Proton Transfer, Strong & Weak Acids

05 April 2023
Proton Transfer, Strong & Weak Acids
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Slide 1: Tekstslide
PhysicsSecondary EducationAge 12,13

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05 April 2023
Proton Transfer, Strong & Weak Acids

Slide 1 - Tekstslide

Content objectives
  • I can describe the characteristic properties of bases in terms of their reactions with (a) acids; (b) ammonium salts.
  • I can describe how to compare hydrogen ion concentration, neutrality, relative acidity, and relative alkalinity in terms of colour and pH using universal indicator paper.
  • I can define acids as proton donors and bases as proton acceptors.
  • I can define a strong acid as an acid that is completely dissociated in an aqueous solution and a weak acid as an acid that is partially dissociated in an aqueous solution.

Slide 2 - Tekstslide

Slide 3 - Tekstslide

Typical reactions of bases
Bases + acids
  • neutralisation reaction occurs
  • Acid + Base → Salt + Water

Slide 4 - Tekstslide

Typical reactions of bases
Alkalis and ammonium salts
  • Ammonium salts undergo decomposition when warmed with an alkali.
  • Even though ammonia is itself a weak base, it is very volatile and can easily be displaced from the salt by another alkali.
  • A salt, water and ammonia ar e produced.

Slide 5 - Tekstslide

NH4Cl + NaOH →NaCl + H2O + NH3

This reaction is used as a chemical test to confirm the presence of the ammonium ion (NH4+).


Slide 6 - Tekstslide

Test for Ammonium Ion (NH4+)
  • Alkali is added to the substance with gentle warming followed by the test for ammonia gas using damp red litmus paper.
  • The damp litmus paper will turn from red to blue if ammonia is present.

Slide 7 - Tekstslide

Proton transfer
  • interaction with protons (H+)
  • A reaction or reaction mechanism step in which a proton (H+) is removed from one species (the acid) and accepted by another species (the base).

Slide 8 - Tekstslide

  • are proton donors as they ionise in solution producing protons, which are H+ ions
  • H+ ions make the aqueous solution acidic

Slide 9 - Tekstslide

  • are proton acceptors as they accept the protons which are donated by the acid 

Slide 10 - Tekstslide

Proton Transfer

Slide 11 - Tekstslide

Strong Acids
  • completely dissociate (or ionise) in water, producing solutions of a very low pH 
  • examples: HCl and H2SO

                   HCl (aq) → H+ (aq) + Cl- (aq)

Slide 12 - Tekstslide

Weak Acids
  • partially dissociate (or ionise) in water and produce pH values that are closer to the middle of the pH scale, whilst still being below 7
  • organic acids such as ethanoic acid, CH3COOH 
  • For weak acids, there is usually an equilibrium setup between the molecules and their ions once they have been added to water.
                  CH3CH2COOH H+ + CH3CH2COO-
The equilibrium lies to the left, indicating a high concentration of intact acid molecules, with a low concentration of H+ ions in the solution.

Slide 13 - Tekstslide

Effect of concentration on strong and weak acids 
  • A concentrated solution of acid contains a higher number of acid molecules per dm3 of solution.
  • It does not necessarily mean that the acid is strong though, as it may be made from a weak acid that does not dissociate completely.

Slide 14 - Tekstslide

Effect of concentration on strong and weak acids 
  • Example: a dilute solution of HCl will be more acidic than a concentrated solution of ethanoic acid since most of the HCl molecules dissociate but very few of the CH3COOH do.

Slide 15 - Tekstslide