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A-Level Chemistry [OCR B Salters] (sorry for any spelling mistakes - there are many) > [Year 1] OZ > Flashcards

[Year 1] OZ Flashcards

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1
Q

What is electronegativity?

A

The ability for an atom to attract electrons towards itself in a covalent bond.

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2
Q

What is the trend in electronegativity on the periodic table?

A

Further up and right you go the more electronegative the element is (Fluorine is the most electronegative).

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3
Q

What makes a bond more ionic?

A

The greater the difference in electronegativity the more ionic the compound will be.

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4
Q

What is the Pauling scale?

A

A scale that helps us quantify electronegativity.

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5
Q

What is the electronegativity difference of a purely covalent bond?

A

0

e.g. Cl-Cl

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6
Q

What make a bond more polar?

A
  • A bigger difference in electronegativity

- which pulls the shared electrons in a covalent bond closer to the more electronegative atom.

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7
Q

How can we show polarity?

A

δ- and δ+

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8
Q

What is a polar molecule?

A

The uneven distribution of charge.

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9
Q

What are the three intermolecular forces/bonds in order of strength (Strongest first)?

A

Hydrogen Bonding.
Permanent dipole-permanent dipole.
Instantaneous dipole-induced dipole.

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10
Q

How are id-id forces made?

A
  • Any molecule or atom with electrons moves near to another atom or molecule.
  • The electrons in the molecule or atom can move from one end to another creating an instantaneous dipole.
  • The δ- on one atom will repel electrons from neighbouring atoms inducing a δ+ near it.
  • This will attract to the δ- on another and a force of attraction is created.
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11
Q

What happens when instantaneous dipoles move away from each other?

A

The id-id interaction is destroyed.

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12
Q

How does Iodine from crystal structures?

A
  • Weak id-id forces hold iodine molecules together.
  • Strong covalent bonds hold the 2 iodine atoms together.
  • This creates a well-defined repeating structure.
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13
Q

Why does Iodine form crystals but Fluorine does not?

A
  • The bigger the molecule or atom, the more id-id forces. As you have larger electron clouds.
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14
Q

What happens when we boil a liquid?

A
  • We break the weak id-id forces NOT the covalent bonds.

- To do so we must have enough energy to overcome these forces.

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15
Q

Why does the boiling point of hydrocarbons increase as you get longer straight-chain hydrocarbons?

A
  • Longer straight-chain hydrocarbons have more id-id forces.
  • More energy is needed to overcome its force.
  • Thus boiling point increases.
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16
Q

How does branching effect id-id forces?

A
  • Hydrocarbons that are branched can’t pack as closely together.
  • This weakens the id-id forces between the chains.
  • Thus lowering there boiling point.
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17
Q

When do we get pd-pd interactions?

A

When we have molecules with a permanent polarity.

This creates a weak electrostatic force between δ- and δ+ atoms of different molecules. (In addition to id-id forces)

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18
Q

How can we test for polar molecules?

A
  • Placing a charged rod near a steady stream of a polar liquid.

(the steady stream can be made by passing the liquid through burette)

  • Polar liquids will bend towards the rod as the molecules align to face the opposite charges rod.
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19
Q

When does Hydrogen bonding occur?

A

When hydrogen on one molecule forms a bond with the lone pair on nitrogen, oxygen, or fluorine.

(alongside pd-pd and id-id forces)

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20
Q

What are the features of Hydrogen bonding?

A
  • Hydrogen bonds in ice form a regular structure, there are further apart than in water, making ice less dense.
  • Hydrogen bonds are the strongest intermolecular force hence hydrogen fluoride has a higher melting point than hydrogen iodide. As more energy is needed to overcome the electrostatic force.
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21
Q

How can we investigate the strength of an intermolecular bond?

A
  • Place dry filter paper around the bulb of a thermometer and take the temperature (control)
  • Dip the filter paper into 3 samples with different strengths of intermolecular bonds (Haxane, Ethanol, and Water) for about 5 minutes.
  • Record temp change.

Hexane (id-id) highest temperature change.
Ethanol (1 hydrogen bond per molecule) lower temperature change.
Water (2 hydrogen bonds per molecule) lowest temperature change.

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22
Q

Define the rate of a reaction?

How can you calculate it?

A

The change of concetration/amount of a reactant or product per unit time.

Rate = (reactant used [OR] product made) / time

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23
Q

What is collision theory?

A
  • For a reaction to occur the particles must collide in the right direction.
  • And have the minimum amount of kinetic energy required.
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24
Q

What is the activation energy?

A

The minimum amount of energy required for a reaction to occur.

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25
Q

How might you show a change in energy in a reaction?

A

With an energy profile diagram.

