Adding these to a buffer, what happens to the pH?

[johnwandering]

A buffer has an initial pH of 7.64.
What happens to it when you add:

a.) HCl
b.) HCN
c.) H2O

And why?

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[pfaction]

a) pH decreases slightly. Addition of an acid always decreases pH.
b) It's a weak acid, so...barely anything.
c) jack ****. You're diluting the entire solution, so the acid molarity decr in equal proportions to the base molarity decr.

 

[Temperature101]

A buffer has an initial pH of 7.64.
What happens to it when you add:

a.) HCl
b.) HCN
c.) H2O

And why?

a) decrease very slightly since it is a strong acid...b) and c) nothing happens since the solution is a buffer i.e resist any pH change.

 

[theseeker4]

a) decrease very slightly since it is a strong acid...b) and c) nothing happens since the solution is a buffer i.e resist any pH change.

You can't say with confidence that a weak acid or a weak base will do NOTHING to the pH of a buffer without other information. How weak of a buffer or strong of a buffer is it? How much weak acid is added?

Likewise, you need to know concentrations and amounts to say the decrease in pH is "very slight" upon the addition of a strong acid.

Know that a strong acid and a strong base will cause a decrease and an increase in pH respectively, while a weak acid and a weak base will cause a decrease/increase in pH based on how the pKa/b of the weak acid/base relates to the pH of the buffer. Also know that water will generally not change the pH of the buffer due to the reason mentioned above.

 

[MedPR]

Adding acid will cause a slight decrease, adding base will cause a slight increase. Adding water = no effect unless you add a ton of water.