2025 WAEC CHEMISTRY: WAEC CHEMISTRY Midnight Essay and Obj Questions and Answers 2025 (2338)

(1a)
(i)An acid is any compound which, in a chemical reaction is able to attach itself to an unshared pair of electrons in another molecule-a base, to form a new compound.

(ii)
Alcl₃

(1b)
Salting out is the process of adding concentrated sodium chloride solution to soap, to decrease the solubility of the soap. It consequently separates out as a hard cake on the surface or cooling.

(1c)
Reagent: {Ammonical solution of Silver trioxonitrate(v) [AgNo₃]}
Condition: {At room temperature}

(1d)
The percentage abundance of an isotope is the percentage of all naturally occurring atoms with a specific atomic mass of an element.

(1e)
(i)The element with atomic number 18 has electronic configuration 2,8,8. It has a completely filled valence shell. It is therefore inert. Hence it cannot have an oxide.

(ii)Being a covalent compound, the intermolecular forces between the Cl₂O molecules are weak and easily overcome.

(1f)
Add barium chloride solution to H₂SO₄ and HNO₃ separately. A white precipitate is formed in H₂SO₄ and no such precipitation is formed in HNO₃.

(1g)
(i)The main difference is that electrochemical cell does not need any external current for operation whereas electrolytic cells need external current to operate.

(ii)Also, Oxidation occurs at the positive electrode and reduction at the cathode, in the electrolytic cell. While the reverse is the case in electrochemical cells.

(1h)
As we go down group 1 from top to bottom, it gets easier to remove the valence electron and form the positively charged cation. Hence group 1 elements increase in chemical reactivity as we go down the group

(1i)
Molecular formula is a chemical formula that gives the total 'copied from e x p o c o d e . n e t free' number of atoms of each element in each molecule of a substance.

(1j)
(i)Ammonia, NH₃ will deviate more than hydrogen gas H₂

(ii)
-Ammonia have stronger intermolecular forces than H₂
-Ammonia has more volume than H₂ at the same concentration