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EDEXCEL AS Chemistry > large concepts - chemistry > Flashcards

large concepts - chemistry Flashcards

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1
Q

Explain why the boiling temperatures increase from chlorine to iodine. (2)

A
  • from chlorine to iodine / down the group, the number of electrons (in the molecule / atom)
    increases / changes from 34 to 106 / 17 to 53
  • so the strength of the London / instantaneous dipole-(induced) dipole forces increases / there are more London / instantaneous dipole-(induced) dipole forces and more energy is needed to separate the molecules
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2
Q

By referring to any changes in oxidation numbers when these halides react with concentrated sulfuric acid, explain which halide is the strongest reducing agent. (3)

A
  • iodide ions are the strongest reducing agent because iodide ions / I / (potassium) iodide reduces sulfur (in sulfuric acid) from +6 to 0 in sulfur / -2 in H2S)
  • (whereas) bromide ions / Br / (potassium) bromide reduces sulfur (in sulfuric acid) from +6 to +4
  • (whereas) chloride ions / Cl / (potassium) chloride do not reduce sulfuric acid / sulfur /S (as there is no change in oxidation number of Cl or S
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3
Q

Explain why the first ionisation energy of magnesium is higher than that of sodium. (3)

A

Nuclear charge
magnesium (atom) / Mg has more protons than sodium (atom) / Na
or
magnesium / Mg has a greater (effective) nuclear charge (than sodium / Na)
Shielding
(outer) electron in magnesium (atom) / Mg in the same (quantum) shell / energy level / sub-shell / orbital as in a sodium atom / Na
or
shielding in magnesium atom / Mg similar to / same as that in sodium atom / Na
Attraction
so the force of attraction between the nucleus and the (outer) electron is greater in magnesium (atom) / Mg
(than in sodium atom / Na)

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4
Q

Describe the apparatus that would be used to compare the decomposition of metal carbonates. Include how the rate of decomposition would be compared.(2)

A
  • use of a delivery tube to bubble gas into limewater
  • compare the time taken for the limewater to go cloudy
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5
Q

Explain why magnesium carbonate decomposes much more readily on heating than barium carbonate.(3)

A
  • the magnesium ion/ cation is smaller than the barium ion/ cation
  • which polarises the (large) carbonate (ion)/anion
  • and weakens the carbon-oxygen bond (C-O/C=0) bonds
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6
Q

Explain why magnesium carbonate decomposes much more readily on heating than barium carbonate.(3)

A
  • the magnesium ion/ cation is smaller than the barium ion/ cation
  • which polarises the (large) carbonate (ion)/anion
  • and weakens the carbon-oxygen bond (C-O/C=0) bonds
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7
Q

Explain why both water and carbon dioxide molecules have polar bonds but only water is a polar molecule. (4)

A
  • oxygen is more electronegative than hydrogen and carbon
  • which results in a polar bond with oxygen so carbon and hydrogen
  • carbon dioxide is a symmetrical/linear molecule and so the dipole moments/vectors cancel
  • the lone pairs of electrons of oxygen/ the V-shape of the water molecule mean that the dipole moments/ vectors do not cancel
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8
Q

This question is about transition metals and transition metal complexes. Describe the bonding in the element chromium and use your answer to justify why it has such a high melting temperature.(4)

A
  • lattice of positive ions / regular arrangement of positive ions
  • (in sea of) delocalised electrons
  • strong forces of attraction between ions and delocalised electrons (so high melting temperature)
  • so lots of (heat) energy needed to break attraction between ions and delocalised electrons / metallic bonds
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9
Q

Explain the trend in thermal stability of Group 2 nitrates.(3)

A
  • nitrates increase in stability down group 2 as ionic radius increases as you go down the group
  • so the polarising ability of the metal ion decreases
  • weakening of N-O bonds (in nitrate ion) is less
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10
Q

Explain why the first ionisation energy of sodium is greater than that of potassium.

A
  • the outer electron in a sodium atom is closer to the nucleus (than that in potassium)
  • (and) less shielding from inner electron shells
  • these outweigh the greater nuclear charge / number of protons in potassium
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11
Q

Why is there a small drop from Mg to Al?

A

Al is starting to fill a 3p sub shell
whereas Mg has its outer electrons in the 3s sub shell
The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s electrons

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12
Q

Why is there a small drop from P to S?

A
  • With sulphur there are 4 electrons in the 3p sub shell and the 4th is starting to doubly fill the first 3p orbital.
  • When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove
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13
Q

Ionic bonding is

A

the strong electrostatic force of attraction between oppositely charged ions formed by electron transfer.

