TEST Flashcards
Describe an experiment to determine the empirical formula for a compound
Weigh crucible
Put a sample of magnesium into the crucible and weigh it.
Calculate the mass of magnesium by subtracting the mass of the empty crucible
Heat over Bunsen burner
Carefully lift lid from time to time to allow some oxygen into the crucible for the magnesium to fully oxidise without letting any magnesium oxide escape.
Heat until mass of crucible it at its max
Repeat step 2
To find ep formula you need mass of magnesium and mass of oxygen- to find mass of oxygen atoms subtract the mass of magnesium used from the mass of magnesium oxide.
Divide two masses by relative atomic masses and simplify.
What is a mole of particles
One mole is the Avogadro number of particles (atoms, molecules, ions or electrons) in a substance.
What is the mass of a product formed in a reaction controlled by?
The mass of reactant that is not in excess
State the meaning of the term ‘electrolyte’
An ionic substance/liquid with freely moving ions that electrolysis takes place in
What happens in electrolysis? (SUMMARY!!!!!)
The process of using electricity to break apart the ions in an ionic substance that is either dissolved in water or molten.
Explain the movement of ions during electrolysis
Positively charged ions move to the negative electrode (CATHODE) during electrolysis. They gain electrons and are reduced.
Negatively charged ions move towards the positive electrode (ANODE) during electrolysis. They lose electrons and are oxidised.
What happens to the electrons in oxidation
Electrons are lost (+ charge)
What happens to the electrons in reduction
Electrons are gained (- charge)
Where does oxidation occur
At the anode
Where does reduction occur
At the cathode
Recall the products formed from the electrolysis of a variety of common compounds and solutions
Copper chloride solution Sodium chloride solution Sodium Sulphate solution Acidified water Molten lead Bromide
HOW TO REMEMBER the order of the reactivity series from most reactive downwards
People Say Little Children Make A Zebra Ill Constantly Sniffing Giraffes.
Why are displacement reactions redox reactions
displacement reactions are when more reactive elements replace other elements in a compound, Redox means reduction/oxidation (having to do with reactivity and electron transfer)
what is a cation
a positively charged ion which would be attracted to the cathode
recall meaning of the term ORE
naturally occurring rocks that contain metal or metal compounds in sufficient amounts to extract them.
Recall some metals that are found uncombined in the earths crust
GOLD
SILVER
COPPER
(LESS REACTIVE)
How and why are some metals extracted from their ores by heating carbon
Less reactive metals such as iron are extracted by reduction with carbon. The metal oxide loses oxygen, and therefore is reduced. The carbon gains oxygen and therefore is oxidised
Explain how and why some metals are extracted from their ores by electrolysis
More reactive metals such as aluminium are extracted by electrolysis.
Oxidation in terms of oxygen
The addition of oxygen to a substance in a reaction, or the reaction of a substance with oxygen
How are all metals extracted
by reduction of their ores
Advantages and disadvantages of recycling a metal
Helps limit amount of metals that must be produced
SUSTAINABLE
Process of recycling metals usually creates much less pollutants
and uses less energy therefore less fossil fuels are being burnt
HOWEVER
Can be expensive
Time consuming
Requires energy
How do we recycle plastic
Sorting it into different polymers and then chipping it and melting i- re shaping and molding it
Pros and Cons of recycling
Reduces pollution Reduces global warming Reduce energy usage Be sustainable However High in cost Recycling sites can be unsafe, unsightly and unhygienic
What happens in reversible reactions
The products can react to produce the original reactants again
⇄ (Use of the symbol in chemical equations)
Shows the reaction goes both ways
What is dynamic equilibrium
Both the backwards and forwards reactions occur but the substances are in balance
Describe the formation of Ammonia
Also known as the haber process
Nitrogen from the air reacts with hydrogen derived mainly from natural gas (methane) into ammonia.
This reaction is reversible and exothermic
Recite the equation for Ammonia creation
N2 + 3H2 ⇄ 2NH3 (+heat)
Recite the 3 conditions used in the Haber process
450*
200 atmosphere pressure
Iron catalyst
Uses of Haber processes
Fertilizers
Explosives
Cleaning fluids
Changes in pressure will not affect the position of equilibrium if…
the number of moles of gases on both sides of equation are equal
How does changes temperature effect equilibrium
Increasing the temperature always favours the endothermic reaction.Decreasing the temperature always favours the exothermic reaction.
