Metals

Question 1

How do metals react with cold water?

Answer 1

K, Na, Ca, Mg displace H2 from cold water with decreasing reactivity (K, violently, MG very slowly), forming the corresponding hydroxide

Eg: 2NA +2H20 –> 2NaOH +H2

Al –> Au do not displace H2 from cold water

Question 2

How do Metals react with steam

Answer 2

K –> Sn Displace H2 from steam with decreasing vigour (K most violently, SN very slowly) forming the corresponding oxide

Eg: Mg + H20 –> Mg + H2

Cu –> Au do not displace H2 from steam

Question 3

How do Metals react with strong acid

Answer 3

K –> SN displace H2 from dilute strong acid with decreasing vigour (K, explosively ; Mg very vigorously; Pb very slowly)

Note: Dilute strong acid refers to dilute HCl or dilute H2SO4. Using dilute HnO2 may produce NO or NO2 instead of H2 gas.

Eg Zn + 3H+ –> Zn2+ +H2

Cu –> Au do not displace H2 from dilute strong acid

Question 4

Describe metals strength as reducing agents down the reactivity series

Answer 4

K –> Au; decreasing strength as reducing agents (ie electrons donated less readily by metal)

Question 5

Describe metal reactions with other aq cations

Answer 5

more reactive metal displace less reactive metal from its solution

Question 6

Metals reaction with Cl2 on heating

Answer 6

all metal react with Cl2 on heating to form corresponding chloride with decreasing vigour

Question 7

The more reactive the metal, the _____________ thermally stable the metal

Answer 7

more

Question 8

How to determine whether metal is reactive (Practical)

Answer 8

1) heat sample of metal carbonate
2) Observe to see if it has decomposed

If it did, metal is not reactive
If it did not, metal is reactive

Question 9

Action of heat on metal carbonates

Answer 9

K –> Ca
Stable to heating
Eg (K2CO3 –> (heat) does not decompose)

Mg –> Cu
Decompose to form metal oxide and CO2
Eg: CuCO3 –> CuO + CO2
[exception: aluminum carbonate too unstable to exist]

Ag –> Au
Decompose to the metal, CO2 and hydrogen

Question 10

When metals react, what happen

Answer 10

Its atoms become ions by losing electrons, and thus it will form a compound and the metal will disappear

Question 11

Conditions that speed up rusting

Answer 11

-Water or air containing other ionic substances
(eg, air from the sea which has a lil salt solns, polluted air as it contain droplets of water with dissolved gas like sulfur dioxide)
-dilute acids

• when iron is touching a metal less reactive than iron, as it will lose electrons to them and also to oxygen and waster, thus rusting even quicker.

Question 12

Ways to prevent rusting and corrosion

Answer 12

• Apply a protective layer eg paint/oil, or cover it with a layer of less reactive metal)
• Sacrificial corrosion (ie attaching a more reactive metal to iron)
• Aluminum react with oxygen to form a thin non-porous layer of aluminum oxide on its surface, protecting the metal as it prevents water and oxygen to penetrate to the metal
• Sodium is kept under oil
• Iron is painted

Question 13

Why does sodium look dull, while gold looks shiny

Answer 13

Sodium is more reactive than golf, thus it reacts with oxygen to form a dull oxide layer on its surface, however gold is less reactive so it does not react with oxygen and retain its shininess.

Question 14

Why are larger sized atoms more reactive

Answer 14

As atoms become larger, the outer shell electrons become further away from nucleus. Attraction of +ve is less on these ‘far away’ electrons, thus the outer electrons of larger atoms are lose more readily

Question 15

Ba has larger atomic radius than Ca, why is it more reactive than Ca.

Answer 15

Ba has larger atomic radius du to more electron shells and thus its valence electrons is in a shell further from nucleus hence less attracted to +ve nucleus and more readily to lose electrons to undergo oxidation, so its more reactive

Question 16

Why does alloying make a metal harder and stronger?

Answer 16

Introduction of another type of atom of a different size disrupts the regular roles of metal atoms thus the atoms do not slide across each other easily

Question 17

Which extraction method is used for what metals? Why?

Answer 17

K –> Al
Electrolysis is used as a lot of energy is required to overcome the strong bonds it formed

Zn –> Cu
Heat the metal oxides with carbon to extract metals (reason same as above)

Ag –> Au
Found free in ground as unreactive

Question 18

How does sacrificial corrosion work (can use zinc and iron as part of explanation)

Answer 18

Zinc more reactive than iron, thus in prescence of water and oxygen, zinc atoms will form zinc ions first.

Iron atoms remain, so iron is prevented from rusting.

As long as some part of zinc is in touch with some part of iron it still gives protection since both metals are conductors and movement of electrons can occur easily

Question 19

Why unlike aluminium, iron corrode when left exposed to air

Answer 19

Iron forms a porous oxide layer on surface. This porous oxide layer allows oygen and moisture to continue to penetrate and attack the metal underneath. Moreover, this porous oxide layer tends to fall off to expose more of the metal to corrosion

Question 20

How can aluminium oxide layer be made thicker

Answer 20

THrough an electrolysis process called anodizing which introduces dyes which are absorbed into the oxide layer

Question 21

What determine the reactivity of a metal

Answer 21

the ease in which a metal atom loses its electrons. Atoms of more reactive metals lost electrons more easily

Question 22

Main reactions in blast furnace (3)

Answer 22

C (s) + O2(g) –> CO2(g) +heat
CO2(g) + C(s) –> 2CO (g)
Fe2O3(s) + 3CO(g) –> 2 Fe(l) +3CO2(g)