Question

A student who is performing this experiment pours an 8.50mL sample of saturated borax solution into a 10mL graduated cylinder after the borax has 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. 12.00mL of the HCl solution is needed to reach the endpoint of the titration. Calculate the value of Ksp for borax at temperature, T.
0.176
equation : B4O5(OH)4+2H+3H2O-->4H3BO3
1st convert 12mL to L:12mL/1000mL=.012L and 5mL to L 5mL/1000mL=.005L
2nd Calculate mole of HCL: .800M(mol/L)*.012L=.0060mol
3rd Calculate mole of B4O5(OH)4th:.0060/2=.0030mol
4th Calculate B4O5(OH)concentration: .0030mol/ .005L=.60M
5th Ksp of B4O5(OH): .4(.60)^3=?
answer: .864
you were supposed to divide .0030 by 0.0085 and not by 0.005

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