Chem 2 Exam 3
Classify these salts as acidic, basic, or neutral.
Acidic: NH4ClO4 Basic: K3PO4, NaF Neutral: KCl, LiBr
What is Δn for the following equation in relating Kc to Kp? N2(g) + 3 Br2(g) ⇌ 2 NBr3(g)
-2
Calculate the value of [N2]eq if [H2]eq = 1.5 M, [NH3]eq = 0.5 M, and Kc = 2. N2(g) + 3 H2(g) ⇌ 2 NH3(g)
0.037 M
Consider the following reaction: CH4(g) + 2 H2S(g) ⇌ CS2(g) + 4 H2(g)A reaction mixture initially contains 0.50 M CH4 and 0.75 M H2S. If the equilibrium concentration of H2 is 0.44 M, find the equilibrium constant (Kc) for the reaction.
0.038
Which solution will be the most basic?
0.10 M Ba(OH)2 or 0.10 M KOH
Determine the ammonia concentration of an aqueous solution that has a pH of 11.30. The equation for the dissociation of NH3 (Kb = 1.8 × 10-5) isNH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq)
0.22 M
The equilibrium constant is given for two of the reactions below. Determine the value of the missing equilibrium constant. A(g) + B(g) ⇌ AB(g) Kc= 0.24 AB(g) + A(g) ⇌ A2B(g) Kc= 3.8 2A(g) + B(g) ⇌ A2B(g) Kc= ?
0.91
The Kp for the reaction below is 1.49 × 108 at 100.0°C: CO(g) + Cl2(g) ⇌ COCl2(g)In an equilibrium mixture of the three gases, PCO = PCl2 = 8.60 × 10-4 atm. The partial pressure of the product, phosgene (COCl2), is ________ atm.
1.10 x 10 2
Calculate the pH of a 0.40 M H2SO3, solution that has the stepwise dissociation constants Ka1 = 1.5 × 10-2 and Ka2 = 6.3 × 10-8 .
1.15
An equilibrium mixture of CO, O2 and CO2 at a certain temperature contains 0.0010 M CO2 and 0.0100 M O2. At this temperature, Kc equals 1.4 × 102 for the reaction: 2 CO(g) + O2(g) ⇌ 2 CO2(g). What is the equilibrium concentration of CO?
1.2 x 10 -1 or 8.4 x 10 -4
The Ka of some acid, HA, at 25.0 °C is 4.9 × 10-10. What is the pH of a 0.050 M aqueous solution of A-?
11.00
Calculate the pH of a 0.500 M aqueous solution of NH3. The Kb of NH3 is Kb = 1.77 × 10-5.
11.47
A 1.0 × 10-2 M aqueous solution of Ca(OH)2 at 25.0 °C has a pH of ________.
12.30
The reaction below has a Kp value of 41.0. What is the value of Kc for this reaction at 275. K? N2(g) + 3 H2(g) ⇌ 2 NH3(g)
2.09 x 10 4
The base-dissociation constant of ethylamine (C2H5NH2) is 6.4 × 10-4 at 25.0°C. The [H+] in a 0.014 M solution of ethylamine is ________ M.
3.7 x 10 -12
What is the pH of 0.626 M anilinium hydrochloride (C6H5NH3Cl) solution in water, given that Kb for aniline is 3.83 × 10-4?
5.39
What is the concentration (in M) of hydronium ions in a solution at 25.0 °C with pH = 4.146?
7.15 × 10-5
What is the pH of a buffer solution that is 0.172 M in hypochlorous acid (HClO) and 0.131 M in sodium hypochlorite? The Ka of hypochlorous acid is 3.8 × 10-8.
7.30
Identify the Lewis acid and Lewis base in each of the reactions.
A Lewis acid is an electron acceptor A Lewis base is an electron donor Cl- + AlCl3 -> AlCl4- Cl- (Base) AlCl3 (acid) BF3 + F- -> BF4- BF3 (acid) F- (base) NH3 + H+ -> NH4+ NH3 (base) H+ (Acid)
Identify the conjugate base for each acid. conjugate base of H2SH2S: HS−(aq)HS−(aq) conjugate base of HS−HS−: S2−S2− conjugate base of NH+4NH4+:
A conjugate base has one less H in its formula and it decreases in charge by one unit compared to the acid H2S <-> H+ + HS- => HS- is conjugate base) HS-<-> H+ + S2- => (S2- is conjugate base) NH4+ <-> H+ + NH3 (NH3 is conjugate base)
The reaction between nitrogen and hydrogen to produce ammonia is described by the following equilibrium reaction. 3H2+N2↽−−⇀2NH33H2+N2↽−−⇀2NH3 What substances are present in the reaction mixture when equilibrium has been obtained?
H2 , N2, NH3
In a 11 M solution of NH3(aq)NH3(aq), arrange the species by their relative molar amounts in solution.
