<span>When pKas of polyprotic intermediates have a difference of 2 or more you just average them using the equation: pH = (pKa2 + pKa3) / 2 </span>
<span>pKa2 = -log(Ka2) ; pKa3 = -log(Ka3) </span>
<span>so, for this problem, REGARDLESS OF THE CONCENTRATION GIVEN, the answer is: </span>
<span>pH = (7.2076+12.3767) / 2 </span>
<span>pH = 9.79</span>
water in scientific knowledge is H20
Answer : The volume for 6.0m HCl solution required = 62.5 ml
Solution : Given,
Initial concentration of HCl solution = 6.0m
Final concentration of HCl solution = 1.5m
Final volume of HCl solution = 250 ml
Initial volume of HCl solution = ?
Formula used for dilution is,

where,
= initial concentration
= final concentration
= initial volume
= final volume
Now put all the given values in above formula, we get the initial volume of HCl solution.

= 62.5 ml
Therefore, the volume for 6.0m HCl solution required = 62.5 ml
They are all rocks and they are all solid