chemistry paper 2 Flashcards
why do giant ionic structures have high melting and boiling points?
1- the ions are held together in a closely pack 3D lattice arrangement by the attraction between the oppositely charged ions
2- the electrostatic attraction between oppositely charged ions is very strong- a lot of energy is needed to overcome the strong attraction so ionic compounds have high melting and boiling points
how do the charges affect the strength of ionic bonding?
higher charge ions have stronger forces of attraction between them so have higher melting and boiling points
draw the structure of sodium chloride
Na+ and Cl- alternate
describe the bonding in diamond and draw its structure
- each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure.
- this structure makes diamond the hardest natural substance- used for drill tips and cutting tools
describe the bonding in graphite and draw its structure
- each carbon atom forms 3 covalent bonds, creating layers which are free to slide over each other.
- this makes graphite useful as a lubricant
- also leaves free electrons so graphite is the only non-metal which is a good conductor of electricity
what’s the equation for percentage yield?
percentage yield= actual yield (g)/ theoretical yeild (g) x 100
what is the number 6.023 x 10^23 called?
Avogadro’s number or the Avogadro constant
what is Avogadro’s law?
one mole of any gas always occupies 24 dm^3 at room temperature and pressure (25 ‘C and 1 atmosphere)
volume (dm^3) =
moles of gas x 24 = mass of gas/Mr of gas x 24
how do you calculate volumes in reactions if you know the masses?
1) find the reacting mass
2) convert the mass into a volume using vol=moles x 24
what forms in the electrolysis of aqueous solutions?
ions from the ionic compound, hydrogen ions H+ and hydroxide ions OH- from the water
what happens at the cathode of the electrolysis of aqueous solutions?
if H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions are more reactive than the H+ ions. If the metal ions are less reactive than the H+ ions then a solid layer of pure metal will be produced instead
what happens at the anode of the electrolysis of aqueous solutions?
if OH- and halide ions (Cl-, Br-, I-) are present, molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, the oxygen will be formed
what does a solution of sulfuric acid (H2SO4) contain?
3 different ions: SO4^2-, H+ and OH-
what happens at the cathode of the electrolysis of sulfuric acid?
hydrogen ions from the water or sulfuric acid accept electrons, so at the cathode hydrogen gas is produced
2H+ + 2e- –> H2
what happens at the anode of the electrolysis of sulfuric acid?
hydroxide ions lose electrons more easily than sulfate ions, so at the anode oxygen and water are produced
4OH- —> O2 + 2H2O + 4e-
what does a solution of sodium chloride (NaCl) contain?
4 different ions: Na+, Cl-, OH- and H+
what happens at the cathode of the electrolysis of sodium chloride?
hydrogen ions accept electrons more easily than sodium ions, so at the cathode, hydrogen gas is produced
2H+ +2e- –> H2
what happens at the anode of the electrolysis of sodium chloride?
chloride ions lose electrons more easily than hydroxide ions, so at the anode chlorine gas is produced
2Cl- –>Cl2 + 2e-
what does a solution of copper (ll) sulfate (CuSO4) contain?
4 different ions: Cu^2+, SO4 ^2-, H+ and OH-
what happens at the cathode of the electrolysis of copper (ll) sulfate?
copper ions accept electrons more easily than hydrogen ions, so at the cathode, copper metal is produced
Cu^2+ + 2e- –> Cu
what happens at the anode of the electrolysis of copper (ll) sulfate?
hydroxide ions lose electrons more easily than sulfate ions, so at the anode oxygen and water are produced
4OH- –> O2 + 2H2O + 4e-
how does the number of electrons transferred increase?
with time and current
what is the amount of product made by electrolysis depend on?
the number of electrons that are transferred
what does one amp flowing for one second mean?
a charge of one coulomb has movec
charge=
current x time
what’s one faraday?
96000 coulombs
what does one faraday F contain?
one mole of electrons
how do you convert coulombs to faradays?
divide coulombs by 96000
how many moles of electrons to make one mole of atoms with a 1+ charge?
1 mole of electrons (1 faraday)
how many moles of electrons to make one mole of atoms with a 2+ charge?
2 moles of electrons
how many moles of electrons to make one mole of atoms with a 3+ charge?
3 moles of electrons
what are the steps to find the mass of product produced when you are give time, current and reactant?
1) write out the balanced half-equation for electrode where the product is produced - cathode
2) calculate the no. of faradays:
coulombs= (amps x time (s) )
no. of faradays= coulombs/ 96000
3) calculate the number of moles of product produced:
divide the number of faradays by the number of electrons in the half-equation
4) write in the Mr values from the periodic table to work out the mass of product produced- mass = Mr x no. of moles
why do atoms lose electrons more easily down group 1?
1) all group 1 metals have 1 electron in their outer shell
2) as you go down group 1, the outermost electron is in a shell that’s further from the nucleus.
3) which means the attraction between the outermost electron and the nucleus becomes less
4) so as you go down Group 1 the atoms get bigger, the outer electron is more easily lost and the metals are more reactive
how can ethanol be produced from ethene and steam?
