Exam questions Flashcards
two characteristics of a homologous series (2)
- general formula
- similar chemical properties
suggest why the branched chain isomer shown above has a lower boiling point? (2)
- less surface area
- weaker van der waals
state what is meant by the term stereoisomers (2)
- same structural formula
- different orentation
explain how these oxides of nitrogen are formed (2)
when there is a spark and a high-temperature nitrogen and oxygen in the air bond together
Nucleophile (1)
electron pair donator
substitution, as applied to nucleophilic substitution in a haloalkane (1)
halogen is substituted
hydrolysis (1)
splitting molecules using water
describe how ions are formed in a time of flight mass spectrometer (2)
- high voltage is applied to the sample
- element vapourised into gas
- electron knock out or orbit
a mass spectrometer can be used to determine the relative molecular mass of molecular substances.
explain why it is necessary to ionise molecules when measuring their mass in a mass spectrometer (2)
- ions are accelerated by an electric field
- only ions will create a current when they hit the plate
outline how the mass spectrometer is able to separate two species to give two peaks (4)
- positive ion accelerates by an electric field
- to a constant kinetic energy
- lighter ions travel quicker
- so will be detected first
why is the first ionisation energy of Krypton is greater than that of bromine (1)
more protons than bromine
in 1963, Krypton was found to react with fluorine. state why this discovery was unexpected
krypton is a noble gas
Describe how ions are formed in time of flight mass spectrometer
Element go into the mass spectrometer and are bombarded with electron which knocks the electron out of orbit making it a positive ion. High voltage is applied to the sample
The element is vaporised into a gas
Mass spectrometer can be used to determine the relative molecular mass of molecular substance
Explain why it is necessary to ionise molecules when measuring their mass in a mass spectometer
Ions are accelerated by an electric field
Only ions will create a current when they hit the plate
Outline how the TOF mass spectrometer is able to separate two species to give two peaks
Positive ion accelerate by an electric field
To constant kinetic energy
Lighter ion travels quicker
So will be detected first
Define the term relative atomic mass
Average mass of one atom / (1/12) of a carbon 12 atom
State why the isotope 10B and 11B have similar chemical reactions
Same number of electrons
Explain why the second ionisation energy of boron is higher than the first ionisation energy of boron
You have to remove an electron from a positive ion which requires more energy
Give one reason why the second ionisation energy of silicon is lower than the second ionisation energy of aluminium
You have to remove an electron from a shell (3p orbital) needs more energy shell than the ‘s’ shell
State the type of reaction that occurs when calcium carbonate reacts with nitric acid
Neutralisation
Explain why the melting point of sodium chloride is high
Strong electrostatic attraction between the positive and negative ions, you need a lot of heat to overcome the forces
Name the type of bonding in sodium chloride
Ionic
Suggest why the melting point if sodium iodide is lower than the melting point of sodium bromide
Iodide is lower on the periodic table than sodium so its less reactive
What is the formula of calcium nitrate (IV)
A CaNO3
B Ca(NO3)2
C Ca2NO2
D Ca(NO2)2
B
State the meaning of the term covalent bond
Chemical bond where a pair of electrons are shared between two atoms
BF4-
Name the type of bond formed when a molecule of BF3 reacts with an F- ion. Explain how the bond is formed
Co-ordinate bonding
The 4 fluorine shares its electrons with boron but that fluorine hasn’t lot a full outer shell so has a negative charge
Explain why nickel has a high melting point
They are strong because a lot of force has to be used to overcome the force of attraction between electron and positive ions
Explain why nickel is ductile
Its layers can side over each other
Define the term electronegativity
The power of the atom to attract an electron in a covalent bond
Explain how the strongest type of intermolecular force in liquid HF arises
Large difference in electronegativity between H and F and there is a dipole formed which are then attracted into each other
Explain the trend in the boiling points of hydrogen halides from HCl and HI
Van der waals
Increasing size
Give one reason why the boiling point of HF is higher than that of all the other hydrogen halides
Hydrogen bonding needs more energy to break the bonds
Iodine and diamond are both crystalline solids at room temperature. Identify one similarity in the bonding, and one difference in the structure of these two solids. Explain why these two solids have very different melting points
Iodine
Covalent bonds
Molecular
Weak van der waals forces
Diamond
Giant molecular
Covalent bonds
Higher melting point
Predict the shape of the AlH4-
Explain why it has this shape
Tetrahedral
Equal repulsion form four bonding pairs
