Structure 1. Models of the particulate nature of matter

1.1 Introduction to the particulate nature of matter

1.2 The nuclear atom

1.3 Electron configurations

1.4 The mole

1.5 Ideal gases

Structure 2. Models of bonding and structure

2.1 The ionic model

2.2 The covalent model

2.3 The metallic model

2.4 From models to materials

Structure 3. Classification of matter

3.1 The periodic table

3.2 Functional groups: Organic compounds

Reactivity 1. What drives chemical reactions?

1.1 Measuring enthalpy changes

1.2 Energy cycles

1.3 Energy from fuels

Reactivity 2. How much, how fast and how far?

2.1 Amount of chemical change

2.2 Rate of chemical change

2.3 Extent of chemical change

Reactivity 3. What are the mechanisms of chemical change?

3.1 Proton transfer reactions

3.2 Electron transfer reactions

3.3 Electron sharing reactions (Radicals)

3.4 Electron-pair sharing reactions

IB Chemistry HL 3.2 Electron transfer reactions Question Bank

[Maximum number: 2]

Hydrogen cyanide, HCN , is a very toxic compound.

(a)

The cyanide ion, $\mathrm{CN}^{-}$ , can form complex ions, such as $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}$ .

[ 2 ]

(i)

Outline, giving a reason, whether $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ is a stronger or weaker oxidizing agent than $\mathrm{Fe}^{3+}$ (aq).

Use $E^{\ominus}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}(\mathrm{aq})+\mathrm{e}^{-} \rightleftharpoons\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}(\mathrm{aq})=+0.37 \mathrm{~V}$ and section 19 of the data booklet.

[ 2 ]

[Maximum number: 1]

Ethane-1,2-diol, $\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$ , has a wide variety of uses including the removal of ice from aircraft and heat transfer in a solar cell.

(a)

Ethane-1,2-diol can be oxidized first to ethanedioic acid, $(\mathrm{COOH})_{2}$ , and then to carbon dioxide and water. Suggest the reagents needed to oxidize ethane-1,2-diol.

[ 1 ]

[Maximum number: 2]

Ethyne, $\mathrm{C}_{2} \mathrm{H}_{2}$ , reacts with oxygen in welding torches.

(a)

Product $\mathbf{B}, \mathrm{CH}_{3} \mathrm{CHO}$ , can also be synthesized from ethanol.

[ 2 ]

(i)

Suggest the reagents and conditions required to ensure a good yield of product B.

Reagents:

Conditions:

[ 2 ]

[Maximum number: 2]

Hydrogen peroxide, $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})$ , releases oxygen gas, $\mathrm{O}_{2}(\mathrm{~g})$ , as it decomposes according to the equation below.

2 \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})

$50.0 \mathrm{~cm}^{3}$ of hydrogen peroxide solution was placed in a boiling tube, and a drop of liquid detergent was added to create a layer of bubbles on the top of the hydrogen peroxide solution as oxygen gas was released. The tube was placed in a water bath at $75^{\circ} \mathrm{C}$ and the height of the bubble layer was measured every thirty seconds. A graph was plotted of the height of the bubble layer against time.

(a)

The decomposition of hydrogen peroxide to form water and oxygen is a redox reaction.

[ 2 ]

(i)

State two half-equations for the decomposition of hydrogen peroxide.

Oxidation:

Reduction:

[ 2 ]

[Maximum number: 1]

A student used the technique of titration to determine the concentration of ascorbic acid $\left(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}\right)$ in a sample of orange juice. Excess potassium iodide, KI(aq), was added to acidified orange juice. The resulting solution was titrated with potassium iodate, $\mathrm{KIO}_{3}(\mathrm{aq})$ , in the presence of starch as an indicator. The end-point of the titration was shown by a blue-black colour.

Step $1 \quad \mathrm{IO}_{3}{ }^{-}(\mathrm{aq})+5 \mathrm{I}^{-}(\mathrm{aq})+6 \mathrm{H}^{+}(\mathrm{aq}) \rightarrow 3 \mathrm{I}_{2}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$

lodine is only slightly soluble in water; but in the presence of excess iodide ions, $\mathrm{I}^{-}(\mathrm{aq})$ , it forms the soluble tri-iodide ion, $\mathrm{I}_{3}{ }^{-}$ (aq).

