WAEC GCE 2025 CHEMISTRY PRACTICAL ANSWER



(1ai)
Mass of KMnO? used: 1.58 g
Volume of solution: 500 cm³ = 0.5 dm³

Molar mass of KMnO? = 39 + 55 + 4 × 16 = 158g/mol

Moles = 1.58/158 = 0.01
Concentration = 0.1/0.5 = 0.02mol/dm³

(1aii)
Mass of hydrated FeSO? salt = 5.65 g
Volume of solution = 250 cm³ = 0.25 dm³

Concentration in g/dm³
= 5.65/0.25 = 22.6g/dm³

(1b)
From titration, 25 cm³ (0.025 dm³) of FeSO? uses 24.80 cm³ (0.0248 dm³) of KMnO?

Equation: MnO?? + 5Fe²? --> Mn²? + 5Fe³?

Moles of KMnO? in 24.80 cm³: 0.02 × 24.80 = 0.000496

Moles Fe²? = 5 × 0.000496 = 0.00248

5.65 g in 250 cm³ = 22.6 g/dm³
Molar mass FeSO?·xH?O = 22/0.992 = 228g/mol
FeSO?·xH?O = 56 + 32 + 4×16 + x(2+16) = 152 + 18x

152 + 18x = 228
x = 228 - 152/18
x = 4.22
x = 4


(1c)
HNO? is an oxidizing acid and may oxidize Fe²? or interfere, causing inaccurate titration results. It can also oxidize Mn²? to higher oxides, affecting the outcome.

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(2a)


(2b)
-Salt A: Zinc carbonate (or Lead(II) carbonate or Aluminium carbonate)

-Salt B: Calcium chloride


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(3ai)
No, the titre value would not be affected.

(3aii)
Washing down the splashed acid or base with a small amount of distilled water does not change the titre because distilled water does not react with the solution. It only ensures that all the reacting solution is inside the main bulk so the reaction goes to completion. The number of moles of acid and base remains the same, so the titre is unchanged.

(3bi)
(i) The pH range of the indicator.
(ii) The type of acid–base reaction or the pH of the equivalence point.

(3bii)
Different acid–base combinations have different pH values at the end point. An indicator must change colour within the pH range where the equivalence point occurs. Therefore, the chosen indicator must have a colour change interval that matches the pH jump of the titration.


(3ci)
Concordant titre values are two or more titre values that are very close to each other (usually within 0.1 cm³), indicating consistent and reliable titration results.

(3cii)
The final burette reading is recorded above the initial reading to account for the volume of liquid delivered and to avoid negative values or confusion in volume calculation.

(3ciii)
A burette filled with aqueous NaOH must be washed thoroughly after use to remove any residue that could react with the next solution used or affect accuracy in subsequent titrations.


(3di)
SO?

(3dii)
HNO?


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WAEC GCE 2025 CHEMISTRY THEORY and OBJ ANSWER


CHEMISTRY OBJ
NOTE: kindly trace it from your system. The options are being reshuffled. You might see number 1 as any number, so trace and be fast. You might also see option A as option C, B or D. Just use the answers in words and and trace properly. Kindly Trace it carefully to avoid errors!!!!

1: (B) hygroscopic
2; (A) Fructose
3; (C) molecule
4; (C) 2, 2, 4-trimethylpentane.
5; (A) working capital.
6; (C) sublimation.
7; (A) CCI?
8; (D) 0.040 moldm-³
9; (C) Fe(s) +Cl_²(g) FeCl-²
10; (B) is attacked by moist air.
11: (B) N²(g) + O²(g)--->2NO(g)
12: (A) 19 protons, 19 electrons and 20 neutrons
13: (D) HNO³
14: (A) in which large hydrocarbon molecules are broken into smaller units
15: (A) AgF
16: (B) +6
17: (B) ?H? < ?H?
18: (C) neutral
19: (D) CuO
20; (D) 1.00 mol
21: (B) are widely spaced.
22: (A) activation energy
23: (C) less dissociated in solution.
24: (B) almost the entire mass of the atom is in the nucleus.
25: (B) 0.05 mol/dm³
26: (B) occurs in gases.
27: (D) Displacement.
28: (D) paraffin oil.
29: (D) Hex-1-ene.
30: (B) Na, Mg, Al.
31: (B) Alkaline earth metals
32: (C) I-
33: (C) saturated solution
34: (A) Iron
35: (C) Cl,Cl-Cl+
36: (D) Atomic number
37: (C) cracking
38: (A) Na²CO³
39: (C) Si
40: (B) C + e - ----> C-
41: (A) electron
42: (C) solubility
43: (D) tertiary alkanol
44: (C) H²CO³
45: (B) neutral oxides
46: (B) Separation of sand from water
47: (D) rise in boiling point and fall in melting point.
48: (A) hardness
49: (D) melting
50: (A) esterification


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(1a)
(i)Law of Conservation of Mass.
(ii)Law of Definite Proportions
(iii)Law of Multiple Proportions

(1b)
standard solution is prepared by dissolving an accurately weighed amount of a primary standard substance in a definite volume of a solvent (usually water).

