A student actually used 0.847g sample of impure KHP and the endpoint was reached after 19.82 ml of sodium hydroxide solution was added, What is the percent KHP in the unknown to four significant figures.

100KHP/(KHP+NaHO)

=100(0.847)/(0.847+19.82)
=4.098...%

I don't agree with this answer. It's nonsense.

To find the percent KHP in the unknown, we need to know the molecular weight of KHP and the balanced equation for the reaction between KHP and NaOH.

KHP (potassium hydrogen phthalate) has a molecular formula of C8H5KO4 and a molecular weight of 204.22 g/mol.

The balanced equation for the reaction between KHP and NaOH is:
KHP + NaOH → H2O + KNaP

From the balanced equation, we can see that the mole ratio between KHP and NaOH is 1:1. This means that for every mole of KHP, we need one mole of NaOH to reach the endpoint.

First, calculate the number of moles of NaOH used:
moles of NaOH = volume of NaOH solution (L) × molarity of NaOH (mol/L)

Since you provided the volume of NaOH solution in milliliters (mL), we need to convert it to liters (L):
volume of NaOH solution (L) = 19.82 mL ÷ 1000 mL/L = 0.01982 L

Next, we need to determine the molarity of NaOH. If you have this information, use it in the calculation. If not, you'll need to perform a titration to determine the molarity of the NaOH solution.

Once you have the moles of NaOH used, you can calculate the moles of KHP that were present in the initial sample.

moles of KHP = moles of NaOH

Next, find the mass of KHP used in the experiment. You provided the mass of the sample, which is 0.847 g. This mass includes both KHP and any impurities present.

Finally, calculate the percent KHP in the unknown:

percent KHP = (moles of KHP × molecular weight of KHP) ÷ mass of sample × 100

Make sure to round the final answer to four significant figures as requested.