3.5 Metals Flashcards
Metallic Structure
- A lattice of positive metal ions.
- A ‘sea’ of delocalized electrons.
-The delocalized electrons were lost by the metal ions, and they move freely through the lattice.
Define metallic bonding
Metallic bonding is the (strong) electrostatic attraction between the positive metal ions and the negative delocalised electrons.
Metal properties
- Metals tend to have high melting points:
-because the metallic bonding is usually very strong so lots of energy is needed to break it. - Metals conduct electricity:
-because the delocalized electrons are free to move through the lattice. - Metals are malleable:
-because the layers of metal ions can slide over each other
Define thermal decomposition
A thermal decomposition reaction is when heat energy is used to break down a substance.
Thermal decomposition reaction equation
Metal carbonate –> Metal oxide + Carbon dioxide
Thermal decomposition of copper carbonate
Copper carbonate (green solid) →Copper oxide (black solid) + Carbon dioxide (colourless gas)
Reactivity series (lowest to highest)
Au Ag Cu H Pb Fe Zn C Al Mg Ca Li Na K
Metal + Water reaction
Metal + Water → Metal hydroxide + Hydrogen
What are 2 observations of a metal + water reaction? (Magnesium)
Magnesium + Water → Magnesium hydroxide + Hydrogen
1. Effervescence - due to the hydrogen gas produced.
2. Solid disappears - due to being used up in the reaction.
What are Group 1 metals called and explain their reactions?
-Alkali metals
-React violently with water:
Metal + Water → Metal hydroxide + Hydrogen
-e.g. Lithium + Water → Lithium hydroxide + Hydrogen
What similar observations do the reactions of Li, Na and K with water share?
-Solid floats: it is less dense than water.
-Effervescence: hydrogen gas is produced.
-Solid moves: the effervescence propels it around the surface of the water.
-Solid disappears: it is used up in the reaction.
What colour and why does universal indicator turn when added to water after its reaction with a Group 1 metal?
-Dark blue
Why are metal hydroxides alkalis?
-Because they donate OH:
NaOH –> Na + OH
How do Li, Na & K react with water and what is the trend?
-Reactivity increases: reactions become more vigorous
Li: Fast
Na: Faster (Na melts)
K: Fastest (Lilac flame)
Group 1 Metal Reactivity Trend
The group 1 metals get more reactive as you go down the group
When a group 1 metal atom reacts, it loses its outer-shell electron to get a full outer shell. This happens more easily why?
- The atoms get bigger and have more shells
- The outer-electron is further from the nucleus
- The attraction between the nucleus and the outer-electron is weaker
- So less energy is needed to break the attraction
Metal + Steam reaction
Metal + Steam → Metal oxide + Hydrogen
Explain the reaction between magnesium and steam?
-Magnesium + Water → Magnesium oxide + Hydrogen
-This reaction is usually conducted in a horizontal tube:
-Some wet wool is heated to generate steam for the Mg to react with.
-The H2 gas produced is ignited to safely destroy it.
Why do metals react with cold water and hot steam to produce different products?
Steam has more energy, so both bonds in the water molecule can break
e.g. COLD: Hydroxide + Hydrogen
HOT: Oxide + Hydrogen
Acid + Metal reaction
Acid + Metal → Salt + Hydrogen
Magnesium + Sulphuric acid reaction
-Magnesium + Sulphuric acid → Magnesium sulphate + Hydrogen
-A salt is a compound formed when H is displaced from an acid.
-Mg displaces the H
What are important observations of a acid + metal reaction?
e.g. Magnesium + Sulphuric acid
* The metal disappears:
This is because it is used up in the reaction.
* There is fizzing:
This is because a gas (hydrogen) is produced.
The more reactive a metal is, the faster it will react with an acid.
