Question

A 5.00 mL saturated sample of borax was collected at 31.7 C. It required 6.77 mL of 0.2345 M HCl to titrate. Calculate the Ksp for this sample. This question was posted in this website before but there were 2 or three different answer so I'm just asking this again to make sure I get the right one.

Answer 1

Borax is------>Na₂B₄O₇*10H₂O

The reaction with HCl is:

You can calculate the moles of Borax using the moles of HCl

0.00677L of HCl 0.2345M

The concentration of Borax dividing the moles over the volume of sample:

<-----This is the concentration of Borax

You need to calcualte the Ksp, since the solution is saturated it means the concentration is the maximum borax can achieve at that temperature, and the Ksp is calculated according to the following reaction:

<-----H2O and solids are not included in mass action equations

You know the conentration of

since there are 1 mole of the ion borate and 2 moles of sodium in the borax molecule the concentrations are: