WAEC Chemistry Revision Questions - Part 5

 

WAEC Chemistry Revision Questions (True/False) - Part 5

Wrap up your final WAEC chemistry test prep with this final set of 40 true or false questions covering core syllabus material.

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1. Solvation is an endothermic process when the energy required to break bonds is less than the energy released when new bonds form.

False

If more energy is released when new bonds form than is consumed breaking old ones, the process is exothermic (releases heat).

2. The element with atomic number 17 is a member of the halogen family.

True

Atomic number 17 is Chlorine, which sits in Group 7 (halogens) and has 7 valence electrons.

3. Covalent compounds generally conduct electricity in their molten states.

False

Covalent compounds consist of neutral molecules and lack free-moving ions or delocalized electrons to conduct electricity.

4. Carbon(II) oxide gas turns lime water milky.

False

Carbon(IV) oxide ($CO_2$) turns lime water milky. Carbon(II) oxide ($CO$) has no reaction with lime water.

5. During the electrolysis of copper(II) tetraoxosulfate(VI) solution using copper electrodes, the anode decreases in mass.

True

The copper anode dissolves into the solution as copper ions ($Cu \rightarrow Cu^{2+} + 2e^-$), causing it to lose mass over time.

6. Concentrated $H_2SO_4$ is used to prepare volatile acids like $HCl$ and $HNO_3$ from their respective salts.

True

Because concentrated tetraoxosulfate(VI) acid has a high boiling point and is non-volatile, it can displace more volatile acids from their salts.

7. A normal salt contains replaceable hydrogen ions.

False

A normal salt is formed when all the replaceable hydrogen ions of an acid are completely replaced by metallic or ammonium ions.

8. Noble gases are highly reactive elements because they possess complete valence electron shells.

False

Noble gases are chemically stable and inert precisely because they have a complete octet or duplet of valence electrons.

9. Alkenes decolorize acidified potassium tetraoxomanganate(VII) ($KMnO_4$) solution.

True

Alkenes readily undergo oxidation across their double bonds, changing the purple $KMnO_4$ solution to colorless.

10. The principal ore of lead is galena.

True

Galena is lead(II) sulfide ($PbS$), which is roasted in air to extract lead metal.

11. A substance that gains electrons in a chemical reaction is oxidized.

False

Gaining electrons is reduction (OIL RIG: Reduction Is Gain). The substance that gains electrons is reduced.

12. Isotopes of an element have different atomic numbers but the same mass numbers.

False

Isotopes must have the same atomic number (same element) but different mass numbers due to varying neutron counts.

13. Pure covalent substances have very high electrical conductivity when dissolved in water.

False

Covalent molecules generally remain intact as neutral entities in water and do not form ions to conduct electricity, unless they are polar acids like $HCl$.

14. The functional group for alkanals (aldehydes) is the formyl group (-CHO).

True

The formyl group contains a carbonyl center bonded to a hydrogen atom at the end of a carbon chain.

15. Increasing pressure on a gaseous system at equilibrium always shifts the reaction to the right.

False

Increasing pressure shifts the equilibrium to the side with the fewer number of gaseous moles, which may be left, right, or cause no shift at all.

16. Hydrogen gas can be dried using concentrated tetraoxosulfate(VI) acid.

True

Hydrogen does not react with concentrated $H_2SO_4$, making it a safe and efficient choice for removing moisture from the gas.

17. Electropositive character increases down a group in the periodic table.

True

As atomic size increases down a group, the outer electrons are farther from the nucleus and are lost more easily, increasing metallic/electropositive character.

18. Neutralization reactions are always endothermic.

False

Neutralization reactions between acids and bases are classic examples of exothermic reactions, consistently releasing heat energy.

19. Methyl orange indicator turns red or pink in an acidic solution.

True

Methyl orange turns red/pink in solutions with a pH below 3.1, making it a reliable indicator for strong acid titrations.

20. Water becomes temporarily hard due to the presence of dissolved calcium chloride ($CaCl_2$).

False

Calcium chloride causes permanent hardness. Temporary hardness is caused by calcium or magnesium hydrogen trioxocarbonate(IV).

