Aqueous H₂SO₄: Degrees of Dissociation

The experimental data are listed in the tables below. Notes at the end of each one define the tabulated quantities, and identify the sources of the measurements.

New measurements by the following groups have been made since the work of Clegg and Brimblecombe (1995):

• D. A. Knopf, B. P. Luo, U. K. Krieger and T. Koop (2003) J. Phys. Chem. A 107, 4322-4332.
• C. E. L. Myhre, D. H. Christensen, F. M. Nicolaisen and C. J. Nielsen (2003) J. Phys. Chem. A 107, 1979-1991.
• K. Tomikawa and H. Kanno (1998) J. Phys. Chem. A 102, 6082-6088.
• N. Minogue, E. Riordan and J. R. Sodeau (2003) J. Phys. Chem. A 107, 4436-4444.

Data from Knopf et al. (2003) and Myrhe et al. (2003) are listed here. At the molalities studied by these authors the first dissociation of sulphuric acid, to produce HSO4⁻ and H⁺, is essentially complete.

1.  Degrees of Dissociation of H2SO4 and HSO4⁻ in Aqueous H2SO4

   mH2SO4     alpha       T     reaction  ref. weight           
   2.6258     0.34      298.15     1       a    1.0
   3.8020     0.30      298.15     1       a    1.0
   4.9921     0.29      298.15     1       a    1.0
   5.5153     0.30      298.15     1       a    1.0
   6.6437     0.29      298.15     1       a    1.0
   8.4843     0.26      298.15     1       a    1.0
  10.619      0.25      298.15     1       a    1.0
  13.082      0.21      298.15     1       a    1.0
  19.489      0.12      298.15     1       a    1.0
  29.263      0.05      298.15     1       a    1.0
  62.959      0.66      298.15     2       a    1.0
 117.86       0.40      298.15     2       a    1.0
1324.4        0.04      298.15     2       a     -
 42.619       0.0489    298.15     1       b     -
 32.925       0.0750    298.15     1       b    1.0
 25.070       0.1607    298.15     1       b    1.0
 19.623       0.1167    298.15     1       b    1.0
 15.300       0.2295    298.15     1       b    1.0
 11.854       0.2525    298.15     1       b    1.0
  9.0336      0.2510    298.15     1       b    1.0
  7.8031      0.2347    298.15     1       b    1.0
  6.6735      0.2850    298.15     1       b    1.0
  4.6607      0.2729    298.15     1       b    1.0
  3.7579      0.2553    298.15     1       b    1.0
  2.9150      0.2429    298.15     1       b    0.0
  2.1225      0.2806    298.15     1       b    1.0
  1.3769      0.1920    298.15     1       b    0.0
  1.0905      0.2371    298.15     1       b    1.0
  0.80900     0.2156    298.15     1       b    1.0
  0.53437     0.2027    298.15     1       b    1.0
  0.26414     0.1678    298.15     1       b    0.0
  0.00090651  0.883     298.15     1       c    1.0
  0.0041970   0.695     298.15     1       c    1.0
  0.021941    0.415     298.15     1       c    1.0
  0.057308    0.289     298.15     1       c    1.0
  0.11003     0.232     298.15     1       c    1.0
  0.26169     0.196     298.15     1       c    1.0
  0.46798     0.197     298.15     1       c    1.0
  0.72233     0.212     298.15     1       c    1.0
  1.0143      0.238     298.15     1       c    1.0
  1.3459      0.266     298.15     1       c    1.0
  1.7267      0.291     298.15     1       c    1.0
  2.1578      0.314     298.15     1       c    1.0
  2.6344      0.338     298.15     1       c    1.0
  0.00025074  0.960     298.15     1       d    1.0
  0.0010030   0.874     298.15     1       d    1.0
  0.0050157   0.668     298.15     1       d    1.0
  0.0062698   0.632     298.15     1       d    1.0
  0.012542    0.522     298.15     1       d    1.0
  0.025095    0.422     298.15     1       d    1.0
  0.050232    0.344     298.15     1       d    1.0
327.44        0.19326   298.15     2       e     -
 78.315       0.63054   298.15     2       e     -
 54.667       0.81555   298.15     2       e     -
 40.059       0.99707   298.15     2       e     -
 40.059       0.02158   298.15     1       e    1.0
 21.154       0.10138   298.15     1       e    1.0
 11.802       0.23018   298.15     1       e    1.0
  8.0010      0.30050   298.15     1       e    1.0
  4.7309      0.32746   298.15     1       e    1.0
  3.3419      0.32881   298.15     1       e    1.0
  1.5591      0.29932   298.15     1       e    1.0
  1.0190      0.27551   298.15     1       e    1.0
  0.50212     0.29471   298.15     1       e    0.0
  0.33685     0.26807   298.15     1       e    1.0
  0.20604     0.27451   298.15     1       e    1.0
  0.10165     0.31683   298.15     1       e    1.0
  0.050232    0.34000   298.15     1       e    1.0  
 78.469       0.67253   273.15     2       e     -
 54.667       0.85733   273.15     2       e     -
 40.151       0.99278   273.15     2       e     -
 40.151       0.02135   273.15     1       e    1.0
 21.203       0.14545   273.15     1       e    1.0
 11.791       0.26482   273.15     1       e    1.0
  8.0071      0.36184   273.15     1       e    1.0
  4.7440      0.42184   273.15     1       e    1.0
  1.5639      0.47106   273.15     1       e    1.0
  0.50379     0.48387   273.15     1       e    0.0
 78.276       0.65625   323.15     2       e     -
 54.625       0.80267   323.15     2       e     -
 40.106       0.90842   323.15     2       e     -
 40.106       0.01600   323.15     1       e    1.0
 21.167       0.05607   323.15     1       e    1.0
 11.825       0.16861   323.15     1       e    1.0
  8.0226      0.21997   323.15     1       e    1.0
  4.7271      0.20460   323.15     1       e    1.0
  1.5596      0.20647   323.15     1       e    1.0
  1.0166      0.17580   323.15     1       e    1.0
  0.33608     0.21341   323.15     1       e    1.0 
  0.010038    0.566     300.15     1       f    0.0 
  0.020084    0.458     300.15     1       f    0.0
  0.040194    0.379     300.15     1       f    0.0
  0.060330    0.324     300.15     1       f    0.0
  0.080498    0.291     300.15     1       f    0.0
  0.10069     0.269     300.15     1       f    0.0
  0.15130     0.242     300.15     1       f    0.0
  0.20209     0.230     300.15     1       f    0.0
  0.25307     0.219     300.15     1       f    0.0
  0.30423     0.212     300.15     1       f    0.0

