Units 3 & 4 Multiple Choice Questions #2

Calculate the concentration of H⁺ ions in solution if the [OH⁻] = 1.8 x 10⁻⁹ M.

• 3.56 x 10⁻⁶ M

• 4.56 x 10⁻⁶ M

• 5.56 x 10⁻⁶ M

• 6.56 x 10⁻⁶ M

Answer explanation

To find [H⁺], use the water dissociation constant: Kw = [H⁺][OH⁻] = 1.0 x 10⁻¹⁴. Given [OH⁻] = 1.8 x 10⁻⁹ M, [H⁺] = Kw / [OH⁻] = 5.56 x 10⁻⁶ M. Thus, the correct answer is 5.56 x 10⁻⁶ M.

Determine in which of these equations water is acting as a Bronsted-Lowry base.

• H₂O (l) + NH₃ (aq) ⇌ OH⁻ (aq) + NH₄⁺ (aq)

• H₂O (l) + H₂PO₄⁻ (aq) ⇌ H₃O⁺ + PO₄²⁻

• H₂O (l) + HCl (aq) ⇌ OH⁻ (aq) + H₃O⁺ (aq)

• CuSO₄.6H₂O ⇌ NiCl₂ + 6H₂O

Answer explanation

In the equation H₂O (l) + H₂PO₄⁻ (aq) ⇌ H₃O⁺ + PO₄²⁻, water acts as a Bronsted-Lowry base by accepting a proton (H⁺) from H₂PO₄⁻, forming H₃O⁺.

A protein is formed when:

• amino acids are joined by peptide bonds.

• amino acids are joined by glycosidic bonds.

• glucose molecules are joined by peptide bonds.

• glucose molecules are joined by glycosidic bonds

Answer explanation

A protein is formed when amino acids are linked together by peptide bonds, which are specific covalent bonds. The other options incorrectly refer to bonds associated with carbohydrates, not proteins.

Cellulose, starch, and glycogen are all:

• addition polymers of glucose.

• condensation polymers of glucose.

• addition polymers of glycerol.

• condensation polymers of glycerol

Answer explanation

Cellulose, starch, and glycogen are all polysaccharides formed by the condensation reaction of glucose monomers, resulting in glycosidic bonds. Therefore, they are correctly classified as condensation polymers of glucose.

Deduce the oxidation number of S in S₂O₃²⁻.

• +2

• +3

• +4

• +6

Answer explanation

In S₂O₃²⁻, the total oxidation state of oxygen is -6 (3 O x -2). The overall charge is -2, so the total oxidation state of sulfur must be +4 (2 S x +2). Thus, each S has an oxidation number of +2.

In which of the following reactions is the species in bold type acting as an oxidising agent

• Mg + 2H⁺ → Mg²⁺ + H₂

• 2Al + 3Cu → Al³⁺ + 3Cu

• Cl₂ + 2Br^- → 2Cl^- + Br₂

• K → K⁺ + e^-

Answer explanation

In the reaction Mg + 2H⁺ → Mg²⁺ + H₂, the 2H⁺ ions are reduced to H₂, meaning they gain electrons. Therefore, 2H⁺ acts as the oxidising agent.

Which of these compounds is likely to be most soluble in water?

• CH₃CH₂CH₂Cl

• CH₃COCH₃

• CH₃CH₂COOH

• CH₃CH₂CH₃

Answer explanation

CH3CH2COOH (acetic acid) is most soluble in water due to its polar -COOH group, which can form hydrogen bonds with water. The other compounds are less polar and thus less soluble.

Which of the following graphs shows the effect of temperature on rate (velocity) of a typical enzyme-catalysed reaction

• [Graph a]

• [Graph b]

• [Graph c]

• [Graph d]

Answer explanation

Graph c correctly illustrates the effect of temperature on enzyme activity, showing an increase in reaction rate up to an optimal temperature, followed by a decline due to denaturation, which is typical for enzyme-catalyzed reactions.

Which of the following will most readily undergo substitution reactions?

• ethene

• ethyne

• CF₂CF₂

• 1-chloromethane

Answer explanation

1-chloromethane readily undergoes substitution reactions due to the presence of a carbon-chlorine bond, which can be replaced by other groups. In contrast, ethene and ethyne are more likely to undergo addition reactions.

Identify which of the compounds shown below would produce the following IR spectrum.

• hexane

• hexan-1-ol

• hexan-3-one

• 2-methylhexanal

Answer explanation

The IR spectrum of hexan-1-ol shows a strong O-H stretch around 3300 cm-1, characteristic of alcohols. The other compounds lack this feature, making hexan-1-ol the correct choice.