Separate Chemistry 1

What are the physical properties of transition metals?

• High melting-point (except for mercury which is a liquid at room temperature)

• High density

• Stronger and harder than group 1 and 2 metals so they are often more suitable in construction materials

What are the chemical properties of transition metals?

• Formation of coloured compounds

• Catalytic activity

What are catalysts?

Substances that speed up the rate of reaction without:

• Altering the products of a reaction

• Changing chemically

• Changing in mass at the end of a reaction (They are never used up)

What are the physical properties of group 1 and 2 metals?

• Relatively low melting point

• Relatively low density

• Formation of white or colourless compounds

• Lack of catalytic activity

What is corrosion?

The oxidation of metals

What is the corrosion of iron and steel called?

Rusting

What is needed for rusting to occur?

oxygen and water

How can we prevent rust on iron or steel?

• Painting an object

• Using oil or grease

• Coating with plastic

• Coating with another metal

  Storing item in a vacuum container (so oxygen can’t get to it)

• Put the item in a container with a desiccant (which absorbs water vapour)

What is electroplating and how is it done?

• A thin layer of an unreactive metal like silver or gold is deposited on the surface of a metal object, keeping air and water out

• This is done through electrolysis where silver ions lose their electrons to become positive

• They move throughout the electrolyte and are attracted to the negative cathode which would be the object to be plated

• The silver ions gain electrons to become silver atoms and the object which was used as a cathode is now plated with silver

Why is electroplating used?

• To improve appearance

• To improve an item’s resistance to corrosion

What is an alloy?

A mixture of a metal with one or more other elements

Why is iron by itself not used for many purposes and what is it made into?

Because it is too soft and needs to be mixed with other elements to make alloys that are stronger. When mixed with carbon, iron makes a steel

What are the most common types of steel?

• Carbon steels

• Consist of iron with up to 2% carbon

• Are harder and stronger than iron alone

What is stainless steel?

• An iron alloy that resists corrosion

• Used to make cutlery, washing machine drums and dishwashers

• Stainless steel contains chromium which forms an invisible layer of chromium oxide and top, stopping oxygen and water from reaching the iron

What are some alloys and their uses?

Alloy	Main metal	Mixed with	Typical properties	Uses
Carbon steel	Iron	Carbon	Hard, strong	Building, bridges, car
Magnalium	Aluminium	Magnesium	Low density	Car and plane parts
Jewellery gold	Gold	Copper	Resistant to corrosion	jewellery
Brass	Copper	Zinc	Hard, resistant to corrosion, good electrical conductor	electrical plugs, coins, instruments

Why are alloys stronger than normal metal atoms?

• Normal metal atoms are arranged in neat rows, thins make it easy for them to slide over each other which is why they are malleable (can be bent)

• Alloys have a mixture of a main metal and a different element, these different sized particles mean that it is harder for the rows of atoms to slide over each other so they are not malleable

What is the equation for concentration involving solutes and volume?

Concentration (Mol/dm³)= amount of solute (mol)/volume (dm³)

How can we convert between g/dm³ and mol/dm³?

• mol/dm³→g/dm³ - multiply the concentration by the Mr

• g/dm³→mol/dm³ - divide the concentration by the Mr

What is a theoretical yield?

The amount of product you can make in theory if no substance is lost

What is an actual yield?

The amount of mass you really get at the end of a reaction, this is always less than the theoretical yield

What is the equation for percentage yield?

percentage yield= (actual yield/theoretical yield) x 100

For what reasons may we not obtain the theoretical yield from a chemical reaction?

• The reaction may not have finished or has reached equilibrium

• There can be competing, unwanted reactions creating by-products

• Losses during purification e.g. filtration

• Liquid left behind after transferring containers

What is the equation for atom economy?

Atom economy= (Mr of desired products/Mr of all products) x 100

What is atom economy?

A way of measuring the number of atoms wasted when making a substance

How is 100% atom economy achieved?

• When there is only one product

  OR

• When all the by-products are used as a feedstock for other processes

Why are reactions with high atom economies preferred in industrial processes?

• It produces less waste so it is less harmful to the environment

• Conserves limited resources

• More sustainable

What does the volume occupied by a gas depend on?

• The number of particles present

• The temperature of the gas

• The pressure of the gas

What is the molar volume?

The volume occupied by one mole of any gas at room temperature and atmospheric pressure

What is the value for molar gas volumes?

24 dm³/mol or 24,000 cm³/mol (This will be given to you if you need them for calculations)

What is the equation for the volume of a gas involving molar volume and moles?

Molar volume x moles

What is the equation to calculate the amount of moles in a gas involving volume of gas and molar volume?

Amount= volume of gas/molar volume

What is the calculation for mass involving Mr and moles?

Mass= Mr x amount of moles

What are reversible reactions?

Reactions where the reactants form the products and the products can form the reactants again

What is dynamic equilibrium?