Step $2 \quad \mathrm{I}_{2}(\mathrm{aq})+\mathrm{I}^{-}(\mathrm{aq}) \rightleftharpoons \mathrm{I}_{3}{ }^{-}(\mathrm{aq})$
Ascorbic acid reacts with tri-iodide ions as follows.

Step $3 \quad \mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}(\mathrm{aq})+\mathrm{I}_{3}{ }^{-}(\mathrm{aq}) \rightarrow \mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{6}(\mathrm{aq})+2 \mathrm{H}^{+}(\mathrm{aq})+3 \mathrm{I}^{-}(\mathrm{aq})$

(a)

(i)

Identify the oxidizing and reducing agents in step 1.

Oxidizing agent:

Reducing agent:

[ 1 ]

[Maximum number: 2]

Iron tablets are often prescribed to patients. The iron in the tablets is commonly present as iron(II) sulfate, $\mathrm{FeSO}_{4}$ .

(a)

This experiment involves the following redox reaction.

5 \mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{MnO}_{4}^{-}(\mathrm{aq})+8 \mathrm{H}^{+}(\mathrm{aq}) \rightarrow 5 \mathrm{Fe}^{3+}(\mathrm{aq})+\mathrm{Mn}^{2+}(\mathrm{aq})+4 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})

[ 1 ]

(i)

Define the term reduction in terms of electrons.

[ 1 ]

(b)

(i)

Following the experiment, the students proposed the following hypothesis:
"Since sulfuric acid is a strong acid, two other strong acids such as nitric acid, $\mathrm{HNO}_{3}(\mathrm{aq})$ or hydrochloric acid, HCl(aq), could also be used in this experiment".

Suggest one problem with this hypothesis.

[ 1 ]

[Maximum number: 1]

An organic compound, A, has the following composition by mass when its only combustion products, carbon dioxide and water, are analysed.

(a)

A can be converted to compound E, which has a higher molecular mass, by heating it under reflux with acidified potassium dichromate(VI), $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ .

Identify one functional group present in E based on this information only.

[ 1 ]

[Maximum number: 2]

3.26 g of iron powder are added to $80.0 \mathrm{~cm}^{3}$ of $0.200 \mathrm{~mol} \mathrm{dm}^{-3}$ copper(II) sulfate solution. The following reaction occurs:

\mathrm{Fe}(\mathrm{~s})+\mathrm{CuSO}_{4}(\mathrm{aq}) \rightarrow \mathrm{FeSO}_{4}(\mathrm{aq})+\mathrm{Cu}(\mathrm{~s})

(a)

A student electrolyzed aqueous iron(II) sulfate, $\mathrm{FeSO}_{4}(\mathrm{aq})$ , using platinum electrodes. State half-equations for the reactions at the electrodes, using section 24 of the data booklet.

Anode (positive electrode):

Cathode (negative electrode):

[ 2 ]

[Maximum number: 1]

Pasteurization is used to eliminate pathogenic bacteria. The concentration of vitamin C was monitored over a period of time in pasteurized and unpasteurized orange juice.

(a)

The concentration of vitamin C (ascorbic acid) can be measured by performing a redox titration using acidified iodate, $\mathrm{IO}_{3}{ }^{-}$ , and iodide ions. Starch reacts with excess iodine once the vitamin C is consumed to produce a dark-blue complex.

Reaction 1: $\mathrm{IO}_{3}{ }^{-}(\mathrm{aq})+5 \mathrm{I}^{-}(\mathrm{aq})+6 \mathrm{H}^{+}(\mathrm{aq}) \rightarrow 3 \mathrm{I}_{2}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})$

Reaction 2: ascorbic acid (aq) $+\mathrm{I}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{I}^{-}(\mathrm{aq})+$ dehydroascorbic acid (aq)

[ 1 ]

(i)

Identify the oxidizing agent in reaction 1 .

[ 1 ]

[Maximum number: 2]

Ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$ , is used as a high nitrogen fertilizer.

(a)

Predict, using the given values, the reaction that would take place at the anode and cathode for the electrolysis of an aqueous solution of ammonium nitrate using graphite electrodes.

Anode:

Cathode:

[ 2 ]

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