2021 NECO CHEMISTRY ANSWERS

 

2021-NECO-CHEMISTRY-ANSWERS

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CHEMISTRY-THEORY

INSTRUCTIONS: YOU ARE TO ANSWER FOUR(4) QUESTIONS ONLY. WE HAVE ANSWERED 1,2,3,4,5,6. PLS PICK ONLY FOUR(4) THANK YOU
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(1ai)
(i) Base has bitter taste
(ii) Base is soapy to touch
(iii) Base turns litmus paper blue

(1aii)
The steps involved are:
(i)Shift conversion
(ii)Removal of carbon (iv) oxide
(iii)Steam reforming

(1aiii)
Cracking is the process by which heavier hydrocarbon molecule is splitted into two or more lighter molecules

(1aiv)
Thermal cracking

(1bi)
P ion = 1s²2s²2p⁶

(1bii)
Formula of chloride is Pcl2

(1biii)
Reducing agent
This is because it undergoes oxidation by losing electrons

(1ci)
Electron affinity is the energy released when a gaseous atom gains an electron to form a gaseous negative ion.

(1cii)
This is because it has lone pairs of electrons

(1di)
(i) By adding a catalyst

(ii) FeS(s) + 2HCl(g) —–> FeCl(g) + H2S(s)

Xg = ?
No. of FeCl2 = 127g/mole
No. of FeS= 88g/mole

Mole = Mass/ No. of Mass = 3.2/127 = 0.025mole of FeCl2

By comparison,
1 mole of FeS = 1 mole of FeCl2
X moles of FeS = 0.025 of FeCl2
X = 0.025mole of FeS

Recall,
Mass = Mole * molar mass
Mass = 0.025*88
Mass = 2.2g of FeS
X = 2.2g

(1dii)
(i)Chlorofluorocarbons
(ii)Ammonia
=================================

(2ai)
(i)Molecules of gases are in constant random motion
(ii)The collision of gases is perfectly elastic
(iii)An increase in temperature leads to an increase in the average kinetic energy of the molecules of gases

(2aii)
(i)They both turn blue litmus paper red
(ii)They both dissolve in water to produce an acid

(2aiii)
Copper<Iron<Aluminium<Magnesium

(2aiv)
Copper

(2bi)
Activation energy can be defined as the minimum energy required for a reaction to occur.

(2bii)
Catalyst lowers activation energy

(2biii)
Nikel

(2biv)
(i)Sodium trioxocarbonate (iv)
(ii)Hydrogen gas

(2ci)
(i)It reacts with metals to liberate hydrogen
(ii)It reacts with base to produce salt and water only

(2cii)
(i) 2KI + 2Cl2 —-> 2Kl2 + I2

(ii) 2Zn + Cl2 —–> 2ZnCl

(2ciii)
Cl2

(2civ)
Covalent bond

(2d)
(i) Butane
(ii) Propene
(iii) Ethanol
(iv) Ethyne
=================================

(3)

(3a)
(i) Iron (Fe)
(ii) Fe3C4
(iii)
– chlorine displace bromine
– The displaced bromine gives the reddish brown colour
(iv) 2KBr(aq) + Cl2(g) —-> 2KCl(aq) + Br2(l)

(3b)
(i)
– Cement industries
– Glass industries
(ii) Quick lime
(iii) TABULATE PLS
=>Salt to be prepared<=
– KNO3
– CaCl2
– FeCl3
– CuSO4
– PbSO4

=>Starting material<=
– KOH
– CaCO3
– Fe(s)
– CuO
– Pb(NO3)2

=>Method of preparation<=
– Neutralization
– Dilute acid and trioxocarbonate (iv)
– Combination of constituent elements
– Dilute acid and insoluble base
– Double decomposition

(3c)
(i) By burning sulphur in dry air
(ii) 2SO2(aq) + O2(g) ——> 2SO3(aq) + heat

(iii)
– Combining sulphur (iv) oxide with oxygen in excess to firm sulphur (vi) oxide
– Cooling and passing the SO3 formed through and absorption tower to produce the acid

(3d)
(i) 2*9600C produces 119g
(1.5*2*3600)C produces xg
x= 1.5*2*3600*119/2*96500
x= 6.66grams

(ii) Strong electrolyte conducts large currents WHILE Weak electrolyte do not conduct electricity readily

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(4a)
(i)Enthalpy of combustion can be defined as the amount of heat evolved when one mole of a substance burns in air or oxygen

(ii) Isomerism can be defined as a phenomenon in which organic compounds are having the same molecular formula but different structural formula

(4bi)
NO2 – Acidic oxide
CO – Neutral oxide
Fe2O3 – Basic oxide
Al2O3 – Amphoteric oxide

(4bii)
(i)Nitrous oxide
(ii)Carbon (iv) oxide

(4c)
(i) Fractional distillation of liquid air

(ii) 2KNO3 —–> 2KNO2(s) + O2(g)

(NH)CO3(s) ——>2NH3(g) + CO2(g) + H2O(g)

(iii) No. of molecules = 4/16 × 6.02 × 10²³
= 1.5 × 10²³

(4di)
(i)Sodium
(ii)Potassium

(4dii)
(i)Carbon (iv) oxide
(ii)Carbon

(4diii)
(i)Hydration
(ii)Oxidation
=================================

(5ai)
Gay Lussac’s states that when gaese react, they do so in volume which bear a simple whole number ratio to one another and to the volume of their products.

(5aii)
2CO + O2 —-> 2CO2
2 1 2
100cm³ 70cm³ 100cm³

Total volume = 100+70+100 = 270cm³

(5bi)
(i)It is used in the production of other chemical substances
(ii)It is used as a drying or dehydrating agent

(5bii)
(i) ZnCO3 —–> ZnO + CO2

->Conditions<-
– High temperature
– High pressure

(ii) ZnO + H2SO4 —-> ZnSO4 + H2

->Conditions<-
– Catalyst
– Surface area

(5biii)
(i) Crystallization method
(ii) By heating the ZnSO4 with an alkali metal carbonate

(5c)
(i) This is due to the presence of extra electrons not used for bonding graphite
(ii) This is because sodium salts are soluble and double decomposition is used for the production of insoluble salts
(iii) It is an alkali substance ie possesses basic properties

(5di)
(i)Bitumen coal
(ii)Peat coal

(5dii)
Fractional distillation

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(6a)
(i) DIAGRAM

 

(6aii) Vanadium (v) oxide : It enables equilibrium equilibrium to be reached in a shorter time

(6b)
(i) Caustic soda solution
(ii) Pure Alumina in molten cryolite
(iii) Graphite rods: Oxygen is given off at the anode, slowing burning away the anode as CO2

(6ci)
– Dilute acids have a sour taste
– Acids turn blue litmus red
– Concentrated forms of strong acids are corrosive

(6cii) HCl will have a larger electrical conductivity because it ionizes completely in water to give hydrogen ions with concentration very high

(6ciii)
(i) As an acid with bases
NaCl(aq) + HNO3(aq) —> NaNO3(aq) + H2O(l)

(ii) H2S(g) + 2HNO3(aq) —-> S(s) + 2H2O(l) + 2NO2(g)

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COMPLETED

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