H2O>NH3>NH4+~OH->H3O+
What is the conjugate acid of HSO3⁻ ?
H2SO3
Identify each reactant and product in this reaction as a Brønsted acid or base. H2Y- + H2Z- <-> H3Y + HZ 3-
H2Y- = base H2Z- = acid H3Y = acid HZ2- = base
Based on the structures of H3PO2(l), H3PO3(l), and H3PO4(l), determine the number of ionizable protons (acidic hydrogen atoms) per formula unit.
H3PO2 : 1:monoprotic H3PO3 : 2:diprotic H3PO4 : 3:tripotic
Which of the following acids will have the strongest conjugate base?
HCN
Of the following, which is the strongest acid?
HIO4
Of the following, which is the weakest acid?
HPO3-
Express the equilibrium constant for the following reaction. 3 P4(s) + 15 O2(g) ⇌ 3 P4O10(s)
K =1/([O2]15)
Of the compounds below, a 0.1 M aqueous solution of ________ will have the highest pH.
KCN, Ka of HCN = 4.0 × 10-10
Using chemical equations, show how the triprotic acid H3PO4H3PO4 ionizes in water. Phases are optional.
Ka1: H3PO4+H2O↽−−⇀H3O++H2PO−4 Ka2: H2PO−4+H2O↽−−⇀H3O++HPO2−4 Ka3: HPO2−4+H2O↽−−⇀H3O++PO3−4
Write the balanced 𝐾aKa and 𝐾bKb reactions for HSO−3HSO3− in water. Include physical states for each species.
Ka: HSO−3(aq)+H2O(l)↽−−⇀SO2−3(aq)+H3O+(aq) Kb: HSO−3(aq)+H2O(l)↽−−⇀H2SO3(aq)+OH−(aq)
For the reaction 4PH3(g)↽−−⇀6H2(g)+P4(g)4PH3(g)↽−−⇀6H2(g)+P4(g) the equilibrium concentrations were found to be [PH3]=0.250 M,[PH3]=0.250 M, [H2]=0.560 M,[H2]=0.560 M, and [P4]=0.750 M.[P4]=0.750 M. What is the equilibrium constant for this reaction?
Kc = [H2]^6[P4]/[PH3]^4 =(0.560)^6(0.750)/0.250)^4 = 5.92
Consider the reaction. PCl5(g)↽−−⇀PCl3(g)+Cl2(g)𝐾c=0.0420PCl5(g)↽−−⇀PCl3(g)+Cl2(g)Kc=0.0420 The concentrations of the products at equilibrium are [PCl3]=0.230 M[PCl3]=0.230 M and [Cl2]=0.170 M[Cl2]=0.170 M. What is the concentration of the reactant, PCl5PCl5, at equilibrium?
Kc = [PCl3][Cl2]/[PCl5] swap kc and [PCl5] [PCl5] = [PCl3][Cl2]/Kc =[0.230][0.170]/[0.0420] =0.0391/0.0420 = 0.931 M
Write the equilibrium‑constant expression for the reaction shown in terms of [A],[B], [C], and [D]. A(g)+B(g)↽−−⇀2C(g)+D(g)A(g)+B(g)↽−−⇀2C(g)+D(g) Note that 𝐾c,Kc, which is sometimes symbolized as 𝐾K or 𝐾eq,Keq, denotes that the equilibrium constant is expressed using molar concentrations. For this question, 𝐾cKc means the same thing as 𝐾K and 𝐾eq.
Kc = [products] / [reactants] = [C]^2 [D]/[A][B]
At a certain temperature, nitrogen and hydrogen react to form ammonia: N2(g) + 3 H2(g) ⇌ 2 NH3(g). When initial amounts of N2, H2, and NH3 are mixed, the concentration of NH3 increases. Which statement below is TRUE?
Kc > Q
The elementary reaction 2H2O(g)↽−−⇀2H2(g)+O2(g)2H2O(g)↽−−⇀2H2(g)+O2(g) proceeds at a certain temperature until the partial pressures of H2O,H2O, H2,H2, and O2O2 reach 0.0650 atm,0.0650 atm, 0.00900 atm,0.00900 atm, and 0.00850 atm,0.00850 atm, respectively. What is the value of the equilibrium constant at this temperature?
Kp = (PH^2)^2 (PO2)/(PH2O)^2 = (0.00900)^2 (0.00850)/(0.0650)^2 = 0.000163 or 1.63 x 10 ^-4
The equilibrium constant for the chemical equation N2(g)+3H2(g)↽−−⇀2NH3(g)N2(g)+3H2(g)↽−−⇀2NH3(g) is 𝐾p=0.0461Kp=0.0461 at 209 ∘C.209 ∘C. Calculate the value of 𝐾cKc for the reaction at 209 ∘C.
