In: Chemistry
a) [H3O+] and [OH-] of Little Echo Pond:
given pH = 4.2
b) [H3O+] and [OH-] of a lake that has a pH of 6.5
Using the same analogy as above:
c) The additional [H3O+] that has to be neutralized to bring the pH from 4.2 to 6.5 is:
but the volume of lake is 1 kiloliters (1000 L), therefore the total amount (moles) of [H3O+] to be neutralized is:
(Remember M is nothing but mol/L)
Note that, H2SO4 is a diprotic acid, i.e, one molecule ionizes to give 2 protons or 2 [H3O+] as below:
Therefore, moles of acid in the lake must be half the moles of [H3O+]
So, moles of H2SO4 = 0.0682/2 = 0.0314 moles
Now, The balanced chemical reaction between H2SO4 and CaCO3 is:
According to the stoichiometry of the reactants, one mole of H2SO4 is neutralized by one mole of CaCO3.
Therefore, moles of CaCO3 required = 0.0314 moles
The molar mass of CaCO3 is 100.09 g/mol. So,
grams of CaCO3 required is: