Question

A student who is performing this experiment pours an 8.50 mL sample of the saturated borax solution into a 10 mL graduated cylinder after the borax solution had cooled to a certain temperature T. The student rinses the sample into a small beaker using distilled water, and then titrates the solution with a 0.500 M HCl solution. 12.00 mL of the HCl solution is needed to reach the endpoint of the titration.
Calculate the value of Ksp for borax at temperature T. (Answer: 0.176 Show your work.)

Here is a suggested procedure for doing this calculation:

(a) Calculate the number of moles of HCl that were added during the titration.

(b) Use reaction (2) in the lab manual to relate the number of moles of HCl to the number of moles of tetraborate ion in the 8.50 mL sample.

(c) Calculate the concentration of tetraborate ions in the 8.50 mL sample.

(d) Use reaction (1) in the lab manual to relate the concentration of tetraborate ions to the concentration of sodium ions.

(e) Use the concentrations of tetraborate ions and sodium ions to calculate the equilibrium constant (Ksp) at temperature T for reaction (1) in the lab manual.

Answer 1

Answer:

Ksp = 0.1762

Explanation:

Applying

a) moles of HCl added, n= CV=0.5×0.012 = 6×10-3mol

b) since 0.006mol is present in 0.012dm3 of HCl

It implies moles of borax

C) Concentration = 0.706M

Ksp = [0.5]^2[0.706]= 0.176