(1c)
Both bromine (Br²) and iodine (I²) are non-polar molecules that exhibit London dispersion forces as their primary intermolecular forces. The strength of these forces increases with the number of electrons and molar mass. Iodine has a higher molar mass and more electrons than bromine, resulting in significantly stronger London dispersion forces. These stronger forces require more energy to overcome, which is why iodine is a solid and bromine is a liquid under the same conditions. 

(1d)
Dalton's law of partial pressures states that in a mixture of ideal gases, the total pressure is the sum of the partial pressures of the individual gases present.

(1e)
(i)Gas particles are assumed to have negligible volume, but real gas particles occupy a finite volume.
(ii)There are no intermolecular forces between ideal gas particles, but real gas particles experience attractive forces.

(1fi)
Aluminium chloride is a covalent compound

(1fii)
(i) High charge density of the aluminium ion
(ii) High electronegativity of the chlorine atom

(1g)
(i) Metals: Sodium (Na), Magnesium (Mg) (also Aluminium, Al).
(ii) Non-metals: Phosphorus (P), Sulfur (S) (also Chlorine, Cl).

(1h)
(i) Manufacture of plastics (e.g. polyethene).
(ii) Manufacture of alcohols (e.g. ethanol from ethene).
(v) Used in making detergents.

(1i)
=SIMILARITY=
(i) Both involve sharing of electrons between atoms.

=DIFFERENCE=
(i) In a covalent bond, each atom contributes electrons, while in a dative bond the shared pair is supplied by only one atom.

(1j)
(i) Oxidizing agent: Cl?
(ii) Product of reduction: Cl?

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(2ai)
A transition element is a d-block element that has an atom or ion with an incomplete d-subshell.

(2aii)
(?) Coloured compound formation: Transition metals form coloured compounds due to d-d electron transitions within the partially filled d-orbitals when they absorb certain wavelengths of light.

(?) Complex ion formation: Transition metals can form complex ions by bonding with ligands due to their ability to use empty d orbitals for coordinate covalent bonding.

(?) Catalytic abilities: Transition metals act as catalysts because they can change oxidation states easily and provide a surface for reactants to adsorb, lowering activation energy.

(2bi)
(?) Potassium and oxygen: K?O
(?) Sulphur and aluminium: Al?S?
(?) Nitrogen and magnesium: Mg?N?

(2bii)
K?O: Potassium oxide
Al?S?: Aluminium sulphide
Mg?N?: Magnesium nitride

(2ci)
(?) Atom
An atom is the smallest particle of an element that can exist alone and retains the chemical properties of that element; it consists of a nucleus (protons and neutrons) surrounded by electrons.

(?) Molecule
A molecule is a neutral group of two or more atoms chemically bonded together, representing the smallest particle of a substance that can exist while retaining its chemical identity.

(?) Ion
An ion is an atom or group of atoms that has acquired a net electrical charge by losing or gaining electrons.

(2cii)
Atom: Cl (chlorine atom)
Molecule: Cl? (chlorine molecule)
Ion: Cl? (chloride ion)

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(3a)


(3b)


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(5a)
(i)2NaOH + Cl_2 NaCl + NaClO + H2O
(ii)Cl_2 + H2O HOCl + HCl

(5aii)
(I)Chlorine: Gas
(II) Fluorine: Gas
(III) Astatine: Solid

(5aiii)
The strength of Van der Waal's forces increases down the group due to the increase in atomic size and polarizability.

(5bi)
(i)Low temperature
(ii)High pressure

(5bii)
The choice of conditions is governed by Le Chatelier's principle, which states that a system at equilibrium will adjust to counteract any changes in concentration, temperature, or pressure.

(5biii)
(i) For fertilizer production.
(ii)For cleaning agent
(iii)For Industrial applications

(5ci)
(i)High electrical conductivity
(ii)Ductility
(iii)Resistance to corrosion

(5cii)
(i)Oxidizing properties.
(ii)Antimicrobial activity.

(5di)
(i)For Construction.
(ii)It is use as an food and nutrition for humans.
(iii)It is use for manufacturing products, including paper, glass, and ceramics.

(5dii)
(i)Coke
(ii)Coal tar

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