1. (a) Define the term isotope.
.. Isotopes are atoms of the same
element with different numbers of neutrons ..... (1)
(b) Identify x, y, and z in the following nuclear processes:
94Be + 42He
-----> 126C + x
3215P -----> 3216S + y
23592U + 10n
-----> 9438Sr + z + 210n
x: .. a neutron ...........................................
y: ... an electron ..............................................................
z: .... 14054Xe
............................................................. (4)
(c) The third of these reactions is the basis for the
nuclear power industry.
What feature makes this possible?
... This is a fission reaction
in which 1 more neutron is formed than is used. ..............
......................................................................................................................................
(1)
(d) The diagram shows part of the mass spectrum for chloroethane,
C2H5Cl.
What ions are responsible for the peaks at m/e 66 and
64, and 29 and 28?
66: ...... C2H5Cl+
with the isotope chlorine 37
64: ....... C2H5Cl+
with the isotope chlorine 35 ..........................................................
29: ........ C2H5+.............................................................................................
28: ........ C2H4+.................................................................................................(4)
(e) Define the term first ionisation energy.
....... The enthalpy change when
1 mole of gaseous ions each with a single positive charge,
are formed from gaseous atoms of
an element. .............
...........................................................................................................................(2)
(f) The graph shows a plot of lg(ionisation energy) vs number of the electron removed for sodium. Explain the form of this graph in terms of the electron structure of sodium.
.. Electrons 10 and 11 are in the
same energy level close to the nucleus so have the highest ionisation energy.
The next 8 are in a shell further away from the nucleus so are easier to
remove. Electron 1 is in a shell furthest from the nucleus so has
the lowest ionisation energy..........(3)
TOTAL 15 marks
(c) Give the electronic configuration for Fe and for Fe3+ in the table below.
Suggest why Fe3+ is a more stable ion than
Fe2+ under normal conditions.
... Fe3+ is stable due
to its half filled 3d sub-shell. ... (3)
(d) (i) Name the types of reaction involved in the following changes:
aqueous NH3
aqueous NH3
[Cu(H2O)6]2+
-----> blue precipitate -----> deep blue solution
A
B
C
A to B ..... deprotonation
........................
B to C ....... ligand
exchange .................................................
(ii) Give the formula of compound B.
.........Cu(OH)2.....................................................................
(iii) Draw the structure of the ion responsible for the colour in solution C and show its shape.
(5)
(e) Addition of aqueous copper(II) ions to aqueous iodide ions gives a precipitate of copper(I) iodide and liberates iodine; the iodine can be titrated with aqueous sodium thiosulphate, so these reactions form the basis for a volumetric analysis of copper, for example in metal alloys.
(i) Write an ionic equation for the reaction of copper(II)
ions with iodide ions.
.............. 2Cu2+(aq)
+ 4I-(aq) -----> 2CuI(s) + I2(aq)
..........................
(ii) Given that the reaction of iodine with sodium thiosulphate
is
I2(aq) + 2S2O32-(aq)
-----> 2I-(aq) + S4O62-(aq)
find the volume of sodium thiosulphate solution of concentration
1.00 mol dm-3 needed to react with the iodine liberated by copper
ions from a brass screw of mass 2.00g, containing 60% of copper by mass.
mass of copper = 60% of 2.00 =
1.20g
amount of copper = mass/molar mass=
1.20g/63.5gmol-1 = 0.0189mol
so amount of copper(II) ions =
0.0189mol
amount of I2 formed/amount
of Cu2+ reacting = 1/2
so amount of I2 formed
= 2*amount of Cu2+ = 0.5*0.0189mol = 0.00945mol
amount of thiosulphate/amount of
iodine = 2/1
so amount of thiosulphate = 2*amount
of iodine = 2*0.00945 =0.0189mol
volume of thiosulphate = amount/comcentration
= 0.0189mol/1.00moldm-3 = 0.0189dm-3
so volume of thiosulphate =
18.9cm-3
(4)
TOTAL 16 marks
Why is the boiling temperature of water higher than would
be expected from the group trend?
