Posted by missqi:
plus the acid is neutralised already.
Posted by mystiv :
u say neutralised.. u sure?
My 2 comments :
1st comment.
Neutralization technically occurs between an acid and a base. A
base is a substance that absorbs hydronium / hydroxonium ions
(H3O+) when dissolved in water (a proton acceptor). Other than the
common bases (oxides of metals and hydroxides of alkali metals),
sodium carbonate and ammonia are by this definition also considered
bases.
Metals by *themselves* however, such as calcium, are not quite
considered bases. But when they react with oxygen or water, as long
as they're reactive enough, such as calcium is, they *do* form
metal oxides and hydroxides which are bases, and thus can carry out
neutralization.
And this is what occurs here.
2nd comment.
To determine if the acid is truly "completely neutralized", which
was the topic of discussion between "missqi" and "mystiv", one
would have to determine (by simple mathematics) the limiting
reactant.
The mathematical procedure/working is simple (memorize this method,
'O' level Chem students!) :
Compare the Experiment Reactant Mole Ratio to the Equation Reactant
Mole Ratio. Remember that the Experiment is "what you have", while
the Equation is "what you need".
Let's take a simple equation, 2H2O + O2 ---> 2H2O2
Say you have (you might be given values in mass (g) or (for gases)
in volume (dm3), if so convert to moles) 1 mole of H2O and 2 moles
of O2, for the experiment. Therefore, taking H2O as numerator and
O2 as denominator, we have Experiment mole ratio (of reactants) of
1:2 or 0.5
From Eqn mole ratio, the corresponding Equation mole ratio (of
reactants) is 2:1 or 2.0
Comparing Exp mole ratio with Eqn mole ratio, we see that our Exp
mole ratio is less than our Eqn mole ratio.
And (ALWAYS) looking at the NUMERATOR reactant (in our case we have
chosen H2O), we realize that "what we have" (ie. Exp mole ratio) of
H2O, is less than "what we need" (ie. Eqn mole ratio) of H2O.
Therefore, H2O is the limiting reactant.
If, on the other hand our Exp mole ratio was greater than our Eqn
mole ratio, which means what we have (for the numerator reactant)
is more than what we need, so the numerator reactant (in this case
H2O) is the excess reactant, therefore the limiting reactant must
be the other reactant (in this case O2).
May this be of some usefulness or helpfulness to any 'O' level Chem
student reading this. I make sure my students use this very clear,
simple method, to determine limiting reactants.
