Cuestionario: Chemistry Revision Map — 33 preguntas

1. How does a weak acid differ from a strong acid in aqueous solution?

A. A weak acid dissociates partially, while a strong acid dissociates completely

B. A weak acid dissociates completely, while a strong acid reaches equilibrium

C. A weak acid donates two protons, while a strong acid donates one

D. A weak acid cannot form ions, while a strong acid forms ions reversibly

Answer: (A)

Explicación

A strong acid dissociates completely in solution, whereas a weak acid dissociates only partially and establishes an equilibrium.

2. How many protons can a diprotic acid donate per molecule?

A. Two protons

B. One proton

C. An unlimited number of protons

D. Three protons

Answer: (A)

Explicación

A diprotic acid can donate two H⁺ ions, whereas a monoprotic acid can donate one.

3. Which expression correctly defines the acid dissociation constant for HA?

A. K_a = [A⁻]/([H⁺][HA])

B. K_a = [H⁺][HA]/[A⁻]

C. K_a = [HA]/([H⁺][A⁻])

D. K_a = [H⁺][A⁻]/[HA]

Answer: (D)

Explicación

For HA ⇌ H⁺ + A⁻, the acid dissociation constant is K_a = [H⁺][A⁻]/[HA].

4. A 1:1 acid–base titration reaches its equivalence point when which condition is satisfied?

A. The acid and base concentrations are equal

B. The acid and base volumes are equal

C. The amounts of acid and base are equal, with volumes expressed in litres

D. The pH reaches exactly 7 regardless of the reactants

Answer: (C)

Explicación

At the equivalence point of a 1:1 titration, the acid and base amounts are equal. Volumes used in calculations must be converted to litres.

5. Where does oxidation occur and where does reduction occur in an electrochemical cell?

A. Oxidation occurs at the anode, and reduction occurs at the cathode

B. Oxidation and reduction both occur at the cathode

C. Oxidation and reduction both occur at the anode

D. Oxidation occurs at the cathode, and reduction occurs at the anode

Answer: (A)

Explicación

Oxidation, which involves loss of electrons, occurs at the anode. Reduction, which involves gain of electrons, occurs at the cathode.

6. What are the charges of the anode and cathode in a galvanic cell?

A. The anode is negative, and the cathode is positive

B. Both electrodes are positive

C. Both electrodes are negative

D. The anode is positive, and the cathode is negative

Answer: (A)

Explicación

In a galvanic cell, oxidation at the anode produces electrons, making the anode negative, while the cathode is positive and receives electrons.

7. In a galvanic cell, which direction do electrons flow and how do salt-bridge ions migrate?

A. Electrons flow from cathode to anode; both ions move toward the anode

B. Electrons flow from anode to cathode; both ions move toward the cathode

C. Electrons flow from anode to cathode; anions move to anode and cations to cathode

D. Electrons flow from cathode to anode; anions move to cathode and cations to anode

Answer: (C)

Explicación

Electrons travel from the anode to the cathode. Salt-bridge anions migrate to the anode, while cations migrate to the cathode.

8. During electrolysis of molten sodium chloride, what occurs at the cathode?

A. Cl⁻ is reduced to chlorine gas

B. Cl⁻ is oxidised to sodium metal

C. Na⁺ is reduced to sodium metal

D. Na⁺ is oxidised to sodium metal

Answer: (C)

Explicación

At the cathode, Na⁺ gains electrons and is reduced to sodium. Chloride ions are oxidised to chlorine at the anode.

9. What happens to an equilibrium when a reactant is added?

A. It shifts toward the reactants to consume added product

B. It shifts toward whichever side has more gas particles

C. It remains unchanged because concentrations do not affect equilibrium

D. It shifts toward the products to consume the added reactant

Answer: (D)

Explicación

Adding a reactant causes the equilibrium to shift toward the products, consuming some of the added reactant.

10. For a gaseous equilibrium, what is the effect of increasing pressure?

A. The equilibrium shifts toward the side with fewer gas particles

B. The equilibrium constant necessarily becomes smaller

C. The equilibrium shifts toward the side with more gas particles

D. The equilibrium shifts toward the side with more liquid particles

Answer: (A)

Explicación

Increasing pressure favours the direction containing fewer gas particles. Non-gaseous species are not counted when comparing gas-particle numbers.

