Arrhenius and Bronsted-Lowry
According to Arrhenius, a substance that releases H+ in water.
Acid
100%
The value of Kw at 25 degrees C
1.0x10-14
Expression for Ka of acetic acid.
Ka = [CH₃COO⁻][H₃O⁺] / [CH₃COOH]
Term for when an ion from a salt reacts with water as an acid or base.
Hydrolysis
Point in a titration where moles of acid equal moles of base according to their stoichiometric ratios.
Equivalence point.
Solution that resists changes in pH when small amounts of acid or base are added
Buffer
According to Bronsted-Lowry, a substance that accepts a proton (it doesn't have to be in water!)
Base
HCl, HBr, HI, HNO3, HClO4, H2SO4
PH of a solution with [H3O+]=1.0x10-5. Give answer to correct number of significant figures.
5.00
Kb of fluoride ion. Give answer to correct number of significant figures.
Kb = 2.9x10-11
Will a solution of sodium acetate be acidic, basic, or neutral? Why?
Base. Acetate ion is a weak base, while sodium ion is a spectator ion.
pH at the equivalence point of a titration of a strong base with a strong acid.
7.00
Environmental issue caused by the release of non-metal anhydrides into the atmosphere.
Acid rain
Species formed when a Bronsted-Lowry acid donates a proton.
Conjugate base
Strongest base that can exist in aqueous solution.
The pOH of a 0.010M NaOH solution. Give answer to correct number of significant figures.
2.00
If doing an ICE table calculation using hydrogen oxalate ion as the acid, is the small x assumption valid?
Yes. Ka of hydrogen oxalate ion is 6.4x10-5, <1.0x10-3, so you can use the small x assumption.
NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺
Acidic. Chloride is conjugate 'base' of a strong acid.
Suitable indicator for a weak base-strong acid titration.
Bromcresol Green
Methyl Red
Chlorophenol Red
Explain why the pH of a buffer doesn't change when diluted.
Both [HA] and [A-] are diluted equally, so the ratio of [A-] and [HA] remains constant; from Ka = [H3O+] x [A-]/[HA], if the A / HA ratio remains constant, then [H3O+] remains constant, and thus pH remains constant.
A solution of ammonia in water is basic. Explain in terms of Bronsted-Lowry theory.
Ammonia accepts a proton from water, forming hydroxide ions.
Explain why solutions 1.0M HCl and 1.0M HClO4 both have the same pH despite being different acids. Give the specific term that describes this phenomenon as part of your answer.
Levelling effect. All strong acids dissociate 100% in water to form H30+ ions, thus all strong acids of the same concentration will have the same [H3O+] = same pH.
A solution has pH 4.50. What is [OH-]? Is solution acidic or basic? Give answer to correct number of significant figures.
Acidic (pH<7). [OH-]=3.2x10-10M
The weak acid HA has Ka = 5.3x10-3. Calculate the pH of a 0.050M solution of this acid. Give answer to correct number of significant figures.
pH=1.86 (cannot use small x approximation).
Is a solution of iron (III) nitrate acidic, basic, or neutral? Explain.
Acidic. Iron (III) is a highly charged metal ion, which form complex ions with water than are able to donate protons.
Reason why the equivalence point pH is >7 for a weak acid - strong base titration.
Salt produced has a basic anion, so hydrolysis produces OH-
Why does the pH of pure water change a lot when a few drops of 1.0mL HCl are added to it, but the same volume of a solution containing 1.0M ammonia and 1.0M ammonium nitrate does not see much pH change?
Pure water has no weak base to neutralize the added H3O+ and convert it to a weak acid, so the concentration of H3O+ increases significantly and the pH drops. In the ammonia / ammonium nitrate solution (a buffer solution) the ammonia can neutralize the added H3O+, converting it to ammonium and preventing it from changing the pH much at all.
Conjugate acid H3PO4, conjugate base HPO4 2-. Dihydrogen phosphate ion can both donate a proton (acid) and accept a proton (base), therefore it is amphiprotic.
Predict whether the equilibrium below favours reactants or products, and explain in terms of Keq.
H₂CO₃ + CN⁻ ⇌ HCO₃⁻ + HCN
HCN weaker than H2CO3, therefore products favoured. Keq = 880. (>>1)
At 50 degrees C, Kw = 5.48 x 10-14. Calculate the pH of neutral water at this temperature. Is it still 7? Explain. Give answer to correct number of significant figures.
pH=6.631, <7. Self ionization of water is endothermic, so equilibrium shifts right as temperature increases.
A 0.20M solution of a weak base B has pH=9.80. What is the value of Kb (sig figs!).
Kb = 5.0x10-8
Is ammonium nitrite acidic, basic, or neutral? Explain in terms of Ka and Kb.
Acidic. Ka (ammonium) > Kb(nitrite ion)
11.7%