Section D: ions Flashcards
what is implied about the direction of reaction when Q is less than K?
ΔG is negative; products are favoured
what is implied about the direction of reaction when Q > K?
ΔG is positive; reactants are favoured
what is Arrhenius’ definition of acids and bases?
acid = increases the concentration of H+ ions base = increases the concentration of OH- ions
what is the Brønsted-Lowry definition of acids and bases?
acid = releases H+ ions (proton donor) base = accepts H+ ions (proton acceptor)
what is the Lewis definition of acids and bases?
acid = accepts a pair of electrons base = donates a pair of electrons
what is meant by a large Ka?
large Ka = small pKa = strong acid
how do buffers work?
- buffers resist changes in pH by providing a source or sink for protons
- a buffer solution contains roughly equal concentrations of a weak acid and its conjugate base
what is the Henderson-Hasselbalch equation?
pH = pKa + log (base [A-] / acid [HA] )
what are the steps for designing a buffer?
- choose an acid/conjugate base with the pKa ≈ pH required
- calculate the ratio cA/cB using the H-H equation
- check with the pH meter and adjust as necessary
what is the common ion effect?
- when a sparingly soluble electrolyte is dissolved in a solution containing one of the ions, the solubility is markedly decreased
- due to le Chatelier’s principle - an increased ion concentration causes the equilibrium to shift to the left to counter the change, resulting in a decreased solubility
- only applies to sparingly soluble salts
what does electrochemistry study?
only reactions involving the transfer of electrons or redox reactions that are thermodynamically stable
what are the main variables of electrochemistry?
- voltage = driving force of a reaction (thermodynamics)
- current = quantity of electricity (extent of reaction)
in what other units can 1 V be expressed?
1 V = 1 J.A^-1.s^-1
in what other units can 1 A be expressed?
1 A = 1 C.s^-1
how can an electrochemical cell be represented for a mixture of solids and liquids?
red (s) | ox (l) || ox (l) | red (s)
how can an electrochemical cell be represented for a mixture of liquids?
Pt | red (l) , ox (l) || ox (l) , red (l) | Pt
how is the cell reaction written using the representation of the electrochemical cell?
left (red) + right (ox) —> left (ox) + right (red)
represent a calomel electrode as an electrochemical cell
Cl- (aq) | Hg2Cl2 (s) , Hg (s) | Pt
what is the electrode reaction of a calomel electrode?
1/2 Hg2Cl2 (s) + e- —> Hg (s) + Cl- (aq)
what is the potential of a calomel electrode?
+ 0.2676 V at 25C
what is the Nernst equation?
E = E0 - RT/nf lnQ
how are ΔG0 and E0 related?
ΔG0 = - nfE0
what is the difference between a galvanic cell and an electrolytic cell?
galvanic cell - produces electricity; the reaction will proceed until equilibrium
electrolytic cell - drive a non-spontaneous reaction using an external source of current
how are C and F related?
1 F = 96485 C
