Answer the following questions for Thermodynamics of Borax Stability Write the e

Question

Answer the following questions for Thermodynamics of Borax Stability Write the equilibrium constant expression Name the indicator used in the experiment A student who is performing the Thermodynamics of Borax Stability experiment pours 9.50 ml sample of the saturated borax solution into a 10 ml graduated cylinder after the borax solution cooled to 20 degree C. The student rinses the sample into a small beaker using water, and then titrates the solution with a 0.0500 M HCI solution. It took 15.00 ml of HCI solution to reach the endpoint of the titration. Calculate the value for K_sp for borax at temperature 20 degree C.

Explanation / Answer

Q1

Na2B4O5(OH)4*8H2O -> 2Na+ + B4O5(OH)4-2+ 8H2O

so

B4O5(OH)4-2 + 4H3O+ + H2O --> H3BO3

a)

K = [B4O5(OH)4-2][Na+]^2

b)

indicator must be phenolphjtalein must likely

c)

[HCl] = 0.05

V = 15 mL

mmol of HCL = MV = 15*0.05 = 0.75 mmol fo H+

sp

B4O5(OH)4-2 = 4*Hcl = 4*0.75 = 3 mmol

so..

[B4O5(OH)4-2 ] = mmol/V = 3/15 = 0.2 M

Ksp = [Na+]^2[B4O5(OH)4-2 ]

Ksp = (2*0.2)^2(0.2) = 0.032

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