Chem 2a Q Flashcards
(50 cards)
Explain why an incorrect value for the number of moles of iron(II) chloride would have been obtained if the original solution had been titrated with potassium manganate(VII)
KMnO4 would oxidise Cl- as well as Fe2+, so titration value would be too large.
In what way does the NH3 behave as a Brønsted–Lowry base?
Proton acceptor
In what way does the NH3 behave as a Lewis base?
Electron pair donor
State and explain the effect of a catalyst on rate in a reversible reaction.
- Increases the rate at which eqm .is reached
- Catalyst provides alternative reaction route w/ lower Ea
- More particles have this Ea so the reaction is faster
State and explain the effect of a catalyst on eqm. yield in a reversible reaction.
- No effect on eqm yield
- Forward & backward reaction rate speeded up equally.
Reactions for Fe2+ as a homogenous catalyst for the reaction of I- and S2O8(2-).
2Fe^(2+) + S2O8^(2–) –> 2SO4^(2–) + 2Fe^(3+)
2Fe^(3+) + 2I– –> 2Fe^(2+) + I2
Ligand
Electron pair donor
Complex ion
Central metal atom or ion surrounded by ligands attached by coordinate bonds
Co ordinate number
The number of coordinate bonds made by a metal atom or ion to the ligands
A ligand substitution reaction which occurs with no change in the co-ordination number but a change in the charge on the complex ion.
[Fe(H2O)6]^(2+) + 3C2O4^(2–) –> [Fe(C2O4)3]^(4–) + 6H2O
Explain why the pH of a solution of iron(II) chloride is higher than that of a solution of iron(III) chloride of the same concentration.
The charge density on Fe2+ is less than on Fe3+ so it is less polarising to the water ligands and fewer H+ ions are released
State the origin of the colour of transition-metal complexes
Movement of electrons within the d sub-level orbitals
Give three changes to a transition-metal complex which result in a change in colour
Oxidation state
Coordination number
Ligand substitution
Coordinate bond
Where one of the atoms involved donates both electrons to the shared pair
Bidentate ligand
One which uses two lone pairs to link onto a metal atom or ion.
Suggest why the enthalpy change for a reaction may be close to zero
Because the bonds formed are approximately the same strength as those broken
Zwitterion in acidic conditions
NH2 becomes NH3+
COOH becomes COO-
Why can Vanadium(III) catalyse the reaction between S2O8^(2-) and I- but Mg(II) can’t?
Vanadium(III) can be oxidised to a higher state whereas Mg(II) cannot.
Why is the complex formed when a copper aq ion reacts with EDTA^(4-) more stable than the Cu aq ion?
Large increase in entropy as 2 particles form 7 - increases stability.
Reagent needed to carry out
CrO4^(2–) (aq) → Cr2O7^(2–) (aq)
Strong acid like HCl
Reagent needed to carry out
VO^(2+) (aq) → [V(H2O)6]^(2+) (aq)
Zn metal and HCl
Reagent needed to carry out
[Ag(NH3)2]^(+)(aq) → Ag(s)
Aldehyde
CH3CHO
chelate
A central metal ion complexed with a multidentate ligand forming a more stable complex
Give one reason why sulphur dioxide gas may be found in the exhaust gases of cars.
Sulphur present in petrol
