www.apchemsolutions.com
Lecture 31
Acids and Bases III
Tutorial
Write balanced net ionic equations for the reactions that occur in questions 1-5.
1) Equal volumes of 0.15 M sulfurous acid and 0.1.5 M lithium hydroxide are mixed.
H2SO3(aq) + OH-(aq) Æ HSO3-(aq) + H2O(l)
2) Solutions of ammonium nitrate and sodium cyanide are poured into a beaker.
NH4+(aq) + CN-(aq) Æ NH3(aq) + HCN(aq)
3) Carbon dioxide gas is bubbled through a solution of 0.5 M potassium hydroxide.
CO2(g) + OH-(aq) Æ HCO3-(aq)
4) Hydrogen bromide gas is mixed with ammonia gas.
HBr(g) + NH3(g) Æ NH4Br(s)
5) Solid sodium acetate is stirred into a beaker of distilled water.
NaCH3CO2(s) + H2O(l) Æ Na+(aq) + CH3COOH(aq) + OH-(aq)
6) Which mixture, 1.5 M NH4Cl or 1.5 M NaCl, has the lowest pH? Justify your
answer.
1.5 M NH4Cl will have the lowest pH. Its pH will be less than 7. NH4+ is an acidic
anion. Acidic anions lower the pH.
Cl- is a neutral anion, which will not affect the pH.
1.5 M NaCl will have the highest pH. NaCl and water produces a neutral solution with a
pH of 7, as both ions are neutral. Na+ is the conjugate acid of a strong base, and Cl- is the
conjugate base of a strong acid.
© 2009, 2008 AP Chem Solutions. All rights reserved.
1
www.apchemsolutions.com
7) One mixes 150 mL of 0.3 M HCl with 150 mL of 0.4 M LiOH. What is the pH of
the solution?
[OH-] = 0.3 – 0.4 = 0.1 M
pOH = -log[OH − ] = − log(0.1) = 1
pH = 14 - pOH = 14 - 1 = 13
8) The acid dissociation constants for hypoiodous acid, HOI, and lactic acid,
HC3H5O3, at 298 K are 2 x 10-11 and 1.38 x 10-4 respectively. Which solution is
more basic: 1.0 M NaOI or 1.0 M NaC3H5O3? Justify your answer.
HOI is the weaker acid, as 2 x 10-11 < 1.38 x 10-4. This means that its conjugate base, OI, is stronger than C3H5O3-. Weaker acids have stronger conjugate bases.
Because OI- is a stronger base than C3H5O3-, the equilibrium for
OI-(aq) + H2O(l) U HOI(aq) + OH-(aq)
lies further to the right than it does in C3H5O3-(aq) + H2O(l) U HC3H5O3(aq) + OH-(aq).
Thus, 1.0 M NaOI produces a higher concentration of OH-, making a more basic solution.
© 2009, 2008 AP Chem Solutions. All rights reserved.
2