chem 123
Which of the followings statements is (are) true for a galvanic (voltaic) cell when E° = +1.00 V? 1. The reaction is spontaneous 2. At equilibrium, K = 1. 3. ∆G° is negative.
1 & 3
If E°(red) of a given half-cell is more negative than E°(red) for a standard hydrogen electrode, the half-cell will:
tend to oxidixe, The half cell with the higher E°(red) in a galvanic cell will be reduced, so if a half-cell has a more negative E°(red) than a standard hydrogen electrode, it will tend to oxidize while hydrogen ion is reduced.
autoionization
the transfer of a proton from one molecule to another of the same substance
A neutral solution contains equal amounts of H3O^ + and OH-.
true
A spontaneous process occurs without ongoing outside intervention
true
The stronger an acid, the weaker is its conjugate base.
true
In the redox reaction 6 Fe²⁺ + Cr₂O₇²⁻ + 14 H⁺ → 2 Cr³⁺ + 6 Fe³⁺ + 7 H₂O, what is the reducing agent?
Fe2
As the pH of a solution increases (gets higher), what happens to the acidity of the solution?
acidity decreases
Electrons always flow in a voltaic (galvanic) cell from
anode to cathode
What is the purpose of a salt bridge?
charge balance to each cell, As the voltaic cell operates, the anode will create positive metallic ions and the cathode will deplete positive metallic ions. The salt bridge is needed to balance this charge imbalance that occurs.
conjugate acid-base pair
consists of two substances related to each other by the donating and accepting of a single hydrogen ion ex) During the reaction a hydrogen ion is added to the NH3 to form NH4+ Therefore, NH3 and NH4+ are a conjugate pair. A hydrogen ion is removed from H2O to form OH-. H2O and OH- are another conjugate acid-base pair.
bond strength
energy required to break a bond
A nonspontaneous process is impossible
false
spontaneous reactions are always fast
false
Would a hydrogen ion attach to the nitrogen atom or the carbon atom in ?
nitrogen
If ∆H > 0 and ∆S < 0, a reaction will be:
non spontaneous
What is the conjugate acid of the Brønsted-Lowry base, (CH₃)₃N?
(CH₃)₃NH⁺
Determine E° for the reaction Al(s) + 3 Ag⁺(aq) → 3 Ag(s) + Al³⁺(aq).
(E=e-e ) .80-(-1.66)= +2.46
ion product constant for water
(Kw) (sometimes called the dissociation constant for water). At 25 °C, Kw = 1.0 × 10-14.
Determine ∆G° for a reaction when ∆G = -176.5 kJ/mol and Q = 0.043 at 298 K. (R = 8.314 J/mol ･ K)
-168.7 kj/mol
What is ∆G° for a redox reaction where 6 moles of electrons are transferred and E° =-2.50 V? (F = 96,500 J/(V･mol))
1.45x10^6
For pure water, what is the sum of the pH and pOH?
14
What is the equilibrium constant K at 25°C for an electrochemical cell when E° = +0.0930 V and n = 2?(F = 96,500 J/(V･mol), R = 8.314 J/(mol･K))
1402.8
For the galvanic (voltaic) cell Cd²⁺(aq) + Fe(s) ⟶ Cd(s) + Fe²⁺(aq) (E° = 0.0400 V), what is the ratio [Fe²⁺]/[Cd²⁺] when E = 0.002 V? Assume T is 298 K
22.5
Determine ∆G° for the reaction N₂O₄(g) ⇌ 2 NO₂(g) (K= 0.144 at 25°C).
4.8 kj/mol
The oxidation number of Cl in HClO₃ is
5, O always has an oxidation number of -2 for compounds other than peroxides, and H is always +1 in compounds other than metal hydrides. Therefore in HClO₄, Cl must have an oxidation number of +7.
Considering the redox reaction Cr + Ni²⁺ → Cr³⁺ + Ni, how many electrons are transferred in the balanced reaction?
6
What is the oxidation number of S in the compound Na₂SO₄?
6, .O always has an oxidation number of -2 for compounds other than peroxides, and Na is always +1 when in a compound. Therefore in Na₂S₂O₅, S must oxidation number of +4.
