[mrroboto40]

I did this lab a few days ago in class, and I'm having a hard time figuring out what I need to do.

I started off by making a solution of Potassium Hydrogen Phthalate (KHP) with an Inert salt (NaCl) and water, to make a a 250 mL solution.

I then pipetted 10 mL of that solution into a beaker, and added a few drops of Phenolphthalein.

I procedded to fill up a burette with NaOH, and titrated until my solution turned perfect pink, it took about 5.5 mL of NaOH to turn it pink.

What I need to find out: The %W/W of KHP in my original KHP and NaCl solution.

What I know:
To make my KHP and NaCl solution, I used a total of 5.0 grams of KHP and NaCl, unknown masses of each, but they add up to 5.0 grams.
The concentration of the NaOH I used was 0.0408 moles/g
It took 5.5 mL of NaOH to turn my KHP and NaCl solution pink



If someone could just tell me the steps I could use to solve this using stoichiometry equations, (moles= mass/molar mass or concentration=number of moles/volume) it would be greatly appreciated.

Thanks alot.

[Borek]

Write and balance equation of reaction that took place during titration.

[mtr]

What's the equation? I can't figure that out.

[Borek]

What is KHP? If you don't know - try to google it or check wikipedia.

[mtr]

KHP is potassium hydrogen phthalate

[Borek]

OK, is it acid, base, something else?

[mtr]

NaOH is the base, so what's the acid?

[mtr]

KHP is the acid
and NaCl?

[Borek]

First things first - what are products of reaction between acid and base?

[mtr]

Usually a salt is produced, but I don't think one was.

[Arkcon]

Usually a salt is produced, but I don't think one was.

Ok, here's a small tip.  Since you don't know what salt was formed, let's try a net ionic equation:

H⁺ + OH^- -> H2O

The Na⁺ and pthalate^- ions are just coming along for the ride, they appear on both sides, so we can claim they "cancel out"

Let's try to pull some facts together.  You start with an acid, you add phenolpthalein, which gives no color in acid.  You add base, and no color appears, because the acid is turning it to water as fast as the base is added, until the acid is all gone, then one drop of base turns the phenolpthalein pink. 

How much base did you add?  That is how much acid there was.  The rest is conversion of units --  mls to moles to moles to grams.

[mtr]

We already know the mass og the KHP + NaCl it's 5.0g. We have to figure out the mass of KHP alone.

[Borek]

Usually a salt is produced, but I don't think one was.

You are right that salts are produced, you are wrong later. KHP reacts with NaOH giving sodium potassium phthalate.

Does NaCl react with NaOH?