8 ACIDS AND BASES 1CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 2011

8 Acids and bases

Acids and basesI am able to:

complete the following equations:

CaCO3 + H2SO4 → NaOH + HCl → CuO + HNO3 → Mg + CH3COOH →

state the di� erence between an alkali and a base

de� ne an acid and a base according to the Brønsted–Lowry de� nition

de� ne an acid and a base according to the Lewis de� nition

identify a Brønsted–Lowry base and Brønsted–Lowry acid in:

NH4+ + H2O NH3 + H3O+

give the formula of the conjugate acid of OH−

explain whether BCl3 can act as a Lewis acid or base

write an equation for the dissociation of ethanoic acid in water and identify conjugate acid and base pairs

explain, using examples, the di� erence between a strong and a weak acid

explain two methods by which strong and weak acids may be distinguished from each other in the laboratory

classify the following as strong or weak acids or bases:

H2SO4 CH3CH2NH2 CH3COOH NH3 CsOH Ba(OH)2 H2CO3 (CO2(aq)) HNO3 HCl LiOH

de� ne pH

work out how the pH changes when 10 cm3 of 0.1 mol dm−3 HCl is diluted with 90 cm3 of water

arrange the following in order of increasing pH:

1.0 mol dm−3 NH3 0.010 mol dm−3 HCl 1.0 mol dm−3 NaOH

0.001 mol dm−3 CH3CH2COOH 0.10 mol dm−3 H2SO4

0.010 mol dm−3 CH3CH2COOH 0.0010 mol dm−3 NH3 0.10 mol dm−3 HCl

work out how the concentration of H+(aq) changes when the pH changes from 2 to 5

calculate the pH of 0.1 mol dm−3 HCl and 1 × 10−5 mol dm−3 HNO3

write an expression for Ka for:

CH3COOH(aq) H+(aq) + CH3COO−(aq)

write an expression for Kb for:

C2H5NH2(aq) + H2O(l) C2H5NH3+(aq) + OH−(aq)

de� ne pKa and pKb

arrange the following acids in order of acid strength (strongest � rst):

Acid Ka / mol dm−3

propanoic (CH3CH2COOH) 1.3 × 10−5

nitric(III) (HNO2) 4.7 × 10−4

hydrofl uoric (HF) 5.6 × 10−4

chloric(I) (HOCl) 3.7 × 10−8

HL

2 CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 20118 ACIDS AND BASES

arrange the following acids in order of acid strength (strongest � rst):

Acid pKa

ethanoic 4.8

carbonic 6.4

benzoic 4.2

ammonium ion 9.3

calculate the pH of a 0.01 mol dm−3 solution of an acid HA if pKa = 5, stating any assumptions made

calculate Ka for an acid HA if the pH of a 0.1 mol dm−3 solution is 3

write an equation to represent the dissociation of water

write an expression for the ionic product constant of water (Kw) and give its units

de� ne pOH and pKw

state the value of Kw and of pKw at 25 °C

calculate the [H+], [OH−] and pH for water at 323 K, given that Kw at 323 K is 5.5 × 10−14 mol2 dm−6

calculate pH, pOH, [H+(aq)] and [OH−(aq)] for each of the following solutions

0.1 M HCl 0.1 M NaOH 0.02 M Ba(OH)2

calculate the pH of a 0.0500 mol dm−3 solution of ethylamine (CH3CH2NH2) at 25 °C, given that pKb = 3.27

state the relationship between Ka, Kb and Kw and between pKa, pKb and pKw

calculate Ka for NH4+, given that pKb for NH3 is 4.75

calculate pH of a 0.100 mol dm−3 solution of potassium cyanide (KCN), given that pKa for hydrocyanic acid (HCN) is 9.40

explain the relationship between the strength of an acid and its conjugate base

sketch titration curves for the following titration combinations:

strong acid–strong base strong acid–weak base

weak acid–strong base weak acid–weak base

state the approximate pH at the equivalence point for each of the titrations above

explain how an acid–base indicator works

state the connection between the pH range of an indicator and the value of pKa for the indicator

select an appropriate indicator for each of the titrations above

Indicator pKa pH range

methyl yellow 3.5 2.9–4.0

methyl red 5.1 4.2–6.3

phenol red 7.9 6.8–8.4

phenolphthalein 9.3 8.2–10.0

predict whether solutions of the following salts will be acidic, basic or neutral:

NaCl CH3COONa NH4Cl KNO3

write equations for the reactions of the following ions with water:

NH4+ CH3COO−

explain why solutions containing [Fe(H2O)6]3+ are acidic

arrange 0.1 mol dm−3 solutions of Na+(aq), Mg2+(aq), Al3+(aq) in order of acidity and explain the order

explain what quantities can be deduced from the pH at the half equivalence point in a weak acid–strong base titration or from the pOH at the half equivalence point in a weak base–strong acid titration

explain what is meant by a bu� er solution

HL

8 ACIDS AND BASES 3CHEMISTRY FOR THE IB DIPLOMA © CAMBRIDGE UNIVERSITY PRESS 2011

explain how you would make a bu� er solution

explain how a bu� er solution works when small amounts of acid or alkali are added

calculate the pH of a bu� er solution containing 0.0200 mol dm−3 butanoic acid (pKa = 4.82) and 0.0100 mol dm−3 sodium butanoate

calculate the pH of a bu� er solution made by mixing together 25.0 cm3 of 0.200 mol dm−3 ethanoic acid (pKa = 4.76) and 50 cm3 of 0.100 mol dm−3 sodium ethanoate

calculate the ratio of sodium ethanoate : ethanoic acid in a sodium ethanoate/ethanoic acid (pKa = 4.76) bu� er of pH = 4.2

explain how much sodium hydroxide of concentration 0.1 mol dm−3 would have to be added to 50 cm3 of 0.1 mol dm−3 ethanoic acid (pKa = 4.76) to produce a bu� er of pH 4.76

HL