MC test: Strong & weak acids & bases

Multiple choice test on 8.4 Strong & weak acids & bases

Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).

If you get an answer wrong, read through the explanation carefully to learn from your mistakes.

Which acid is ionized the least in aqueous solution?

HNO3, H2SO4 and HCl are all strong acids. Ethanoic acid is the only weak acid and is only slightly dissociated into its ions in aqueous solution.

 

Which is an aqueous solution of a weak base?

 

NaCl is not a base and NaOH is a strong base.

 

Which will have a pH closest to 7?

The pH of 0.1 mol dm−3 NaOH is 13, the pH of 0.1 mol dm−3 HCl is 1 and the pH of 0.1 mol dm−3 H2SO4 is < 1. All of these have a difference of at least 6 units from pH = 7.  0.1 mol dm−3 CH3COOH is only slightly dissociated so [H+(aq)] << 0.1 mol dm−3, so its pH will be > 1 and < 7.

 

Which solution will have the highest electrical conductivity?

The total concentration of ions in 0.5 mol dm−3 H2SO4  = 1.5 mol dm−3 (assuming it is a strong diprotic acid, which is not actually true). In 1.0 mol dm−3 NaCl the total concentration of ions = 2 mol dm−3 and in 1.0 mol dm−3 CH3COOH it is considerably less than 2 mol dm−3. In 1.0 mol dm−3 Ba(OH)2 the total concentration of ions = 3 mol dm−3, so it will have the highest electrical conductivity.

 

The equation for the reaction between aqueous hydrogen ions and aqueous hydroxide ions is:

H+(aq) + OH−(aq) → H2O(l)  ΔH⦵ = − 56.8 kJ mol−1

Which are correct statements?

I. When 1 mol of hydrochloric acid is neutralized by 1 mole of sodium hydroxide in solution the amount of heat evolved = 56.8 kJ.

II. When 1 mol of ethanoic acid is neutralized by 1 mole of sodium hydroxide in solution the amount of heat evolved ≠ 56.8 kJ.

III. When 1 mol of nitric acid is neutralized by 1 mole of potassium hydroxide in solution the amount of heat evolved ≠ 56.8 kJ.

I and III involve a strong acid being neutralized by a strong base so the only reaction taking place is the formation of water from hydrogen ions and hydroxide ions so III is wrong as ΔH⦵ does equal − 56.8 kJ mol−1 . Ethanoic acid is a weak acid so O−H bonds are also being broken and hydrated. This means other enthalpy changes as well as neutralization are also involved so ΔH⦵ does not equal − 56.8 kJ mol−1 and so II is correct.

 

It requires 10.0 cm3 of 1.0 mol dm−3 sulfuric acid solution, H2SO4(aq) to neutralize 20.0 cm3 of a solution of sodium hydroxide NaOH(aq).

What volume of 1.0 mol dm−3 ethanoic acid solution, CH3COOH(aq) would be required to neutralize  20.0 cm3 of the same solution of  sodium hydroxide NaOH(aq)?

The dissociation of a weak acid is an equilibrium process so once some of the H+ ions are neutralized more of the acid will dissociate to replace them. Because ethanoic acid is a monoprotic acid (contains one acidic hydrogen atom) and sulfuric acid is diprotic, twice the volume of ethanoic acid with the same concentration as the sulfuric acid will be required.

 

The Kb or pKb values of four bases are:

ammonia Kb = 1.8 x 10−5

phenylamine Kb = 7.4 x 10−10

methylamine pKb = 3.3

diethylamine pKb = 3.2

Which the correct order of their increasing basic strength (weakest first)?

The smaller the Kb value and the greater the pKb value the weaker the base. The weakest base is phenylamine. Ammonia will have a pKb value between 4 and 5 so is the next weakest. The pKb value of methylamine is larger than that of diethylamine, so diethylamine is the strongest of the four weak bases.

 

The Ka or pKa values of four acids are:

4-nitrophenol Ka = 7.1 x 10−8

trichloroethanoic acid pKa = 0.66

ethanoic acid Ka = 1.8 x 10−5

3-nitrophenol pKa = 8.4

Which the correct order of the degree of dissociation into their ions (most dissociated first)?

The larger the Ka value and the smaller the pKa value the more the acid is dissociated.

 

10.0 cm3 of a 0.100 mol dm−3 aqueous solution of an acid was added to 1.0 g of powdered calcium carbonate. The process was repeated under the same conditions using different acids.

Which acid will produce the slowest rate of evolution of carbon dioxide?

Because ethanoic acid is a weak acid and the other three are all strong acids the concentration of H+ ions will be less so the rate of reaction with carbonate ions will be slower.

 

Which will be the strongest conjugate base?

Weak acids have strong conjugate bases and vice-versa. The carbonate ion is the conjugate base of carbonic acid, which is a weak acid. The other three ions are all conjugate bases of strong acids.

 

Total Score:
All materials on this website are for the exclusive use of teachers and students at subscribing schools for the period of their subscription. Any unauthorised copying or posting of materials on other websites is an infringement of our copyright and could result in your account being blocked and legal action being taken against you.