73

Transition elementsTransition elements

• Transition elements are metalsand have typical metallic properties. They:– conduct heat– are shiny– conduct electricity– are sonorous (ring when struck)– are malleable– are ductile.

• Copper and iron are examples of transition elements.

• A compound that contains a transition element is often coloured:– copper compounds are blue– iron(II) compounds are pale green– iron(III) compounds are orange/brown.

• A transition element and its compounds are often catalysts:– iron is used in the Haber process to make ammonia, which is used in fertilisers– nickel is used to harden the oils in the manufacture of margarine.

G–E

D–C

Thermal decompositionG–E

D–C

D–C

Grades

1 What are the symbols for copper and nickel?

2 What colour are iron(III) compounds?

3 What’s a precipitation reaction?

4 There’s a difference between Fe2+ ions and Fe3+ ions.How would you show this using sodium hydroxide.

Questions

Sodium hydroxide solution

72

1 Which electrode is the positive electrode?

2 The ratio of hydrogen gas to oxygen gas madeduring the electrolysis of water is 2:1. Explain why.

ElectrolysisConducting liquids

The electrolysis of dilute sulphuric acid

Grades

G–E

D–C

3 What’s the mineral from which aluminium isextracted?

4 What happens to the anodes during the processof electrolysis of aluminium?

Questions

C3 T

HE

PE

RIO

DIC

TA

BL

EC

3 T

HE

PE

RIO

DIC

TA

BL

E

• Electrolysis is the decomposition of a liquid using electricity. During electrolysis:– the electrolyte is a liquid that conducts electricity– the anode is the positive electrode– the cathode is the negative electrode– anions are negative ions attracted to the anode– cations are positive ions attracted to the cathode.

• The key features of the electrolysis of dilute sulphuric acid are:– the electrolyte is a dilute solution of sulphuric acid– two electrodes are connected to a dc source of electric current,

between 6 V and 12 V, and placed into the electrolyte– the electrode connected to the negative terminal is the cathode– the electrode connected to the positive terminal is the anode.

• When the current is switched on, bubbles of gas appear at both electrodes. Water splits into two ions: H+ is the positive ion and OH– is the negative ion.– H+ is attracted to the negative cathode and discharged as hydrogen gas, H2.– OH– is attracted to the positive anode and discharged as oxygen gas, O2.

• Twice the volume of hydrogen gas is given off as oxygen gas because the formula of thecompound breaking up is H2O.

– negative ion movestowards anode

Key:

+ positive ion movestowards cathode

+

+ –

–

–

– +

+

electrolyte (solution that conducts electricity)

negative electrode(cathode)

positive electrode(anode)

An electrolysis cell.

• Thermal decomposition is a reaction in which a substance is brokendown into at least two other substances by heat.

• If a transition metal carbonate is heated, it decomposes to form a metal oxide and carbon dioxide. On heating:– FeCO3 decomposes forming iron oxide and carbon dioxide– CuCO3 decomposes forming copper oxide and carbon dioxide– MnCO3 decomposes forming manganese oxide and carbon dioxide– ZnCO3 decomposes forming zinc oxide and carbon dioxide.

• The metal carbonates change colour during decomposition.

• Sodium hydroxide solution is used to identify the presence of transition metal ions in solution:– Cu2+ ions form a blue solid– Fe2+ ions form a grey/green solid– Fe3+ ions form an orange gelatinous solid.

Precipitation reaction

G–E • Precipitation is a reaction between solutions that makes an insoluble solid. When a yellow solution of potassium chromate is added to a colourless solution of silvernitrate, a precipitate (solid) is formed. The precipitate is orange-coloured silver chromate.

G–E

D–C

Testing for hydrogen and oxygen

Electrolytic decomposition

• Sulphuric acid solution can be broken down into hydrogen and oxygen.

• To test for the two gases: a lighted splint burns with a ‘pop’ in hydrogen, a glowingsplint relights in oxygen.

• Aluminium is extracted from its mineral using electricity. The mineral is called bauxite.

• The key features in the production of aluminium by electrolytic decomposition are:– the use of molten aluminium oxide– aluminium is formed at the graphite cathode; oxygen is formed at the graphite anode– the anodes are gradually worn away by oxidation– the process requires a high electrical energy input.

• The word equation for the decomposition of aluminium oxide is:aluminium oxide aluminium + oxygen

1 2 3 4 5 6 7

8

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La*

Ac* Rf Db Sg Bh Hs Mt

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

Ne

He H

Ar

Kr

Xe

Rn

lithium

sodium

potassium

rubidium

caesium

francium

beryllium

magnesium

calcium

strontium

barium

radium

scandium

yttrium

lanthanum

actinium rutherfordium dubnium seaborgium bohrium hassium meitneriumDs

darmstadtiumRg

roentgenium

titanium

zirconium

hafnium

vanadium

niobium

tantalum

chromium

molybdenum

tungsten

manganese

technetium

rhenium

iron

ruthenium

osmium

cobalt

rhodium

iridium

nickel

palladium

platinum

copper

Elements with atomic numbers 112–116 have been reported but not fully authenticated.

