Summary booklet containing the content needed for 3.9 WJEC A level Chemistry. Useful for learning the content and creating flashcards.
Includes
- Acid and Base definitions
- Calculating pH of strong acids
- Kw and the ionic product of water
- Calculating pH of strong bases
- Reactions of st...
Monoprotic Acid – Releases one H+ ion e.g. HCl, HNO3
Diprotic Acid – Releases two H+ ions e.g. H2SO4
Strong Acid – Fully dissociates in solution to release H+ ions e.g. HCl H+ + Cl-
Weak Acid – Partially dissociates in solution to form H+ ions e.g. CH3COOH ⇌ CH3COO- + H+
Calculating pH of strong acids
pH – measure of hydrogen ion concentration of a solution
pH = -log[H+]
[H+] = 10-pH
- For monoprotic acids [acid]=[H+]
- For diprotic acids 2[acid]=[H+]
Dilution of a strong acid
1. Calculate moles in original volume
2. Calculate new conc. with original moles and new volume
3. Put [H+] into pH expression
Kw and Ionic Product of Water
H2O ⇌ H+ + OH-
- When water dissociates it is a reversible reaction and establishes an equilibrium
- There are equal moles of OH- and H+
Able to use equilibrium expression:
Kw = [H+][OH-]
Units – mol2dm-6
Pure water:
[H+] = [OH-]
Kw = [H+]2
, Impure water:
e.g. an alkali
Dissociation of water is endothermic
- As temperature increases, pH decreases
- This means more H+ released and [H+] increases
- Equilibrium shifts to endothermic side as temperature increases to reduce the change
- Shifts to dissociated side so the dissociation of water is endothermic
Does water remain neutral even as pH changes?
- Yes – there is no excess of H+ or OH-
- Neutralisation – H+ + OH- H2O
Base Definitions
Base – Proton acceptor (releases OH- ions in solution)
Monobasic bases – Releases one OH- ion e.g. NaOH
Dibasic bases – Release two OH- ions in solution e.g. Ca(OH)2
Calculating pH of strong bases
- Need to find [H+] but bases only release [OH-] ions in solution
- Use the ionic product of water (Kw)
Kw = [H+][OH-]
Under standard conditions Kw = 1.0 x10-14
1. Calculate [OH-]
Monobasic [base] = [OH-]
Dibasic 2[base] = [OH-]
2. Use Kw to calculate [H+]
3. Put [H+] into pH expression
Dilution of a strong base
1. Calculate moles in original solution
2. Calculate [base] using new volume
3. Use [base] to find [OH-]
4. Use in Kw expression to find [H+]
5. Put [H+] in pH expression
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller meganjoeyb. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.95. You're not tied to anything after your purchase.
