Chemistry: Acids

Acids

Acids and Bases

A) Explain that an acid releases H+ ions in aqueous solutions

• A strong acid donates protons to a base very easily and is fully dissociated into ions in aqueous solutions
• HCl + aq → H+ + Cl-
• H2 SO4 + aq → H+ + HSO4-
• A weak acid also donates protons to a base but is only partially dissociated into ions in aqueous solutions
• CH3COOH + aq → H+ + CH3COO-

B) State the difference between bases and alkalis

• A base accepts protons form an acid
• Common bases are metal oxides, metal hydroxides and ammonia
• An alkali is a soluble base that releases OH- ions in aqueous solutions
• An alkali is dissociated into ions in aqueous solutions
• the hydroxide ions from alkalis neutralise the protons from acid to form water

C) Describe amphoteric substances

• Some amphoteric substances are able to accept and donate protons according to their situation
• e.g. water:
• HCl + H2O → H3O+  + Cl-
• NH3 + H2O → NH4+ + OH-

D) List the common reaction forms with acids

• Carbonate + Acid → Salt + Water + CO2
• Base + Acid → Salt + Water
• Metal + Acid → Salt + Hydrogen
• Ammonia + Acid → Ammonium salt

Salts

E) Explain that a salt is formed when the H+ ion of an acid is replaced by a metal or other positive ion

F) Explain key terms

Anhydrous: A substance containing no water molecules

Hydrated: A crystalline compound containing water molecules

Water of Crystallisation: refers to water molecules that form an essential part of the crystalline structure of a compound

Cation: a positively charged ion

Anion: a negatively charged ion

Ionic equations:

• These equations remove the ions that do not change
• Ionic substances in solution are no longer in fixed lattices but can behave as independent ions.
• To write an ionic equation, write out the separate ions then remove the spectator ions (the ones that don't change)
• Na(aq)+  +  OH-(aq)  + H+(aq)  + Cl- (aq)→ H2O(l) + Na+(aq)  + Cl-(aq)
• H+(aq)  + OH-(aq) → H2O(l)
• The salt is made from the metal cation and the negative part of the acid, so as both these ions remain aqueous, they cancel out so are not in the ionic equation.