Use the data from Table 21.2 to work out the pH values of the following solutions:

a. 0.0200 mol dm^–3 aqueous benzoic acid

b. 0.0100 mol dm^–3 hydrated aluminium ions

c. 0.100 mol dm^–3 aqueous methanoic acid.

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Acid or ion Equilibrium in aqueous solution K/moldm-3 pK, nitric HNO, H' + NO,- about 40 -1.4 H,S0, H" + HSo, [Fe(H,0), H" + sulfuric(IV) 1.5 x 10-2 1.82 hydrated Fe ion [Fe(H,O),(OH))?* 6.0 x 10-3 2.22 hydrofluoric HEPH + F- 5.6 x 104 3.25 nitric(1II) HNO, H* + NO, 4.7 x 104 3.33 methanoic HCOOH Ht + HCO0- 1.6 x 104 3.80 CH,COOHH* + CH,CO0- CH,COOH H* + CH,CO0- benzoic 6.3 x 10-5 4.20 ethanoic 1.7 x 10-5 4.77 propanoic CH,CH,COOH H* + CH,CH,COO- 1.3 x 10-5 4.89 [Al(H,0) H* + [Al(H,0),(OH)]? Co, + H,0H* + HCO,- Sio, + H,0 H* + HSIO,- HCO, H + Co,2- hydrated Al* ion 1.0 x 10-5 5.00 carbonic 4.5 x 10-7 6.35 silicic 1.3 x 10-10 9.89 hydrogencarbonate ion 4.8 x 10-11 10.3 hydrogensilicate ion HSIO,PH + Sio,- 1.3x 10-12 11.9 water H,0H* + OH- 1.0 x 10-14 14.0