Question

When a 27.2 mL sample of a 0.371 M aqueous hydrocyanic acid solution is titrated with a 0.316 M aqueous potassium hydroxide solution, what is the pH at the midpoint in the titration?

pH =

note

Acid/Base Ionization Constants at 25 oC
Acid	Formula	Ka1	Ka2	Ka3
Acid/Base Ionization Constants at 25 oC
Acid	Formula	Ka1	Ka2	Ka3
Acetic acid	CH3COOH	1.8×10-5
Acetylsalicylic acid (aspirin)	HC9H7O4	3.0×10-4
Aluminum ion	Al(H2O)43+	1.2×10-5
Arsenic acid	H3AsO4	2.5×10-4	5.6×10-8	3.0×10-13
Ascorbic acid	H2C6H6O6	7.9×10-5	1.6×10-12
Benzoic acid	C6H5COOH	6.3×10-5
Carbonic acid	H2CO3	4.2×10-7	4.8×10-11
Ferric ion	Fe(H2O)63+	4.0×10-3
Formic acid	HCOOH	1.8×10-4
Hydrocyanic acid	HCN	4.0×10-10
Hydrofluoric acid	HF	7.2×10-4
Hydrogen peroxide	H2O2	2.4×10-12
Hydrosulfuric acid	H2S	1.0×10-7	1.0×10-19
Hypochlorous acid	HClO	3.5×10-8
Nitrous acid	HNO2	4.5×10-4
Oxalic acid	H2C2O4	5.9×10-2	6.4×10-5
Phenol	C6H5OH	1.0×10-10
Phosphoric acid	H3PO4	7.5×10-3	6.2×10-8	3.6×10-13
Sulfuric acid	H2SO4	very large	1.2×10-2
Sulfurous acid	H2SO3	1.7×10-2	6.4×10-8
Zinc ion	Zn(H2O)42+	2.5×10-10

Base	Formula	Kb
Ammonia	NH3	1.8×10-5
Aniline	C6H5NH2	7.4×10-10
Caffeine	C8H10N4O2	4.1×10-4
Codeine	C18H21O3N	8.9×10-7
Diethylamine	(C2H5)2NH	6.9×10-4
Dimethylamine	(CH3)2NH	5.9×10-4
Ethylamine	C2H5NH2	4.3×10-4
Hydroxylamine	NH2OH	9.1×10-9
Isoquinoline	C9H7N	2.5×10-9
Methylamine	CH3NH2	4.2×10-4
Morphine	C17H19O3N	7.4×10-7
Piperidine	C5H11N	1.3×10-3
Pyridine	C5H5N	1.5×10-9
Quinoline	C9H7N	6.3×10-10
Triethanolamine	C6H15O3N	5.8×10-7
Triethylamine	(C2H5)3N	5.2×10-4
Trimethylamine	(CH3)3N	6.3×10-5
Urea	N2H4CO	1.5×10-14

Answer 1