WAEC Chemistry Revision Questions Part 4

 

WAEC Chemistry Revision Questions (True/False) - Part 4

Sharpen your knowledge with the final installment of our WAEC Chemistry review. Evaluate the statements and read the concise explanations.

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1. Soluble salts can be recovered from their solutions by filtration.

False

Filtration only separates insoluble solids from a liquid. Soluble salts must be recovered using crystallization or evaporation to dryness.

2. The element with electronic configuration 2, 8, 8, 1 is a highly reactive metal.

True

This configuration belongs to Potassium (Group 1, Period 4), which readily loses its single valence electron to form a stable ion.

3. Electrovalent bonding involves the sharing of pairs of electrons between atoms.

False

Electrovalent (ionic) bonding involves the transfer of electrons from a metal to a non-metal. Covalent bonding involves the sharing of electrons.

4. Carbon(IV) oxide ($CO_2$) gas supports combustion for most ordinary fires.

False

$CO_2$ does not support combustion, which is why it is widely used in fire extinguishers to smother flames.

5. Direct current (D.C.) is used during electroplating to ensure ions travel in a constant direction.

True

Alternating current (A.C.) would constantly switch electrode polarities, preventing a smooth, continuous layer of metal from depositing.

6. Concentrated tetraoxosulfate(VI) acid turns blue copper(II) sulfate crystals white.

True

Concentrated $H_2SO_4$ is a powerful dehydrating agent that removes the water of crystallization, converting blue hydrated $CuSO_4 \cdot 5H_2O$ into white anhydrous $CuSO_4$.

7. An acid salt contains replaceable hydrogen atoms.

True

Acid salts like $NaHSO_4$ or $NaHCO_3$ still possess ionizable hydrogen atoms that can react with a base.

8. The fractional distillation of liquid air separates nitrogen and oxygen based on their densities.

False

It separates them based on differences in their boiling points. Nitrogen boils off first at -196°C, leaving oxygen behind at -183°C.

9. Homologous series share the same general formula and similar chemical properties.

True

Members of a homologous series (like the alkanes or alkenes) also show a regular gradation in physical properties as molecular mass increases.

10. Bauxite is the main ore of iron.

False

Bauxite is the primary ore of aluminum. Hematite ($Fe_2O_3$) and magnetite ($Fe_3O_4$) are the main ores of iron.

11. Oxidation number increases during an oxidation process.

True

By definition, oxidation is an increase in oxidation number resulting from the loss of electrons.

12. Isotopes have the same mass number but different atomic numbers.

False

Isotopes have the same atomic number (same number of protons) but different mass numbers (different number of neutrons).

13. Ethene undergoes substitution reactions with chlorine in the presence of sunlight.

False

Ethene is an unsaturated alkene and undergoes rapid addition reactions at room temperature without requiring sunlight. Alkanes undergo substitution in sunlight.

14. The catalyst used in the industrial Contact Process for making $H_2SO_4$ is vanadium(V) oxide.

True

Vanadium(V) oxide ($V_2O_5$) is favored because it is cheaper and less easily poisoned by impurities than platinum.

15. In a reversible exothermic reaction, lowering the temperature increases the yield of the products.

True

According to Le Chatelier's principle, cooling favors the exothermic direction, shifting the equilibrium to the right to produce more heat and more product.

16. Hydrogen sulfide ($H_2S$) gas has a smell resembling rotten eggs.

True

This highly characteristic offensive odor is a key qualitative observation for identifying $H_2S$ gas in laboratory practicals.

17. Group 7 elements (halogens) become more reactive as you go down the group.

False

Halogens react by gaining an electron. As atomic radius increases down the group, the nuclear pull weakens, making them less reactive (Fluorine is the most reactive).

18. A physical change is easily reversible and forms no new substance.

True

Processes like melting ice, boiling water, or dissolving salt in water are examples of physical changes.

19. Litmus paper remains blue when dipped into a neutral solution.

True

Neutral solutions (pH 7) do not change the color of litmus. Blue litmus stays blue, and red litmus stays red.