Kp=Kc(RT) ^ delta n Delta n = moles of gas in products - moles of gas in reactants = 2-4= -2 Kp= 0.0461 = Kc (0.08206 x (209+273K)^-2 = 72.1
At 850 K, the equilibrium constant for the reaction 2SO2(g)+O2(g)↽−−⇀2SO3(g)2SO2(g)+O2(g)↽−−⇀2SO3(g) is 𝐾c=15.Kc=15. If the given concentrations of the three gases are mixed, predict in which direction the net reaction will proceed toward equilibrium.
Left: [So2] = 0.14 M ; [O2] = 0.20 M ; [So3] = 0.40 M No Net Reaction: [SO2] = 0.20 M ; [O2] = 0.60 M ; [SO3] = 0.60 M Right: [So2] = 0.80 M ; [O2] = 0.70 M ; [SO3] = 0.16 M
In the gas phase reaction below, NH3 is acting as a(n) ________.
Lewis base
At a certain temperature, 0.42110.4211 mol of N2N2 and 1.5611.561 mol of H2H2 are placed in a 2.002.00 L container. N2(g)+3H2(g)↽−−⇀2NH3(g)N2(g)+3H2(g)↽−−⇀2NH3(g) At equilibrium, 0.20010.2001 mol of N2N2 is present. Calculate the equilibrium constant, 𝐾cKc.
Make your ice table with the given values and find the equilibrium by subtracting the initial from the equilibrium: 0.4221-0.2001 = 0.2210 Then determine the change in amount of H2 and NH3 N2: 0.2210 3H2: 3(0.2210)=0.898 2NH3: 2(0.2210)=0.4420 Then calculate the molar concentrations using the given volume [N2] = 0.2001/2.00 = 0.100 M [H2] = 0.898 /2.00 = 0.449 M [NH3] = 0.4420 / 2.00 = 0.221 Then the equilibrium constant expression for the reaction is Kc = [NH3] ^2 / [N2][H2]^3 = (0.221)^2/(0.100)(0.449)^3 = 5.39
Of the following substances, an aqueous solution of ________ will form basic solutions.
NaHS, KHCO3 and NaF
Which of the following aqueous solutions has the highest [OH-]?
Pure Water
Consider this equilibrium reaction at 400 K. Br2(g)+Cl2(g)↽−−⇀2BrCl(g)𝐾c=7.0Br2(g)+Cl2(g)↽−−⇀2BrCl(g)Kc=7.0 If the composition of the reaction mixture at 400 K is [BrCl]=0.00182[BrCl]=0.00182 M, [Br2]=0.00503[Br2]=0.00503 M, and [Cl2]=0.000924[Cl2]=0.000924 M, what is the reaction quotient, 𝑄Q? How is the reaction quotient related to the equilibrium constant, Kc, for this reaction?
Q = [products]/[reactants] = [BrCl]^2/[Br][Cl] = (0.00182)^2/(0.00503)(0.000924) = 0.710 Q<Kc
Consider this system at equilibrium. A(aq) <-> B(aq) DeltaH = +250 kJ/mol. What can be said about Q and K immediately after an increase in temperature? How will the system respond to a temperature increase?
Q>K because Q increased and will shift to the right
Which of the following 0.5 M aqueous salt solutions will have a pH of 7.0 at room temperature. LiF RbBr NaClO4 NH4Cl
RbBr and NaClO4
Consider the equilibrium reaction 4A+B↽−−⇀3C4A+B↽−−⇀3C Write the equation for the reverse reaction. Write the equilibrium‑constant expression in terms of [A],[A], [B],[B], and [C][C] for the reverse reaction. If the equilibrium concentrations are 1.31 M A,1.31 M A, 1.39 M B,1.39 M B, and 2.07 M C,2.07 M C, calculate the value of the equilibrium constant of the reverse reaction.
Reverse Reaction: 3c<->4A + B Kreverse: products/reactants = [B][A]^4/[C}^3 Kreverse value: (1.39 M B) (1.31 M A) ^4 / (2.07 M C) ^3 = 0.462
For which reaction will Kp = Kc?
S(s) + O2(g) ⇌ SO2(g)
Write the equilibrium‑constant expression for the reaction A(s)+3B(l)↽−−⇀2C(aq)+D(aq)A(s)+3B(l)↽−−⇀2C(aq)+D(aq) in terms of [A], [B], [C], and [D], as needed. Note that 𝐾c,Kc, which is sometimes symbolized as 𝐾eq,Keq, denotes that the equilibrium constant is expressed using molar concentrations. For this question, 𝐾cKc means the same thing as 𝐾eq
Since solids and liquids have constant concentrations they are not included in Kc expressions so -> [C]^2 [D] / 1
Two reactions and their equilibrium constants are given. A+2B2C↽−−⇀2C↽−−⇀D𝐾1𝐾2=2.93=0.108A+2B↽−−⇀2CK1=2.932C↽−−⇀DK2=0.108 Calculate the value of the equilibrium constant for the reaction D↽−−⇀A+2B.
