Topic 4 - Extracting metals and Equilibria Flashcards
What is really mesured in the reactivity series?
How easily the metals form positive ions -> how easily they react
Displacement reactions
When more reactive metals replace less reactive metals.
How do you extract metal ores that are less reactive than carbon?
Reduction with carbon
1.
How do you extract metal ores that are more reactive than carbon?
electrolysis
What happens in reduction with carbon?
It switches with the metal oxide to form carbon dioxide, leaving the metal by itself, rreduced.
Bio-leaching
Uses bacteria to seperate metals from their ores, e.g. copper can be seperated from copper sulfate this way. The bacteria get energy from the bonds between atoms in the ore, seperating out the metal from the ore in the process. The leachate produced contains metal ions that can be extracted (e.g. electrolysis or displacement)
a Bacterial method of extracting metals
Phyto-mining
Involves growing plants in soil that contains metal compounds. The plants can’t use or get rid of metals so they gradually build up in leaves. The plants can be harvested, dried and burned in a furnace. The ash contains metal compounds from which the metal can be extracted (by electrolysis or displacement reactions)
What is a reversible reaction?
where the products can react with eachother to create the original reactants ( it goes both ways)
What is na example of a reversible reaction?
The Haber process:
N2+3H2 ⇌ 2NH3 ( + Heat )
Where are the reactants come from in the Haber process?
Nitrogen - easily from air, about 78% N
Hydrogen - From Hydrocarbons e.g. natural gas and crude oil
What are the conditions for the Haber process?
450”C
Pressure - 200 atm
Iron Catalyst
Why is equilibruim reached in Reversible reactions?
As (reactants or Products) React, their concentration will fall, the other products concentration will rise, leading to their rate of reaction to increase.
What is Dynamic equilibrium?
The forward and backward reactions are both happening at the same time and at the same rate, and the concentration of both have reached a balance and wont change
When can equilibrium be reached?
In a closed system
What 3 things can change position of equilibrium?
Temperature
Pressure (For GASES)
Concentration
Ho
How does temperature affect Equilibruim
Higher temperature favours the Endothermic side
to absorb more heat
How does Pressure affect equilibrium?
( IN GASES ONLY) Raising pressure favour side of least moles to lower pressure
How does concentration affect equilibrium?
If you increase the conc of reactants the equilibrium will shift tothe right to use up the reactants
What is oxidation?
The reaction with, or addition with oxygen
What is reduction?
can be the removal of oxygen
What do combustion reactions involve?
Oxidation + reduction of oxygen
Exothermic
What is the reactivity series ?
a table that lists metals in order of their reactivity
Why is Carbon often included in the reactivity series?
Because a metals position in the reactivity series compared to carbon dictates how its extracted from ore
Hydrogen may also be included
What is the reactivity series ( with dilute acids)?
The Reactivity Series
Potassium. - K
Sodium. - Na
Calcium. - Ca
Magnesium. - Mg
Aluminium. - Al
Carbon. - C
Zinc. - Zn
Iron - Fe
Hydrogen - H
Copper - Cu
Silver - Ag
Gold. - Au
Top : Least resistant to oxidation / Most reactive
How do you determine a metals position in the reactivity series?
by reacting it with water and dilute acids
What is a classic experiment to show the reacitvity of metals?
Metals in dilute HCL
How does the metals in dilute HCl reactivity test work?
1) The more reactive a metal is, the faster the reaction with the acid will go
2) Very reactive metals (e.g. Magnesium), will fizz vigourously, less reactive metals (e.g. zinc) will bubble a bit, and unreactive metals will not react with dilute acids at all
How do you show that Hydrogen is forming in the metals in dilute HCl reactivity test?
The Burning Splint test (squeaky pop)
- The louder the squeaky pop, the more hydrogen has been made in that time period and the more reactive the metal.
- The speed of the reaction is also indicated by the rate that hydrogen bubbles are given off, the faster the bubbles form = faster RofR = More reactive metal
How does metals reacting with water show the reactivity?
Metal + water -> Metal hydroxide + hydrogen
1) Very reactive metals will react vigourously with water
(sodium, lithium, potassium, calcium)
2) Less reactive metals : Mg, zinc and Iron wont react much with cold water, but will react with steam
3) Copper wont react with cold water or steam
What are displacement reactions an example of?
Redox reactions
What happens during a displacement reaction?
The more reactive metal is oxidised, and the less reactive metal is reduced
What is a metal ore?
a rock which contains enough metal to make it economically worthwhile extracting metal from it
In many cases the ore is the oxide of the metal
Where are the metals we commonly use found?