Describe the difference between endothermic and exothermic
Endothermic- requires energy
Exothermic- gives out/releases energy
What is LCA
A life cycle assessment –is used to work out the environmental impact of a product from the raw materials to dispose of the product
Describe the position of transition metals in the periodic table
In the center of the periodic table between groups 2 and 3
What are the chemical and physical properties of transition metals
Chemical- Acts as a catalyst and forms a colored compound and has variable oxidation states
Physical- High density and high melting points
Why has iron got typical properties of a transition metal
High density - 7.8
High melting point- 1538*
Uses as a catalyst- haber process
What is corrosion of metals a result of
oxidation
How does rusting of iron occur
When iron is exposed to oxygen and moisture for a long period of time
Over time, the oxygen combines with the metal at an atomic level forming a new compound oxide
How does sacrificial protection work
Covering the object with a thin layer of zinc (sacrificial metal), this stops the oxygen and water reaching the metal underneath. The zinc is more reactive than iron, so it oxidises in preference to the iron object
Why do metal objects need to become electroplated
increases life of metal
prevent corrosion
Recall some common examples of electroplating
Copper Nickel Tin Zinc Gold Silver
Recall the name of a common alloy
steel
an alloy of iron and carbon
What is an alloy
A mixture of a metal element with one or more other elements (usually metals)
What happens in alloying
Within the mixture of two or more elements, where at least on element is a metal (the alloy) Alloys contain atoms of different sizes, which distort the regular arrangement of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal
Why is iron alloyed with other metals
Pure iron is to soft for many uses
Common uses for Aluminium, copper and gold
Aluminum- bodies of planes
Copper- Electrical wires as its a good conductor
Gold- Jewelry (lack of reactivity)
Common alloys that contain aluminum or copper
Duralium (contains both)
Bronze- copper+tin
Brass-copper+zinc
Difference between empirical formula and molecular formula
Empirical formula tells you the simplest or most reduced ratio of elements in a compound. WHEREAS molecular formula tells you how many atoms of each element are in a compound
Describe a closed system
Same mass after as before the reaction
Describe a open system
Same mass but if it’s a gas it seems like there’s a loss
Describe methods of metal extraction
Bioleaching -using bacteria, absorb copper through its roots, extracted by displacement and purify by electrolysis.
Phytomining- using plants- plants absorb copper- burn plants - H2SO4
Explain how a elements reactivity is related to its resistance to oxidation
The more reactive a metal is the quicker it oxidises eg- a slice of potassium will become dull as it quickly reacts with oxygen, whereas less reactive metals such as gold remain shiny that’s why they are used to make jewellery
What is a redox reaction
A reaction in which both oxidation and reduction occur
Why are alloys often stronger than the metals they contain
They distort the arrangement so the layers don’t slide past eachother as easily
Closed
You will always have the same mass before and after a reaction
How to find empirical formula
Mass
Mass / mr
Divide by smallest
How to calculate relative formula mass (or Mr)
Add relative atomic mass for all atoms shown in its chemical formula e.g.-
Find Mr of H20
Ar of H= 1 O= 16
Mr of H2O = 1+1+16 = 18
What is Ar
Relative atomic mass of an atom in the periodic table eg Oxygen = 16
What is Mr
Relative formula mass
All atomic masses added together
How calculate mass of product/reactant
Find out if you’re being asked to find the mass of product OR reactant
If reactant = Mr of reactant / Mr of product
If product = Mr product / Mr reactant
Then Multiply by known mass
Formula triangle for calculating concentrations of solutions in g dm3
Mass (solute in g)
Conc Vol (solution in dm3)
Converting dm3 to cm3
Cm3-dm3 (divide by 1000)
Dm3-cm3 (multiply by 1000)
Formula triangle for number of moles
Mass
Ar or Mr Moles
Formula triangle for number of particles in a substance
Particles
Moles Number Avo no
What are positive ions also known as
Cations
What are negative ions also known as
Anions
In purification of copper how do we figure out which element will under go (reduction or oxidation)
or which one will be discharged
AT THE CATHODE CONCERNING H+ IONS
If it is less reactive than hydrogen it will be discharged and under go reduction or oxidation
If it is more reactive than hydrogen then hydrogen will take its place
In purification of copper how do we figure out which element will under go (reduction or oxidation)
or which one will be discharged AT THE ANODE CONCERNING OH- IONS
In dilute conditions OH- (hydroxide) will be discharged
But if In a concentrated solution then the halites will be discharged instead of OH-
Where do OH- and H+ ions go in solutions
H+ goes to the negative cathode
OH- goes to the positive anode
How does the electrolysis of copper Sulfate solution using copper electrodes can be used to purify copper
The positive anode is made of impure copper which is to be purified. The negative cathode is a bar of pure copper. The two electrodes are placed in copper(||) sulfate.
