Exam Qs Flashcards
What is meant by the term structural isomers? (1)
compounds/ molecules having the same general formula but different structural formulae
alkane with the lowest BP has the …………….. branching
most
catalyst required to prepare butan-2-ol from butene
H3PO4
What is meant by the term average bond enthalpy? (2)
Average enthalpy change when one mole of gaseous covalent bonds is broken
What properties make CFCs good for use as aerosols?
- low reactivity/ will not burn/ non-flammable
- volatile/ low BP
- non-toxic/ non-poisonous
Explain ‘Life on Earth benefits from the presence of an ozone layer’
Ozone absorbs UV (radiation)
UV at Earth’s surface is reduced
How is the concentration of ozone is maintained in the ozone layer?
O3 ⇌ O2 + O
Formation and breakdown of ozone is in equilibrium
Show how CF2Cl2 produces radicals which catalyse the breakdown of ozone
Production of radicals:
CF2Cl2 → •Cl+ CF2Cl
Breakdown of O3:
•Cl + O3 → ClO• + O2
ClO• + O → Cl• + O2
What happens to molecules when IR radiation is absorbed?
bond vibrates (more)
/ bends
/ stretches
What is meant by the term homologous series? (2)
series of organic compounds with the same functional group
and with each successive member differing by CH2
What does a curly arrow represent in mechanisms?
Movement of an electron pair
What is meant by the term nucleophile?
Electron pair donor
alkene -> alkane
reagents and conditions
H2
Ni catalyst
Suggest reasons why radical substitution produces a mixture of organic products (2)
Further substitution or Produces different termination products or More than one termination step
Substitution at different positions along chain
The calculated value of ΔHc from an experiment where a spirit burner is used to heat a beaker of water is different from the value obtained from data books.
Suggest reasons for the difference
Heat loss Incomplete combustion Non-standard conditions Evaporation of alcohol/water Specific heat capacity of beaker/apparatus
Why does the cyclopentane have a higher BP than cyclopropane? (2)
More carbons (in ring) OR more (surface area of) contact
AND more london forces OR stronger london forces
More energy needed to break the intermolecular forces
Suggest one advantage of adding cyclohexane to hexane in petrol.
cyclohexane will burn more efficiently
Explain what is meant by the term stereoisomers.
(Compounds with the) same structural formula but a different arrangement (of atoms) in space
Explain why the initiation step in radical substitution c fission.
the breaking of an X-X bond and the formation of two radicals
one electron from from the bonding pair goes to each atom
what are 3 features of a dynamic equilibrium?
- closed system needed
- rate of forward reaction = rate of reverse reaction
- relative conc of reactants and products does not change
standard enthalpy change of formation (3)
enthalpy change when one mole of a compound is formed from its elements under standard conditions (298K, 100kPa)
How is a salt formed in a reaction?
A hydrogen ion of an acid has been replaced by a metal ion
Describe what is meant by the term ionic lattice, in terms of type and arrangement of particles present
Regular repeating pattern
Of oppositely charged ions
Explain what is meant by the term base
A substance which readily accepts H+ ions from an acid
Explain what is meant by the term alkali
Species which releases OH- ions into aqueous solution
Explain what is meant by first ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Describe and explain the trend in first IE across P2
First IE increases
- similar shielding
- atomic radius decreases
- nuclear charge increases
-> outermost electron experiences greater electrostatic attraction to nucleus so requires more energy to remove
Describe and explain the trend in first IE down a group
- first IE decreases
- outer e experiences greater electron shielding
- increasing atomic radius
- despite increased nuclear charge
-> outer e experiences less attraction to nucleus so is easier to remove
Explain what is meant by isotopes
Atoms of the same element with different no. Neutrons and different masses
Explain what is meant by relative isotopic mass
The mass of an isotope compared with 1/12th the mass of an atom of C-12
Explain what is meant by relative atomic mass
The weighted mean mass of an atom compared with 1/12th the mass of an atom of C-12
Explain what is meant by the term orbital
Region around the nucleus that can hold up to two electrons with opposite spins
Sequence of tests for unknown salts
- carbonate
- sulfate
- halide
- NH4+
Describe the carbonate ion test
Add dilute nitric acid
Effervescence and gas produced turns limewater cloudy/milky
Describe the sulfate ion test
Barium chloride solution
White precipitate is barium sulfate
Describe the test for chloride ions
Add aqueous AgNO3
White precip of AgCl
Add dilute NH3
Dissolves
Describe the test for bromide ions
Add aq AgNO3
Cream precip of AgBr
Add dilute NH3 - doesn’t dissolve
Add conc NH3 - does dissolve
Describe the test for iodide ions
Add aq AgNO3
Yellow precip of AgI
Add conc NH3 - doesn’t dissolve
Describe test for NH4+
Add NaOH and warm
Pungent smell
Damp red litmus paper turns blue
Define an acid
A species which releases H+ ions in aqueous solution
Define a base
A compound that neutralises an acid to form a salt.
Proton acceptor
Define an alkali
a species which releases OH- ions in aqueous solution
Neutralisation is the…
reaction of H+ and OH- to form H20
Why is the reaction between copper(II) oxide and Hal slow at room temperature?
high activation energy because ions have to be separated from the solid before they can react
What observations do you make when copper(II) carbonate is added to HCl?
Green solid added to colourless solution
Solid disappears, effervescence and the formation of a blue/green solution
why is calcium nitrate an example of a salt?
it is formed when H+ ions from an acid are replaced by calcium ions (Ca2+)
explain how to OH- ion in calcium hydroxide acts as a base when it neutralises dilute nitric acid
the OH- ion accepts an H+ ion from HNO3 to form H2O
state one use of calcium hydroxide in agriculture and suggest why the amount of calcium hydroxide used should not be excessive (2)
- neutralise acidic soils
- Excess will result in soils becoming too alkaline (to sustain crop growth)
why does bp of the halogens increase down the group?
van der Waals’ forces OR induced dipole interactions
Additional Guidance
number of electrons increases
Down the group, intermolecular forces / van der Waals’ forces increase
OR
Down the group, more energy needed to break intermolecular / van der Waals’ forces
state one advantage and one disadvantage of using chlorine in water treatment
Advantage
removes or kills bacteria OR kills germs OR
kills micro-organisms OR make it safe to drink OR sterilises water OR disinfects water
Disadvantage
it is toxic OR poisonous OR could form chlorinated hydrocarbons
ALLOW forms carcinogens OR forms toxins IGNORE harmful
in terms of bond breaking and forming, explain why a reaction is exothermic
bond breaking absorbs energy and bond forming releases energy
more energy is released than absorbed
so exothermic
describe how chemists can reduce environmental damage from disposal of polymers
Incineration to produce energy OR combustion to produce energy
Sorting and recycling OR sorting and remoulding Cracked (to give monomers) OR as an organic feedstock
NUCLEOPHILE
It is an electron pair donor OR can donate a lone pair
lattice enthalpy
(The enthalpy change that accompanies)
the formation of one mole of a(n ionic) compound from its gaseous ions (under standard conditions)
