when we put a salt eg NaCl into an acidic solution eg HCl, does
the pH value of thr solution decrease since NaCl is neutral whilr
HCl is acidic. bt cos there isnt any chemical reaction so im
unsure.
this is wat t think: thr pH value of the entire solution
decreases while the pH of thr acid and salt doesnt change. is that
right?
thanks for the helpf
pH is for a solution, it doesn't matter whether the solution
contains a mixture of acids, a mixture of salts, or a mixture of
salts and acids.
Although not tested at 'O' levels, it may help your
understanding, to be aware that pH may be taken to be -log10 [H+]
where [H+] = molarity (ie. molar concentration) of protons (ie. H+
ions).
Say you have 500cm3 of 0.5mol/dm3 of HCl mixed with
500cm3 of 1mol/dm3 of NaCl. What is the pH of the
solution mixture? Since volume is doubled, molarity of protons is
halved, ie. [H+] = 0.25mol/dm3. Key in -log10(0.25) into
the calculator, and you get 0.6 as the pH of the solution.
Since the acid and the salt have already been mixed,
the sentence "what is the pH of the acid" is incorrect, as is
the sentence "what is the pH of the salt". The only question that
can ask you is, "what is the pH of the resulting solution of the
mixture of acid and salt?" for which you can calculate the
answer as described in the preceeding paragraph.