NABTEB 2017 Chemistry Obj And Essay Answer – May/June Expo


========================= NABTEB CHEMISTRY THEORY 1ai) An ion is any atom or group of atoms
which possesses an electric charge.
An Atom is the smallest particle of an
element which can take part in a
chemical reaction. 1aii)
A molecule is the smallest particle of a
substance that can normally exist
alone and still retain the chemical
properties of that subsstance. 1bi) CLICK HERE FOR THE IMAGE Alpha (α) Ray
-it is symbolically represented by
helium particle 4;2He
-it is relatively massive
-it is strongly deflected in an
electrostatic field. -it is positively charged
-it has little penetrating power
-highest ionization energy Beta (β) Ray
-it is symbolically represented by
-it is slightly deflected in an
electrostatic field.
-they have relatively small mass.
-they have more penetrating power than x-rays
-low ionization energy Gamma Rays
-it has no deflection in an electrostatic
-it is electrically neutral
-it has heighest penetrating power
-it has least ionization energy 2aii)
Half-Life: this is the time taken or
required for radioactive elements to
decay by half of its original mass. 2bi)
-it is used in the treatment of cancer
-it is used to sterilize surgical
equipment 2bii)
N = ?, No = 2.56kg, T1/2 = 6months.
N/No = (1/2)^n
n = 2×12/6 = 4
N/2.56 = (1/4)^4
N/2.56 = 1/16 N = 2.56/16
= 0.16
========================== 3ai)
Experiment to explain the law of
conservation of mass method/
procedure: put some sodium chloride
solution in a conical flask. full a small
test-tube with silver trioxonitrate(v) solution and by a means of two pieces
string, suspend it in a conical flask.
insert a stopper and weigh the whole
apparatus on a balance and the mass
is recorded. mix thye two liquid by
pulling the string attached to the bottom end of the small test-tube.
Weigh the whole apparatus again. Result: the weight of flask and
contents before reaction is equal to
the weight of flask and contents after
reaction. Conclusion: since there is no overall
change in mass when the products are
formed. we can say that, matter can
neither be created nor destroyed
during the chemical reaction. 3aii)
i)Molecular foemula: this is the
formula that gives the exact number
of moles of atoms of the component
elements in one mole of the
compound. ii)An isomer: this is the compound
that exhibit ispomerism.
iii)A chemical equation: this is a
symbolical representation of a
chemical reaction in the form of
symbols and formula. 3bii) CLICK HERE FOR THE IMAGE 3biii)
i)Hydrogen sulphide (H2S)
ii)carbon(iv) oxide (CO2) 3bi)
—————- |Samplei| Sampleii|
Mass of boat alone | 26.7g | 27.2g |
26.3g | Mass of boat + Al2O3 | 77.8g | 72.9g |
82.7g |
Mass of boat + Al | 53.8g | 51.4g |
52.2g |
Mass of aluminium | 27.1g | 24.2g |
29.9g | Mass Of Oxygen | 24.0g | 21.5g | 26.5g
| Percentage of Aluminium |
27.1/51.1×100 = 53.03% |
24.2/45.7×100 = 52.95% |
29.9/56.4×100 = 53.01% |
The percentage of aluminium in all the
three samples are approximately 53% =========================
i)Avogadro’s Hypothesis: it states that
equal volume of all gases at the same
temperature and pressure contain the
same number of molecule. ii)Molar Volume: this is the volume
occupied by one mole of that gas at
S.T.P, and is equal numerically to
iii)Electrolyte: this is a compound
which conducts electricity and is decomposed in the process 4aii)
Amount = mass/volume = 250/32
= 7.8mol 4bi)
The electrolysis of aqeous copper II
tetraoxosulphate VI using platinum
electrodes yield copper deposits at the
cathode and oxygen of anode.
At the cathode: both Cu^2+ and H^+ migrate to the cathode where Cu^2+
are discharged prefrentially. Cu^2+ +
2e^- —-> CU.
At the anode(platinum): both SO4^2-
and OH^- migrate to the anode where
OH^- are prefrentially discharged as oxygen gas.
OH^- —-> OH + e^-
OH + OH —> H2O(l) + O
O + O —–> O2(g) 4bii)
Faraday second law of electrolysis:
this states that, when the same
quantity of electricity is passed
through different electrolytes, the
relative number of moles of the elements discharged are inversely
proportional to the charge on the ions
of the elements. 4biii)
-it is used in purification of metals.
-it is used in extraction of metals
-electroplatino of one metal by
another 4ci) CLICK HERE FOR THE IMAGE Hydrogen can be prepared laboratorily
by the action of dilute hydrochloric
acid on zinc with libertaion of
hydrogen gas.
Zn + HCl —> ZnCl2 + H2 4cii)
Moisten a piece of filter paper with
lead II trioxonitrate (V) solution and
drop it into a gas jar of the unknown
gas. if the gas is hydrogen sulphide
the paper turns black. =========================== 5ai)
i)A period of elements: this is the
horizontal rows of elements which
are numbered from 1 to 7.
ii)periodic table: this is a table
involving the arrangements of atoms in the order of increasing atomic
number. 5aii)
i)sodium belongs to group 1
ii)magnesium belongs to group 2
iii)aluminium belongs to group 3 5aiii)
Nitrogen = 1s^2 2s^2 2p^3
Neon = 1s^2 2s^2 2p^6 5bi)
The iron ore is first roasted in air so
that iron III oxide is produced.
The iron III oxide is then mixed with
coke and limestone and heated to a
very high temperature in a blast furnance. The ingredients are loaded
into the furnance. the temperature
inside the furnance varies from about
2000°C near the bottom to about
200°C at the top.
After a series of exothermic reaction, the molten iron formed sinks to the
bottom of the furnance and is tapped
off. it is run into moulds where it sets
as pig iron. 5bii)
-steel 5ci)
-it is used for making electric wires
-it is used for plumbing and roofing. 5cii)
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