0.237 M
The balanced equation for the reaction is
KHP + NaOH ==> H2O + NaKP
So for each mole of KHP, it takes 1 mole of NaOH to neutralize. So let's determine how many moles of KHP we had. Start with the atomic weights.
Atomic weight potassium = 39.0983
Atomic weight hydrogen = 1.00794
Atomic weight phosphorus = 30.973762
Molar mass KHP = 39.0983 + 1.00794 + 30.973762 = 71.080002 g/mol
Moles KHP = 0.485 g / 71.080002 g/mol = 0.006823298 mol
Because of the 1 to 1 ratio of KHP and NaOH, we know that we used 0.006823298 moles of NaOH.
And since molarity is defined as moles per liter, just divide the number of moles by the number of liters. So
0.006823298 mol / 0.02874 l = 0.237414666 M.
Rounding to 3 significant figures gives 0.237 M