Outline how the mass spectrometer is able to separate these two species to give two peaks
The ion is accelerated by the electric field to a constant kinetic energy. One species would be lighter so would be detected first
Explain in the terms of electronegativity why the boiling point of H2S2 is lower than H2O2
Oxygen has a higher electronegativity change than sulphur
No hydrogen bonding
Describe the structure of and bonding in graphite and explain why the melting point of graphite is very high
Covalent bonds need a lot of energy to break
Graphite has layers
Have to break lots of bonds
Explain why iodine vaporises when heated gently
Weak intermolecular forces (weak van der waals) so not much energy is needed to break the bonds
State why iodine is a very poor conductor of electricity
No delocalised electrons
State two characteristics of a homologous series
General formula
Similar chemical properties
Suggest why the branched chain isomer shown above has a lower boiling point than octane
Less surface area
Van der waals
State what is meant by the term stereoisomers
Same structural formula
Different orientation
Suggest one improvement that would reduce errors due to heat loss in the student experiment ( p= mcΔt )
If you put a lid on the breaker so no gas can escape or heat
Give the meaning of the term mean bond enthalpy
Change in heat breaking the covalent bond
Give one reason why titanium is not extracted from titanium oxide using carbon
Product is brittle
Give the meaning of the term enthalpy change
Heat given out or taken in when bonds are broken at constant pressure
State hess’s law
Heat change at constant pressure
Define the term standard enthalpy of formation
When one mole of substance is bonded to form its elements with all reactants and products in their standard states
Explain the term mean bond enthalpy
The average bond enthalpy produced from different bonds ( enthalpy energy to break a covalent bond)
Define the term atomic number
Amount of protons in the nucleus
Explain why atoms of an element may have different mass number
Different number of neutrons
The first ionisation energy of krypton is greater than that of bromine
More protons than bromine
State and explain the trend in electronegativity values across period 3 from sodium to chlorine
It would increase
Number of protons increase in the same shell
Predict the type of crystal structure in solid zinc fluoride and explain why its melting point is high
Ionic
Strong electrostatic forces between ions so a lot of energy is needed to over come the electrostatic force between oppositely charged ions
Name the device used to ionise atoms in a mass spectrometer
Electron gun
BrF4- ions are also formed when potassium fluoride dissolves in liquid BrF3 to form KBrF4. explain in terms of bonding why KBrF4 has a high melting point
has a high melting point because of ionic bonding is strong because the electron aren’t shared between K+ and BrF4- are attracted to each other. strong electrostatic forces between oppositely charged ions creating on ionic lattice
state the strongest type of intermolecular force between hydrogen fluorine molecules
hydrogen bonding
the boiling points of fluorine and hydrogen Florine are low. explain why?
fluorine is covalently bonded together by weak van Waals forces where the hydrogen bonds are stronger than van waals
identify from the period 2 elements that has the largest atomic radius
lithium
state the general trend in first ionisation energies for the period 2 elements lithium to nitrogen
increases
identify the element that deviates from this general trend, from lithium to nitrogen, and explain your answer
Boron
electron removed from the 2p orbital which is higher in energy
explain in terms of structure and bonding why the melting point of carbon is high
giant molecular
strong covalent bonds
bonds must be broken
name a raw material from which hexane is obtained
crude oil
name the process used to obtain hexane from this raw material
fractional distillation
state the type of cracking that produces a high percentage of alkenes. state the conditions needed for this type of cracking
termal cracking
high temperature and high pressure
explain the main economic reason why alkanes are cracked
short-chain alkanes are more in demand so are worth more money than long-chained alkanes
identity a metal used as a catalyst in a catalytic converter. suggest one reason, other than cost, why the catalyst is coasted on a ceramic honeycomb
platinum
bigger surface area
suggest one reason why the yield of nitrogen dioxide formed during this reaction is often less than expected
decomposition not complete
by-products formed
suggest one reason why it is difficult to obtain a pure sample of nitrogen dioxide from this reaction
hard to separate the two gases
state the type of structural isomerism shown by but-1-ene and but-2-ene
positional
in industry, this fermentation reaction is carried out at 35 rather than 25. suggest a advantage and disadvantage
Ad= reaction would happen quicker Dis= uses more energy
state a condition of thermal cracking
high pressure and high temperature
the reaction is exothermic.