1) Found in their ores in the Earth’s crust - the ores are mined and the metals can be extracted from the ores
2) Some unreactive metals (e.g. gold/platinum) are present in the Earth’s crust as uncombined elements. These can be mined straight out of the ground, then refined before use
How are some metals extracted from their ores by reduction with carbon?
When an ore is reduced, oxygen is removed from it
e.g. Iron oxide + carbon -> Iron + carbon dioxide
Their ability to be reduced with carbon is based on the reactivity series
How does ore extraction depend on the reactivity series?
The Reactivity Series
Potassium. - K
Sodium. - Na
Calcium. - Ca
Magnesium. - Mg
Aluminium. - Al
Carbon. - C
Zinc. - Zn
Iron - Fe
Hydrogen - H
Copper - Cu
Silver - Ag
Gold. - Au
1) Metals above Carbon have to be extracted using electrolysis - expensive
2) Metals below Carbon can be extracted using reduction with carbon
3) Silver/gold are found as uncombined elements
Why can we only use reduction with carbon for ores that are less reactive than carbon?
Carbon can only take oxygen away from metals that are less reactive than itself
Metals extracted by electrolysis
Metals that are more reactive than carbon have to be extracted using electrolysis of molten compounds
Once the metal ore is melted, an electric current is passed through it. The metal is discharged at the cathode and the non-metal at the anode
How is electrolysis ( for metal ores) expensive?
Electrolysis ( for metal ores ) needs large amounts of electricity -> Electicity is expenive, making electrolysis pricey
-> There are also costs associated with melting or dissolving the metal ore so it can conduct electricity properly
How is reduction with carbon (comparatively to electrolysis) cheap?
Relating to the price of seperating metal ores in the reactivity series
Carbon is cheap, and acts as a fuel to provide heat for the reduction reaction to happen
This means that in general, metals lower down the reactivity series (less reactive metals) are cheaper to extract than those higher up the series (more reactive metals)
Why are there new biological methods to extract ore?
1) the supply of some metal-rich ores e.g. copper, is limited
2) The demand for lots of metals is growing and this may lead to shortages in the future
-> Scientists are looking into newer ways to extract metals from lower-grade (less metal) ores or from the waste that is currently produced when metals are extracted
What are the two biological methods to extract metal from ores?
Bioleaching
Phytoextraction
-> The extraction of metals in their ores through the use of living organisms
a Bacterial method of extracting metals
What are the +/- of biological methods of metal extraction?
+ Less damaging to the environment than traditional methods
- Slower
How does recycling conserve rescources and energy?
1) extracting raw materials takes alot of energy - burning fossil fuels
2) Fossil fuels are running out (non- renewable) - conseve them
-> contribute to climate change and can cause acid rain
3) Recycling materials saves energy as it takes less energy than extracting the raw materials
4) Conserves finite non-renewable resources
Its important to recycle materials that are rare
How does recycling protect the environment?
1) Extracting metals damages the environment
-> Mines damage environment & destroy habitats + an eyesore
2) Recycling materials reduces the amount of material sent to landfill
-> Landfill takes up space and pollutes the surroundings
What economic benefits does recycling have?
1) Recycling takes up less energy than extracting materials - energy is expensive
2) Beneficial to recycle materials that are expensive to extract or buy
3) Massive industry that creates jobs - transportation, processing at recycling centres, reprocessing in to market products.
What stages make up the life cycle assesment?
Choice of material
Manufacturing
Product use
Disposal
What does a life cycle assesment do?
(LCA)
Looks at each stage of the life of a product and works out the products environmental impact
LCA
Choice of Material
1) Metals have to be mined and extracted from their ores - High energy = lots of fossil fuels = Pollution
2) Raw materials for chemical manufacture often come from crude oil - non-renewable resource - supplies are decreasing. Obtaining & refining crude oil = lots of energy = Lots of pollution
LCA
Manufacture
1) Manufacturing produces alot of energy and other resources
2) Can cause alot of pollution & produce waste products - disposal
-> Some waste can be recycled and turned into useful chemicals, reducing the amount that ends up damaging the environment
3) Most chemical manufacturing needs water - Businesses have to make sure they dont put polluted water back into the environment at the end of the process
LCA
Product use
Using the product can also damage the environment:
1) Paint gives off toxic fumes
2) Burning fuels releases greenhouse gases & other harmful substances
3) Fertilisers can leach into streams and rivers and cause damage to ecosystems
LCA
Disposal
1) Products are often placed in landfill at the end of their life
-> This takes up space and can pollute land and water
3) Products might be incinerated (burnt) , which causes air pollution
