Why do we not need to determine the exact volume of water needed to make the sol

Question

Why do we not need to determine the exact volume of water needed to make the solution with the KHP in the standardization titration? What is the difference between the end point and the equivalence point of a titration? Will they be at the same or different point? Explain. When a 13.62 ml. volume of vinegar is used in a titration exactly like the one you will perform today, it is found that 27.93 mL of 0.150 M NaOH is needed to reach the equivalence point, Calculate the moles of NaOH added in this titration Calculate the moles of CH_3COOH in the vinegar sample. Calculate the Molarity of CH_3COOH in the vinegar solution. Calculate the moles of CH_3COONa produced in this reaction. Calculate the Molarity of the CH, COONa produced in this titration before any CH_3COO' reacts with water. Calculate the Molarity of CH_3COO^- produced in this titration, assuming that CH_3COONa dissociates completely in water, but before any CH_3COO reacts with water. Calculate the pH of this titrated solution at the equivalence point. (Use the back of this page if necessary.)

Explanation / Answer

2) KHP is used as a primary standard for acid-base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic.used as a primary standard for acid-base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic.

KHP dissociates completely in water, giving the potassium cation (K+) and hydrogen phthalate anion (HP or Hphthalate). As a weak acid hydrogen phthalate reacts reversibly with water to give hydronium (H3O+) and phthalate ions.

HP + H2O P2 + H3O+

KHC8H4O4 + NaOH H2O + NaKC8H4O4

3) End point: An endpoint is indicated by some form of indicator at the end of a titration.

Equivalence point: An equivalence point is when the moles of a standard solution (titrant) equal the moles of a solution of unknown concentration (analyte).ie.. Mole ratio = 1 KHP: 1NaOH

equivalence point and endpoint are not exactly same because,

*The equivalence point is the exact point in a titration when moles of one titrant equal the moles of the substance being titrated. The endpoint is the point where the system changes when the moles of the reacting titrant exceed the moles of the substance being titrated.

4) a) In a titration procedure, 27.93mL of 0.150M NaOH solution was used. How many mols NaOH did this volume of NaOH solution contain?
mols = M x V

mols = 0.004189 mols NaOH

b) mols CH3COOH(vinegar) = mols NaOH(titrant)

mols NaOH = MNaOH x VNaOH,L (from titration)

mols NaOH =0.004189 = mols CH3COOH(vinegar)

c) M CH3COOH(vinegar) =mols CH3COOH(vinegar)/volume(vinegar)

0.150 mols NaOH mols = ----------------------- x 0.02793 L L

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