20. Hard water forms a lot of lather immediately when mixed with synthetic detergents.

True

While hard water forms scum with ordinary soap, it lathers easily with synthetic (soapless) detergents because their calcium and magnesium salts are water-soluble.

21. The chemical formula for sand is $CaCO_3$.

False

Sand is primarily silicon(IV) oxide ($SiO_2$). $CaCO_3$ is the formula for limestone, chalk, or marble.

22. The pH of a 0.1 $\text{mol/dm}^3$ solution of hydrochloric acid is 1.

True

Calculated using $\text{pH} = -\log[H^+]$. Since $HCl$ is a strong monobasic acid, $-\log(0.1) = 1$.

23. Thermoplastics can be recycled easily.

True

Thermoplastics soften on heating and harden on cooling repeatedly, meaning they can be shredded, melted down, and remolded into new products.

24. Nitrogen gas turns lime water milky.

False

Carbon(IV) oxide ($CO_2$) gas turns lime water milky. Nitrogen gas has no effect on lime water.

25. Standard temperature value for gas behavior calculations is 273 Kelvin.

True

0°C is equal to 273 K, which is the standard baseline reference point for gas laws (STP).

26. Water of crystallization is the water chemically combined into the crystalline structure of some salts.

True

It is responsible for the shape and sometimes the color of the crystal lattice, as seen in crystalline copper(II) sulfate ($CuSO_4 \cdot 5H_2O$).

27. Brass is an alloy of copper and tin.

False

Brass is an alloy of copper and zinc. Bronze is the alloy made from copper and tin.

28. Enzymes are biological catalysts that are highly specific in their actions.

True

Enzymes only catalyze particular substrates due to their specific "lock-and-key" active site conformations.

29. Hydrochloric acid ($HCl$) is used as a drying agent in the laboratory.

False

$HCl$ is a highly volatile acid and cannot act as a drying agent. Common laboratory desiccant/drying agents include fused $CaCl_2$, silica gel, and conc. $H_2SO_4$.

30. Boyle's Law applies to systems where temperature is allowed to vary.

False

Boyle's Law strictly requires the temperature of the fixed mass of gas to remain constant.

31. Chlorine gas acts as an oxidizing agent when it bleaches moist colored materials.

True

Chlorine reacts with water to release nascent oxygen, which oxidizes the colored dye molecules into colorless compounds.

32. Carbon(II) oxide ($CO$) is a highly poisonous gas because it forms stable carboxyhemoglobin in blood.

True

It binds irreversibly to hemoglobin, preventing red blood cells from transporting vital oxygen throughout the body.

33. Solid carbon(IV) oxide is commonly known as dry ice.

True

It is named "dry ice" because it sublimes directly from a solid state into a gas without melting into a liquid residue.

34. Alkanols are completely insoluble in water.

False

Lower alkanols like methanol and ethanol are completely miscible in water due to their ability to form hydrogen bonds with water molecules. Solubility only drops as the carbon chain grows longer.

35. The functional group of an alkyne is a carbon-to-carbon triple bond ($C \equiv C$).

True

This triple unsaturated bond defines the alkyne series, with ethyne ($C_2H_2$) being the simplest member.

36. The structural unit of an ionic crystal lattice is the molecule.

False

The fundamental structural units of an ionic crystal lattice are positive cations and negative anions held by electrostatic forces.

37. Soap is prepared by heating a mixture of vegetable oil and a strong alkali.

True

This alkaline hydrolysis of fats/oils is called saponification, yielding soap (sodium salts of fatty acids) and glycerol.

38. Hydrochloric acid ($HCl$) turns phenolphthalein indicator pink.

False

Phenolphthalein remains completely colorless in acidic solutions. It only turns pink in basic (alkaline) environments.

39. Direct separation of immiscible liquids can be achieved using a separating funnel.

True

Because immiscible liquids separate out into distinct layers based on their densities (like oil sitting on water), the lower layer can be drained off cleanly.

40. Fractional crystallization separates solutes based on their varying solubilities at different temperatures.

True

As a hot mixture solution cools down, the solute with lower solubility crystallizes out of the liquid matrix first, allowing separation.