Questions Paper 3 Flashcards
Explain the trend in thermal stability of group 2 nitrates
Thermal stability increases as the ionic radius increases, with less distortion of the anion, and less weakening of N-O bonds
State two observations you would see when hydrated magnesium nitrate is heated
solid dissolves
white solid forms
Colour is often used in chemistry to identify substances.
Compare and contrast the origin of the colour of a copper(II) complex with the origin
of the colour of the copper(II) ion in a flame test.
You do not need to state any specific colours
6 marks
copper(II) complex
Ligand causes d orbital to split into two energy levels
electrons absorb energy in the visible region
to promote electrons to higher energy d orbital levels
the remaining light is transmitted (the colour visible)
copper(II) ion in a flame test.
electrons get excited and move to a higher energy level. an excited electron emits electromagnetic wavelength should when it falls to a lower energy level.
This question is about tests for ions.
An aqueous solution is suspected to be potassium bromide and is tested for the presence of
the anion.
(i) Write the name of the reagent used to test for the anion.
(1)
Silver Nitrate
(ii) State the expected result of this test and the formula of the product.
(2)
Result of test
cream precipitate
AgBr
This question is about hydrated magnesium sulfate, MgSO4·7H2O.
*(a) Devise an experimental procedure to determine the enthalpy change of solution
for hydrated magnesium sulfate.
MgSO4·7H2O(s) + aq → MgSO4(aq)
Details of the method of calculation are not required
IP1 – (accurately) weigh/ use a known mass of
(hydrated) magnesium sulfate
* IP2 – (accurately weigh) known mass of
(distilled / deionised) water
* IP3 – use of polystyrene cup (and lid)
* IP4 – record initial temperature of the water (before adding solid)
* IP5 – add magnesium sulfate (to the water in the cup) and stir
* IP6 - record temperature (at suitable time intervals) /
record final temperature
Iron and zinc are in the d-block of the Periodic Table.
Iron(II) ions, [Fe(H2O)6]*,
*, form a pale green solution but zinc ions, [Zn(H2O)6]2+, form a
colourless solution.
Explain why zinc ions are colourless.l
d-d transitions do not take place as zinc has a full 3d sub shell
State how separate samples of these two enantiomers could be distinguished in a laboratory.
See which direction they rotate plane-polarised light. Each enantiomer will rotate in the opposite direction.
(iii) Describe how you would obtain pure dry crystals from the precipitate.
(4)
solid dissolved in minimum amount of hot solvent
* (hot filtration then) solution allowed to cool and
(re)crystallise/precipitate
* solid filtered under reduced pressure
- rinsed with (cold) solvent
and
dried between (sheets of) filter paper
