Chapter 13 - The Behaviour of Metals Flashcards
8 physical properties of metals
- strong
- malleable
- ductile
- sonorous
- shiny when polished
- good conductors of electricity and heat
- high melting and boiling points
- high density
Formula for density
mass (grams)
density = ———————
volume (cm^3)
4 Chemical properties of metals
- React with oxygen to form OXIDES
- Metal oxides are BASES (neutralise acids, forming salt and water)
- Metals form positive ions when they react
- For the metals in the numbered groups, the charge on the ion is the same as the group number. But transition elements have variable valency
What is VARIABLE VALENCY?
When elements can form ions with different charges e.g Cu+ / Cu2+
Specific properties of iron and its uses
Iron is malleable and strong Rusts easily in damp air Unlike most other metals it's magnetic It melts at 1530 degrees c. - used for gates
Specific properties of sodium
- soft (can cut with a knife)
- floats on water and reacts with it immediately forming a solution
- melts at 98 degrees C
Specific properties of gold and its uses
- unreactive
- malleable, ductile, looks attractive
- quite rare
- melts at 1064 degrees C
- used for jewellery and precious objects
What does reactive mean?
A reactive element has a strong drive to become a compound so that its atoms gain stable outer shells.
Reaction between sodium and water
What’s formed?
Sodium reacts violently with cold water, whizzing over the surface.
Hydrogen gas and a clear solution of sodium hydroxide are formed
Reaction between calcium and water
What’s formed?
The reaction between calcium and cold water is slower.
Hydrogen bubbles off, and a cloudy solution of calcium hydroxide Ca(OH)2 forms.
Reaction between magnesium and water
What’s formed?
Magnesium reacts very slowly with cold water, but vigorously on heating in steam, it glows brightly.
Hydrogen and solid magnesium oxide MgO form.
Potassium reaction with water
Products
Very violent with cold water catches fire
Hydrogen and a solution of potassium hydroxide, KOH
Zinc reaction with water
Products
Quite slow with steam
Hydrogen and solid zinc oxide ZnO
Iron reaction with water
Products
Slow with steam
Hydrogen and solid iron oxide Fe3O4
Copper, silver, gold reaction with water
Products
no reaction
What is the pattern for the products formed when metals react with water
First 3 produce hydroxides and the rest produce insoluble oxides, if they react at all
magnesium reaction with hydrochloric acid
Products
Vigorous
Hydrogen and a solution of magnesium chloride MgCl2
zinc reaction with hydrochloric acid
Products
quite slow
hydrogen and a solution of zinc chloride ZnCl2
iron reaction with hydrochloric acid
Products
slow
hydrogen and a solution of iron(II) chloride FeCl2
lead reaction with hydrochloric acid
Products
slow, and only if the acid is concentrated
hydrogen and a solution of lead (II) chloride PbCl2
Copper, silver, gold reaction with hydrochloric acid
Products
no reaction, even with concentrated acid
Chemical equation between magnesium and hydrochloric acid
Mg (s) + 2HCl (aq) —> MgCl2 (aq) H2 (g)
What happens during a reaction between a metal and water/hydrochloric acid?
When a metal does react with H2O or HCl, it drives hydrogen out (displaces it) and takes its place. This shows that. the metal is more reactive than hydrogen and has a stronger drive to form a compound.
Is the displacement of hydrogen a redox reaction?
Yes
general explanation of redox reaction between magnesium and hydrochloric acid
When magnesium reacts with hydrochloric acid, its atoms lose electrons (is oxidised). The hydrogen ions from the acid gain electrons (are reduced).
The half equations for the reaction between magnesium and hydrochloric acid
Mg –> Mg2+ + 2e- (oxidation)
2H+ + 2e- –> H2 (reduction)
How is the reactivity series ordered?
Metals are put in order based on their reactivity with water and hydrochloric acid
What happens when MgO is mixed with powdered carbon and heated?
What does this mean?
There’s no reaction
This means magnesium is more reactive than carbon
What happens when PbO is mixed with powdered carbon and heated?
What does this mean?
Equation?
Turns into molten lead and CO2 is formed
Carbon is more reactive than lead
2PbO + C —> 2Pb + CO2
The general rule for carbon reacting with metal oxides
Carbon is more reactive than some metals. It will reduce their oxides (be oxidised itself - its a reducing agent) to form the metals.
What happens when powdered iron is heated with copper (II) oxide CuO?
What does this mean?
The reaction gives out heat and the mixture glows. Iron (II) oxide and copper are formed.
The iron is more reactive and takes the oxygen from copper - displaces it.
The chemical equation between iron and copper (II) oxide?
Fe + CuO —> FeO + Cu
What does the iron act as in the reaction between iron and copper (II) oxide?
A reducing agent - reduces copper but is oxidised itself.
What is the general reaction/rule for when a metal is mixed with a metal oxide?
A metal will reduce the oxide of a less reactive metal. The reduction always gives out heat - it is exothermic.
What happens when an iron nail is placed in a solution of copper (II) sulphate?
What does this mean?