The copper ions leave the anode and are attracted to the cathode, where they are deposited as copper atoms. The pure copper cathode increases gently in size, while the anode decreases.p
what happens to an element when it loses an electron
It has a positive charge
What happens to an element when it gains an electron
It has a negative change
What’s an oxidation number
The different charges and number charges of atoms
If in the half equation u have lost an electron how do u write it
You can’t use a - sign therefore u have to write the +e but at the end!
E.g.
Na– Na+ +e
Half equation for copper purification
Cu—Cu2+ + 2e
What is corrosion
Rusting of a metal
What would happen in the haber process of the atmospheric pressure was increased
A high pressure would increase the percentage yield of ammonia but very high pressures are expensive
What would happen in the haber process if temperature was increased
It would cause a faster reaction but decrease the percentage yield of ammonia
What are the 2 half equations for lead and bromide
Lead –
Pb2+ + 2e- —-> Pb (reduction)
Bromide
2Br —-> Br2 + 2e-
Explain what happens in electrolysis of molten lead bromide
Positive lead ions are attracted to negative cathode and are discharged to form molten lead.
The negative bromide ions are attracted to the positive anode electrode and discharged to form bromine vapour.
The products of this electrolysis are lead metal and bromine.
How will the rate of equilibrium change if you change temperature
If temperature is increased the reaction will shift to favour the endothermic reaction to remove extra heat added.
Increase temp= favours endothermic reaction
Decreasing temp= favours exothermic reaction
How will the rate of equilibrium change if you change pressure
High pressure= favours side with lowest volume of gases
Low pressure= favours side with the highest volume of gases
Changes in pressure won’t effect position of equilibrium if…
Number of moles of gas on each side of the equation is equal.
How will the rate of equilibrium change if you change the concentration
Increase conc of reactants- equilibrium will move to right to use up reactants (makes more products)
Increase conc of products- equilibrium will move to left to use up products (makes more reactants)
How will the rate of equilibrium change if you use a catalyst
Reduces time taken to reach equilibrium but doesn’t change position of equilibrium because it increases rates of forward and reverse reactions by the same amount.
What is a rule in equilibrium
Any change made to a reaction which is in equilibrium will result in the equilibrium position moving to minimise Change made.
