- #1

kevvyroo

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## Homework Statement

I'm trying to find the pH change of adding 0.001 mol of HNO[itex]_{}3[/itex] to a buffer solution containing 0.24 M HF and 0.55 M NaF in 0.100 L.

K[itex]_{}a[/itex] = 3.5E-4 therefore pK[itex]_{}a[/itex]=3.47

## Homework Equations

**pH=pK[itex]_{}a[/itex]+log[itex]_{}10[/itex][base]/[acid]**

(Henderson-Hasselbach equation)

and of course

**-log[itex]_{}10[/itex](H[itex]^{}+[/itex])=pH**

## The Attempt at a Solution

I've tried an ICE table but my best guess for a solution was

0.01 M H+ (from HNO[itex]_{}3[/itex]) react with the F[itex]^{}-[/itex] base ions to form HF.

.55 M( fluoride ions)-.01 M( hydronium)=.54 (final fluoride ions)

0.24 M (HF) + 0.01 M (HF produced from above reaction) = 0.25 M HF

So,

pH=3.47+log[itex]_{}10[/itex](.54/.25)

pH=3.80

The answer that is supposed to be correct is 3.79... is this just a sig figs error or did I mess up along the line because I needed exactly 3.79 to be the pH

Sorry if I did anything wrong, I'm new to this forum! (: