[naniekso]

hi guys, im trying to search for my answer on your search but I can't seem to find what I'm looking for, just instructions.
I'm new to this site but i feeel i will be on here for the next 3 years anyway:

I want to fullly understand the meanings of this equation;

Ka= [H30+][A-]
           [HA]

So what does each concentration stand for, because I need to use it in this practice problem:

Calculate the pH of a solution composed of 4 grams of ammonia (17g/mol) dissolved in 1 liter of water.
Ka, NH4+= 5.7x10^-12

so i convert the 4g/17g to get moles, then divide by liters, water 1 liter so its 0.235M, so where does this plug into the equation above and why? what are the other varriables?
I don't understand this concept because the book i have just labels them as HA and A but dosn't tell me what theya re supose to be. Please help if you have the chance, this website looks like it will help me with my pre-med courses too <3

[nj_bartel]

[H⁺][Conjugate base]/[Nondissociated acid]

[naniekso]

i still cant seem to anwser the question using that equation!

[BlowUpEverything]

Remember the definition of pH.  You can use the equation you have to solve for any of those variables!

[Borek]

HA is a placeholder for any acid, that dissociates

HA = H⁺ + A^-

It happens that almost identical question is solved here:

http://www.chembuddy.com/?left=pH-calculation-questions&right=pH-weak-base-q1