Chem 314 Ch 6

What is the pH of a 7.8×10−5 M Ca(OH)2 solution? 10.19 3.81 4.11 9.89

10.19 [OH−]=2×[Ca(OH)2] Calculate the pOH. pOH=−log[OH−] Then calculate the pH. 14.00=pH+pOH

What is the pOH of a 0.036 M HNO3 solution?

12.56 HNO3 is a strong acid, so [HNO3]=[H+]. Calculate the pH of the solution. pH=−log[H+]=−log(0.036)=1.44 Then calculate the pOH. 14.00= pH+pOH= 1.44+pOH pOH=12.56

A reaction has a ΔH∘=−15.2 kJ/mol and a ΔS∘=29.2 J/K·mol. Calculate the temperature at which the change in Gibbs free energy is equal to −17.5 kJ/mol. Assume ΔH and ΔS change little with temperature.

78.8 K The standard change in Gibbs free energy, ΔG∘, is related to ΔH∘ and ΔS∘ through the following equation: ΔG∘=ΔH∘−TΔS∘ T=(ΔH∘−ΔG)/ΔS∘

Identify the Lewis acid in the following reaction: Cl^−+AlCl3⇌[AlCl4]^−

AlCl3^- A Lewis acid accepts a pair of electrons from a Lewis base when the two form a bond. AlCl3 has an electron-deficient aluminum atom with only six electrons, instead of the preferred eight. Therefore, AlCl3acts as a Lewis acid, accepting an electron pair from Cl−.

Water decomposes to form hydrogen and oxygen gas. 2 H2O(g)⇌2 H2(g)+O2(g). ΔH∘=570 kJ/mol If the reaction is at equilibrium and the temperature is decreased, will more or less water be formed? Temperature does not affect how much water is formed. At a lower temperature, more water will be consumed. At a lower temperature, less water will form. At a lower temperature, more water will form.

At a lower temperature, more water will form.

Which of the following is most likely to act as a Lewis acid? BH3 CH4 H2O CN^−

BH3 A Lewis acid accepts a pair of electrons from a Lewis base when the two form a bond. BH3 contains an electron-deficient boron atom with only six electrons, instead of the preferred eight. Therefore, BH3 acts as a Lewis acid.

What is the conjugate acid of HCO3^-?

H2CO3 Conjugate acids and bases are related to each other by the gain or loss of one H+. The conjugate acid has one more proton than the base. Therefore, the conjugate acid of HCO3^- is H2CO3.

Identify the conjugate acid‑base pair. HNO3, NO3^- HNO3, H2NO3^- HNO3, H2NO3 HNO3, NO3^+

HNO3, NO3^- Conjugate acids and bases are related to each other by the gain or loss of one H+. Removing H+ from the acid HNO3 results in the formation of the conjugate base NO−3.

What is the value of K3? K1= 1.764*10^-1 K2= 3.03*10^-5

K3=K1×K2= (1.764×10^−1)×(3.030×10^−5)= 5.345×10^−6

Kb for ethylamine is 6.31×10−4. Calculate the Ka of the ethylammonium ion at 25°C.

Ka=Kw/Kb=1.00×10^−14/6.31×10−4=1.58×10−11

What is the Ksp expression for aluminum carbonate?

Ksp=[Al^3+]^2[CO2^−3]^3

What is the Ksp expression for lead(II) iodide?

Ksp=[Pb2+][I−]2 The solubility product is the equilibrium constant for the reaction in which a solid salt dissolves to give its constituent ions in solution. The dissolution reaction of lead(II) iodide is PbI2(s)⇌Pb2+(aq)+2 I−(aq) for which the solubility product, Ksp, is Ksp=[Pb2+][I−]2 Solid lead(II) iodide is omitted from the expression because it is in its standard state.

What is the conjugate base of HNO2? H2NO−2 H2NO+2 NO−2 NO+2

NO2^-

What is the conjugate base of H2O? H3O OH H3O+ OH−

OH− Conjugate acids and bases are related to each other by the gain or loss of one H+. The conjugate base has one less proton than the acid. Therefore, the conjugate base of H2O is OH−.

Phosgene is a toxic gas produced by the reaction between carbon monoxide and chlorine gas. CO(g)+Cl2(g)⇌COCl2(g) The equilibrium constant, K, for the reaction is 0.250 at a certain temperature. A reaction mixture contains 0.100 M phosgene, 0.300 M carbon monoxide, and 0.360 M chlorine. In which direction will the reaction proceed to reach equilibrium? a) The reaction will proceed in the forward direction. b) The reaction will proceed in the reverse direction. c) First, the reaction will proceed in the forward direction and then in the reverse direction. d) The reaction is at equilibrium.

The reaction will proceed in the reverse direction. The reaction quotient for the reaction is Q=[COCl2]/[CO][Cl2] Substitute the concentrations of the reactants and products into the expression to find the value of Q. Q=0.100/(0.300)(0.360)=0.926. Q=0.926 and K=0.250, so Q>K and the reaction will proceed in the reverse direction until equilibrium is reached.