Pure water has [H3O+]=1.0x 10^-7. What is the pH of pure water?
7
What is the OH- concentration in a solution where H3O+=5.0x10^-3?
7
Polarity
A lack of electrical symmetry in a molecule. Charge differences on opposite ends of a structure.
Electronegativity
A measure of the ability of an atom in a chemical compound to attract electrons
amphoteric species
A species capable of reacting as either an acid or base, depending on the nature of the reactants
Oxyacids
Are acids that contain hydrogen, oxygen, and a third element usually a nonmetal.
Consider the reaction below. Which species is(are) the Brønsted-Lowry acid(s)?
Brønsted-Lowry bases accept protons and Brønsted-Lowry acids donate protons. In the forward reaction, the Brønsted-Lowry acid is HF. In the reverse reaction, the Brønsted-Lowry acid is NH₄⁺.
Consider the reaction below. Which species is(are) the Brønsted-Lowry base(s)?
Brønsted-Lowry bases accept protons and Brønsted-Lowry acids donate protons. In the forward reaction, the Brønsted-Lowry base is F⁻. In the reverse reaction, the Brønsted-Lowry base is CO₃²⁻.
What is the conjugate acid of the Brønsted-Lowry base, CCl₃COO⁻?
CCl₃COOH
What is the conjugate base of the Brønsted-Lowry acid, CCl₃COOH?
CCl₃COO⁻
Which of the Lewis structures contain hydrogen atoms that could be removed as ions.
CH3COOH and H2SO3
What is the conjugate acid of the Brønsted-Lowry base, CH₃NH₂?
CH3NH3+
What is the conjugate base of the Brønsted-Lowry acid, HCNO?
CNO-
What is the conjugate base of the Brønsted-Lowry acid, HClO₂?
ClO2-
A voltaic cell is prepared where copper metal is oxidized to copper(II) and silver(I) is reduced to silver metal. Which of the following reactions occurs at the anode?
Cu(s) → Cu²⁺(aq) + 2e⁻, Oxidation, which is the loss of electrons, occurs at the anode. The correctly balanced half-reaction for the oxidation of Cu is
Write the basic equilibrium equation for C₆H₅NH₂
C₆H₅NH₂(aq) + H₂O(l) ⇌ OH⁻(aq) + C₆H₅NH₃⁺(aq)
For a triprotic acid, Ka3 > Ka2.
For each acidic proton a polyprotic acid has, there will be an acid equilibrium equation. For a given polyprotic acid, the more H+ ions you remove, the stronger the remaining H+ ions will be held. A diprotic acid will have only one amphoteric species in its acid equilibrium series. Ka₁>Ka₂>Ka₃.
As E°(cell) increases:
G decreases, Since ∆G°=-nFE°, ∆G° decreases as E°(cell) increases.
Which of the following processes has a negative ∆S?
H2O = H2O
Write the acidic equilibrium equation for HBrO
HBrO(aq) + H₂O(l) ⇌ H₃O⁺(aq) + BrO⁻(aq)
What is the formula for the conjugate acid of CN-?
HCN
Which of the following is an amphoteric species?
HSO₃⁻
Which compound has phosphorus (P) with an oxidation number of -3?
Hydrogen has an oxidation number of +1 except in elemental hydrogen and in metal hydrides. That gives phosphorus an oxidation number of -3 in PH₃. Phosphorus has positive oxidation numbers in oxyanions where it is paired with oxygen and in binary halide compounds.
Which of the following equations represents the acid equilibrium associated with Ka₂ for H₃PO₃?
H₂PO₃⁻ (aq) + H₂O ⇌ HPO₃²⁻ (aq) + H₃O⁺ (aq) Ka₂ would be the Ka value for the 2nd proton dissociating. H₂PO₃⁻ (aq) + H₂O (l) ⇌ HPO₃²⁻ (aq) + H₃O⁺ (aq)
The conjugate acid of H₂PO₄⁻ is
H₃PO₄
What is the primary species in solution at the halfway point in a titration of HCN with KOH?
If the number of moles of HCN is x, then the halfway point would be when x2x2 moles of KOH have been added. At the halfway point the ideal buffer has been made with the weak base and its conjugate weak acid. This means that the primary species in solution are CN⁻ and HCN.