11. What direction does an equilibrium favour when the temperature is increased?

A. The exothermic direction

B. The endothermic direction

C. The direction with the larger equilibrium constant at the original temperature

D. The direction with fewer reactant molecules

Answer: (B)

Explicación

Increasing temperature favours the endothermic direction because that direction absorbs added heat.

12. What does a value of K_c greater than 1 indicate?

A. The reaction cannot reach equilibrium

B. Reactants and products have equal concentrations

C. Products are favoured at equilibrium

D. Reactants are favoured at equilibrium

Answer: (C)

Explicación

K_c is written as products divided by reactants, with concentrations raised to their stoichiometric coefficients. A value greater than 1 indicates that products are favoured.

13. Which functional group identifies an aldehyde rather than a ketone?

A. A terminal –CHO group

B. A –COOH group

C. A –C≡N group

D. An internal >C=O group

Answer: (A)

Explicación

An aldehyde contains the –CHO functional group, whereas a ketone contains an internal >C=O group.

14. What happens when an alkene reacts with bromine?

A. A nitrile group is reduced to an amine

B. The carbon chain undergoes substitution

C. The alcohol group is oxidised

D. Bromine adds across the C=C bond

Answer: (D)

Explicación

Bromine reacts with an alkene by addition across its carbon–carbon double bond.

15. What is the oxidation pathway of a primary alcohol under progressively stronger oxidation conditions?

A. Alcohol to aldehyde to carboxylic acid

B. Alcohol to nitrile to amine

C. Alcohol to ester to alkene

D. Alcohol to ketone to carboxylic acid

Answer: (A)

Explicación

A primary alcohol first oxidises to an aldehyde and can then oxidise further to a carboxylic acid.

16. What product is formed when a nitrile is reduced?

A. A ketone

B. An ester

C. An amine

D. An aldehyde

Answer: (C)

Explicación

Reduction of a nitrile produces an amine; oxidation of an alcohol is the process associated with forming carbonyl compounds.

17. Which structure represents an ester functional group?

A. R–C≡N

B. R–COO–R

C. R–NH₂

D. R–OH

Answer: (B)

Explicación

An ester contains the functional group R–COO–R, with a carbonyl group bonded to an oxygen-containing carbon group.

18. Two compounds have the same molecular formula but different atom-to-atom connectivity. What type of isomerism do they exhibit?

A. Structural isomerism

B. E/Z isomerism

C. Conformational isomerism

D. Optical isomerism

Answer: (A)

Explicación

Structural isomers share a molecular formula but differ in connectivity. E/Z isomers instead differ in spatial arrangement around a C=C bond.

19. Which infrared absorption most strongly indicates an alcohol O–H group?

A. A broad peak at 3200–3600 cm⁻¹

B. A peak at 1600–1680 cm⁻¹

C. A strong peak near 1700 cm⁻¹

D. A very broad peak at 2500–3000 cm⁻¹

Answer: (A)

Explicación

An alcohol O–H bond gives a broad absorption at 3200–3600 cm⁻¹. The very broad 2500–3000 cm⁻¹ absorption is characteristic of a carboxylic-acid O–H group.

20. An infrared spectrum contains a strong peak near 1700 cm⁻¹ and a very broad peak from 2500–3000 cm⁻¹. Which functional group is indicated?

A. An alcohol

B. An alkene

C. A nitrile

D. A carboxylic acid

Answer: (D)

Explicación

The strong peak near 1700 cm⁻¹ indicates C=O, while the very broad 2500–3000 cm⁻¹ peak indicates carboxylic-acid O–H, identifying a carboxylic acid.

21. What does the molecular ion peak M⁺ represent in a mass spectrum?

A. The infrared absorption of a carbonyl group

B. The lowest-mass fragment ion

C. The highest molecular peak

D. The most intense isotope peak only

Answer: (C)

Explicación

The molecular ion M⁺ is the highest molecular peak in the mass spectrum and corresponds to the ionised molecule.

22. What is the net charge of an amino acid when the pH is below its isoelectric point, pI?

A. Neutral

B. Positive

C. Alternating between positive and negative

D. Negative

Answer: (B)

Explicación

An amino acid is positive when pH < pI. It is neutral at pH = pI and negative when pH > pI.

