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Edexcel IAL Chemistry 14.11 Strong base pH using Kw or pKw

Convert the base formula or mixture into [OH-] first, account for two hydroxide ions where needed and then use Kw, pKw or pOH to obtain the final pH.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Double [OH-] for Ba(OH)2 or Sr(OH)2 before converting to pOH and pH values.
  • Use Kw or pKw at the stated temperature to convert hydroxide concentration into pH.
  • Calculate excess OH- after neutralisation or dilution before giving the final pH.

14.11—The pH of a strong base from its concentration question 1

[Maximum number: 5]

This question is about acids and bases.

A student was given 50.0 cm350.0 \mathrm{~cm}^{3} of a solution of sodium hydroxide.

The pH of this solution was 12.43.
The student was asked to adjust the pH to 12.00 , by dilution with deionised water. The student did not have access to a pH meter.

Calculate the volume of deionised water, in cm3\mathbf{c m}^{3}, the student should add to the original solution.

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