SDSMT - Exam 3 - Redox Chemistry

What is the oxidizing agent in the combustion of methanol (CH₃OH)?

• CO₂

• O₂

• CH₃OH

• H₂O

• No oxidizing agent

Answer explanation

In the combustion of methanol (CH3OH), oxygen (O2) acts as the oxidizing agent. During this reaction, methanol is oxidized to produce carbon dioxide and water, while oxygen is reduced. Therefore, the correct answer is O2.

Tags

Redox

Reaction Types

Combustion

What precipitate forms when mixing copper(II) sulfate and sodium nitrate?

• no precipitate forms

• sodium sulfate

• copper(III) nitrate

• copper(I) nitrate

• copper (II) nitrate

Answer explanation

When copper(II) sulfate and sodium nitrate are mixed together, they undergo a double displacement reaction. However, all the products of this reaction, which are copper(II) nitrate and sodium sulfate, are soluble in water. Therefore, no precipitate forms in this reaction, making 'no precipitate forms' the correct answer.

Tags

Solubility Rules

When Mg(OH)₂ reacts with H₂SO₄ what are the products?

• MgO and H₂SO₄

• MgSO₄ and H₂O

• MgSO₄ and SO₂

• Mg(OH)₂ and H₂SO₄

• No reaction

Answer explanation

The question asks about the reaction between Mg(OH)2 and H2SO4. The correct answer is MgSO4 and H2O. This is because when a base (Mg(OH)2) reacts with an acid (H2SO4), it forms a salt (MgSO4) and water (H2O). This is a typical acid-base reaction.

Tags

Reaction Types

Neutralization

In the following reaction, which element in what species is reduced?

Zn (s) + 2 HCl (aq) → ZnCl₂ (aq) + H₂ (g)

• H in HCl

• Zn²⁺ in ZnCl₂

• Cl in HCl

• Zn

• This is not a redox reaction.

Answer explanation

In the given reaction, Zn is oxidized to Zn2+ and H+ in HCl is reduced to H2. The reduction process involves the gain of electrons. Therefore, the element that is reduced is Hydrogen in HCl. This is why the correct answer is 'H in HCl'.

Tags

Redox

Oxidation Numbers

What is the oxidation number of Cr in a dichromate anion, Cr₂O₇²^-?

• +5

• +4

• +2

• +6

• No oxidizing agent

Answer explanation

The oxidation number of Cr in a dichromate anion, Cr2O7²-, is +6. This is determined by the rule that the sum of the oxidation numbers of all atoms in a molecule or ion equals its charge. In this case, the 7 oxygen atoms each have an oxidation number of -2, totaling -14. The total charge of the ion is -2, so the sum of the oxidation numbers of the 2 chromium atoms is +12, making each Cr atom +6.

Tags

Oxidation Numbers

Which one of the following is the correct dissociation equation for Na₂SO₄?

• Na₂SO₄(s) → 2Na⁺ (aq) + S⁶⁺(aq) +4O^2-(aq)

• Na₂SO₄(s) → Na⁺ (aq) + SO₄²-(aq)

• Na₂SO₄(s) → 2Na⁺ (aq) + SO4²^-(aq)

• 2Na⁺ (aq) + SO4²^-(aq) → Na₂SO₄(s)

• No Reaction

Answer explanation

The correct dissociation equation for Na2SO4 is Na2SO4(s) → 2Na+ (aq) + SO4²-(aq). This is because when sodium sulfate (Na2SO4) dissociates in water, it separates into 2 sodium ions (Na+) and one sulfate ion (SO4²-). The other options either do not correctly represent this dissociation or suggest that there is no reaction, which is incorrect.

Tags

Solubility Rules

Electrolytes

Which one of the following statements is correct about the reaction below?

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

• H⁺ is the reducing agent because it loses electrons.

• Mg is oxidizing agent because it loses electrons.

• The reaction is not a redox reaction.

• Cl^- is the reducing agent because is it an ion.

• H⁺ is the oxidizing agent because it gains electrons.

Answer explanation

In the given reaction, Mg is the reducing agent because it loses electrons. This is a redox reaction where Mg is oxidized to Mg2+ by losing two electrons. These electrons are gained by H+ ions, which are reduced to H2 gas. Therefore, the statement 'Mg is the oxidizing agent because it loses electrons.' is incorrect. The correct statement is 'H+ is the oxidizing agent because it gains electrons.'

Tags

Redox

Oxidation Numbers

The ions formed when C₆H₁₂O₆ (glucose) dissociates in water are

• No ions form, as C₆H₁₂O₆ does not dissociate

• C₆H₁₁O₆ and H⁺

• C₆H₁₂²⁺and O²^-

• C^4-, H⁺, and O^2-

• C₆H₁₂O₅⁺ and OH^-

Answer explanation

The correct answer is that no ions form when C6H12O6 (glucose) dissociates in water. This is because glucose is a covalent compound, not an ionic one. In water, it dissolves by breaking into its individual molecules, but these molecules do not break down into ions.

Tags

Solubility Rules

Which one of the following is a neutralization reaction?

• CaCO₃ (s) + 2HCl(aq) → CaCl₂(aq) + CO₂(g) + H₂O(l)

• HClO₄(aq) + NaOH(aq) → NaClO₄(aq) + H₂O(l)

• Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)

• Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

• 2NaOH(aq) +MgCl₂(aq)

  →

  2NaCl(aq) +Mg(OH)₂(s)

Answer explanation

The correct answer is HClO4(aq) + NaOH(aq) → NaClO4(aq) + H2O(l). This is a neutralization reaction because it involves an acid (HClO4) and a base (NaOH) reacting to form a salt (NaClO4) and water (H2O). Neutralization reactions always produce a salt and water.

Tags

Reaction Types

Neutralization

After balancing of the equation for the following reaction in basic solution,

MnO₄ (aq) + PO₃^3-(aq) → MnO₂(s) + PO₄^3-(aq)

what is the sum of ALL the coefficients in the equation?

• 10

• 7

• 4

• 16

• 13

Answer explanation

Tags

Redox

Balancing Eqns.