317 
On the other hand, SKRABAL got the value 45 for the temperature 
coefficient of the reaction 31, + 60H’ = 5I’ + 10', + 3H,O, in 
presence of sodium carbonate and bicarbonate. Here the hydrolysis 
of the salts produce OH’ ions which are active in the change and 
helps the effect of temperature. The increase of temperature increases 
the hydrolysis and hence the OH’ ions are also increased and the 
velocity of the reaction is increased due to this effect in addition to 
the usual effect of temperature increasing the velocity of the reaction. 
In other words, the effect of temperature is intensified. 
Hence the abnormally large effect of temperature is explained. 
Summary : 
a. A dilute solution of iodic acid and potassium iodide react very 
rapidly even at 0°. The temperature coefficient cannot be exactly 
determined and is probably equal to unity. 
6. In presence of sodium and magnesium sulphates slightly less 
iodine is liberated from iodie acid and potassium iodide at higher 
than at lower temperatures. The explanation is that at higher temper- 
atures more OH’ ions are produced due to increased hydrolysis of 
sodium or magnesium sulphate and these OH’ ions react on the 
iodine which is forming and thus regenerate iodide and iodate. 
Hence in presence of Na,SO,, the temperature effect is partly 
counter-acted. 
c. Manganese sulphate, potassium sulphate, alum ete. have no 
action, whilst in presence of ammonium and zine sulphates, the 
temperature coefficient of the reaction between iodie acid and 
potassium iodide becomes greater than unity. Solutions of zine and 
ammonium sulphates produce more H’ ions at higher temperatures 
and these ions are very active in liberating iodine from iodic acid 
and potassium iodide. 
d. A similar explanation is applicable to the small temperature 
coefficients obtained in the reactions between 1. iodic acid and 
potassium iodide in presence of sodium acetate, sodium phosphate, 
potassium fluoride etc., 2. chromic acid and oxalic acid in presence 
of sodium sulphate, magnesium sulphate, sodium fluoride ete., 
3. hydrogen peroxide and hydrogen iodide in presence of sodium 
bicarbonate. 
e. Abnormally large values of temperature coefficient for the 
reaction 31, + 60H’ — 5I’ + 10’, + 3H,O, in presence of Na,CO, 
and NaHCO,, are also due to hydrolysis of the carbonates. 
f. The following reactions have measurable velocities and their 
21* 
