Neco Gce 2019 Chemistry Obj & Essay Answer Now Available

CHEMISTRY OBJ
1-10: ACDBABDEBB
11-20: ADCCCCBEBA
21-30: DDDCCCDCAB
31-40: CBCCDEBBAC
41-50: EABDDBABDC
51-60: EBABCDEDEB

(3ai)
(i) Physical change
(ii) Chemical change.
(iii) Physical change.

(3aii)
The periodic law states that atomic mass of element is s periodic function of their chemical properties.

(3aiii)
(i) Elements within the same group have the same chemical properties.
(ii) Elements change gradually from metal to non-metals across the period.
(iii) The arrangement of elements in a horizontal form is called period while the vertical arrangement is called group

(3aiv)
(i) Calciumchloridehypochloridte CaCl(OCl)
(ii) Calcium hypochlorite Ca(OCl)₂
(iii) Calcium chloride CaCl₂

(3bi)
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain equal number of molecules.

(3bii)
0.25mole of Argon = 15cm³
Mass of one mole of Argon = 40g
40g = 1 mole
Xg = 0.25 = 10g
Hence 10g of Argon = 15cm³
10g of Neon = 10/20 = 1/2 = 0.5mol will contain 2 × 15cm³ = 30cm³ of gas

(3ci)
Fermentation is the breakdown of substance by bacteria, yeasts or microorganisms typically involving effervescence and the evolution of heat.

(3cii)
H H
\ /
C=C + H₂O
/ \
H H

H H
| |
<=> C-C-OH
| |
H H

<=> C₂H₄ + H₂O <=> C₂H₅

================================

(2ai)
(i) Photosynthesis
(ii) Respiration in plant

(2aii)
(i) Industrial effluent
(ii) Laboratory effluent

(2aiii)
5 electrons

(2bi)
(i) Pig iron
(ii) Cast iron
(iii) Wrought iron

(2bii)
(i) Susceptibility to individual exposure to toxic chemicals
(ii) Irritation of some body parts when toxic gases are inhaled

(2ci)
A – Sulphur
B – Magnesium
C – Oxygen
D – Chlorine

(2cii)
The type of bond between B and D is ionic bond

(2ciii)
Electronic configuration of C using Spdf notation
Oxygen = 1s²2s²2p⁴

(2civ)
(i) Their hardness increases with increasing ionic charge
(ii) They have high melting and boiling points

(2di)

(2dii)
(i) The valency of mercury is +2
(ii) The valency of lead in PbO2 is +4

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