But there are some which we either can’t or won’t use:
-LEAST REACTIVE
Au,Ag,Cu
Not possible: Less reactive than H, so can’t displace it
-MIDDLE REACTIVITY
H,Pb, Fe, Zn, C, Al, Mg, Ca
-MOST REACTIVE
Li, Na, K
Not allowed: Reaction with acids is too violent
What is the test for hydrogen?
(in a test tube) is:
* Lit splint → squeaky pop!
This is because the combustion of the hydrogen causes the test tube to resonate
Define a displacement reaction
More reactive metals can displace less reactive metals from their compounds.
Magnesium + Copper Sulphate reaction
-Magnesium can displace copper from copper sulphate
-Magnesium (Grey Solid)+ Copper sulphate (Blue Solid) → Copper (Pink-orange Solid) + Magnesium Sulphate (Colourless solution)
What are observations of displacement reactions?
-Solid colour change
-Solution colour change
Magnesium + Copper Sulphate reaction observations
- Solid - turns from grey to pink-orange.
- Solution - turns from blue to colourless.
The non-metal part of the compound (sulphate) remains unchanged.
What are the observations for the reaction between Magnesium (grey solid) + Copper sulphate (blue solution) —> Copper (Pink-orange solid) + Magnesium sulphate (colourless solution)
Due to the appearances of the particular substances above, the observations would be:
1. Solid - turns from grey to pink-orange.
2. Solution - turns from blue to colourless.
The non-metal part of the compound (sulphate in the above example) remains unchanged.
A displacement reaction can only occur when?
can only occur if the metal used is more reactive than the metal already in the compound.
Reactivity in displacement reactions
Zn < X < Mg
* Mg is the most reactive, because it displaced both Zn and X.
* Zn is the least reactive, because it did not displace either Mg or X.
* X is in the middle, because it displaced Zn but not Mg
Define an ore
A piece of rock that contains metal and other impurities.
Which elements from least to most reactive are ores?
Au, Ag- Native Ores
Cu,H,Pb,Fe,Zn,C,Al,Mg,Ca,Li,Na,K- Ores
-Gold (Au) and Silver (Ag) too unreactive to have combined with oxygen or sulphur.
-Found ‘native’= chemically uncombined.
Why do native metals don’t need to be chemically extracted?
They already exist on their own
What are methods of chemically extracting metals in ores from their compounds?
-Using electricity
-Carbon extraction
How is electricity used to chemically extract metal in ores from their compounds?
-Metals more reactive than carbon cannot be displaced by carbon.
-Instead, we have to use electricity to break down their ore compounds.
-Aluminium is extracted from its ore in this way
How is carbon extraction used to chemically extract metal in ores from their compounds?
-Metals less reactive than carbon can be displaced by carbon.
-e.g. Copper can be displaced from its ore (copper oxide) by heating with carbon:
-Carbon + Copper oxide → Carbon dioxide + Copper
C(s) + 2CuO(s) –> CO2(g) + 2Cu(s)
-This only works because carbon is more reactive than copper.
Redox reactions (in terms of displacement)
Using carbon to displace a metal from its oxide is a redox reaction.
Define reduction
Loss of oxygen
Define reducing agent
Takes oxygen away from something else
Define oxidation
Gain of oxygen
Define oxidising agent
Gives oxygen to something else
Define redox
Reduction and oxidation in the same reaction
When carbon is used to extract zinc from zinc oxide what is reduced/oxidised?
-C + 2ZnO –> CO2 + 2Zn
-Reduced= ZnO loses O
-Reducing agent= C took away O from ZnO
-Oxidised= C gains O
-Oxidising agent= ZnO gives O to C
Define rusting
Rusting is a chemical process by which iron is oxidized to form rust.
What is the chemical name for rust?
Hydrated iron(III) oxide:
What substances does rusting require?
It requires two substances, oxygen + water
What are the 2 stages of rusting?
- Iron is oxidized by oxygen to form iron(III) oxide:
-4Fe(s) + 3O2(g) → 2Fe2O3(s)
-Fe has gained oxygen and it has also lost electrons to form Fe3+ ions.