Start by combining the two reactions A = 2B <-> 2C k1 = 2.93 2C <-> D k2 = 0.109 = A+2B <-> D k3 = ? k3 = (k1)(k2) =(2.93)(0.109) =0.316 The equilibrium constant for the reverse reaction D<->A+2B is the inverse of K3 K=1/k3 =1/0.316 =3.16
At a certain temperature, the equilibrium constant, 𝐾c,Kc, for this reaction is 53.3. H2(g)+I2(g)↽−−⇀2HI(g)𝐾c=53.3H2(g)+I2(g)↽−−⇀2HI(g)Kc=53.3 At this temperature, 0.800 mol H20.800 mol H2 and 0.800 mol I20.800 mol I2 were placed in a 1.00 L container to react. What concentration of HIHI is present at equilibrium?
Start off with an ice table and get Kc = [HI]^2 / [H2][I] = 53.3 = (2x)^2 / (0.800-x)^2 take sq root of each side 7.30 = 2x/0.800-x multiply both sides by 0.800-x 7.30(0.800-x) = 2x multiply 5.84 - 7.30x = 2x add 7.30x to each side 5.84 = 9.30x divide both sides by 9.30 x=0.628M Since the table says the final concentration of [HI] is 2x: 2(0.628) =1.26 M
Indicate how the concentration of each species in the chemical equation will change to reestablish equilibrium after increasing the pressure. N2(g)+3H2(g)↽−−⇀2NH3(g)
The concentration of N2 will decrease The concentration of H2 will decrease The concentration of NH3 will increase
Select all of the true statements regarding chemical equilibrium.
The concentrations of reactants and products remain constant. Reactants are being converted to products and vice versa. The rates of the forward and reverse reactions are equal.
Consider the following reaction at equilibrium. What will happen if O2 is removed from the reaction? 4 FeS2(s) + 11 O2(g) ⇌ 2 Fe2O3(s) + 8 SO2(g)
The equilibrium will change in the direction of the reactants.
Consider the following reaction at equilibrium. What will happen if SO2 is added to the reaction? 4 FeS2(s) + 11 O2(g) ⇌ 2 Fe2O3(s) + 8 SO2(g)
The equilibrium will change in the direction of the reactants.
A solution NaOH(aq)NaOH(aq) contains 7.87.8 g NaOH(s)NaOH(s) per 100.0100.0 mL of solution. Calculate the pH and the pOH of the solution at 2525 °C.
Use molar mass of NaOh to find number of moles in 7.8 g of NaOH 7.8 x 1mol/40.00 g = 0.20 mol Then determine molarity of the solution 0.20mol/0.1000L = 2.0 M pOH = -log(2.0M) = -0.29 pH = 14.00 - (-0.29) = 14.29
Consider the reversible reaction A(g)↽−−⇀B(g)A(g)↽−−⇀B(g) Which 𝐾K values would indicate that there is more BB than AA at equilibrium?
When [B] is greater that [A], K is greater than 1 K = 5000 and 1x10^7
If the 𝐾bKb of a weak base is 6.7×10−6,6.7×10−6, what is the pH of a 0.21 M0.21 M solution of this base?
You would create an ice table with all the values given leading to Kb=[BH+][OH-]/[B] = x^2/0.21-x =x^2/0.21 x^2=Kb(0.21) x = sq root ((6.7x10^-6)(0.21)) x= 0.0012 M To check the assumption you would 0.0012/0.21 x 100% =56% making the assumption right x=[OH-] = 0.0012 pOH = -log[OH-] -log(0.0012)M =2.93 pH+pOH=14 pH=14-2.93=11.07
The solution turns violet when the univeral indicator is added to it. Is the solution basic, acidic, or neutral?
basic because it turned violet
In a solution, when the concentrations of a weak acid and its conjugate base are equal, ________.
the -log of the [H+] and the -log of the Ka are equal
What is the 𝐾aKa reaction of HCN? The 𝐾aKa of HCNHCN is 6.2×10−10.6.2×10−10. What is the 𝐾bKb value for CN−CN− at 25 °C?
𝐾a reaction: HCN(aq)+H2O↽−−⇀CN−(aq)+H3O+(aq) Kb = Kw/Ka = 1.0 x 10^-14/6.2 x 10 ^-10 = 1.6 x 10 ^-5
For an endothermic reaction, what happens after in increase in temperature? For an exothermic reaction, what happens after in increase in temperature?
𝑄<K so the reaction shifts toward products. 𝑄>K so the reaction shifts toward reactants.
