ATAR Notes: Forum

HSC Stuff => HSC Science Stuff => HSC Subjects + Help => HSC Chemistry => Topic started by: sav07 on January 23, 2019, 08:04:38 pm

Title: pH
Post by: sav07 on January 23, 2019, 08:04:38 pm

Hey! The question says:
HA has Ka 1.6 x 10^-5
Calculate the pH of a 0.001 ml L solution of HA
I was just wondering how I can calsulate the pH from the Ka

Title: Re: pH
Post by: kauac on January 23, 2019, 08:08:41 pm

Quote from: sav07 on January 23, 2019, 08:04:38 pm

Hey! The question says:
HA has Ka 1.6 x 10^-5
Calculate the pH of a 0.001 ml L solution of HA
I was just wondering how I can calsulate the pH from the Ka

Hi, would you be able to clarify your acronyms? :)

HA = hydrochloric acid?
Ka = ??

Title: Re: pH
Post by: sav07 on January 23, 2019, 08:11:01 pm

HA is just an acid it doesn't specify which one, and Ka is the equilibrium constant for the acid dissociation

Title: Re: pH
Post by: david.wang28 on January 23, 2019, 09:17:21 pm

Quote from: sav07 on January 23, 2019, 08:11:01 pm

HA is just an acid it doesn't specify which one, and Ka is the equilibrium constant for the acid dissociation

Hi Sav! If this is HA, then you would want to write H^+ + A^- as your dissociation reaction. Then you would want to write the Ka reaction (products over reactants). You should find the concentration of HA (c= n/v) and once you have done that, draw up an ICE table (I'm sure you can work this out for yourself). Then, find the concentration of H^+, and sub that number into pH = -log(H^+), and you should get the answer! :)