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14
Q

Ionic bonding is stronger and the melting points higher when…

A

the ions are smaller and/ or have higher charges.
E.g. MgO has a higher melting point than NaCl as the ions involved (Mg2+ & O2- are smaller and have higher charges than those in NaCl , Na+ & Cl- )

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15
Q

A covalent bond strong is…

A

the electrostatic attraction between the bonding shared pair of electrons and the two nuclei

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16
Q

Nuclei joined by multiple (i.e. double and triple) bonds have a greater…

A

electron density between them
This causes a greater force of attraction between the nuclei and the electrons between them, resulting in a shorter bond length and greater bond strength.

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17
Q

A dative covalent bond forms when…

A

the shared pair of electrons in the covalent bond come from only one of the bonding atoms.

A dative covalent bond is also called co-ordinate bonding.

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18
Q

Electronegativity is…

A

the relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself.

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19
Q

Electronegativity increases across a…

A

period as the number of protons increases and the atomic radius decreases because the electrons in the same shell are pulled in more.

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20
Q

Electronegativity decreases down a…

A

It decreases down a group because the distance between the nucleus and the outer electrons increases and the shielding of inner shell electrons increases

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21
Q

Main factor affecting size of London forces

A
  • The more electrons there are in the molecule the higher the chance that temporary dipoles will form. - This makes the London forces stronger between the molecules and more energy is needed to break them so boiling points will be greater.
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22
Q

The increasing boiling points of the halogens down the group 7 series can be explained by the…

A

increasing number of electrons in the bigger molecules causing an increase in the size of the London forces between the molecules.
This is why l is a solid whereas Cl, is a gas.

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23
Q

The shape of the molecule can also have an effect on the size of the London forces…

A
  • Long straight chain alkanes have a larger surface area of contact between molecules for London forces to form than compared to spherical shaped branched alkanes and so have stronger London forces.
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24
Q

Permanent dipole-dipole forces occurs between…

A

polar molecules

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25
Q

Permanent dipole-dipole forces occurs between…

A

polar molecules

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26
Q

Hydrogen bonding occurs in compounds that have a …

A

hydrogen atom attached to one of the three most electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of electrons.
- There is a large electronegativity difference between the H and the O,N,F

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27
Q

The smaller alcohols are soluble in water because…

A

they can form hydrogen bonds with water. The longer the hydrocarbon chain the less soluble the alcohol.

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28
Q

Compounds that cannot form hydrogen bonds with water molecules, e.g…

A

polar molecules such as halogenoalkanes or non polar substances like hexane will be insoluble in water.

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29
Q

Non-polar solutes will dissolve in…

A

non-polar solvents. e.g. iodine which has only London forces between its molecules will dissolve in a non polar solvent such as hexane which also only has London forces.

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30
Q

Metallic bonding is…

A

the electrostatic force of attraction between the positive metal ions and the delocalised electrons

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31
Q

The three main factors that affect the strength of metallic bonding are:

A
  1. Number of protons/ Strength of nuclear attraction.
The more protons the stronger the bond
  2. Number of delocalised electrons per atom (the outer shell electrons are delocalised)
The more delocalised electrons the stronger the bond
  3. Size of ion.
The smaller the ion, the stronger the bond.
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32
Q

Metals can conduct electricity well because…

A

the delocalised electrons can move through the structure.

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33
Q

Metals are malleable because…

A

the positive ions in the lattice are all identical. So the planes of ions can slide easily over one another. The attractive forces in the lattice are the same whichever ions are adjacent.

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34
Q

group 2 Atomic radius down a group…

A

increases down the Group. As one goes down the group, the atoms have more shells of electrons making the atom bigger.

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35
Q

Down group 2 the melting points…

A

decrease.
The metallic bonding weakens as the atomic size increases.
The distance between the positive ions and delocalized electrons increases.
Therefore the electrostatic attractive forces between the positive ions and the delocalized electrons weaken.

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36
Q

The reactivity down group 2…

A

increases as the atomic radii increase there is more shielding. The nuclear attraction decreases and it is easier to remove (outer) electrons and so cations form more easily

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37
Q

Group II hydroxides become more/less soluble down the group.

A

more

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38
Q

Group II sulfates become more/less soluble down the group.

A

less

39
Q

Group 2 carbonates become more/less thermally stable going down the group As… the cations get bigger they have less of a polarising effect and distort the carbonate ion less. The C-O bond is weakened less so it less easily breaks down

A
  • more
  • the cations get bigger they have less of a polarising effect and distort the carbonate ion less.
  • The C-O bond is weakened less so it less easily breaks down
40
Q

do Group 1 carbonates decompose?

A

Group 1 carbonates do not decompose with the exception of lithium.
- As they only have +1 charges they don’t have a big enough charge density to polarise the carbonate ion.
- Lithium is the exception because its ion is small enough to have a polarising effect

41
Q

how do you investigate the ease of decomposition?

