Chem 121 Winter 2016: Section 03, Sample Problems
Acids and bases
Problems, with some modifications, from Chemistry - The Central Science, 3rd edition.
1.
(a) Explain the differences between the Arrhenius and Bronsted-Lowry definitions of an acid.
(b) In an intriguing reaction, the two gases NH3(g) and HCl(g) react to directly form the ionic
solid NH4Cl(s). Which material is acting as the B-L acid in this reaction? And which is the base?
The hydrogen oxalate ion, HC2O4- is amphoteric.
2.
(a) Explain what is meant by the term amphoteric.
(b) Write equations showing how this species (i) reacts with water, behaving as an acid, and
(ii) reacts with water, acting as a base.
(c) Identify the conjugate acid and conjugate base of the ion.
3.
Deuterium oxide, often known as heavy water, has the formula D2O, in which D is the
isotope of hydrogen that contains one neutron in the nucleus; deuterium atoms therefore weigh
2 amu. The autoionisation constant for deuterium oxide is 8.9 x 10-16 at 20oC.
(a) Does deuterium oxide ionise to a greater or a lesser extent than ordinary water?
(b) Calculate [D+] and [OD-] in deuterium oxide at 20oC.
(c) (difficult – we haven’t done this in class) Can you think of any reason why the extent of
ionisation of deuterium oxide should be different from that of water?
4.
Complete the following table:
[H+]
[OH-]
pH
pOH
7.5 x 10-3 M
3.6 x 10-10 M
8.25
5.70
acidic or basic?
5.
Calculate [OH-] and the pH for each of the following solutions of strong base or strong acid:
(a) 0.182M KOH.
(b) a solution of 3.165g of KOH in 500 mL of solution.
(c) 10.0 mL of 0.0105 M Ca(OH)2 diluted to 500 mL.
(d) A solution formed by mixing 20.0 mL of 0.015 M Ba(OH)2 with 40 .0 mL of 8.2 x 10-3 M
NaOH.
6.
Aspirin is acetylsalicylic acid (ASA), a monoprotic acid with
Ka = 3.3 x 10-4 at 25oC. What is the pH of a solution obtained by
dissolving two tablets, each containing 500 mg of ASA, in 100 mL
water? The molecular formula of ASA is HC9H7O4.
7.
(a) Calculate the pH of a 2 x 10-9 M solution of NaOH.
(b) Does your answer seem sensible? If not, indicate the problem and try to identify the
source of the difficulty.