Copper coats the nail. The solution turns green, which indicated iron (II) ions.
Iron has pushed (displaced) copper out of the solution - it is MORE REACTIVE.
What is the chemical equation for the reaction between an iron nail and copper (II) sulphate?
Fe + CuSO4 —> FeSO4 + Cu
What is the general rule for metals competing to form ions in solution?
A metal displaces a less reactive metal from solutions of its compounds.
What is the rule for deciding which metal is oxidised?
The more reactive metal forms positive ions more readily - is oxidised more readily
The more reactive metal will give up electrons to form ions and the less reactive one will accept them to form a solid version of the metal.
List reactivity series
Check with book
What is the meaning of the reactivity series?
really a list of metals in order of their drive to form positive ions with stable outer shells,.
The more easily its atoms can give up electrons the more reactive the metal will be
How will a metal react with a compound of a less reactive metal?
It’ll react by displacing (pushing out) the less reactive metal out of the compound and taking its place
Relation between reactivity of metal and its compound
the more reactive a metal is the more stable its compounds are. THEY DO NOT BREAK DOWN EASILY
The relation between the reactivity of a metal and its extraction
The more reactive the metal, the more difficult it is to extract from its ores since their compounds are stable.
The relation between the reactivity of a metal and its chance of forming a compound
The less reactive the metal, the less likely it is to form a compound.
What does thermal decomposition mean?
When a compound breaks down on heating
Effect of heat on sodium carbonate, hydroxide, nitrate
1 & 2 - no change in white compound
Nitrate - White compound partly decomposes to nitrite and oxygen
2NaNO3 —> 2NaNO2 + O2
Effect of heat on copper carbonate
The blue-green compound readily breaks down to black copper (III) oxide and carbon dioxide.
CuCO3 —> CuO + CO2
Effect of heat on copper hydroxide
The pale blue compound readily breaks down to copper (II) oxide and water:
Cu(OH)2 —> CuO + H2O
Effect of heat on copper nitrate
The bright blue compound readily breaks down to copper (II) oxide and the brown gas nitrogen oxide.
2Cu(NO3)2 —> 2CuO + 4NO2 + O2
4 General Rules for Thermal Decomposition
- The lower a metal is in the reactivity series, the more readily its compounds decompose when heated
- Carbonates, (except Na & K) decompose to the oxide and CO2
- Hydroxides, (except Na & K) decompose to oxide and H2O
- Nitrates (except Na & K) decompose to the oxide, NO2 & CO2. (Nitrates of Na & K form nitrites and oxygen)
Name 4 ways in which we make use of the reactivity series
- The thermite process
- In making simple cells
- In the sacrificial protection of iron
- Galvanising
What is the thermite process used for?
To repair rail and tram lines
What two compounds are used in the thermite process?
Powdered aluminium and iron (III) oxide are put in a container over the damaged rail
What happens during the thermite process chemically?
When the mixture is lit, the aluminium reduces the iron (III) oxide to molten iron in a very vigorous reaction.
The iron runs into the cracks and gaps in the rail and hardens.
The chemical equation for the thermite process
Fe2O3 + 2Al —> 2Fe + Al2O3
Look at Making Simple Cells revision aid
yes
Describe the reason why a simple cell works
The difference in reactivity causes a redox reaction that gives out energy in the form of electricity
What does a simple cell consist of?
A simple cell consists of two different metals in an electrolyte.
Which metal is the positive pole in a simple cell? Why?
What’s the other more reactive metal called?
Electrons flow from the more reactive metal, so it is called the negative pole.
The other is the positive pole.
What is the rule for voltage in a simple cell?
The further apart the metals are in reactivity, the higher the voltage will be
What does a voltmeter measure?
Measure the voltage that makes electrons flow
What metals can be used for the sacrificial protection of iron? How is it attached?
zinc, magnesium, etc
anything more reactive than iron
A block of the metal may be welded to the structure e.g a ship
Give the redox reaction for zinc and water (if zinc is used for sacrificial protection and reacts in water)
Oxidation - Zn —> Zn2+ + 2e-
R O2 + 2H2O + 4e- —> 4OH-
Overall equation for zinc used in sacrificial protection
2Zn + O2 + 2H2O —> 2Zn(OH)2
When is galvanising used?
used for the steel in car bodies and the corrugated iron for roofing
What is galvanising?
When iron / steel are coated by zinc
How are car bodies galvanised?
Carried out by a form of electrolysis
How are roofs galvanised?
Iron is dipped in a bath of molten zinc
How is galvanising beneficial?
Zinc coating keeps air and moisture away.
Why is galvanising more effective than sacrificial protection?
In SP, zinc block has to be replaced before it’s dissolved but in galvanising even if the coating is damaged, the iron still won’t be damaged due to SP
How come aluminium is more reactive than iron but is used for things such as satellite dishes, ladders and TV aerials?
Aluminium protects itself
- reacts rapidly with oxygen forming a thin coat of aluminium oxide (which you can’t see)
- this sticks tight to the metal acting as a barrier to further corrosion, leading to aluminium acting as if it was unreactive
