Questions Paper 3 Flashcards
(18 cards)
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
dilute hydrochloric acid and aqeuous barium chloride were added to ab aqueous solution of C. Give a reason why HCL is needed
to remove other elements that interefere with the test by forming their own unwanted precipitate.
Give a reason why, the ether layer was washed with deionized water
to ensure all the aqueous layer has been completely removed from it.
explain why the addition of HCL in step 6 (HCl was added to aq solution in the beaker to precipitate the benzoic acid) results in the precipitation of benzoic acid
HCL is a strong acid and can covert sodium benzoate to benzoic acid as benzoic acid is insoluble in water it will precipitate and recrystallise out.
1-bromobutane can be prepared from butan-1-ol and hydrogen bromide.
CH3CH2CH2CH2OH + HBr o CH3CH2CH2CH2Br + H2O
Hydrogen bromide can be made from sodium bromide and 50% concentrated sulfuric acid.
(a) The steps for the preparation of impure 1-bromobutane are summarised.
Step 1 Dissolve the sodium bromide in distilled water in a pear-shaped flask and
then add 20.0 cm3
of butan-1-ol.
Step 2 Surround the flask with an ice bath to COOL THE MIXTURE, before adding
concentrated sulfuric acid drop by drop.
Step 3 Remove the flask from the ice bath and add a few ANTI BUMPING GRANULES
to the reaction mixture.
Step 4 Set up the apparatus for HEATING UNDER REFLUX. Heat the mixture in the
flask for 30 minutes and then allow the apparatus to cool.
Step 5 Rearrange the apparatus for distillation and heat the mixture until no
more 1-bromobutane distils over.
(i) Parts of the method are given in bold type in Steps 2, 3 and 4.
Give a reason why each of these parts is necessary
Cooling the mixture as (with concentrated
sulfuric acid / H2SO4) is (very) exothermic / releases (a lot of) heat
Anti-bumping granules allow for smooth boiling
heat under reflux prevent vapour from escaping.
Explain why the filter paper and funnel are warmed in an oven before Step 3.
(2)
make sure solution doesnt cool down
to prevent premature crystalisation taking place
which would reduce yield of product
Give two reasons why the wire is made of nichrome and not iron.
(2)
nichrome is unreactive
nichrome does not produce a colour
(ii) Give a reason why the wire is dipped into acid and then heated in the first stage.
(1)
acid to remove residue from previous experiments
(iii) State why fresh concentrated hydrochloric acid is used in the second stage of the flame
test.
to reduce contamination with residues of previous tests
(iv) State why hydrochloric acid is used in the second stage of the flame test.
wire is moisened to allow some solid metals allow to stick