  • Enthalpy by Reaction progress.
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26
Q

What does the Maxwell-Boltzman distibution show?

A

The energy in gas particles.

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27
Q

What is the area under a Maxwell-Boltzman distribution curve?

A

Total number of molecules.

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28
Q

What does the peak of a Maxwell-Boltzman distribution curve show?

A

The most likely energy of a particle in a sample.

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29
Q

Describe why a Maxwell-Bolzman distribution curve changes if the temperature of a reaction increases.

A
  • Particel have, on average, more kinetic energy when they are heated.
  • A larger proportion of the molecules will have energy greater than the activation energy.
  • So there will be a larger area under the curve beyond the activation energy.
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30
Q

State what happens to a Maxwell-Bolzman distribution curve if the temperature of a reaction increases.

A
  • The curve shifts RIGHT
  • The peak is LOWER.
  • The area under the curve is the SAME.
  • The area under the curve beyond the activation energy INCREASES.
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31
Q

Why do we see a faster rate of reaction when temperature increases?

A
  • Particles move around more at higher temperatures.
  • So they collide more often.
  • These collisions are more energetic (seen in Maxwell-Boltzman distribution curve).
  • So a small increase in the temperature leads to a large increase in rate.
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32
Q

How does pressure effect the rate of reaction?

A
  • Inreace in pressure will increas the rate of reaction.
  • As particles are closer together.
  • So the collide more often.
  • More frequent collisions results in a higher chance of a reaction.
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33
Q

How does concentration effect the rate of reaction?

A
  • Increase in concentration will increase the rate of reaction.
  • As particles are closer together.
  • So the collide more often.
  • More frequent collisions results in a higher chance of a reaction.
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34
Q

What is a catalyst?

A
  • A substance that increases the rate of reaction.
  • By providing an alternative pathway that has a lower activation energy.
  • The catalyst is chemically unchanged at the end of the reaction.
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35
Q

How does a catalyst effect a Maxwell-Boltzman distribution curve?

A
  • Shifts the activation energy further to the left.
  • This means the area under the graph beyond the activation enthergy is increased.
  • So more molecules are able to react successfully.
36
Q

How does a catalyst effect a energy profile diagram?

A
  • It provides an alternative pathway.
  • And thus lowertes the activation energy curve.
  • So less energy is required for the reaction to progress.
37
Q

What is a homogeneous catalyst?

A
  • A catalyst that is in the same phase as the reaction.

- For example aqueous in aqueous reactants.

38
Q

How do homogeneous catalysts behave differently to heterogeneous ones?

A
  • They for intermediate species.
  • By reactants combining with the catalyst wich then react to form the products.
  • Being reformed again.
39
Q

Decribe what a energy profile graph looks like with a homogeneous catalyst as oppose to a heterogeneous one?

A
  • They have two activation energies.

- Like a camel hump

40
Q

What are methods of measuring rate?

A

How long it takes for a precipitate to form:

  • Place a cross and time how long it takes for the cross to disappear (precipitate to form).
  • Use the same person to observe to reduce error.

Amount of mass lost:

  • For reactions that produce a gas, place on a balance and measure the mass loss as gas periodically.
  • Use a fume cupboard if gas is harmful or toxic.

Volume of gas produced:

  • If gas is produced, measure the amount of gas produced using a gas syringe.
  • Measure this over a specified time.

Measure change in temperature.
- Usign thermometer and timing periodic change.

Measure the change in pH.
- Usign pH probe and timing periodic change.

Measure via titration:
- by taking samples of the reaction at regular intervals.

41
Q

How can rate be calulated from a graph (linear)?

A
  • From the gradient.

use a bigger section of a graph to get a better accuracy

42
Q

How can rate be calulated from a graph (curved)?

A
  • draw a tangent (at specified time).
  • From the gradient.

(use a bigger section of a graph to get a better accuracy)

43
Q

What is a halo alkane?

A

Alkanes with one or more halogen attached to it.

44
Q

How are haloalkanes named?

A
  1. Find longest carbon chain (the last part of the name)
  2. The names and positions of the halogens on the molecule comes fist.
    - Flouro-
    - Chloro-
    - Bromo-
    - Iodo-
    IN ALPHABETICAL ORFER IF THERE IS MORE THAN ON HALOGEN.
  3. If there are more than one of the same halogen use the prefix ‘di’, ‘tri’, or ‘tetra’.
45
Q

Draw 1-bromo-1,1-dichloro-2-iodoethane.

A

[google image if not clear]

  • 2 carbons.
  • 2 ‘H’ and 1 ‘I’ on one carbon.
  • 2 ‘Cl’ and 1 ‘Br’ on the other.
46
Q

What is the trend in boiling point of halogenoalkanes?

