SPM Chemistry Form 4 Notes – Acids and Bases (Part 6)

by BerryBerryTeacher

in Berry Reference (Notes)

Strength of acids and bases. Most of the cartoons that we watched when we were young depict acids as very very corrosive. It will probably seemed to the young viewers that all acids are very very corrosive. However, this is not the case for both acids and bases. This is due to the different levels of ionisation and dissociation of acids and bases in producing H+ and OH - ions in solutions. So why does it matter if the acids and bases are strong or weak? Of course it matters as their strengths will lead to a myriad of different usage in practical life.

An indication of strength of acids is seen through the conductivity of electricity. An acid which conducts electricity well represents a strong acid. Same goes for bases. On the other hand, an acid which conducts electricity weakly is a weak acid, with once again the same being for bases. So this post, Part 6 of Berry Berry Easy short study notes on the topic of Acids and Bases for SPM Form 4 Chemistry students will be on the strengths of acids and bases, covering strong acids, strong bases, weak acids and weak bases. So do read on.

[Tips: Students who can understand why a strong acid/base is a good electricity conductor has already understand the underlying concept of acids and bases. For those who don't, you have not yet understand the concept of ions in acids (which is linked to how ions can be charge carriers). In simple terms, when acids are strong, they will ionise or dissociate more completely, leading to more ions in solution, which allows ions which work as charge carrier to conduct more electricity.]

SPM Chemistry Form 4 Notes – Acids and Bases (Part 6)

Sodium hydroxide

Sodium hydroxide

Strong Acids

  • Strength of an acid – the degree of ionisation or dissociation of the acid in water.
  • Strong acid – an acid which ionises / dissociates completely in water to form high concentration of hydrogen ions (H+).
  • Example of strong acid: Mineral acid – hydrochloric acid (HCl), nitric acid (HNO3) and sulphuric acid (H2SO4).
  • Example of the strong acid reaction in water: HCl(aq) –> H+(aq) + Cl-(aq)  (The concentration of hydrogen ions is equal to the concentration of hydrochloric acid)

Weak Acids

  • Weak acid – an acid which ionises / dissociates partially in water to form low concentration of hydrogen ions (H+).
  • Example of weak acid: ethanoic acid (CH3COOH) and methanoic acid (HCOOH)
  • Example of the weak acid reaction in water: CH3COOH <—-> CH3COO-(aq) + H+(aq) {The concentration of hydrogen ions is low and the ions (CH3COO- and H+) reacts to reform the ethanoic acid molecule = reversible reaction}

Strong Alkalis

  • Strength of an alkali – the degree of ionisation or dissociation of the alkali in water.
  • Strong alkali – an alkali which ionises / dissociates completely in water to form high concentration of hydroxide ions (OH).
  • Example of strong alkali: Sodium hydroxide (NaOH) solution, potassium hydroxide (KOH) solution and barium hydroxide (Ba(OH)2) solution.
  • Example of the strong alkali reaction in water: NaOH(aq) –> Na+(aq) + OH-(aq)

Weak Alkalis

  • Weak alkali – an alkali which ionises / dissociates partially in water to form low concentration of hydroxide ions (OH).
  • Example of weak alkali: ammonia (NH3) solution.
  • Example of the weak alkali reaction in water: NH3(g) + H2O(l) <—-> NH4+(aq) + OH- (aq)

This is the end of this part. Stay tuned for the upcoming Part 7 in the series of notes by Berry Berry Easy on the topic of Acids and Bases for SPM Form 4 Chemistry students where we will be sharing information on the concentration of acids and alkalis, pelationship between number of moles with molarity and volume of a solution, preparation of standard solutions, dilution method and relationship between pH Values and molarities of acids or alkalis for SPM Chemistry. It sounds long and comprehensive but it is really not, just a compilation of many shorter points.

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