-For both reasons, it has been oxidized. - Iron(III) oxide is hydrated by water:
-Fe2O3(s) + xH2O(l) → Fe2O3*xH2O(s)
-The amount of water gained by the iron(III) oxide varies a lot
How can using barriers prevent rusting?
-Coating the iron in paint, oil, grease or plastic prevents the iron from coming into contact
with oxygen or water:
-Only works as long as the coating is intact - as soon as it breaks, rusting happens.
-Coating material depending on the use for the iron - oil or grease for moving parts (e.g. bike chains), paint or plastic for larger more stationary objects (e.g. buckets).
How does sacrificial protection prevent rusting?
-Attach a block of a more reactive metal (e.g. magnesium) to the iron.
-This works by displacing the iron from rust as soon as the rust forms:
-Displacement reaction: Magnesium + Iron(III) oxide → Magnesium oxide + Iron
-The down-side to this method is that the block of magnesium has to be replaced often.
What is a disadvantage of sacrificial protection?
-The block of magnesium has to be replaced often.
How does galvanising prevent rusting?
-This method specifically involves coating the iron in zinc.
It works both ways:
* Coating prevents O2 and H2O from coming in contact with the iron…
* but even if a crack appears…
* zinc is more reactive than iron so acts as sacrificial protection as well
Define an alloy
Alloys are mixtures of a metal with one or more other elements, usually other metals or carbon.
What are common known alloys?
Steel: Iron + Carbon
Brass: Copper + Zinc
Bronze: Copper + Tin
Why are alloys harder than pure metals?
-The different-sized atoms/ions prevent the layers of metal ions from sliding over each other.
-This means the alloy is less malleable
What is the elements, use and reason of the alloy Iron?
ELEMENTS- Fe
USE- Making steel
REASON- Steel is more useful than iron.
What is the elements, use and reason of the alloy Low-carbon steel?
ELEMENTS- Fe, 0.1% C
USE- Ships, cars, bridges etc.
REASON- Strong, but wow-carbon so can be hammered into various shapes.
What is the elements, use and reason of the alloy stainless steel?
ELEMENTS- Fe, 1% C, 10% Cr
USE- Cutlery, cooking
utensils, kitchen sinks.
REASON- Cr forms oxide layer that resists
corrosion, so stays shiny and clean.
What is the elements, use and reason of the alloy High-carbon steel?
ELEMENTS- Fe, 1% C
USE- Tools e.g. knives,
screwdrivers.
REASON- High-carbon so less malleable and stiffer than low-carbon steel.
What is the elements, use and reason of the alloy copper?
ELEMENTS- Cu
USE- Wires, Cooking pans, Water pipes
REASON- Excellent conductor of electricity.
Excellent conductor of heat. Unreactive and malleable.
What is the elements, use and reason of the alloy aluminium?
ELEMENTS- Al
USE- Aircraft bodies, Power cables
REASON- Low density and high strength, Low density and conducts
How is metal extracted from an ore which contains a metal which is above carbon in the reactivity series?
If the ore contains a metal which is above carbon in the reactivity series then ELECTROLYSIS (or a reaction with a more reactive metal) is used to extract the metal
What are uses and properties of aluminium?
Aircrafts and cans-Low density / resists corrosion
Power cables- Conducts electricity / ductile
Pots and pans-Low density / strong (when alloyed) / good conductor of electricity and heat
What are the uses and properties of copper?
Electrical wires-very good conductor of electricity and ductile
Pots and pans- very good conductor of heat / very unreactive / malleable
Water pipes- unreactive / malleable
Surfaces in hospitals- antimicrobial properties / malleable
What are the uses and properties of of iron?
Buildings- Strong
Saucepans- Conducts heat/high melting point/malleable
What are the uses and properties of steel?
Mild steel- nails, car bodies
High-carbon steel- cutting tools, masonry nails
Stainless steel- cutlery, cooking utensils, kitchen sinks