Called the- La Chateliers principal
Why can’t titrations be done on large scale industry
Volumes of solutions are too large for titration method
Large volumes of liquid need to be heated and crystallised
Why does the voltage of the cell decrease when the cell is left connected in circuit
Reactants are being used up
What factors should we be considering when choosing final pathway on how to make a product
Usefulness of by product, atom economy, cost of energy, yield of product and rates of reaction
How to do gold calculations
Carat given \ 24
What effect does Higher temperature have on equilibrium
Higher temperatures reach equilibrium faster because molecules move faster and therefore more frequent collisions because more molecules have energy. More molecules have required energy therefore yield will be lower because higher temperatures favour the endothermic reaction and so equilibrium shifts to the left hand side
What should model of crystal look like
3D
Particles of different sizes
Why does magnesium oxide have such a high temperature
Magnesium has very strong bonds so requires a lot of energy to separate magnesium and oxygen ions to melt solid
Compare strong and week acids
Strong acid is completely ionised in solution whereas weak acid is only partly ionised
Describe exothermic reactions
One which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature of the surroundings
Describe endothermic reactions
One which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature of the surroundings
Give example of nano particle
Fullerenes include nanotubes, tiny hollow carbon tubes. All those covalent bonds make nano particles very strong
As particle size decreases what happens to the nano particle
Size of surface area increases in relation to their volume- surface area to volume ration increases
What can nano parcels be used for
Catalysts, suncreams, deodorants
Can nano particles conducts electricity
Yes
What can silver nano particles be used for
Added to polymer fibres, used to make surgical masks and wound dressings. Gives fibres antibacterial properties
Nano particles can
Be added to plastics to make them stronger and more durable without adding much mass
How does nano medicine work
Tiny fullerenes are absorbed more easily by the body than most particles. This means they could deliver drugs right into the cells where they’re needed
What happens at the cathode in electrolysis of aqueous solutions
If H+ ions and metal ions are present, hydrogen gas will be produced if the metal is more reactive than hydrogen.
If the metal is less reactive than hydrogen, then a solid layer of the pure metal will be produced instead.
What happens at the anode in the electrolysis of aqueous solutions
At the anode, if halide ions are present- chlorine, bromine and iodine, molecules of them will be formed. If NO halide ions are present then oxygen will be formed from the hydroxide ions
What is electrolysis of aqueous solutions
As well as ions from ionic compound, there will be H+ ions and OH- ions
What happens to positive metals in electrolysis
Reduced at the cathode
What happens to negative ions in electrolysis
Oxidised at anode
How to set up an electrochemical cell
Get two electrodes (should be inert eg- platinum or carbon). Clean the surfaces of the electrodes using a piece of sandpaper. Don’t touch the metals again otherwise you could transfer grease. Place both electrodes in a beaker filled with your electrolyte, connect the electrodes to a power supply using crocodile clips and wires.
Explain how to set up non intert electrodes in electrolysis
Eg- copper electrodes in solution of copper sulfates. Follow same method but use non inert electrodes. As reaction continues, the mass of the anode will decrease and the mass of the cathode will increase. This is because copper is transferred from the anode to the cathode.
Leave cell running for 30 mins to get a decent change in mass
What metals are more and less reactive than hydrogen
Less- copper, silver, gold and platinum
What’s bioleaching- a and d
Uses bacteria to grow on a low grade ore. The Bacteria produce a solution containing copper ions called leachate. Copper is extracted from the leachate by displacement using scrap iron, then purified by electrolysis.
A-doesn’t require high temperatures
D- toxic substances and sulfuric acid can be produced by the process, and damage the environment
What’s phytomining- a and d
Involves growing plants that absorb metal compounds. The plants are burned to form ash, from which the metal is extracted.
A- can extract metals from contaminated soils
D- more expensive than mining some ores, growing plants is dependent on weather conditions
What are native Elements found
Found un combined and unstable - silver and gold
How to extract zinc, iron and copper
Heat / extract with carbon
How to extract potassium, sodium, calcium, magnesium and aluminium
Electrolysis of a moleton compound- stable (because they are more reactive)
Advantages to both bioleaching and phytoextraction
No harmful gases e.g. - sulfur dioxide is produced
Causes less damage to the landscape than mining
Conserves supplies of higher grade ores
What happens if u increase temperature
The equilibrium will move in the endothermic direction to absorb the extra heat
What happens if u decrease the temperature
The equilibrium will move in the exothermic direction to produce more heat
What does change in pressure only effect
Changing pressure only effects equilibrium involving gases
What happens if you increase the pressure
The equilibrium will move towards the side that has fewer moles of gas to reduce pressure
What happens if you decrease the pressure
The equilibrium will move towards the side that has more moles of gas to increase the pressure
What happens if you increase concentration of REACTANTS
The equilibrium will move to the right to use up the reactants (making more products)
What happens if you increase the concentration of the PRODUCTS
the equilibrium will move to the left to use up the products (making more reactants)
What happens if you decrease the concentrations
It will have the opposite effect