How will the solubility of AgCl be affected by the addition of NaCl to a saturated solution of AgCl? The solubility will increase. The solubility will decrease. The solubility will not change. The change in solubility cannot be determined.

The solubility will decrease.

Which is TRUE for pure water at all temperatures? [H3O+]>[OH−] [H3O+]=1.0×10−7 M [H3O+]=[OH−] [H3O+]<[OH−]

[H3O+]=[OH−] Water undergoes self-ionization, called autoprotolysis, in which it acts as both an acid and a base. H2O+H2O⇌H3O^+ + OH^−The autoprotolysis constant (Kw) for the reaction is Kw=[H3O+][OH−]. At 25°C, Kw=1.01×10−14, meaning [H3O+]=[OH−]=1.0×10−7 M at 25°C. Kw varies with temperature, but [H3O+]=[OH−] at all temperatures.

A solution that has a pH<7 at 25∘C is

acidic

Bromine gas and nitric oxide can combine to form nitrosyl bromide, NOBr. Br2(g)+2 NO(g)⇌2 NOBr(g) The equilibrium constant, K, for the reaction is 9.00×103 at a certain temperature. A reaction mixture contains 1.50 M nitrosyl bromide, 0.100 M bromine, and 0.050 M nitric oxide. In which direction will the reaction proceed to reach equilibrium? a)First, the reaction will proceed in the forward direction and then in the reverse direction. b) The reaction is at equilibrium. c) The reaction will proceed in the forward direction. d)The reaction will proceed in the reverse direction.

b) The reaction is at equilibrium The reaction quotient for the reaction is Q=[NOBr]^2/[Br2][NO]^2 Substitute the concentrations of the reactants and products into the expression to find the value of Q. Q=1.502/(0.100)(0.050)2=9 000. Q=9.00×10^3 and K=9.00×10^3, so Q=K and the reaction is at equilibrium.

Identify the conjugate acid‑base pair that consists of the base from the forward reaction and the acid from the reverse reaction. H2CO3+H2O⇌HCO−3+H3O+ a) H2O and H3O+ b) H2CO3 and H3O+ c) H2CO3 and HCO−3 d) H2O and HCO−3

d) H2O and HCO3^- , H2CO3 donates H+to H2O, so H2CO3 is the acid and H2O is the base. In the reverse reaction, HCO−3 accepts H+ from H3O+, so HCO−3 is the base and H3O+ is the acid. H2CO3 and HCO−3 are a conjugate pair and H2O and H3O+ are a conjugate pair

Which statement regarding the following reaction is TRUE? NaNO3(s)⇌Na+(aq)+NO−3(aq). ΔS∘=+89.1 J/K a) The aqueous ions have less energy dispersed than the solid NaNO3. b) The products have lower entropy than the reactants. c) The reaction is endothermic. d) The products have more energy dispersed than the reactant.

d) The products have more energy dispersed than the reactant. A positive ΔS∘ indicates that the products have greater entropy than the reactants.

Lewis acid

electron pair acceptor

What is a Lewis base?

electron pair donor

For a given material, which phase has the highest entropy?

gas

What is the pH of an acidic solution at 25∘C?

pH < 7

Calculate the pH of a 0.025 M solution of HBr.

pH= −log[H+]= −log(0.025)= 1.60

Calculate the standard change in Gibbs free energy, ΔG∘, in kilojoules per mole, for the following reaction at 298 K. N2(g)+3 H2(g)→2 NH3(g). ΔH∘=−91.8 kJ/mol ΔS∘=−198.0 J/K·mol

ΔG∘=ΔH∘−TΔS∘ ΔG∘=−91.8 kJ/mol−(298 K)(−198.0×10−3 kJ/K·mol)=. −32.8 kJ/mol

After mixing two reagents in a beaker, the beaker becomes cold to the touch. Which statement is TRUE? a. ΔH for the reaction is negative. b. Heat is released by the reaction. c.The reaction is exothermic. d. ΔH for the reaction is positive.

ΔH for the reaction is positive.

Which statement regarding enthalpy is TRUE? Please choose the correct answer from the following choices, and then select the submit answer button. ΔH is negative for an exothermic reaction. A positive ΔH indicates that heat is released. Heat is absorbed in an exothermic reaction. ΔH is negative for an endothermic reaction

ΔH is negative for an exothermic reaction.

Pb2+ forms a series of complex ions with OH−. Which cumulative formation constant expression represents the formation of the complex ion Pb(OH)4^2- (aq)?

β4=[Pb(OH)4^2-] / [Pb^2+][OH−]^4 M+nX⇌MXn It is also called the overall formation constant. The reaction for the formation of Pb(OH)2−4(aq) from Pb2+and OH− is Pb2+(aq)+4 OH−(aq)⇌Pb(OH)2−4(aq)