And why?

A
  • Increase as they go down the group.
  • As you go down the group (7) the number of electrons in the halogen increases.
  • This means there are stronger instantaneous diploe-induced dipole forces between the molecules.
  • So more energy is needed to overcome these forces.
47
Q

How does bond polarity and nucleophiles relate to haloalkanes?

A
  • Haloalkanes have a polar bond and so are attacked by nucleophiles.
48
Q

What is a nulceophile?

A

A substance that is an electron pair donor.

49
Q

What are examples of nucleophiles?

A
  • Ammonia (NH₃): one lone pair.
  • Water (H₂O): two lone pairs.
  • Hydroxide ions (OH⁻): two lone pairs.
50
Q

How do haloalkanes react with hydoxide ions?

What are the conditions?

A

Via a nucleophilic substitition.

  • Warm aqeous sodium hydroxide,
  • Under reflux.
51
Q

Decribe the mechanism for the reaction between Sodium hydroxide and chloroethane.

A
  • The lone pair of electrons on the hydroxide ion (the nucleophile) will attack the 𝛿+ Carbon (with the chlorine bonded to it).

(the hydroxide ion was bonded to the sodium but this is ignored as it is the spectator ion.)

  • This heterolyiclalt breaks the C-Cl bond, moving both electrons from the bond onto the 𝛿- chlorine.
  • The halogen is kicked of leaving ethanol and a chlroine ion.

(the chorine can then ionically bond with sodium.)

52
Q

What does heterolytic mean?

A

When both electrons from a bond move.

Shown by a double headed arrow.

53
Q

How do haloalkanes react with water?

What are the conditions?

A

Via a nucleophilic substitition.

  • Heat with water (steam).
54
Q

Decribe the mechanism for the reaction between water and chloroethane.

A
  • A lone pair of electrons on the water (the nucleophile) will attack the 𝛿+ Carbon (with the chlorine bonded to it).
  • This heterolyiclalt breaks the C-Cl bond, moving both electrons from the bond onto the 𝛿- chlorine.
  • The halogen is kicked of and an intermediate is foremed, as the whole molecule of water is bonded.
  • This intermediate is not stable (the O is positively charged).
  • electrons from a O-H bond breaks heterolytically, with its electrons moving to the O.
  • Ethanol is formed leaving a H⁺ ion.
  • The H⁺ ion can then react with the Cl⁻ ion to form HCl.
55
Q

How do haloalkanes react with ammonia?

What are the conditions?

A

Via a nucleophilic substitition.

  • Heat with ethanolic ammonia.
  • Must have excess ammonia.
56
Q

Decribe the mechanism for the reaction between ammonia and chloroethane.

A
  • A lone pair of electrons on the ammonia (the nucleophile) will attack the 𝛿+ Carbon (with the chlorine bonded to it).
  • This heterolyiclalt breaks the C-Cl bond, moving both electrons from the bond onto the 𝛿- chlorine.
  • The halogen is kicked of and an intermediate is foremed, as the whole molecule of ammonia is bonded.
  • This intermediate is not stable (the N is positively charged).
  • The excess ammonia now act as a base and reacts with the H in an N-H bond
  • electrons from a N-H bond breaks heterolytically, with its electrons moving to the N, stabilising it.
  • An amine is formed leaving an NH₄⁺ ion (amonium).
  • The NH₄⁺ ion can then react with the Cl⁻ ion to form ammonium chloride.
57
Q

What happends to the reactivity of haloakalnes as you go down the group?

Why?

A

They become more reactive.

  • because as you go down the group the bond enthaplies of C-X (X = halogen) becomes smaller.
  • C-I has the lowest bond enthalpy and is easiest to break, therefore it is more reactive.
58
Q

What experimanetal evidence can you give to test the reactivity of haloalkanes?

A

React with aqueous silver nitrate.

  • place chloroalkane, bromoalkane, and iodoalkane into 3 test tubes.
  • Add silver nitrate solution and ethanol (solvent) into each tube.
  • Yellow precipitate forms first (silver iodide)
  • Then cream precipitate (silver bromide)
  • And then white precipitate (silver chloride)
59
Q

What is bond fission?

A
  • The breaking of a covalent bond.

- The electron pair in the bond can be distributed in 2 ways. (homolytic and heterolytic)

60
Q

What are the types of bond fissions?

A

Homolytic:
- Electrons distributed equally to form 2 uncharged radicals.
(single-headed arrows showing a single electron moving)

Heterolytic:
- Electrons distributed unequally to form 2 different ions.
(double-headed arrows showing a pair of electrons moving)

61
Q

What are the stages of a free radical chain reaction?

