NECO CHEMISTRY OBJ & ESSAY QUESTIONS AND ANSWERS FOR 25TH JULY 2022
Monday 25th July 2022
Paper III & II: Objective & Essay – Chemistry – 10:00am – 1:00pm
(i) KAl(SO₄)₂. 12H₂O
Number of moles of sodium reascted = reacting mass/molar mass
Number of moles of oxygen reacted = (1/4) x Number of sodium
= 1/4 x (3.6/23)
Reacting mass of oxygen = Number of moles x molar mass
= 0.03913 x (16×2)
Air in gaseous form is first passed through caustic soda to remove CO₂. It is compressed and cooled until ut becomes a liquid at -200°C. It is then led to a fractionating column. On distillation, Nitrogen which has a lowet boiling point of -196°C is evolced first leaving behind Oxygen in liquid form. Further heating converts the liquid to a gas at -183°C.
(i) It is used for combustion
(ii) It is used for artificial respiration
This is because room temperature is warmer
(i) Methyl orange
An ion is an atom or molecule which has a net electric charge due to the loss or gain of one or more electrons.
HCl gas doesn’t contain ions
(i) Noble gases: Neon, Helium
(ii) Halogens: Iodine, Fluorine
(iii) Alkaline earth metals: Calcium, Magnesium
Halogens attain stable octet configuration by accepting an electron from donors Group I elements.
A sol is a colloid where solid particles are dispersed in liquid medium.
(i) Acid-base titrations are used to determine the percentage purity of a substance
(ii) Acid-base titrations are important to determine the number of water molecules in a hydrate.
A molar solution of a compound contains one mole or the molar mass of the compound in one dm³ of the solution.
(i) Identification of gases
(ii) Identification of acidic and metallic radicals
(i) Purification of bauxite
(ii) Electrolysis of alumina
This is because of the presence of copper which is a transition metal
(i) Methanamide is a liquid while the rest amides are crystalline solids
(ii) Melting points and boiling points of aides are much higher than expected.
(i) Heavy chemicals are produced in very large quantities in industries While fine chemicals are produced in small quantities for specific purposes
(ii) Heavy chemicals are in a crude state While fine chemicals are purified.
(i) Million’s reagent
(ii) Feeling’s solution
Graham’s law of diffusion states that at a constant temperature and pressure the rate of diffusion of a gas is inversely proportional to the square root of its density.
RO₂/RCH₄ = √(MCH₄/MO₂)
5/(200/t) = √[(12+4)/(16×2)]
5t/200 = √16/32
t/40 = 1/√2
t = 40/√2
t = (40/√2) × (√2/√2)
t = 20√2 seconds
Time taken = 28.28 seconds.