1) ethene is produced from crude oil by cracking
2) ethene (C2H4) will react with steamm (H2O) to make ethanol
3) needs a temp of 300’C and a pressure of 60-70 atmospheres
4) PHOSPHORIC ACID is used as a catalyst
5) cheap process as ethene is fairly cheap and not much is wasted
- but crude oil is non-renewable so will start running out soon- so will become an expensive process
what’s the equation to make ethanol from steam and ethene?
C2H4 + H2O -> C2H5OH
how can ethanol be produced by fermentation?
1) the raw material for fermentation is sugar e.g. glucose.This is converted into ethanol using yeast
2) this process needs a lower temperature about 30 and simpler equipment than using ethene
3) the raw materials are renewable resources- sugar and yeast are easy to grow
4) ethanol isn’t very concentrated so it needs to be distilled to increase its strength and purified.
how can ethanol be dehydrated to form ethene?
1- remove water from the ethanol in a dehydration reaction
2) ethanol vapour is passed over a hot catalyst of aluminium oxide, Al2O3- the catalyst provides a large surface area for the reaction
what’s a laboratory experiment set up fort the dehydration of ethanol to form ethene?
- soak ceramic wool in ethanol and put at the bottom of a test tube.
- in the centre of the test tube put aluminium oxide powder
- put a bung in the tube attached with a delivery tube to a measuring cylinder using upward delivery through a water bath.
- place a Bunsen burner beneath the aluminium catalyst in the tube
what’s the chemical equation for the dehydration of ethanol?
C2H5OH –> C2H4 + H2O
what is bond energy?
the amount of energy in a bond- each type of chemical bond has a particular bond energy associated with it
enthalpy change=
Total energy absorbed to break bonds - Total energy released in making bonds
if it’s negative change then the reaction is exothermic
how do you calculate the molar enthalpy change?
1- calculate the amount of energy transferred
2- fine how many moles of fuel produced this heat- mass of fuel burnt/ Mr
3- the heat produced by 1 mole o fuel = joules of energy produced/ moles (if it is an exothermic reaction then the joules of energy will be negative)
draw chloroethene and poly(chloroethene)
CH2=CHCl and CH2- CHCl
what’s condensation polymerisation?
- involves two different types of monomer
- the monomers react together and bonds form between them, making polymer chains
- for each new bond that forms, a small molecule, e.g. water, is lost
give an example of condensation polymerisation
nylon
draw two monomers -> condensation polymer + water
what’s poly(chloroethene) used for?
making clothes, and pipes for insulating electrical cables
what is the contact process?
it’s used to make sulfuric acid
what are the 4 stages of the contact process?
1) first forming SULFUR DIOXIDE (SO2) gas- BURNING sulfur in air or roasting sulfide ores
S + O2 -> SO2
2) the sulfur dioxide is then OXIDISED with a catalyst, to form SULFUR TRIOXIDE (SO3)
2SO2 + O2 –> 2SO3
3) the sulfur trioxide is DISSOLVED in concentrated sulfuric acid to form liquid OLEUM
SO3 + H2SO4 –> H2S2O7
4)oleum is DILUTED with measure amounts of water to form concentrated sulfuric acid
H2S2O7 + H2O –> 2H2SO4
What type of reaction is step two in the contact process?
exothermic-gives out heat- there are 2 moles of product compared to 3 moles of reactants so the product has less volume than the reactants
how do you get maximum yield in the contact process?
reduce the temperature and increase the presuure but reducing temp slows down the reaction
what are the conditions needed in the contact process?
1) TEMPERATURE: 450’C
2) PRESSURE: 2 atmospheres
3) CATALYST: Vanadium (V) oxide , V2O5
what’s sulfuric acid used for in industry?
1- fertilisers- mostly used to make phosphate fertilisers- farmers use them to improve the amount of nutrients in the soil to increase plant growth
2- detergents- used for cleaning anything
3- paints- sulfuric acid is used to make TITANIUM DIOXIDE, which is a white PIGMENT that’s used in paints and white lines on tennis courts
what is brine?
sodium chloride solution
how is brine electrolysed industrially? and what does it produce?
using a diaphragm cell- 3 useful products: hydrogen gas, chlorine gas and sodium ions
what happens at the cathode in the electrolysis of brine?
hydrogen gas is given off -2 hydrogen ions accept 2 electrons to become one hydrogen molecule
2H+ +2e- –> H2
what happens at the anode in the electrolysis of brine?
chlorine gas is given off- two chloride ions (Cl-) lose their electrons and become one chlorine molecule
2Cl- –> Cl2 + 2e-
what happens to the sodium ions in the electrolysis of brine?
they stay in solution and the hydroxide ions from the water are also left behind. this means that sodium hydroxide is left in the solution
what’s chlorine used for?
to sterilise water supplies- chlorination. and to make bleach and HCl
what’s hydrogen used for?
used in the Haber process and to change oils into fats for making margarine
what’s sodium hydroxide used for?
very strong base and used widely in the chemical industry- to make soap, bleach and paper pulp
