Module 17a Oxidation And Reduction Ii j1b25

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

Change of Fe2+ ion → Fe3+ and Fe3+ → Fe2+

1. Complete the table for the reaction that take place in the test tubes below. Change of of Fe2+ ion → Fe3

Change of and Fe3+ → Fe2+

Bromine water

Iron(III) chloride solution solution

Iron(II) sulphate solution

zinc

Observation Half-equation oxidation Half equation reduction Overall equation Confirmatory test

1

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

2.

Bromine water

Iron(II) sulphate solution Diagram 1 A few drops of bromine water is added into iron(II) sulphate solution. The mixture is shaken and heated slowly as shown in diagram 1. a) Write the half equation for the i) oxidation reaction. : ………………………………………………………………. ii) reduction reaction.

: ……………………………………………………………….

b) Write the overall ionic equation for this redox reaction. ………………………………………………………………………………………………………….. c) State the substance that is oxidized and the substance that is reduced. i) substance that is oxidized : …………………………………………… ii) substance that is reduced : …………………………………………… d) What is the oxidising agent in this reaction? ………………………………………………………………………………………………………….. e) What is the reducing agent in this reaction? ………………………………………………………………………………………………………….. f) State the observation occur when sodium hydroxide solution is added into the mixture. ………………………………………………………………………………………………………….. g) Name the product that is formed in (h) . …………………………………………………………………………………………………………..

2

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

3. Excess of zinc is added into iron(III) chloride solution. The mixture is then heated slowly.

Iron(III) chloride solution Zinc a) Write the half equation for i) oxidation reaction : ………………………………………………………… ii) reduction reaction : ………………………………………………………… b) Write the overall ionic equation for this redox reaction. c) State the substance that is oxidized and the substance that is reduced. Substance that is oxidized : ……………………………………………………. Substance that is reduced : ……………………………………………………. d) Name the oxidising agent and the reducing agent in this reaction. Oxidising agent : ……………………………………………………………. Reducing agent : ……………………………………………………………. e) State the observation occur when sodium hydroxide solution is added into the mixture. f) Name the product that is formed in (h) g) Name one other substance that can replace zinc granule.

Rusting / corrosion of iron 1. Rusting occur in the presence of water droplets on the surface of iron metal and oxygen in air . The centre of water droplet serves as …………….. , where iron metal undergoes .................... . Iron .......................... electrons and change into........................... . 2. Oxidation half equation:

Fe(aq)

................................................................................

The electrons released travel through ............................... to the edge of the water droplet where there is plenty of dissolved oxygen.

3

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

The iron surface at the surrounding of water droplet acts as……… ….. . The electrons are received by the dissolved ……………………. . Oxygen is reduced into …………….. . 3. Reduction half equation : O2(g) + .................. + .................. → .......................... …………..…… is then oxidised into …………………… in air to form brown solid known as rust. The ..... ions and the ............ ions combine to form green solid, ………………………….. . Ionic equation : Fe2+(aq) + 2OH- → ......................... Chemical equation : ………………………………………………………………. .

.......................... is then rapidly oxidized by oxygen into ........................ to form brown solid known at rust. Fe(OH)2

Fe2O.2H2O

4. Diagram 1 shows a series of experiments A, B and C to investigate the effect of other metals on the rusting process of iron.

Iron nail

Iron nail

Magnesium ribbon

Copper strip

Agarl + Potassium hexacynoferrate(III) solution + Phenolphtalein

Test tube A B

Metal pairing Iron nail only

Intensity of dark blue spot A few number of dark blue spot No dark blue spot

Intensity of the pink colour. None

Iron nail and Very high magnesium ribbon C Iron nail and copper Many dark blue spot None strip a) Write the formula of the metal ion that is formed when iron nail rusts. ………………………………………………………………………………………………………….. b) Write the ionic equation of the rusting process. …………………………………………………………………………………………………………..

4

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

c) Name the type of reaction occurs during the rusting of iron. ………………………………………………………………………………………………………….. d) Why does potassium hexacynoferrate(III) solution used in this investigation? ………………………………………………………………………………………………………….. e) Based on the observation, which test tube shows that rusting has not occured? ………………………………………………………………………………………………………….. f) Name the metal that can prevent rusting of iron. Explain your answer. ………………………………………………………………………………………………………….. ………………………………………………………………………………………………………….. g) Name the gas that is produced in this experiment. ………………………………………………………………………………………………………….. h) Name the ion that causes the pink colour to form in the mixture. ………………………………………………………………………………………………………….. Electrolytic and chemical cell Electrolytic cell 1. An electrolytic cell is prepared as shown in diagram 2 by using carbon electrodes that are immersed in copper(II) sulphate solution 0.1 moldm-3 .

A

Carbon electrodes

Copper(II) sulphate solution

a) State one observation that occur at i) anode : ii) cathode : b) Name the product that is formed at i) anode

:

ii) cathode : c) Write the half equation of anode and cathode.