...... Hydrogen bonding is present
in water but not the other hydrides so water molecules need more energy
to separate them. ...............
....................................................................................................................
(2)
(b) Why is solid water less dense than liquid water?
.... Hydrogen bonds in ice hold
molecules far apart in an open structure with low density. When melted
many of these bonds are broken so the structures collapses and the water
molecules become closer giving a higher density...........
.......................................................................................................................
(2)
(c) Silicon tetrachloride, SiCl4, is a colourless
liquid; its bonds are polar, but the molecule is not. Explain.
...... SiCl4 is tetrahedral
so the dipoles in each bond cancel out. .........................
.....................................................................................................................
(2)
(d) Silicon tetrachloride, SiCl4, reacts with
water to give silicon dioxide, SiO2, and HCl; it will react
with atmospheric moisture unless kept in a sealed tube. 1.00g of
a poorly-kept sample of SiCl4 was added cautiously to water.
When reaction was complete the solution was made up to 250cm3 with
pure water. 25.0cm3 portions of this required on average 21.6cm3
of 0.100 mol dm-3 sodium hydroxide solution for neutralisation.
What percentage of the sample analysed was SiCl4?
amount of NaOH = concentration
* volume = 0.100moldm-3 * 21.6/1000dm3 = 2.16*10-3mol
amount of HCl in 25cm3
= amount of NaOH = 2.16*10-3mol
amount of HCl in 250cm3
= 10* 2.16*10-3mol = 2.16*10-2mol
SiCl4 + 2H2O
-----> SiO2 + 4HCl
so amount of SiCl4 /
amount of HCl = 1/4
amount of SiCl4 = 0.25
* 2.16*10-2mol = 5.40 *10-3mol
mass of SiCl4 = amount
* molar mass = 5.40 *10-3mol * 170gmol-1 = 0.918g
so % of in original sample =
0.918*100/1 = 91.8%
(4)
(e) Single crystals of metals conduct electricity equally
well in all directions, but a single crystal of graphite will conduct in
only one direction. Suggest an explanation in terms of the structures
of these materials.
..... A metal has free electrons
between atoms which are able to move in any direction......
...... Graphite has free electrons
between layers which are only able to move in the layers. ....
...................................................................................................................................
...................................................................................................................................
................................................................................................................................
(4)
TOTAL 14 marks
| Na | Mg | Al | Si | P | S | Cl |
| Na2O | MgO | Al2O3 | SiO2 | P4O6 | SO2 | Cl2O |
| P4O10 | SO3 | |||||
| basic | basic | amphoteric | acidic | acidic | acidic | acidic |
(b) Group 4 elements show a trend from non-metallic to
metallic behaviour with increasing atomic number. How is this shown
by the acid base properties of carbon dioxide, CO2, silicon
dioxide, SiO2, and lead(II) oxide, PbO? Write equations
to illustrate this behaviour.
........Carbon dioxide and silicon
dioxide are acidic but lead(II) oxide is amphoteric. ..........
........CO2 + H2O
-----> H2CO3 ..............
........SiO2 + 2NaOH
-----> Na2SiO3 +H2O.....................................
....PbO as base
PbO +2HCl -----> PbCl2 + H2O...............
... PbO as acid
PbO + 2NaOH -----> H2O + Na2Pb(OH)4
..............
..........................................................................................................................
(5)
(c) PbO and PbO2 differ strikingly in their properties. Illustrate this by giving the reactions between these two oxides and concentrated HCl, stating the nature of each reaction.
For PbO:
equation: ...............PbO +2HCl
-----> PbCl2 + H2O...................
nature of reaction: ..... acid-base.................................................
For PbO2:
equation: .... PbO2
+ 4HCl -----> PbCl2 + Cl2 + H2O
nature of reaction: ... redox
...............................................
....................................................................................................................
(4)
(d) The +2 oxidation state of tin is reducing. Give
a reaction illustrate this property.
........ Sn2+(aq)
+ Hg2+(aq) ---> Sn4+(aq) +
Hg (l).
...................................................................................................................
(2)
TOTAL 15 marks