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Calculating pH of a Strong Base City and Islington College
David Martin City and Islington College To Print Students Name: …………………………………………………………………..
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Topic Aims Method Equipment Duration
Calculating the pH of Strong Bases Aims This worksheet provides guidance on how to calculate the pH of strong bases Level Level 3 Method PowerPoint slides (hand-out) – Slide 3 to 4 to print off, slide 5 to 6 Answers Equipment Laptop & Projector Hand-out Pens Duration >10-20 minutes Hidden
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pH Water dissociates (splits up) to form H+ & OH- ions.
In order to find the pH of a strong base we need to find which ion concentration? H2O H+ + OH- Hydrogen ion concentration [H+] ____________________________________________________________________ Write a Ka expression for the equilibrium above Ka = As water is in a much greater concentration than the ions the expression can be simplified. Ka = The Kw for water has a value of 1 x mol2dm-6 Problem Find the pH of a 0.1 moldm-3 NaOH solution NaOH is a strong alkali and is fully dissociated in water. NaOH Na OH- [OH-] = Kw = [H+] [OH-] [H+] = Kw/[OH-] [H+] = 1 x 10-14/0.1 [H+] = 1 x pH = -log10[H+] = -log10 1 x = 13 pH 13 sound right for a strong alkali To Print
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pH Practise problems 1. Find the pH of a 0.2 moldm-3 KOH solution
1. Find the pH of a 0.2 moldm-3 KOH solution 2. Find the pH of a moldm-3 NaOH solution Find the pH of a moldm-3 LiOH solution Find the pH of a 2 moldm-3 NaOH solution To Print
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ANSWERS To Print
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pH Water dissociates (splits up) to form H+ & OH- ions.
In order to find the pH of a strong base we need to find which ion concentration? H2O H+ + OH- Hydrogen ion concentration [H+] Write a Ka expression for the equilibrium above Ka = [H+] [OH-] [H2O] As water is in a much greater concentration than the ions the expression can be simplified. Ka = [H+] [OH-] or Kw = [H+] [OH-] The Kw for water has a value of 1 x mol2dm-6 Problem Find the pH of a 0.1 moldm-3 NaOH solution NaOH is a strong alkali and is fully dissociated in water. NaOH Na OH- [OH-] = Kw = [H+] [OH-] [H+] = Kw/[OH-] [H+] = 1 x 10-14/0.1 [H+] = 1 x pH = -log10[H+] = -log10 1 x = 13 pH 13 sound right for a strong alkali To Print
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pH Practise problems 1. Find the pH of a 0.2 moldm-3 KOH solution 13.3
1. Find the pH of a 0.2 moldm-3 KOH solution 13.3 2. Find the pH of a moldm-3 NaOH solution 11.7 Find the pH of a moldm-3 LiOH solution 11.0 Find the pH of a 2 moldm-3 NaOH solution 14.3 To Print
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