Key

silver

gold

zinc

cadmium

mercury

boron

aluminium

gallium

indium

thallium

carbon

silicon

germanium

tin

lead

nitrogen

phosphorus

arsenic

antimony

bismuth

oxygen

sulfur

selenium

tellurium

polonium

fluorine

chlorine

bromine

iodine

astatine

neon

heliumhydrogen

atomic symbolname

argon

krypton

xenon

radon

1

relative atomic mass

7 9

23

39 40 45 48 51 52 55 56 59 59 63.5 65 70

115

204

73 75 79 80 84

27 28 31 32 35.5 40

131

24

11 12 14 16 19 20

4

85 88 89 91 96 [98]93 101 103 106 108 112 119 122 128 127

[222][209] [210]133 137 139 178 181 184 186 190 192

[223] [226] [227] [261] [262] [266] [264] [277] [268] [271] [272]

195 197 201 207 209

1

atomic (proton) number

3 4

11

19 20 21 22 23 24 25 26 27 28 29 30 31

49

81

32 33 34 35 36

13 14 15 16 17 18

54

12

5 6 7 8 9 10

2

37 38 39 40 42 4341 44 45 46 47 48 50 51 52 53

8684 8555 56 57 72 73 74 75 76 77

87 88 89 104 105 106 107 108 109 110 111

78 79 80 82 83

The periodic table with the transition elements shaded in grey.

TopTip!

The test for carbondioxide is that itturns limewatermilky.

Electrolysis of sulphuric acid in the laboratory.

Grades G-E

Grades D-C

Grades G-E

Grades D-C

TopTip!

A catalyst is an element orcompound that changes the rate ofa chemical reaction without takingpart in the reaction. Catalysts areunchanged during the reaction.

Grades G-E

Grades D-C

Grades G-E

Grades D-C

Size : 297mm x 210mm (Bleed 3mm)

1 U135799 1.30 S4-4 175# U

Size : 297mm x 210mm (Bleed 3mm)

1 U135799 1.30 S4-4 175# U

10 OCR Sci Found p67-75.qxd 21/11/08 14:40 Page 72

199

2 a When a yellow solution of potassium chromate is added to a colourless solution of silver nitrate a yellow solid is formed. What is this type of reaction called?

_______________________________________________________________________ [1 mark]

198

ElectrolysisC

3 T

HE

PE

RIO

DIC

TA

BL

E

Grades

Transition elements C3 T

HE

PE

RIO

DIC

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E

G–E

D–C

Grades

G–E1 a Transition elements have typical metallic properties. Write down six properties.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ [6 marks]

b A compound that contains a transition element is often coloured.i What is the colour of copper compounds?

_______________________________________________________________________

ii What is the colour of iron(II) compounds?

_______________________________________________________________________

iii What is the colour of iron(III) compounds?

_______________________________________________________________________ [3 marks]

c A transition metal and its compounds are often catalysts.i Which transition metal is used in the Haber process to produce ammonia?

_______________________________________________________________________ [1 mark]

ii If the metal used to harden margarine is number 28, suggest whether this is a transition metal or not. Use the periodic table on page 238 to help you.

_______________________________________________________________________ [1 mark]

D–C2 a Explain the key features of the electrolysis of dilute sulphuric acid.

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________ [6 marks]

b Explain why the volume of hydrogen gas and the volume of oxygen gas given off in this process are different.

_________________________________________________________________________ [1 mark]

G–E3 a The two gases given off during the electrolysis of sulphuric acid can be tested.i Describe the test for hydrogen.

_________________________________________________________________________

_________________________________________________________________________ [2 marks]

ii Describe the test for oxygen.

_________________________________________________________________________

_________________________________________________________________________ [2 marks]

D–C4 a Write about the key features of the production of aluminium by electrolytic decomposition.

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________ [4 marks]

b Write down the word equation for the decomposition of aluminium oxide.

_________________________________________________________________________ [1 mark]

G–E

3 a In a reaction a substance is broken down into at least two other substances by heat. What is this type of reaction?

_______________________________________________________________________ [1 mark]

b If a transition metal carbonate is heated it decomposes to form a metal oxide and carbon dioxide. Write down the word equation for the decomposition of copper carbonate.

_______________________________________________________________________ [1 mark]

D–C

4 a Sodium hydroxide solution is used to identify the presence of transition metal ions in solution. Finish the table.

[3 marks]

D–C

1 a Finish the sentences by choosing the best words from this list. You may use any word more than once.

anode cathode electrolysis electrolyte negative positive

The decomposition of a liquid by using electricity is called _______________________.

The _______________________ is a liquid that conducts electricity. There are two

electrodes called the _______________________ and the _______________________.

The _______________________ is the positive electrode and the _______________________

is the negative electrode.

During electrolysis the _______________________ ions are attracted to the anode

and the are _______________________ ions attracted to the cathode. [8 marks]

ion colour

Cu2+

Fe2+

Fe3+

26 OCR Sci Found p193-201.qxd 21/11/08 14:42 Page 198