20.5 - pH and Strong Bases Flashcards Preview

OCR A Chemistry A Level - Chapter 20 > 20.5 - pH and Strong Bases > Flashcards

Flashcards in 20.5 - pH and Strong Bases Deck (4)
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1

What occurs during the ionisation of water?

2

Derivd Kw using Ka

Ka = [H+][OH-]/[H2O]

Water is mainly undissociated (very slightly)

1dm3 (1000g) of water...

nH2O = 1000/18 = 55.6moldm-3

n=cv, v = 1, therefore n=c, 55.6 = [H2O]

Ka.[H2O] = [H+][OH-]

= Kw

3

What is Kw?

The ionic product of water - [H+][OH-]

Kw varies with temperature

At 25oC or 298K, Kw is a constant at 1 x 10-14 mol2dm-6

 

4

How is pH calculated with whole numbers?

Proton and hydroxide indices add up to -14