WAEC 2022 Chemistry Essay And Obj Answer-May/June Expo

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CHEMISTRY OBJ

01-10: ABACCABBCD

11-20: DCDBCCDCDB

21-30: BDCADAABCA

31-40: CBDCCDCBBD

41-50: CACCCDADCA

COMPLETED

CHEMISTRY ANSWERS

(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 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

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(2ai)

Ionization energy can be defined as the energy required to remove a loosely bound electron from the outermost shell of a gaseous covalently bonded atom.

(2aii)

This is because B has more shells than Be which makes the valence electrons to be far from the nucleus making it require less energy due to lesser nuclear attraction.

(2b)

I = 0.12A, t = 500seconds

m = 0.015g, F =96500C

M = 48.0, Charge = ?

Using;

m = MIt/CF

C = MIt/mF

C = (48x0.12x500)/(0.015x96500)

C = 2

(2ci)

Al₂O₃

(2cii) 

(i) Electricity supply

(ii) Nearness to source of material

(2di)

This can be defined as a property of metal which are weakly attracted to an applied magnetic field

(2dii)

(i) I → ₂₄Cr²⁺ → 2

₂₄Cr⁶⁺ → 0

(ii) ₂₄Cr²⁺

(iii) It has unpaired electrons.

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(5a)

(i) It melts to clear mobile liquid

(ii) A brownish gas is evolved.

(5bi)

(i) Carbon(ii)oxide

(ii) Lead(ii)oxide

(5bii)

Methane(CH₄)

(5biii)

(i) It leads to erosion

(ii) It causes pollution

(5biv)

This is because it has more surface area than it occupies leading to a faster rate of reaction.

(5bv)

Ammoniacal liquor

(5ci)

When water is added to white anhydrous CuSO₄ it turns blue.

(5cii)

(i) It removes the hardness by precipitating the trioxocarbonate(iv)

(ii) It removes the hardness by removing the calcium or magnesium ion and precipitating trioxocarbonate(iv).

(5ciii)

Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂

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