5

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

i) anode : ii) cathode : d) Determine the type of reactions that occur at anode and cathode. i) anode : ii) cathode : e) State the electron transfer in this experiment. f) Determine the substance that acts as i) oxidising agent : ii) reducing agent : g) Write the ionic equation for the experiment. h) Calculate the oxidation state of sulphur in copper(II) sulphate solution.

Chemical cell A Daniel cell is prepared as shown in diagram 3. Zinc plate and copper plate are dipped into zinc sulphate solution and copper(II) sulphate solution respectively. The zinc and copper plate is connected to an ammeter with connecting wires. The solutions are separated by porous pot.

V

Porous pot berliang

Zinc plate

Copper plate Zinc sulphate solution

Copper(II) sulphate solution

a) Which electrode is the positive terminal? b) State the observations at the i) negative terminal :

6

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

ii) positive terminal : c) Determine the products at the i) negative terminal : ii) positive terminal : d) Write the half equation for the reactions that take place at the i) negative terminal : ii) positive terminal : e) Determine the type of reaction at the i) negative terminal : ii) positive terminal : f) Write the ionic equation for the reaction in the above chemical cell. g) Name the substance that acts as the reducing agent h) State what happen to the ammeter reading if zinc plate and zinc sulphate solution are replaced with magnesium ribbon and magnesium sulphate solution?

Transfer of electron at a distance 1. Figure 1 shows the set-up apparatus to investigate redox reaction between potassium iodide solution and chlorine water.

G

M

N

Chlorine water

Potassium iodide solution

Dilute sulphuric acid

a) What is the function of i) the galvanometer

7

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

ii) the dilute sulphuric acid solution b) What is expected to be observed around electrode M after ½ hour the experiment has taken place? c) Suggest a test to identify the product formed around electrode M.

d) In the above experiment, name the substance that undergoes i) reduction : ii) oxidation : e) Write the ionic equation for the reaction that occurs in this experiment. f) Draw the direction of electrons flow via the external circuit. g) Name one substance that can replace chlorine water in order to get the same products at electrode M. h) If potassium iodide is replaced with iron(II) sulphate solution, what will be observed at electrode M. Explain your answer.

2. a) The following are the formulae of two compounds.

Al2O3

PbO2

i) Based on the two formulae, state the oxidation number for aluminium and lead. …………..…………………………………………………………………………………….. ii) Name both compounds based on the IUPAC nomenclature system. …..…………………………………………………………………………………………….. iii) Explain the difference between the names of the two compounds based on the IUPAC nomenclature system. …….…………………………………………………………………………………………….. …….……………………………………………………………………………………………..

8

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

b) Diagram 1 shows the set-up of apparatus for an experiment to investigate electron transfer at a distance.

G

Carbon electrode (negative terminal)

Carbon electrode (positive terminal)

Acidified potassium dichromate(VI) solution, K2Cr2O7

Iron(II) sulphate solution, FeSO4

Dilute sulphuric acid, H2SO4

i) Name the oxidising agent in the experiment. …………………………………………………………………………………………………….. ii) Write the half equation for the reaction that occur at the negative and positive terminals. …………………………………………………………………………………………………….. iii) Based on your answer in 2(b)(ii), describe the oxidation and reduction process in of the electron transfer that occurs at the negative and positive terminals. State also the changes that can be observed after 10 minutes.

9

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

Reactivity Series of Metals Figure 1 shows an experiment to investigate the reactivity of metals P, Q and R with oxygen. P

Q

R

Heat

Hydrogen peroxide

Manganese(IV) oxide

The observations of the experiment are shown in Table 1. Metal P Q R

Observation Burns brightly and produces a yellow powder when hot and becomes white when cooled. Burns with clear luminous flame and produces white powder Glows faintly. The residue is black

a) State the variables involved in this experiment i) manipulated variable : ii) responding variable : iii) constant variable : b) Write the chemical equation for the decomposition of hydrogen peroxide. c) State the function of manganese(IV) oxide in this experiment. d) Identify metal P and metal Q. i) metal P : ii) metal Q : e) Chemical formula of R oxide is RO. This oxide can be reduced by hydrogen gas to form metal R. i) Draw the set-up of apparatus used to conduct the experiment

10

TUISYEN IBNU SINA

CHEMISTRY MODULE 17 OXIDATION AND REDUCTION

ii) Write the chemical equation for the reaction between RO and hydrogen gas. iii)) Name the oxidising agent and the reducing agent in this experiment. Oxidising agent : Reducing agent : f) Figure 1 shows an experiment to determine the reactivity of metals. Carbon powder is mixed with lead(II) oxide and the mixture is heated strongly. The experiment is repeated with zinc oxide and iron(II) oxide.

Mixture of substances ribbon

Crucible

Bunsen burner

The result of the experiment is shown in Table 1. Metal oxide Lead(II) oxide Zinc oxide Iron(II) oxide

Tripod stand

Observation Bright embers No change Embers

ii) Based on the observation, arrange lead, zinc and iron according to the reactivity of the metals in decreasing order.

……………………………………………………………………………………………..

11