TPR Cracking 3 (PS - Q38)

[Synapsis]

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I completely understand their logic, but with respect to the passage, how do we know that the solution is basic at step 6?

 

[onedirection]

What did you think about TPR Cracking 3's PS section? I felt it was actually pretty hard because of all of those Heat system passages

Anyway you knew that this question was basic because they added the 0.1 mL of NaOH

Also

After replacement of exchangeable aluminum and hydrogen ions by potassium ions, the total acidity is determined by titration with sodium hydroxide. The measurement of exchangeable aluminum is made by first forcing the dissociation of all aluminum hydroxide complexes with potassium fluoride by back titration with hydrochloric acid.

So it had to have become basic in order to be able to titrate it with HCl