• When the rate of forward reaction=the rate of backward reaction

• The concentrations of the reacting substances do not change

• The forward and backward reaction keep on going, they do not stop at equilibrium

What is the Haber process?

• The reaction of nitrogen and hydrogen to make ammonia

• This reaction is exothermic

• It is a reversible reaction- nitrogen and hydrogen from ammonia and ammonia breaks down to become nitrogen and hydrogen

• See image

How does the Haber process work?

• Nitrogen and hydrogen into the reaction vessel where they can mix together

• The temp inside the vessel is 450 degrees celsius and the pressure is 200 atmospheres

• There is an iron catalyst that speeds up the rate of reaction

• Some of the N and H reacts to form ammonia but some N and H will still be in the vessel because it is a reversible reaction

• The entire mixture is passed through a condenser and because ammonia has a low boiling point, it condenses into a liquid

• The hydrogen and nitrogen in the condenser stay as gasses and are passed back into the reaction vessel so they are not wasted and this repeats the process again

• See image

Why is a temperature of 450 degrees celsius used for the Haber process?

• A lower temperature is needed to favour the forward reaction which gives a higher percentage yield

• High temperatures are needed to increase the rate of reactions as the particles need a lot of kinetic energy

• 450 is used as a compromise because even though gives lower yield, it increases the rate of reaction

• Generating heat is expensive

Why is a pressure of 200 atmospheres used for the Haber process?

• A high pressure is needed for a higher percentage yield

• A higher pressure favours the side with less molecules which would be the right side (ammonia)

• High pressures increase the rate of reaction as it causes the particles to collide more frequently

• Maintaining a high pressure is very expensive

• High pressures can be very dangerous

How can changing the temperature, pressure, concentration of a reactant and adding a catalyst to an equilibrium reaction affect the rate of reaction?

Change in condition	Effect on equilibrium position	Effect on the rate of reacting equilibrium
Temp increase	Moves in direction of endothermic reaction	Rate increased
Pressure increase	Moves in direction of fewest molecules of gas	Rate increased (if reacting gases are present)
Concentration of reactant increased	Moves in direction away from reactant	Rate increased
Catalyst added	No change	Rate increased

What are the conditions chose for industrial processes of equilibrium related to?

• The availability of raw materials and energy supplies. Air and water are easily obtained but natural gas is difficult and expensive to obtain

• The control of temperature and pressure. Many industrial processes are not allowed to reach equilibrium because this would take too long

• The use of suitable catalyst such as iron. Processes can work at lower temps with catalysts, reducing cost and increasing yield

What are NPK fertilisers?

• Fertilisers supplying the elements nitrogen, phosphorous and potassium

• These elements must be supplied in soluble compounds:

  • Nitrogen- nitrate and ammonium salts

  • Phosphorous- phosphate salts

  • Potassium- potassium salts

How do chemical cells work with lead and bromine for example?

• Negatively charged bromine ions lose their electrons and become neutral atoms

• The electrons they lose are transported along the wire into the cathode

• At the negative cathode positively charged lead ions pick up those electrons and become neutral lead atoms

This is our flow around the circuit which produces electricity. This process will continue until all of the electrolyte is used up. When they are used up the battery is ‘flat’.

How do hydrogen-oxygen fuel cells work?

• Be aware that the anode is negative and the cathode is positive, the opposite of how it is in electrolysis

• The electrodes are made of porous carbon which contains tiny holes

• The electrodes also contains catalysts to speed up the rate of reaction

• Hydrogen atoms come in through the side with the anode and lose their electrons, becoming hydrogen ions

• The electrons move through the wire and to the cathode

• The hydrogen ions then move towards the cathode through the electrolyte

• Oxygen comes in from the side with the cathode and combines with the hydrogen and electrons to become water molecules

• The water molecules leave the cell though the outlet

The movement of electrons from the anode to the cathode creates an electrical current

What happens when hydrogen gets to the anode in a hydrogen oxygen fuel cell?

• Hydrogen is oxidised

• This sets up a potential difference across the two electrodes

• This is what drives the electrons around the circuit

What are the advantages and disadvantages of fuel cells?

• Suitable for portable appliances

• Cheap to manufacture

• May contain harmful substances

• Does not produce a voltage when one of the reactants is used up

What are the advantages of hydrogen-oxygen fuel cells?

• Produces water as it’s only waste

• Produces a voltage as long as the fuel and air are supplied

• Lasts longer than batteries because they have simple designs

• Less polluting to dispose of

What are the disadvantages of hydrogen-oxygen fuel cells?

• Not suitable for portable appliances

• Expensive to manufacture

• Hydrogen is a gas meaning it takes more space to store than fossil fuels or batteries

• Hydrogen is explosive when mixed with air- dangerous to store

• To make the hydrogen fuel it requires energy, normally from fossil fuels