Gchem??

[jdoc04]

Advertisement - Members don't see this ad

You have 9 grams of HCl in a 300mL solution. The acid completely ionizes. What is the resulting pH?

This is how I worked this problem:
pH= -log [H] Moles=grams/MM Molarity= moles/liters

Completely ionizing would mean [HCl] = [H]
Moles= 9/36 --> Molarity= (9/36)/.3 .3~~1/3
so Molarity= (9/36)/(1/3) --> (9/36)*(3/1) --> (9*3)/36

Answer --> -log (9*3)/36

kaplan answer--> -log (9)/(36*.3)

Either kaplan is wrong or I screwed the last step. Help anyone??????????

 

[DDS4tehwin]

[HCL] = (9g/36g)/(300ml/3000ml)

thus

(9/36)/(3/10) = (9/36) X (1/.3) = (9/36X.3)

 

[DrBob]

Dont let my craptastic GC score deter you from my recommendations. Your approach is absolutly correct..however the over simplification of .3 approx = 1/3 is where I would do it different. Why round .3 to 1/3 when it actually equals 3/10? Therefor you have (9/36)/(3/10L)--> (9/36)*(10/3)=(90/108) or simplified slopply (9/10.8) which is equal to what kaplan says and with this answer if kaplans answer was presented on a test you could quickly see 30% of 36 is 10.8.---In no way am I saying my way is best but I like to keep my numbers as close to real as possible.

 

[jdoc04]

Yeah I agree. I just thought about that.


THX!!!!!!!