What is the formula for the conjugate base of HNO3?
NO3-
Which compound contains chlorine (Cl) with an oxidation number of +3
O always has an oxidation number of -2 for compounds other than peroxides. If Cl has an oxidation number of +3, only Cl₂O₃ would be a neutral compound.
The conjugate base of HPO₃²⁻ is
PO₃³⁻
If the Gibbs free energy for an equilibrium is a large, negative number, the equilibrium constant is expected to be _____ A) a large, negative value B) a large, positive value C) a small, negative value D) a small, positive value E) Zero
Since ∆G° = - RTlnK, when ∆G° is a large negative number, K must be a large positive number, indicating the reaction is spontaneous and the equilibrium lies far to the right.
Which of the following species is the best oxidizing agent?
The best oxidation agent is the one most easily reduced, which is the one with the highest reduction potential. From the choices listed, Cl₂, with a reduction potential of +1.36 V will be the best oxidizing agent.
Consider the reaction below. Which species are conjugate acid/base pairs?
The conjugate acid is the species that is formed after the base accepts a proton. In the forward reaction, HSO3−HSOX3X− is the base and H2SO3HX2SOX3 is the conjugate acid. In the reverse reaction, H2SO3HX2SOX3 is the acid, and HSO3−HSOX3X− is the conjugate base.
Given the standard electrode reduction potentials, which reaction will occur spontaneously?
The half cell with the higher reduction potential will be reduced while the one with the lower oxidation potential will be oxidized. Cu²⁺, with a reduction potential of +0.15 will be reduced while V, with a reduction potential of -1.18 will be oxidized, so the reaction will be V + 2Cu²⁺ → V²⁺ + 2Cu⁺
Which of the following is true for a reaction when ∆G is a positive value?
The reverse reaction would have a negative value of ∆G and be spontaneous because the forward reaction is nonspontaneous.
Considering the redox reaction Sn⁴⁺ + Mn → Mn²⁺ + Sn, how many electrons are transferred in the balanced reaction?
To balance the charges in the equation Mn must have a coefficient of 2 ,Sn⁴⁺ + 2 Mn → 2 Mn²⁺ + SnSn⁴⁺ + 2 Mn → 2 Mn²⁺ + Snso a total of 4 electrons are transferred in the balanced reaction.
What is the maximum amount of work that is possible for an electrochemical cell where E = 1.38 V and n = 2? (F = 96,500 J/(V･mol)
What is the maximum amount of work that is possible for an electrochemical cell where E = 1.38 V and n = 2? (F = 96,500 J/(V･mol)
The weak acid HY is much stronger than weak acid HX. Which one of the following statements is true?
Y⁻ is a weaker base than X⁻. Ka×Kb=KwKa×Kb=KwA large KaKa would result in a small KbKb, indicating a weak base. Therefore, the stronger the weak acid, the weaker the conjugate base.
What is the oxidizing agent in the reaction Zn + 2 H⁺ → Zn²⁺ + H₂?
Zn increases in oxidation number from 0 to +2 and H⁺ decreases in oxidation number from +1 to 0. Therefore Zn is being oxidized, and H⁺ is the oxidizing agent.
Brønsted-Lowry base
a molecule or ion that is a proton acceptor
NaOH is a Brønsted-Lowry base because
a proton acceptor
Amphoteric
a substance that can act as both an acid and a base
Arrhenius acid
a substance that increases the concentration of hydronium ions in aqueous solution. EX) HCl, because when HCl dissolves in water the concentration of aqueous hydrogen ions increases.
Arrhenius base
a substance that increases the concentration of hydroxide ions in aqueous solution EX)NaOH, because when NaOH dissolves in water the concentration of aqueous hydroxide ions increases.
Brønsted-Lowry acid
proton donor (H+)
A solution has a pOH of 7.84. This tells us
slightly acidic The relationship between pH and pOH is pH+pOH=14pH+pOH=14. Solve for pH by plugging the pOH into the equation. pH+7.84=14pH+7.84=14pH=6.16pH=6.16 This is slightly acidic.
