HSC 2006 Q17b (1 Viewer)

[SkimDawg]

Calculate the pH after 20mL of 0.01 mol/L sodium hydroxide is added to 50mL of 0.2mol/L hydrochloric acid. Include a balanced chemical equation in your answer.
I think I've gotten the values for the pH for both the solutions, but what do I do now? thanks

 

[tommykins]

NaOH + HCl -> NaCl + H2O

n(NaOH) = cv = 0.02*0.01 = whatever
n(HCl) = 0.05*0.2 = whatever

HCl is in excess.

n(HCl) - n(NaOH) = n(HCl) remaining.

-log nHCl is your new pH

 

[SkimDawg]

Thanks again. I hate these pH / mole / titration style questions, the concept never stuck with me.

 

[minijumbuk]

NaOH + HCl -> NaCl + H2O

n(NaOH) = cv = 0.02*0.01 = whatever
n(HCl) = 0.05*0.2 = whatever

HCl is in excess.

n(HCl) - n(NaOH) = n(HCl) remaining.

-log nHCl is your new pH

That part is incorrect. You still need one more step.
pH = -log [H+]
= -log (n/0.07)

 

[tommykins]

ah yeah, -log concentration, forgot about that ^^