acids & bases

Aqueous:

• When a substance dissolves in water, it forms an aqueous solution.
• These solutions can be acidic, basic (alkaline), or neutral, depending on the types of ions they release.

Ionisation

• Ionisation is the process by which a neutral atom or molecule becomes an ion.
• For acids and alkalis, this means:
  • Acids ionise by releasing H⁺ ions into solution.
  • Alkalis ionise by releasing OH⁻ ions into solution.
• Ionisation can be complete (strong acids) or partial (weak acids) depending on how fully the substance splits into ions.

Acids

• Acids are substances that are capable of donating protons, in the form of H+ ions, when

  dissolved in an aqueous solution, an example of this would be hydrochloric acid.

• They are proton donors.

• Acids dissociate in water—this means the molecules split into ions.Example: HCl(aq) → H⁺ + Cl⁻

• This process is called ionisation.

Alkalis

• Alkalis are soluble bases.
• They release hydroxide ions (OH⁻) when dissolved in water.Example: NaOH(aq) → Na⁺ + OH⁻
• All alkalis are bases, but not all bases are alkalis (because not all are soluble).

Bases

• Bases are substances that are capable of donating electrons, in the form of OH- ions

  when dissolved in an aqueous solution, an example of this would be ammonia

• Bases accept protons (H⁺).

• They react with acids in neutralisation reactions.

• Types of bases include:

  • Metal oxides (e.g., Na₂O)
  • Metal hydroxides (e.g., NaOH) – also called alkalis when soluble
  • Metal carbonates (e.g., Na₂CO₃)

Strong vs Weak:

• A strong acid is any acid that completely ionises in solutions, this means that when placed in a solution it gives off the greatest number of hydrogen ions or protons. Strong acids are chemical species with a high capacity to lose a proton, H+. In water, a strong acid loses one proton, which is captured by water to form the hydronium ion.

• Bases donate a hydroxide ion. These are often reversible. Sometimes the alkali donates a large amount of its Hydroxide ions, so much so that it can be said that very little of the reserve reaction takes place, therefore, it can be said that the alkali is virtually 100% ionised. If at any one time, virtually 100% of the Hydroxide ions of the alkali have dissociated and forms Hydroxide ions, it can be said that the alkali is a strong alkali.

• A weak acid is any acid that does not fully dissociate when in water. The acid would still react with water to form a salt and hydronium ion, however the reverse reaction easily takes place and is more common than the dissociation reaction. The ions react very easily to form the acid and water, so only a small part of the solution is ionised. At any one time, if virtually 1% of the hydrogen ions of the acid have formed hydronium ions, it can be said that the acid is a weak acid.

• Weak bases are bases that do not fully dissociate when in water. The base however does still react with water to dissociate, however the reverse reaction would easily take place is more common than the dissociation reaction. The ions react very easily to form the alkali and water, hence only a small part of the solution is ionised. If at any one time, 1% of the hydrogen ions of the acid have formed hydroxide ions, it can be said that the acid is a strong acid.

• Strong acids: Fully ionise in water.

  • Example: HCl(aq) → H⁺ + Cl⁻
  • Weak acids: Partially ionise. Some molecules remain un-ionised.
    • Example: H₂CO₃ ⇌ 2H⁺ + CO₃²⁻
  • Strong acids produce more ions, so they are better conductors of electricity.

<aside> 💡

Concentrated vs. Dilute

• Concentrated: More solute (acid or base) in a given volume of solvent.
• Dilute: Less solute in the same volume.
  • Note: Concentration is not the same as strength. </aside>

pH scale and indicators