A
  • Initiation.
  • Propagation.
  • Termination.
62
Q

What happens in the initiation stage of a radical chain reaction?

A
  • Radicals are produced using visable or UV light - called a photochemical reaction.
  • The bond breaks homolytically producing 2 radicals.
63
Q

What happens in the propagation stage of a radical chain reaction?

A
  • Radicals react with non radical molecules.
  • New eadicals are created which go onto react with other non radicals.
  • Hence called a chain reaction.
64
Q

What happens in the termination stage of a radical chain reaction?

A
  • Two radicals react, forming a non-radical molecule.

- This ends the chain reaction.

65
Q

What are CFCs?

A

Chlorofluorocarbons.

66
Q

What happends to CFCs in the stratosphere?

A
  • Their C-Cl bonds are broken homolytically by UV radiation.
  • Radicals are formed which catalyse the break down of ozone.
67
Q

Are more CFCs broken down in the stratoshere or troposphere?

A

More in stratosphere.

  • Troposhpere is below the stratosphere so most of the high frequency UV has already been absorbed by the ozone layer further up.
  • Hence little CFCs are broken down here.
68
Q

What determines the ability for a photochemical reaction to take place?

A

The frequency of radiation (usually UV).

69
Q

Why are C-Cl bonds in CFCs more likely to be broken than C-F bonds by UV?

A

C-Cl bonds have the lowest bond enthalpy in CFCs.

70
Q

Describe how CFCs break down ozone.

A

Initiation:

  • Sunlight (UV) breaks the C-Cl bonds in a CFC molecule and produces two radicals.
  • There reacti with ozone.

Propigation:

  • Cl• reacts with O₃ to from the ClO• intermediate and O₂
  • ClO• reacts with more O₃ to make 2O₂ and Cl•
  • As Cl• is reformed it acts as a homogeneous catalyst.

Termination:
- 2 radicals react (e.g. 2Cl• → Cl₂)

71
Q

What is the overall equation for CFCs reaction with ozone?

A

2O₃ → 3O₂

Cl• is a catalyst

72
Q

Other than CFCs what can also break down ozone?

A

Nitrogen oxides

73
Q

How can we quntify electronegativity?

A

The pauling scale.

74
Q

Is CO₂ a polar molecule?

A

No.

  • although it contains polar bonds, the overall distribution of electrons within the molecule is symmetricall.
  • and therefore evenly distributed.
75
Q

How does size of molecule relate to the number of Instatanous dipole - induced dipole attractions?

A
  • The bigger the molecule or atom, the more instantaneous dipole -inmduced dipole forced.
  • As you have larger electron clouds.
76
Q

What bonds are broken when water is boiled?

A

No bonds are broken.

  • The weak instatanous dipole - induced dipole attractions are.
77
Q

Where is ozone found?

A

The stratosphere.

78
Q

How is ozone formed?

A

When UV radiation hits an oxygen molecule.

O₂ + hν → O• + O•
O₂ + O• → O₃

79
Q

How is ozone broken down? (naturally)

A

When UV radiation hits it.

O₃ + hν → O₂ + O•

80
Q

What happens when ozone is formed in the troposphere?

A
  • Photochemical smog.
  • when solid carbon particulate and ozone mix.
  • this harms the respiratory system in animals and damages plants.
  • Ozone is also toxic to humans.
81
Q

How is ozone formed in the troposphere?

A

When sunlight, hydrocarbons and nitrogen dioxide react together.

(a lot of the hydrocarbons and nitrogen dioxide comes from cars and factories.)

82
Q

Why do we use parts per million?

A

Because when measuring air, there is a tiny percentage of many gasses.

83
Q

How is radiation from the sun remitted by the earth?

A
  • Nuclear fusion occurs in the sun and emits IR, Visible, and UV light.
  • The atmosphere absorbs some of this radiation.(ozone layer in the stratosphere)
  • The surface of the earth absorbs radiation and remits it as infrared (a lower frequency)
84
Q

Describe what must happen for oxygen free radicals to form.

A
  • Electrons sit in discrete energy levels.
  • If they absorb the right amount of energy they can move to another energy level as they are quantised.
  • If UV or visible light hits a gas molecule the electrons absorb the energy but can only absorb specific frequencies.
  • If the right energy is absorbed bonds break forming free radicals.

O=O → O• + O•

85
Q

How is energy related to wavelength?

A 
E=hν
(h= planks constant, ν= frequnecy)
ν = c/λ
(c= speed of light, λ= wavelngth)
∴
E=hc/λ

A-Level Chemistry [OCR B Salters] (sorry for any spelling mistakes - there are many) (14 decks)

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