explain the effect of a change of temperature on both the position of equilibrium and the rate of reaction, and justify why a compromise temperature is used industrially
High temperature
- le chameliers principle predicts that equilibrium shifts to oppose any increase in temperature
- exothermic reaction
- high temperature= reduce yield
high temperature
- more high energy molecules
- more collisions
- rate of reaction increase
in a trial experiment the student failed to fill the burette correctly so that the gap between the tap and the tip of the burette still contained air. suggest what effect this would have on the measured volume of bromine water in this trial. explain your answer
- measured volume would be greater
- level in burette falls as the tap is filled before any liquid is delieved
other an not filling the bottom of the tap, suggest a reason for an inconsistency in the students results
drop size may vary
outline how the student could improve this practical procedure to determine the number of c=c double bonds in a molecule of the oil so that more consistent results are obtained
- larger single volume of oil
- dissolve oil
- transfer to conceal flask and make up 250cm3
- tritate (25cm3) sample from the flask
which statement about ethene is correct?
A- it has no geometric isomers because there is free rotation around the C=C bond
B-it reacts with HBr in a nucleophilic addition reaction
C-it burns in excess oxygen to produce carbon dioxide and water
D-the C=C bond is twice as strong as the C-C bond in ethane
C
what statement about ethanal is correct?
A-reacts with Tollens’ reagent to form silver
B-higher boiling point than ethanol
C-empirical and molecular formulas are different
D-belongs to a homologous series with general formula CnH2n+1O
A
which of these substances does not contribute to the greenhouse effect? A-unburned hydrocarbons B-carbon dioxide C-water vapour D-nitrogen
D
suggest a name for this type of reaction that iron(III) nitrate undergoes
thermal decomposition
suggest why the iron (III) oxide obtained is pure
other products are gases
explain, in terms of its structure and bonding, why nickel has a high melting point
nickel has a high melting point because its metallic bonded where there is a sea of delocalised electrons around the positive ions
explain why nickel is ductile
layers that can slide over each other
name the strongest attractive force between two ammonia molecules
hydrogen bonding
give the meaning of the term electronegativity
ability of an molecules to attract on electron pair in a covalent bond
oxides of nitrogen are also produced during the combustion of paraffin in air. explain how these oxides of nitrogen are formed
a spark in engine creates a high temperature where nitrogen an oxygen in the air
explain why the melting point of Dodecanese is higher than the melting point of the straight-chain alkane produced by cracking dodecane
melting point is higher because dodecane has more van Der Waals forces so if it has longer chains than more energy is needed so the melting point is higher
thallium bromide (TlBr) is a crystalline solid with a melting point of 480 degrees. suggest the type go bonding present in thallium (I) bromide and state why the melting point is high
ionic bonding
oppositely charged ions
strong attraction between ions
suggest one reason other than incomplete combustion or heat transfer to the atmosphere why the students value of enthalpy is different
heating in the container
the student said correctly that using a thermometer with an overall uncertainty for this experiment was ±0.25 was adequate for this experiment.
explain why this thermometer was adequate for this experiment
heat loss is a bigger uncertainty
octane and isooctane can be separated in the laboratory. name a laboratory technique that could be used to operate isooctane from a mixture of octane and isooctane
distillation
heat the mixture up
distilled off then condensed
explain how a catalyst works
provides an alternate route with a lower activation energy
platinum, palladium and rhodium are metals used inside catalytic converters. a very thin layer of the metals is used on a honeycomb ceramic support.
explain why a thin layer was used in this way
large surface area reduces cost (uses less money)
identify a reagent that could be used in a chemical test to show that oleic acid is unsaturated
state that would be observed in this test
bromine solution
orange to colourless
explain why 1,1,1-trifluoroethane does not lead to the depletion of the ozone in the upper atmosphere
C-F bond is strong
anti-bumping granules are placed in the flask when refluxing. suggest why these granules bumping
preventing vicious boiling
Magnesism oxide is a white solid with a higher melting point
Explain how the ions are held together in solid magnesium oxide
Electrons are transferred
Electrostatic attraction between charged ions