Notes and References

• Key: mH2SO4 - the molality of the acid; alpha - the measured degree of dissociation; reaction - (1) HSO4⁻ = SO4²⁻ + H⁺, (2) H2SO4 = HSO4⁻ + H⁺; T - temperature (K); ref. - source of data; weight - values of 0.0 indicate that the measurement was excluded from the fits carried out by Clegg and Brimblecombe (1995) (and in which the first dissociation was assumed to be complete).
• Sources: a - G. C. Hood and C. A. Reilly (1957) J. Chem. Phys. 27, 1126-1128; b - H. Chen and D. E. Irish (1971) J. Phys. Chem. 75, 2672-2681; c - R. E. Lindstrom and H. E. Wirth (1969) J. Phys. Chem. 73, 218-223; d - M. S. Sherrill and A. A. Noyes (1926) J. Amer. Chem. Soc. 48, 1861-1873; e - T. F. Young, L. F. Maranville and H. M. Smith (1959) Raman spectral investigations of ionic equilibria in solutions of strong electrolytes. In: The Structure of Electrolytic Solutions, Ed. W. J.Hamer, Wiley, New York, pp35-63; f - J. T. Edward and I. C. Wang (1965) Can. J. Chem. 43, 2867-2871.
• We have not included in results of D. J. Turner (J. Chem. Soc., Faraday Trans. I, 70, 1346-1356, 1974) who presents two sets of dissociation constants in his Table I, for concentrations from 0.02 to 4.00 mol dm^-3, based upon different assumptions made in the analysis.
• The experimental temperatures of Edward and Wang (1965) are subject to an uncertainty of (+ or -) 1.5 K.

