The pH values of the 1:1 and 1:4 buffers should remain unchanged on the addition of small amounts of strong acid or base.
In your experiment, you prepared 1:1 and 1:4 NH₃/NH₄⁺ buffers. You measured the pH of each with phenolphthalein. Then you added 1 drop of HCl and 1 drop of NaOH to separate test tubes of the buffers.
We can calculate the pH of an NH₃/NH₄Cl buffer from the equation:
The value of
Phenolphthalein is pink between pH 8.2 and pH 10. Its colour at pH 8.65 might be a little less pink at pH 9.25, but it would be hard to tell the difference.
Your 1:1 and 1:4 solutions are both buffers. Their pH values should not change significantly on the addition of one drop of strong acid or base.