Asked by Audrey
Calculate the value of [H3O+] in a 0.01 M HOBr solution. Ka = 2.5E-9
I'm having a problem with just writing the equilibrium expression.
do you add H2O to the HOBr?
HOBr + H2O <---> H3O+ + OBr-
but then you could say that because HOBr = .01 M, then 0Br- = .01 M, and H3O+ would equal the Ka. but that is not the answer...
I'm having a problem with just writing the equilibrium expression.
do you add H2O to the HOBr?
HOBr + H2O <---> H3O+ + OBr-
but then you could say that because HOBr = .01 M, then 0Br- = .01 M, and H3O+ would equal the Ka. but that is not the answer...
Answers
Answered by
DrBob222
Yes, technically, one adds water but many people omit the water.
HOBr + H2O ==> H3O^+ + OBr^- OR
HOBr ==> H^+ + OBr^-
Ka = 2.5E-9 = (H3O^+)(OBr^-)/(HOBr)
What you are doing wrong is you are assuming the ionization is 100% and it isn't (otherwise the Ka would be infinity). A solution 0.01 M in HCl will be 0.01M in H^+ and 0.01M in Cl^-; but that is because HCl is 100% ionized. HOBr, having a Ka of 2.5E-9 isn't anywhere close to 100% and you cannot do it this way. You set up an ICE chart, substitute into Ka expression, and solve for the unknown.
initial:
HOBr = 0.01
H^+ = 0
OBr^- = 0
change:
H^+ = +x
OBr^- = +x
HOBr = -x
equilibrium:
H^+ = +x
OBr^- = +x
HOBr = 0.01-x
Substitute into Ka expression above and solve for x.
HOBr + H2O ==> H3O^+ + OBr^- OR
HOBr ==> H^+ + OBr^-
Ka = 2.5E-9 = (H3O^+)(OBr^-)/(HOBr)
What you are doing wrong is you are assuming the ionization is 100% and it isn't (otherwise the Ka would be infinity). A solution 0.01 M in HCl will be 0.01M in H^+ and 0.01M in Cl^-; but that is because HCl is 100% ionized. HOBr, having a Ka of 2.5E-9 isn't anywhere close to 100% and you cannot do it this way. You set up an ICE chart, substitute into Ka expression, and solve for the unknown.
initial:
HOBr = 0.01
H^+ = 0
OBr^- = 0
change:
H^+ = +x
OBr^- = +x
HOBr = -x
equilibrium:
H^+ = +x
OBr^- = +x
HOBr = 0.01-x
Substitute into Ka expression above and solve for x.
Answered by
Audrey
thanks!!!
There are no AI answers yet. The ability to request AI answers is coming soon!
Submit Your Answer
We prioritize human answers over AI answers.
If you are human, and you can answer this question, please submit your answer.