Reactions of ions in aqueous solution
No description yet. This curated deck is ready for daily study.
Card preview (20)
What is a metal aqua ion?
A complex ion where a metal ion is bonded to six water ligands
Which metal aqua ions must be known for AQA?
[Fe(H₂O)₆]²⁺ [Cu(H₂O)₆]²⁺ [Fe(H₂O)₆]³⁺ [Al(H₂O)₆]³⁺
What are the colours of the required metal aqua ions?
Fe²⁺ = green Cu²⁺ = blue Fe³⁺ = yellow/orange Al³⁺ = colourless
Why are metal aqua ions acidic? (act A - dnte. H - wtr. frmg. x)
They act like acids by donating H⁺ ions to water, forming H₃O⁺
What is the general equation for acidity of metal aqua ions?
[M(H₂O)₆]²⁺/³⁺ + H₂O ⇌ [M(OH)(H₂O)₅]⁺/²⁺ + H₃O⁺
Why are [M(H₂O)₆]³⁺ ions more acidic than [M(H₂O)₆]²⁺? ([M(H₂O)₆]³⁺ hghr. chrg. dnsty. - strngr. atrctn. elctrns. i O-H bnd. - grtr. plrstn. - H+ rlsd. >esly.)
Higher charge density, stronger attraction to O–H electrons, greater polarisation, H⁺ released more easily
How do pH values compare for equal concentrations of 2+ and 3+ aqua ions?
3+ ions have lower pH (more acidic)
Observations with OH⁻ for Fe²⁺, Fe³⁺, Cu²⁺ and Al³⁺ ions?
Fe²⁺ = green ppt Fe³⁺ = brown ppt Cu²⁺ = blue ppt Al³⁺ = white ppt
What happens when excess OH⁻ is added to Al³⁺?
White precipitate dissolves to form a colourless solution
Write the equation for the reaction between excess OH- and [Al(H₂O)₃(OH)₃]
[Al(H₂O)₃(OH)₃] + OH⁻ → [Al(H₂O)₂(OH)₄]⁻ + H₂O
What is an amphoteric hydroxide?
A hydroxide that reacts with both acids and bases
Which hydroxide is amphoteric in this topic?
[Al(H₂O)₃(OH)₃]
When excess acid is added to [Al(H₂O)₃(OH)₃], what happens, outline the reaction
[Al(H₂O)₃(OH)₃] + 3H⁺ → [Al(H₂O)₆]³⁺
When excess alkali is added to [Al(H₂O)₃(OH)₃], what happens, outline the reaction
[Al(H₂O)₃(OH)₃] + OH⁻ → [Al(H₂O)₂(OH)₄]⁻ + H₂O
What is the role of NH₃ in reactions with metal aqua ions?
Acts as a base (accepts H⁺)
Observations with NH₃ (few drops)?
Fe²⁺ = green ppt Fe³⁺ = brown ppt Al³⁺ = white ppt Cu²⁺ = pale blue ppt
What happens when excess NH₃ is added to Cu²⁺?
Forms deep blue solution [Cu(NH₃)₄(H₂O)₂]²⁺.
Equation for the reaction between excess NH₃ and
[Cu(H₂O)₄(OH)₂] + 4NH₃ ⇌ [Cu(NH₃)₄(H₂O)₂]²⁺ + 2OH⁻ + 2H₂O
What happens when CO₃²⁻ is added to 2+ ions, compared to when added to 3+ ions? (frms. mtl. crbnt. ppt. whrs. 3+ ions. /crbnte. ppt. frmd. CO2 gs. prdcd. - mtl. hydrx. ppt. frms.)
Forms a metal carbonate precipitate, whereas with 3+ ions no carbonate participate is formed, CO₂ gas produced, metal hydroxide precipitate forms
Why do 3+ ions react differently with CO₃²⁻? (>acdc. + dcmpse. crbnte. CO2)
They are more acidic and decompose carbonate to CO₂