Waec
Chemistry Obj!
1ABACCABBCD
11DCDBCCDCDB
21BDCADAABCA
31CBDCCDCBBD
41CACCCDADCA
Completed
CHEMISTRY-THEORY-ANSWERS!
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(2ai)
Ionization energy can be defined as the energy required to remove a loosely bound electron from the outermost shell of a gaseous covalently bonded atom.
(2aii)
This is because B has more shells than Be which makes the valence electrons to be far from the nucleus making it require less energy due to lesser nuclear attraction.
(2b)
I = 0.12A, t = 500seconds
m = 0.015g, F =96500C
M = 48.0, Charge = ?
Using;
m = MIt/CF
C = MIt/mF
C = (48×0.12×500)/(0.015×96500)
C = 2
(2ci)
Al₂O₃
(2cii)
(i) Electricity supply
(ii) Nearness to source of material
(2di)
This can be defined as a property of metal which are weakly attracted to an applied magnetic field
(2dii)
(i) I → ₂₄Cr²⁺ → 2
₂₄Cr⁶⁺ → 0
(ii) ₂₄Cr²⁺
(iii) It has unpaired electrons.
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(3ai)
This can be defined as the number of atoms or molecules in one mole of a substance which is equal to 6.02 ×10²³
(3aii)
Mass/m.m = no. of molecules/Avogadro’s number
(2.30/m.m) × (3.01×10²²/6.02×10²³)
m.m = (2.30×6.02×10²³)/3.01×10²²
m.m = 46g/mol
(3aiii)
Since the molar mass = 46g/mol
The formula is NO₂
:. 14+(16×2)
14+32 = 46g/mol
:. NO₂
(3bi)
(i) There is no reaction but rather forms a layer underneath the water
(ii) It reacts violently with water forming white silicon dioxide and hydrogen chloride gas.
(3bii)
The reaction is different because CCl₄ is an organic substance while SiCl₄ is not.
(3ci)
Extraction of copper
(3cii)
(i) CuSO₄
(ii) CuCl₂
(3ciii)
Cu²⁺ + 2e⁻ —> Cu
(3civ)
Using; m = ZIt
Z = m/It
Z = 3.2/(50x(3×60)+13)
Z = 3.2/(50×193)
Z = 3.2/9650
Z = 0.000332g/Asec
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(5a)
(i) It melts to clear mobile liquid
(ii) A brownish gas is evolved.
(5bi)
(i) Carbon(ii)oxide
(ii) Lead(ii)oxide
(5bii)
Methane(CH₄)
(5biii)
(i) It leads to erosion
(ii) It causes pollution
(5biv)
This is because it has more surface area than it occupies leading to a faster rate of reaction.
(5bv)
Ammoniacal liquor
(5ci)
When water is added to white anhydrous CuSO₄ it turns blue.
(5cii)
(i) It removes the hardness by precipitating the trioxocarbonate(iv)
(ii) It removes the hardness by removing the calcium or magnesium ion and precipitating trioxocarbonate(iv).
(5ciii)
Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂
(5d)
Oxygen can be prepared by heating KClO₃ in the presence of manganese(iv)oxide which acts as a catalyst to produce KCl and oxygen gas. The reaction takes place at a lower temperature and much faster rate.
KClO₃ (MnO₂)heat—–> KCl + O₂
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(1ai)
According to Lewis, an acid can be defined as a substance that can accept a pair of non-bonding electrons i.e an electron pair acceptor.
(1aii)
AlCl₃
(1b)
Salting out is a process through which soap is precipitated as solid from the suspension by adding common salt to the suspension. It is a purification process.
(1c)
Reagent – Silver trioxonitrate(v)
Condition – The reaction takes place at high temperatures and pressure.
(1d)
This is the proportion at which isotopes of an element are to each other in its composition.
(1e)
(i) It has a stable configuration
(ii) This is because they have a covalent bond.
(1f)
They can be differentiated using barium chloride. When barium chloride is added to concentrated H₂SO₄ a white precipitate is formed with concentrated HNO₃
(1g)
[TABULATE]
-ELECTROCHEMICAL CELL-
(i) There are two electrolytes
(ii) Salt bridge is present.
-ELECTROLYTIC CELL-
(i) There is only one electrolyte
(ii) There is no salt bridge present.
(1h)
The lower the ionisation energy, the higher the reactivity of metals. Since it decreases down the group, the reactivity increases down the group I.
(1i)
This can be defined as a formula that shows the actual number of atoms in a compound.
(1j)
(i) NH₃
(ii) This is because its interaction is perfectly inelastic.
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