pg 57 and 58 made easy inorganic book
hydrolysis of both Mg2+ and Al3+ produces 1 mol of HCl.
However, pH of soln containing Al3+ is lower than Mg2+. means
concentration of H+ is higher for the hydrolysis of Al3+ compared
to Mg2+.
so what does 1 mol entails? it doesn't really mean equal amounts
of a particular substance, even if two seperate solns have 1 mol of
that particular substance? always must look at position of
equilibrium, which one lies further to the right and, which
equilibrium has its forward reaction of a greater extent to the
right?
one way is to use ICE table?
You cockanaden! If hydrolysis of both Mg2+ and Al3+ produces 1
mol of HCl, wouldn't the pH be the same?!? Obviously the extent of
hydrolysis is significantly greater for AlCl3, and lesser for
MgCl2, hence the different pH values. Cambridge will require you to
explain why, and the balanced equations will (of course) be
required.
If a single source or book confuses you, cross-reference with
other sources and books, to come to a better understanding of the
subject matter. If you did so in this case, and you *still* came to
the cockanaden conclusion that "hydrolysis of both Mg2+ and Al3+
produces 1 mol of HCl", then you might as well voluntarily
withdraw from the 2016 A level exam, save yourself the pain of
waiting for your U grade results in March 2017.
