Potassium hydrogen tartrate is an acid used in making cookies such as snicker doodles. (In your home, it is called cream of tartar.) It can be titrated with a base such as KOH to determine purity. A sample of 0.500 g is titrated to a pink endpoint with 21.58 mL of 0.1125 M KOH. Determine the percentage of potassium hydrogen tartrate (KHC4H4O6) in the sample. The acid/base ratio is 1:1.

91.4%

Explanation:

Potassium hydrogen tartrate, KHT, reacts with KOH as follows.

KHT + KOH → H₂O + K₂T

where 1 mole of acid (KHT) reacts per mole o base (KOH), -That is acid/base ratio 1:1

The endpoint of a titration is the point in which moles of KOH = moles of KHT, you can see this endpoint with an indicator or doing a potentiometric titration.

As the endpoint requires 21.58mL = 0.02158L of a 0.1125M KOH, moles of KOH = moles of KHT are:

0.02158L × (0.1125mol / L) = 2.428x10⁻³ moles of KOH = moles of KHT

To convert these moles to grams you use molar mass of KHT (188.177g/mol):

2.428x10⁻³ moles of KHT × (188.177g / mol) = 0.457g of KHT are in the sample.

As you add 0.500g of sample, percentage of KHT in the sample is:

(0.457g / 0.500g) × 100 =

-That is the purity of the sample-