23. During electrophoresis, in which direction does a negatively charged amino acid move?

A. Toward the negative electrode

B. It remains stationary regardless of its charge

C. Toward the midpoint between the electrodes

D. Toward the positive electrode

Answer: (D)

Explicación

Negative ions are attracted to the positive electrode, so a negatively charged amino acid moves toward the positive electrode.

24. Which ranking correctly compares the relative strengths of intermolecular forces?

A. Hydrogen bonding > dispersion forces > dipole–dipole forces

B. Dispersion forces > dipole–dipole forces > hydrogen bonding

C. Dipole–dipole forces > hydrogen bonding > dispersion forces

D. Hydrogen bonding > dipole–dipole forces > dispersion forces

Answer: (D)

Explicación

The relative strength follows the order hydrogen bonding > dipole–dipole forces > dispersion forces.

25. Which structural change would generally increase the water solubility of an organic molecule?

A. Adding a longer hydrocarbon chain

B. Replacing an NH₂ group with a hydrocarbon group

C. Adding an OH group

D. Removing a COOH group

Answer: (C)

Explicación

OH, COOH, and NH₂ groups increase solubility by forming hydrogen bonds with water, whereas longer hydrocarbon chains reduce solubility.

26. Which ion moves toward the cathode in an acidic hydrogen fuel cell?

A. Hydroxide radicals

B. H⁺

C. Electrons

D. OH⁻

Answer: (B)

Explicación

In an acidic hydrogen fuel cell, H⁺ ions move toward the cathode. In an alkaline cell, OH⁻ ions move toward the anode.

27. How are charge carriers distributed in a hydrogen fuel cell?

A. Electrons travel through the electrolyte, while ions travel through the external circuit

B. Electrons travel through the external circuit, while ions travel through the electrolyte

C. Both electrons and ions travel through the external circuit

D. Both electrons and ions travel through the electrolyte

Answer: (B)

Explicación

Electrons pass through the external circuit, producing electrical current, while ions move through the electrolyte.

28. A reaction uses reactants with a combined relative formula mass of 250 and produces a desired product with a relative formula mass of 150. What is the atom economy?

A. 100%

B. 60%

C. 166.7%

D. 40%

Answer: (B)

Explicación

Atom economy = (Mr of desired product ÷ Mr of all reactants) × 100 = (150 ÷ 250) × 100 = 60%. Higher atom economy is preferable.

29. Which process has the better environmental performance based on its E-factor?

A. A process with an E-factor of 0.8

B. A process with an E-factor of 1.5

C. A process with an E-factor of 25

D. A process with an E-factor of 12

Answer: (A)

Explicación

The E-factor is waste divided by product, so a lower value indicates less waste and is environmentally preferable.

30. Which expression correctly calculates pH and pKa, respectively?

A. pH = [H⁺] ÷ log and pKa = Kₐ ÷ log

B. pH = log[H⁺] and pKa = log Kₐ

C. pH = −log Kₐ and pKa = −log[H⁺]

D. pH = −log[H⁺] and pKa = −log Kₐ

Answer: (D)

Explicación

pH is calculated using −log[H⁺], whereas pKa is calculated using −log Kₐ.

31. What should a complete response to a Calculate question include?

A. One brief identification without numerical work

B. A formula, substituted values, and an answer with units

C. A numerical answer without working

D. A prediction, evidence, and chemical reasoning

Answer: (B)

Explicación

A Calculate response should show the formula, substitute the values, and report the result with appropriate units.

32. Which elements are required in a strong Justify response?

A. A formula, substituted values, and units

B. A claim, relevant data, and chemical reasoning

C. A prediction, a reason, and a numerical estimate

D. A definition, an example, and a concluding question

Answer: (B)

Explicación

A Justify response must connect a claim to relevant data and explain the claim using chemical reasoning.

33. What is required for a three-mark short response?

A. A formula, numerical substitution, and units

B. An answer and one relevant reason

C. A prediction, chemical reason, and supporting evidence or data

D. A claim without evidence or chemical explanation

Answer: (C)

Explicación

A three-mark response requires a prediction, a chemical reason, and evidence or data. A two-mark response requires an answer and a reason.