Question 1a

Marks: 3

a)

Chlorine reacts with water to form chlorine water via the following equation.

Cl₂ + H₂O → HOCl + HCl

State the oxidation number of chlorine in the following species

Cl₂ …………………..

HOCl ………………….

HCl …………………..

Key Concepts

Deducing Oxidation Numbers

Question 1b

Marks: 1

b)

Chlorine is an oxidising agent.

Define oxidising agent in terms of electrons.

Key Concepts

Oxidizing & reducing agents

Question 1c

Marks: 2

c)

Nitrogen monoxide, NO, is formed when silver metal reduces nitrate ions, NO₃^- , ions in an acidic solution. State the oxidation numbers of nitrogen in NO and NO₃^-.

Key Concepts

Deducing oxidation numbers

Question 1d

Marks: 1

d)

State the half equation for the formation of silver ions, Ag⁺(aq), from silver metal.

Key Concepts

Half equations

Question 2a

Marks: 6

a)

Deduce the oxidation numbers of of the elements in the following species.

S^2- …………………

Sn²⁺…………………

V³⁺…………………

Si …………………

Sb³⁺ …………………

H^- …………………

Key Concepts

Deducing oxidation numbers
Variable Oxidation Numbers

Question 2b

Marks: 3

b)

Oxidation states are sometimes visible in the names of chemicals. Deduce the oxidation numbers of the stated elements in the following species.

Copper in copper(I) oxide ………………..

Iron in iron(III) oxide ………………..

Phosphorus(V) oxide …………………

Key Concepts

Deducing Oxidation Numbers
Variable Oxidation Numbers

Question 2c

Marks: 2

c)

The dichromate(VI) ion, Cr₂O₇^2- (aq) , reacts with sulfite ions, SO₃^2-(aq), as follows.

Cr₂O₇^2- (aq) + 8H⁺ (aq)+ 3SO₃^2- (aq) → 2Cr³⁺ (aq) + 4H₂O (l) + 3SO₄^2- (aq)

i)

State whether the sulfite ions, SO₃^2- (aq), are acting as an oxidising or reducing agent.

ii)

Justify your answer to part (i).

Key Concepts

Identifying oxidizing & reducing agents

Question 2d

Marks: 3

d)

Redox reactions can be identified by either reduction and oxidation occurring or the presence of a reducing agent and an oxidising agent.

i)

Deduce if the reaction between hydrochloric acid and sodium hydroxide is a redox reaction.

HCl + NaOH → NaCl + H₂O

ii)

Justify your answer.

Key Concepts

Identifying oxidizing & reducing agents

Question 3a

Marks: 1

a)

An iron tablet, weighing 1.35 g was dissolved in dilute sulfuric acid. The sample was dissolved in sulfuric acid to oxidise all of the iron to Fe²⁺ ions.

The solution is then titrated with 0.02 mol dm^-3 potassium dichromate, K₂Cr₂O₇, producing Fe³⁺ and Cr³⁺ ions in acidic solution. The titration requires 31.00 cm³of K₂Cr₂O₇ for 1.35 g of the sample.

Balance the following half equations:

Fe²⁺ (aq) → Fe³⁺ (aq) + ………

Cr₂O₇^2-(aq) + 14H⁺(aq) + ……… → …….Cr³⁺(aq) + …...H₂O (l)

Key Concepts

Half equations

Question 3b

Marks: 2

b)

The overall equation for the reaction in part (a) is as follows.

6Fe²⁺ (aq) + Cr₂O₇^2- (aq) + 14H⁺(aq) → 6Fe³⁺ (aq) + 2Cr³⁺ (aq) + 7H₂O (l)

i)

Using the information in part (a), calulate the number of moles of potassium dichromate, K₂Cr₂O₇ used.

ii)

Use your answer to part (b) (i) to determine the number of moles of Fe²⁺ in the sample.

Key Concepts

Redox Titrations

Question 3c

Marks: 2

c)

Using the information in part (a) calculate the mass, in grams, of iron in the original sample.

Key Concepts

Redox Titrations

Question 3d

Marks: 1

d)

Using the information in part (a) and your answer to part (c) calculate the percentage of iron in the original 1.35 g iron tablet.

Key Concepts

Redox Titrations

Question 4a

Marks: 2

a)

Zinc metal will react with copper sulfate solution. State the equation for this reaction.

Key Concepts

The activity series

Question 4b

Marks: 1

b)

Predict the products, if any, of the reaction between lead(IV) oxide and zinc.

Key Concepts

Deducing the feasibility of a redox reaction

Question 4c

Marks: 5

c)

A voltaic cell is made from a half-cell containing a zinc electrode in a solution of zinc nitrate and a half-cell containing a silver electrode in a solution of silver nitrate. Using section 25 in the data booklet, label the following diagram.

Key Concepts

Voltaic cells

Question 4d

Marks: 3

d)

State three differences between a voltaic cell and an electrolytic cells.

Key Concepts

Electrolytic cells
Voltaic cells

Question 5a

Marks: 1

a)

A 500 cm³ sample of lake water was analysed using the Winkler Method. 0.0600 mol dm^-3 sodium thiosulfate solution, Na₂S₂O₃(aq), was titrated against liberated iodine. It was determined that the average titre of Na₂S₂O₃was 19.30 cm³.

Calculate the amount, in moles, of sodium thiosulfate used in the titration.

Key Concepts

The Winkler Method
Winkler Method Calculation

Question 5b

Marks: 1

b)

In the Winkler method 1 mol of O₂ is equivalent to 4 mol of Na₂S₂O₃ Deduce the amount, in moles, of oxygen that has reacted.

[1]

Key Concepts

Winkler Method Calculation

Question 5c

Marks: 2

c)

Use your answer to part (b) and section 6 in your data booklet to calculate the following

The concentration, in mol dm^-3, of oxygen in the water ………………..
The concentration, in g dm^-3, of oxygen in the water …………………

Key Concepts

Winkler Method Calculation

Question 5d

Marks: 3

d)

Define the biological oxygen demand (BOD).

Key Concepts

The Winkler Method

DP IB Chemistry: SL

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9.1 Redox Processes

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