You may want to use this equation:
pH=pKa+log[HA][A−]It is simply a logarithmic form of the Ka equation you are used to.
Remember
[A−] and
[HA] are the concentrations of conjugate base and undissociated acid at equilibrium.
So
log[HA][A−] represents the log to base 10 of conjugate base: acid ratio.
You need to find
[HA][A−] at equilibrium but in order to do this you need to find the
pKa value for the carbonic acid first.
1. The clue is to notice that you have been given the ratio at a particular pH, so this will enable you to find
pKa and use it to answer the question.
2. Once you have found pKa you sub it into the equation with the pH of blood the patient has and solve for the ratio.
I can't really type out all the working but I'll attach a picture:
Alternatively you may use the
other form of the Ka equation, but that will involve more anti-logging I think.