21. Quartz and sand are both structural forms of silicon(IV) oxide ($SiO_2$).

True

Both materials share the same fundamental atomic composition, consisting of a giant covalent network of silicon and oxygen atoms.

22. A solution with a pH of 13 is highly acidic.

False

A pH of 13 indicates a strongly alkaline (basic) solution. Acidic solutions have a pH below 7.

23. Thermosetting plastics cannot be softened or remolded once they are set.

True

During their initial molding, thermosetting polymers form extensive cross-links that burn or decompose rather than melt when reheated.

24. Sulfur(IV) oxide gas forms a white precipitate when passed into barium chloride solution acidified with dilute hydrochloric acid.

False

Barium sulfite ($BaSO_3$) dissolves in hydrochloric acid, so no precipitate forms. Only tetraoxosulfate(VI) ions ($SO_4^{2-}$) form an acid-insoluble white precipitate with $BaCl_2$.

25. One mole of any gas at S.T.P. occupies a volume of 22.4 $\text{dm}^3$.

True

This constant is known as Avogadro's molar volume of gases at standard temperature and pressure.

26. Anhydrous salts contain a specific number of molecules of water of crystallization.

False

Anhydrous means the salt has lost its water of crystallization or contains no water. Salts containing water are called hydrated salts.

27. Steel is an alloy of iron and carbon.

True

Carbon is added to iron in small percentages (usually under 2%) to dramatically improve its tensile strength and hardness.

28. Catalysts speed up a chemical reaction by increasing the activation energy requirement.

False

Catalysts work by providing an alternative reaction pathway that lowers the activation energy, allowing more molecules to react per second.

29. Fused calcium chloride can be used to preserve dry specimens because it is hygroscopic.

True

Hygroscopic substances absorb moisture from the atmosphere without dissolving, keeping the surrounding air in a sealed container dry.

30. According to Boyle's Law, the volume of a gas is directly proportional to its pressure.

False

Boyle's Law states that volume is inversely proportional to pressure ($V \propto 1/P$) at a constant temperature.

31. Chlorine gas bleaches dry litmus paper instantly.

False

Chlorine requires moisture to form oxochlorate(I) acid ($HOCl$), which acts as the real bleaching agent. It cannot bleach dry litmus paper.

32. Carbon(IV) oxide ($CO_2$) gas is highly toxic because it forms a covalent bond with blood hemoglobin.

False

This property describes Carbon(II) oxide ($CO$). $CO_2$ is an asphyxiant at high concentrations but is not a chemical blood poison.

33. Solid ammonium chloride sublimes when heated.

True

Ammonium chloride ($NH_4Cl$) changes directly from a solid phase into a gas (dissociating into $NH_3$ and $HCl$ vapors) upon heating.

34. All alcohols are toxic and unsafe for human consumption.

False

While methanol is highly toxic, ethanol ($C_2H_5OH$) is the specific, non-lethal alcohol found in standard alcoholic beverages.

35. The functional group of an alkene is a carbon-to-carbon double bond ($C=C$).

True

Alkenes are unsaturated hydrocarbons categorized by the presence of at least one reactive double bond.

36. An element with atomic number 11 forms a basic oxide when reacted with oxygen.

True

Atomic number 11 is Sodium, a Group 1 metal. Metals form basic oxides ($Na_2O$) that dissolve in water to produce alkaline solutions ($NaOH$).

37. Saponification involves the reaction of an ester with an acid to produce soap.

False

Saponification requires an alkali (like $NaOH$ or $KOH$), not an acid, to hydrolyze fats/oils into soap and glycerol.

38. Phenolphthalein indicator is colorless in an alkaline medium.

False

Phenolphthalein turns a sharp pink/crimson color in alkaline mediums and is colorless in acidic conditions.

39. Liquid mixtures with overlapping boiling points can be separated perfectly using a simple distillation apparatus.

False

Simple distillation only works when components have a large difference in boiling points. Closely matched liquids require a fractionating column (fractional distillation).

40. Fractional distillation of crude oil is a chemical process that breaks down complex molecules.

False

Distillation is a physical separation process based on boiling points. The chemical process that breaks large molecules down into smaller fragments is known as catalytic cracking.