Relative Acidity and Basicity
Which is more acidic: NH3 or H2O?
H2O (O is more electronegative than N)
Write the ionic equation for the dissolution and the Ksp expression for CaCO3 (a slightly soluble ionic compound).
CaCO3(s) ⇌ Ca2+(aq) + CO32-(aq)
Ksp = [Ca2+][CO32-]
NaOH is an example of a ______, which is a substance that, when dissolved in water, increases the concentration of hydroxide ions (OH-) in the solution.
Arrhenius Base
The pH at the equivalence point of a titration is 9.31. Which indicator will appropriately show the end point of the acid/base reaction?
Methyl yellow (pH 2.9-4.0), Methyl red (pH 4.4 - 6.2), Thymol blue (pH 8.0-9.6), Alizarin yellow (pH 10.1-12.0)
Thymol blue
Explain why the ionization constant, Ka, for H2SO4 is larger than the ionization constant for H2SO3.
A higher Ka indicates a stronger acid. H2SO4 is stronger than H2SO3 because it is an oxyacid with more oxygens.
Consider the following reaction: HNO2 + H2O ↔ NO2- + H3O+
How would adding each of the following affect the degree of ionization of the acid? NaCl, KNO2, HNO3
NaCl would not affect ionization
KNO2: shift to the left by adding NO2-
HNO3: shift to the left by adding H+
H3O+ is an example of a ____________, which is any species that is capable of donating a proton (H+)
Brønsted-Lowry acid
The hydroxide ion concentration in household ammonia is 3.2 × 10-3 M at 25 °C. What is the concentration of hydronium ions in the solution?
[OH-] = 3.1 × 10-12 M
Put the following molecules in order based on their pH for a 0.1 M aqueous solution from lowest to highest: Ba(OH)2, BaCl2, NaC2H3O2, CH3COOH, NaOH.
CH3COOH (WA) < BaCl2, (neutral) < NaC2H3O2 (WB) < NaOH (SB x 1) < Ba(OH)2 (SB x 2)
Predict if Ag2S is more or less soluble if NH3 and HNO3 are added (consider each case separately).
Added NH3: more soluble (product removed)
Ag+ + 2NH3 <-> Ag(NH3)2+
Added HNO3: more soluble (product removed)
2H+ + S2- -> H2S
In the reaction below, which species is the Lewis base?
Cr3+ + 6H2O ↔ Cr(H2O)63+
H2O (acts as an e- donor)
You are performing a titration of 35 mL of 0.437 M malic acid with 0.676 M KOH. At what volume of added KOH will the titration reach equivalence point?
VKOH = 22.6 mL
(35 mL)(0.437 M) = (VKOH)(0.676 M)
Which of the following is the weakest acid: H2SO4, H2SO3, HSO4-, H2S?
H2S
Binary acids tend to be weaker than oxyacids because the H-X bond is less polarized.
Determine the molar solubility of Ag2S in aqueous solution. Ksp = 6.0 x 10-50
Ag2S (s) ↔ 2Ag+ + S2-
I X 0 0
C X +2x +x
E X 2x x
6.0 x 10-50 = (2x)2(x) -> x = 2.5 x 10-17
What type of acid/base reaction is shown below, and which species is the acid and which is the base?
BF3 + HF ↔ H+BF4-
Lewis acid/base reaction
BF3 is the acid (accepts e-) and HF is the base (donates e-)
Nicotine, C10H14N2, is a base that will accept two protons (Kb1 = 7 × 10-7, Kb2 = 1.4 × 10-11). What is the concentration of each species present in a 0.050 M solution of nicotine?
[C10H14N2] = 0.049 M
[C10H14N2H+] = 1.9 × 10−4 M
[C10H14N2H22+] = 1.4 × 10-11 M
[OH-] = 1.9 × 10-4 M
[H3O+] = 5.3 × 10-11 M
The Ka value for HClO2 is 1.1 x 10-2, while the Ka value for HNO2 is 4.6 x 10-4. For the following reaction, is ClO2- or NO2- the stronger base and is the product or reactant side favored?
NO2- is the stronger base (HNO2 is a weaker acid) and the reactant side is favored (the stronger acid and stronger base are on the product side)
What is the molar solubility of Ag2S when 0.756 M Na2S is added to the solution?
Ag2S (s) ↔ 2Ag+ + S2-
I X 0 0.756
C X +2x +x
E X 2x 0.756+x
6.0 x 10-50 = (2x)2(0.756+x) -> x = 1.4 x 10-25
Classify the following species as a Bronsted acid, Bronsted base, or both: HCOO-, HClO, HS-, CH3CH2NH2.
HCOO-: base
HClO: acid
HS-: both
CH3CH2NH2: base
You are asked to prepare a buffer solution at pH 4.95, using one of the following weak acids: HA (Ka = 2.7 x 10-3), HB (Ka = 4.4 x 10-6), or HC (Ka = 2.6 x 10-9). Which acid should you pick?
HB
pKa HB = 5.35;
Buffer capacity: pH = pKa ± 1