2.  Degrees of Dissociation of the HSO4⁻ Ion in Aqueous Sulphuric Acid

 wtH2SO4  mH2SO4  alpha     T     ref.
   12.3    1.43   0.345    293     a      
   12.3    1.43   0.385    288     a            
   12.3    1.43   0.411    283     a            
   12.3    1.43   0.426    278     a            
   12.3    1.43   0.503    273     a            
   12.3    1.43   0.554    268     a            
   12.3    1.43   0.618    263     a            
   20.2    2.60   0.335    295     a            
   20.2    2.60   0.416    288     a            
   20.2    2.60   0.448    283     a            
   20.2    2.60   0.471    278     a            
   20.2    2.60   0.530    273     a            
   20.2    2.60   0.568    268     a            
   20.2    2.60   0.776    263     a            
   20.2    2.60   0.662    258     a            
   20.2    2.60   0.685    253     a            
   20.2    2.60   0.733    248     a            
   20.2    2.60   0.736    243     a            
   29.1    4.19   0.386    295     a            
   29.1    4.19   0.425    288     a            
   29.1    4.19   0.465    283     a            
   29.1    4.19   0.485    278     a            
   29.1    4.19   0.531    273     a            
   29.1    4.19   0.568    268     a            
   29.1    4.19   0.602    263     a            
   29.1    4.19   0.633    258     a            
   29.1    4.19   0.660    253     a            
   29.1    4.19   0.687    248     a            
   29.1    4.19   0.713    243     a            
   29.6    4.28   0.382    295     a            
   29.6    4.28   0.547    273     a            
   29.6    4.28   0.635    263     a            
   29.6    4.28   0.730    248     a            
   29.6    4.28   0.755    238     a            
   29.6    4.28   0.861    223     a            
   29.6    4.28   0.859    213     a            
   48.6    9.63   0.335    293     a            
   48.6    9.63   0.415    273     a            
   48.6    9.63   0.490    263     a            
   48.6    9.63   0.558    248     a            
   48.6    9.63   0.621    238     a            
   48.6    9.63   0.768    223     a            
   57.8   13.94   0.247    293     a            
   57.8   13.94   0.337    273     a            
   57.8   13.94   0.366    263     a            
   57.8   13.94   0.434    248     a            
   57.8   13.94   0.471    238     a            
   57.8   13.94   0.529    223     a            
   57.8   13.94   0.607    213     a            
   60.5   15.64   0.277    290     a            
   60.5   15.64   0.322    273     a            
   60.5   15.64   0.357    263     a            
   60.5   15.64   0.421    248     a            
   60.5   15.64   0.465    238     a            
   60.5   15.64   0.520    223     a            
   60.5   15.64   0.587    213     a            
   67.5   21.18   0.225    291     a            
   67.5   21.18   0.260    273     a            
   67.5   21.18   0.263    263     a            
   67.5   21.18   0.302    248     a            
   67.5   21.18   0.331    238     a            
   67.5   21.18   0.370    223     a            
   67.5   21.18   0.426    213     a            
   71.8   25.96   0.206    290     a            
   71.8   25.96   0.182    273     a            
   71.8   25.96   0.199    263     a            
   71.8   25.96   0.209    248     a            
   71.8   25.96   0.240    238     a            
   71.8   25.96   0.261    223     a            
   71.8   25.96   0.294    213     a            
   77.1   34.37   0.090    295     a            
   77.1   34.37   0.056    273     a            
   77.1   34.37   0.071    263     a            
   77.1   34.37   0.089    248     a            
   77.1   34.37   0.097    238     a            
   77.1   34.37   0.130    223     a            
   77.1   34.37   0.147    213     a            
   81.2   44.04   0.089    296     a            
   81.2   44.04   0.085    273     a            
   81.2   44.04   0.087    263     a            
   81.2   44.04   0.084    248     a            
   81.2   44.04   0.100    238     a            
   81.2   44.04   0.139    223     a            
   81.2   44.04   0.158    213     a            

Notes and References

• Key: wtH2SO4 - mass percent of H2SO4 in the aqueous solution; mH2SO4 - H2SO4 molality (mol per kg of water); alpha - degree of dissociation of HSO4⁻(aq), equal to mSO4²⁻/(mSO4²⁻ + mHSO4⁻), T - temperature (K).
• Source: a - C. E. L. Myhre, D. H. Christensen, F. M. Nicolaisen and C. J. Nielsen (2003) J. Phys. Chem. A 107, 1979-1991.

