXN° = DS_products° - DS_reactants° Students must look up the DS° for each product and reactant. The numbers are as follows: DS° (FeCl₃_(s)) = 142.3 J/mol K DS° (Na_(s)) = 51.3 J/mol K DS° (Fe_(s)) = 27.2 J/mol K DS° (NaCl_(s)) = 72.3 J/mol K Therefore DS_rXN° = [(1mol * 27.2 J/mol K) + (3mol * 72.3 J/mol K) ] - [ (1mol * 142.3 J/mol K) +(3mol * 51.3 J/mol K)] DS_rXN° = -52.1 J/K ***mole amounts come from the stoichiometry

Question 9

In a galvanic cell (aka a voltaic cell), you have zinc and copper reacting. The shorthand version of these reactions is Zn|Zn⁺²| |Cu⁺²|Cu. Find the potential energy (E _cell°) of this battery.

Accepted Answer

Solution is as follows: The short hand reaction Zn|Zn⁺² yields a halF^-reaction of Zn -> Zn⁺² + 2 e-. This is an oxidation reaction because the zinc's charge increases and it loses electrons. The corresponding half reaction for copper is Cu⁺² + 2 e- -> Cu, which is a reduction reaction. The total reaction happening in this cell is: Zn + Cu⁺² --> Zn⁺² + Cu Use the equation E _cell °= E_oxidation° + E_reduction° Look up the standard reduction potential (V) for both half reactions. Zn --> Zn⁺² + 2 e- has a V = -0.76V Cu⁺² + 2 e- --> Cu has a V = 0.34V Adding those values yields E _cell °= -0.42V

Question 10

A substance has a lustrous surface, conducts electricity, and displays the characteristics of malleability and ductility. This substance is a nonmetal.

Accepted Answer

The statement is false; the substance is not a nonmetal. Each of the attributes listed is characteristic of a metal. Metals have a shiny surface and readily conduct electric current. Due to their delocalized bonding, metals can also be hammered into sheets (malleability) and pulled into wire (ductility).

Question 11

Many of the properties of metals can be accounted for with the delocalized electron model.

Accepted Answer

This statement is true. The electrons in a metal are free to roam in a "sea of electrons." This property accounts for malleability, ductility, electrical conductivity and other properties of metals.

Question 12

Molal concentration, m, is expressed as (kilograms of solute) / (kilograms of solvent).

Accepted Answer

The statement is false. Molal concentration is expressed as (moles of solute) / (kilograms of solvent). Molal concentration is not an especially common convention, but it must still be understood for problems involving colligative properties of solutions.

Question 13

In an electrolytic cell, oxidation occurs at the anode.

Accepted Answer

The statement is true. In an electrolytic cell, anions flow to the anode to deposit electrons and undergo oxidation.

Question 14

Na⁺ --> Na²⁺ + e^- The reaction above is endothermic.

Accepted Answer

The statement is true. Energy must be added in order to drive this non-spontaneous reaction. Ionization almost always requires energy input.

Question 15

The electron configuration 1s²2s²2p⁶3s¹3p⁵ represents an excited state.

Accepted Answer

The statement is true. Normally, the 3s orbital is filled with two electrons before any electrons fill the 3p orbital. However, the configuration 1s²2s²2p⁶3s¹3p⁵ indicates that an electron has the excess energy to jump from the 3s orbital to the 3p orbital. Thus, the configuration must be for an excited state.

Quiz 2: Chemistry

According to Grahm's law, which of the following gases would effuse through a small hole in a closed container the fastest?

Compound X donates a pair of electrons in a chemical reaction. This compound is best classified as a(n)

CH₃COOH + H₂O --> CH₃COO^- + H₃O⁺ Which of the following descriptions best characterizes CH₃COO^- in the reaction above?

Using the ideal gas equation, find the pressure of 22.4L of helium at 273K when n=1.00 mol. Adjust this calculation using the real gas equation to find the actual pressure. What are the ideal and real pressures?

Find the pH of the a 0.500M solution of the weak base Ammonia (NH₃) . The k_b = 1.78*10^-5 NH₃ +H₂O --> NH₄⁺ + OH^-

Which of the following isn't true about electrostatic force?

Calculate the change in entropy of the following equation: FeCl₃(s) + 3Na(s) --> Fe(s) + 3NaCl(s)

In a galvanic cell (aka a voltaic cell) , you have zinc and copper reacting. The shorthand version of these reactions is Zn|Zn⁺²| |Cu⁺²|Cu. Find the potential energy (E _cell°) of this battery.

A substance has a lustrous surface, conducts electricity, and displays the characteristics of malleability and ductility. This substance is a nonmetal.

Many of the properties of metals can be accounted for with the delocalized electron model.

Molal concentration, m, is expressed as (kilograms of solute) / (kilograms of solvent).

In an electrolytic cell, oxidation occurs at the anode.

Na⁺ --> Na²⁺ + e^- The reaction above is endothermic.

The electron configuration 1s²2s²2p⁶3s¹3p⁵ represents an excited state.

Quiz 2: Chemistry

According to Grahm's law, which of the following gases would effuse through a small hole in a closed container the fastest?

Compound X donates a pair of electrons in a chemical reaction. This compound is best classified as a(n)

CH3COOH + H2O --> CH3COO- + H3O+ Which of the following descriptions best characterizes CH3COO- in the reaction above?

Using the ideal gas equation, find the pressure of 22.4L of helium at 273K when n=1.00 mol. Adjust this calculation using the real gas equation to find the actual pressure. What are the ideal and real pressures?

Find the pH of the a 0.500M solution of the weak base Ammonia (NH3) . The kb = 1.78*10-5 NH3 +H2O --> NH4+ + OH-

Which of the following isn't true about electrostatic force?

Calculate the change in entropy of the following equation: FeCl3(s) + 3Na(s) --> Fe(s) + 3NaCl(s)

In a galvanic cell (aka a voltaic cell) , you have zinc and copper reacting. The shorthand version of these reactions is Zn|Zn+2| |Cu+2|Cu. Find the potential energy (E cell°) of this battery.

A substance has a lustrous surface, conducts electricity, and displays the characteristics of malleability and ductility. This substance is a nonmetal.

Many of the properties of metals can be accounted for with the delocalized electron model.

Molal concentration, m, is expressed as (kilograms of solute) / (kilograms of solvent).

In an electrolytic cell, oxidation occurs at the anode.

Na+ --> Na2+ + e- The reaction above is endothermic.

The electron configuration 1s22s22p63s13p5 represents an excited state.

CH₃COOH + H₂O --> CH₃COO^- + H₃O⁺ Which of the following descriptions best characterizes CH₃COO^- in the reaction above?

Find the pH of the a 0.500M solution of the weak base Ammonia (NH₃) . The k_b = 1.78*10^-5 NH₃ +H₂O --> NH₄⁺ + OH^-

Calculate the change in entropy of the following equation: FeCl₃(s) + 3Na(s) --> Fe(s) + 3NaCl(s)

In a galvanic cell (aka a voltaic cell) , you have zinc and copper reacting. The shorthand version of these reactions is Zn|Zn⁺²| |Cu⁺²|Cu. Find the potential energy (E _cell°) of this battery.

Na⁺ --> Na²⁺ + e^- The reaction above is endothermic.

The electron configuration 1s²2s²2p⁶3s¹3p⁵ represents an excited state.