40 Simple WAEC Chemistry Revision Questions

 

40 Simple WAEC Chemistry Revision Questions 

Test your knowledge on core WAEC Chemistry concepts. Read the statement, decide if it's True or False, and check the brief explanation below.

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1. Isotopic elements have the same physical properties but different chemical properties.

False

Isotopes have the same chemical properties (because they have the same number of electrons) but different physical properties due to different mass numbers.

2. Dynamic equilibrium can only be achieved in a closed system.

True

In an open system, reactants or products can escape, preventing the forward and reverse reactions from balancing out.

3. Alkanes are unsaturated hydrocarbons.

False

Alkanes are saturated hydrocarbons because they contain only single carbon-carbon bonds. Alkenes and alkynes are unsaturated.

4. Oxygen gas is collected by downward displacement of water.

True

Oxygen is slightly soluble in water and has a density close to air, making downward displacement of water the best method to collect it purely.

5. Oxidation involves the loss of electrons.

True

Remember the acronym OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).

6. Concentrated tetraoxosulfate(VI) acid ($H_2SO_4$) is used as a drying agent because it is highly dehydrating.

True

It has a strong affinity for water and can even remove chemically combined water elements from compounds like sugar.

7. Hard water forms lather easily with soap.

False

Hard water contains $Ca^{2+}$ and $Mg^{2+}$ ions which react with soap to form scum instead of lather.

8. The bond angle in a water molecule ($OH_2$) is exactly 180°.

False

Water has a bent/V-shape with a bond angle of about 104.5° due to the repulsive force of two lone pairs of electrons.

9. Catalysts alter the rate of a chemical reaction but remain chemically unchanged at the end.

True

They provide an alternative pathway with lower activation energy without being consumed by the reaction.

10. Chlorine gas turns moist blue litmus paper red and then bleaches it.

True

Chlorine reacts with water to form acidic HCl (turning blue litmus red) and HOCl, which acts as a powerful bleaching agent.

11. Endothermic reactions release heat to the surroundings.

False

Endothermic reactions absorb heat from the surroundings, causing a drop in temperature. Exothermic reactions release heat.

12. Sodium is stored under paraffin oil because it reacts violently with air and water.

True

As a highly reactive Group 1 alkali metal, sodium must be kept away from atmospheric moisture and oxygen.

13. Universal indicator can be used to determine the exact pH value of a solution.

False

Universal indicator gives an approximate pH based on color matching. For an exact value, a pH meter is required.

14. The functional group of alkanols is the hydroxyl group (-OH).

True

Alkanols (alcohols) are characterized by the presence of one or more covalent -OH groups attached to a carbon atom.

15. Diamond and graphite are allotropes of carbon.

True

They are different structural forms of the same element (carbon) existing in the same physical state.

16. Cathode rays are streams of positively charged particles.

False

Cathode rays are streams of fast-moving electrons, which carry a negative charge.

17. Electrovalent (ionic) compounds generally have high melting and boiling points.

True

They have strong electrostatic forces of attraction holding the crystal lattice together, requiring high thermal energy to break.

18. Temporary hardness of water can be removed by boiling.

True

Boiling decomposes soluble calcium hydrogen trioxocarbonate(IV) into insoluble calcium trioxocarbonate(IV) precipitate (scale).

19. Nitrogen gas constitutes about 21% of atmospheric air.

False

Nitrogen makes up roughly 78% of air, while oxygen makes up about 21%.

20. The empirical formula of a compound always matches its molecular formula.

False

The empirical formula is the simplest ratio. For example, glucose has an empirical formula of $CH_2O$ but a molecular formula of $C_6H_{12}O_6$.

21. Copper is extracted from its ore using the blast furnace.

False

The blast furnace is specifically used for the extraction of iron. Copper is typically extracted via smelting and electrolytic refining.

22. According to Charles's Law, volume is directly proportional to absolute temperature at constant pressure.

True

Mathematically stated as $V \propto T$, meaning gases expand when heated if pressure is kept steady.

23. Solid sodium chloride (NaCl) conducts electricity.

False

Solid NaCl does not conduct because its ions are locked in fixed positions. It only conducts when molten or dissolved in water.

24. Fractional distillation is used to separate crude oil into its विभिन्न components.

True

It separates mixtures based on differences in the boiling points of the constituent liquids.

25. Zinc can displace copper from a solution of copper(II) tetraoxosulfate(VI).

True

Zinc is higher than copper in the electrochemical (activity) series, making it more reactive.

26. Acid rain is primarily caused by carbon monoxide gas.

False

Acid rain is primarily caused by sulfur dioxide ($SO_2$) and nitrogen oxides ($NO_x$) reacting with atmospheric moisture.

27. A neutralization reaction produces salt and water only.

True

When an acid reacts completely with a base, they neutralize each other's properties to form ionic salt and neutral water.

28. Helium is used to fill weather balloons because it is lighter than hydrogen.

False

Hydrogen is lighter than helium, but helium is preferred because it is inert and non-flammable, making it much safer.

29. Hydrochloric acid ($HCl$) is a weak acid.

False

Hydrochloric acid is a strong mineral acid because it ionizes completely in aqueous solution.

30. Elements in the same group on the periodic table have the same number of valence electrons.

True

This is why elements in the same vertical group exhibit very similar chemical behaviors.

31. The process of iron rusting requires both oxygen and water.

True

Rusting is an electrochemical process forming hydrated iron(III) oxide; it fails to happen if either moisture or air is absent.

32. Ethyne gas will decolorize bromine water.

True

Ethyne is an alkyne (unsaturated). It undergoes an addition reaction with bromine, removing the reddish-brown color.

33. Deliquescent substances absorb moisture from the atmosphere to form a solution.

True

Examples include $NaOH$ pellets and $CaCl_2$. They absorb so much water that they completely dissolve in it.

34. The Haber process is used for the industrial manufacture of tetraoxosulfate(VI) acid.

False

The Haber process manufactures ammonia ($NH_3$). The Contact process is used for manufacturing $H_2SO_4$.

35. Atoms are generally electrically neutral.

True

An unreacted atom contains an equal number of positively charged protons and negatively charged electrons.

36. Fine sand can be separated from water using a separating funnel.

False

Separating funnels are used for immiscible liquids (like oil and water). Sand and water are best separated using filtration.

37. Global warming is intensified by the accumulation of greenhouse gases like $CO_2$ in the atmosphere.

True

Greenhouse gases trap infrared radiation (heat) radiated from the earth's surface, causing temperatures to rise.

38. The valency of Aluminum is 2.

False

Aluminum belongs to Group 3 and loses 3 electrons during chemical combinations; its valency is 3.

39. Direct current (D.C.) is required to carry out electrolysis.

True

Direct current ensures that the electrodes maintain fixed polarities (anode stays positive, cathode stays negative) to guide the ions.

40. Soap is produced via the chemical process known as saponification.

True

Saponification is the alkaline hydrolysis of fats and oils (esters) using sodium or potassium hydroxide.