3.  Degrees of Dissociation of the HSO4⁻ Ion in Aqueous Sulphuric Acid

 mH2SO4  alpha     T         mH2SO4   alpha    T     ref. 
  0.54   0.22    321.0        6.79    0.49   269.6    a        
  0.54   0.22    316.0        6.79    0.53   259.8    a         
  0.54   0.19    311.0        6.79    0.58   249.9    a         
  0.54   0.23    306.0        6.79    0.63   239.9    a         
  0.54   0.30    297.1        6.79    0.68   230.3    a         
  0.54   0.34    290.4        6.79    0.73   220.5    a         
  0.54   0.38    280.5        6.79    0.78   210.5    a         
  0.54   0.46    270.7        6.79    0.83   200.7    a         
  0.54   0.46    260.8        6.79    0.87   190.9    a         
  0.54   0.53    251.0        6.79    0.90   181.2    a         
  0.54   0.59    241.0        9.84    0.28   324.9    a         
  1.13   0.37    289.4        9.84    0.30   320.9    a         
  1.13   0.42    279.4        9.84    0.31   315.9    a         
  1.13   0.48    269.6        9.84    0.32   311.0    a         
  1.13   0.54    259.8        9.84    0.32   306.1    a         
  1.13   0.59    254.9        9.84    0.34   298.4    a         
  1.13   0.60    249.9        9.84    0.35   296.7    a         
  1.13   0.68    240.1        9.84    0.36   289.8    a         
  2.55   0.42    290.8        9.84    0.39   280.1    a         
  2.55   0.46    280.1        9.84    0.42   270.3    a         
  2.55   0.51    270.1        9.84    0.45   260.3    a         
  2.55   0.57    260.8        9.84    0.49   250.4    a         
  2.55   0.64    251.2        9.84    0.53   240.4    a         
  2.55   0.67    246.1        9.84    0.57   230.4    a         
  2.55   0.70    240.1        9.84    0.61   220.5    a         
  2.55   0.73    236.1        9.84    0.66   211.5    a         
  2.55   0.75    233.0        9.84    0.71   200.6    a         
  2.55   0.75    231.0        9.84    0.76   190.8    a         
  4.37   0.34    325.9        9.84    0.81   181.0    a         
  4.37   0.34    320.8       15.23    0.23   326.0    a         
  4.37   0.35    315.9       15.23    0.24   321.0    a         
  4.37   0.36    310.9       15.23    0.25   316.0    a         
  4.37   0.37    306.0       15.23    0.25   311.0    a         
  4.37   0.39    301.0       15.23    0.25   306.1    a         
  4.37   0.40    297.4       15.23    0.27   298.3    a         
  4.37   0.40    289.7       15.23    0.27   296.6    a         
  4.37   0.47    279.9       15.23    0.28   289.7    a         
  4.37   0.52    269.8       15.23    0.30   279.8    a         
  4.37   0.58    259.8       15.23    0.32   270.2    a         
  4.37   0.64    249.7       15.23    0.35   260.4    a         
  4.37   0.70    239.9       15.23    0.37   250.7    a         
  4.37   0.76    230.0       15.23    0.40   240.9    a         
  4.37   0.83    219.7       15.23    0.43   230.7    a         
  4.37   0.85    209.5       15.23    0.47   221.0    a         
  4.37   0.89    199.7       15.23    0.51   211.2    a         
  4.37   0.92    190.0       15.23    0.55   201.3    a        
  6.79   0.41    289.9       15.23    0.59   191.3    a         
  6.79   0.45    279.1       15.23    0.64   181.5    a       

Notes and References

• Key: mH2SO4 - H2SO4 molality (mol per kg of water); alpha - degree of dissociation of HSO4⁻(aq), equal to mSO4²⁻/(mSO4²⁻ + mHSO4⁻); T - temperature (K).
• Source: a - D. A. Knopf, B. P. Luo, U. K. Krieger and T. Koop (2003) J. Phys. Chem. A 107, 4322-4332.