NABTEB Chemistry OBJ And Essay Answer – 2017 Expo
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NABTEB CHEMISTRY THEORY
1ai)
An ion is any atom or group of atoms which possesses an electric charge. While
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)
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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 field
-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
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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)
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3biii)
i)Hydrogen sulphide (H2S)
ii)carbon(iv) oxide (CO2)
3bi)
TABULATE
—————- |Samplei| Sampleii| Sampleiii|
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%
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4ai)
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 22.4dm^3.
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)
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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.
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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)
-maganese
-carbon
-steel
5ci)
-it is used for making electric wires
-it is used for plumbing and roofing.
5cii)
-air(oxygen)
-water
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