[aemalcolm]

So i've been out of chem for a few years and I'm struggling to understand this question on determining the acidity of gastric HCl...
Any pointers would be wonderful
In a hospital laboratory, a 10mL sample of gastric juice, obtained several hrs before a meal, was titrated with 0.1 M NaOH to neutrality: 7.2 mL of NaOH was required. The patient's stomach contained no food (so assume no buffers). What was the pH of the gastric juice.
I know I need to Henderson-Hasselbalch equation pH= pKa + log (A-/HA), I'm just not sure on how to go about doing that. I would imagine you would set the pH equal to 7 since it's neutral and go from there....

[macman104]

You don't need the H-H equation.  This is a standard titration of a strong acid with a strong base.

Find your moles of NaOH that were used (from your volume and concentration), and that is equal to the moles of HCl in the sample.

Once you have the moles of HCl, you can find the concentration in the sample (since you have volume and moles).

Now you calculate pH, using the standard equation of pH = -log[concentration H+].

[aemalcolm]

Thank you so much! I knew I was making it harder then it was suppose to be. This might sound like a dumb question but are the moles of an acid and a base always the same at equilibrium?

[Borek]

At equivalence.