A
  • heat a known mass of carbonate in a side arm boiling tube and pass the gas produced through lime water.
  • Time for the first permanent cloudiness to appear in the limewater.
  • Repeat for different carbonates using the same moles of carbonate/same volume of limewater/same Bunsen flame and height of tube above flame.
42
Q

Group 2 nitrates decompose on heating to produce…

A

group 2 oxides, oxygen and nitrogen dioxide gas.
- You would observe brown gas evolving (NO2)

43
Q

Explanation for occurrence of flame ?

A
  • In a flame test the heat causes the electron to move to a higher energy level.
  • The electron is unstable at the higher energy level and so drops back down.
  • As it drops back down from the higher to a lower energy level, energy is emitted in the form of visible light energy with the wavelength of the observed light
44
Q

Fluorine (F2) appearance and reactivity?

A
  • very pale yellow gas
  • It is highly reactive
45
Q

Chlorine : (Cl2) appearance ?

A

greenish, reactive gas, poisonous in high concentrations

46
Q

Bromine (Br2): appearance?

A

red liquid, that gives off dense brown/orange poisonous fumes

47
Q

lodine (I2) : appearance ?

A

shiny grey solid sublimes to purple gas.

48
Q

mp and bp of the halogens down the group…

A

Increase down the group- As the molecules become larger they have more electrons and so have larger London forces between the molecules. As the intermolecular forces get larger more energy has to be put into break the forces. This increases the melting and boiling points

49
Q

As one goes down the group the electronegativity of the halogens…

A

decreases, As one goes down the group the atomic radii increases due to the increasing number of shells. The nucleus is therefore less able to attract the bonding pair of electrons

50
Q

The reactivity of the halogens down the group…

A

decreases as the atoms get bigger with more shielding so they less easily attract and accept electrons. They therefore form -1 ions less easily down the group

51
Q

The oxidising strength of halogens down the group.

A

decreases

52
Q

Chlorine will displace both…

A

bromide and iodide ions

53
Q

bromine will displace…

A

iodide ions

54
Q

The reducing power of the halides down the group…

A

increases as They have a greater tendency to donate electrons. This is because as the ions get bigger it is easier for the outer electrons to be given away as the pull from the nucleus on them becomes smaller.

55
Q

All the hydrogen halides react readily with ammonia to give…

A

the white smoke of the ammonium halide

56
Q

The hydrogen halides are all soluble in water. They dissolve to form…

A

acidic solutions

57
Q

Testing for Negative ions (anions). Testing for presence of a carbonate CO3- and hydrogencarbonates HCO3

A
  • Add any dilute acid and observe effervescence.
  • Bubble gas through limewater to test for CO2
  • will turn limewater cloudy.
  • Fizzing due to CO2 would be observed if a carbonate or a hydrogencarbonate was present.
58
Q

Testing for Negative ions (anions). Testing for presence of a carbonate CO3- and hydrogencarbonates HCO3

A
  • Add any dilute acid and observe effervescence.
  • Bubble gas through limewater to test for CO2
  • will turn limewater cloudy.
  • Fizzing due to CO2 would be observed if a carbonate or a hydrogencarbonate was present.
59
Q

Acidified BaCl2, solution is used as a reagent to test for…

A

sulfate ions
- If Barium Chloride is added to a solution that contains sulfate ions, a white precipitate forms.
- The acid is needed to react with carbonate impurities that are often found in salts which would form a white Barium carbonate precipitate and so give a false result

60
Q

AgNO3 -
Fluorides produce…
Chlorides produce …
Ag(aq) + Cl (aq) → AgCI(s)
Bromides produce…
Ag(aq) + Br (aq) → AgBr(s)
lodides produce …
Ag*(aq) + l- (aq) → Agls)

A
  • Fluorides produce no precipitate
  • Chlorides produce a white precipitate
    Ag*(aq) + Cl (aq) → AgCI(s)
  • Bromides produce a cream precipitate
    Ag*(aq) + Br (aq) → AgBr(s)
  • lodides produce a pale yellow precipitate
    Ag*(aq) + l- (aq) → Agls)
61
Q

Test for ammonium ion NH4+…

A
  • by reaction with warm NaOH(aq) forming NH3
  • Ammonia gas can be identified by its pungent smell or by turning damp red litmus paper blue
62
Q

Enthalpy change is…

A

the amount of heat energy taken in or given out during any change in a system provided the pressure is constant

63
Q

In an exothermic change energy is transferred…

A

from the system (chemicals) to the surroundings

64
Q

In an endothermic change, energy is transferred…

A

from the surroundings to the system (chemicals). They require an input of heat energy e.g. thermal decomposition of calcium carbonate

65
Q

In an exothermic reaction the ∆H is…

A

is negative

66
Q

In an endothermic reaction the ∆H is…

A

positive

67
Q

The standard enthalpy change of formation of a compound is…

A

the enthalpy change when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), all reactants and products being in their standard states

68
Q

The standard enthalpy of combustion of a substance is defined as the…

A

enthalpy change that occurs when one mole of a substance is combusted completely in oxygen under standard conditions. (298K and 100kPa), all reactants and products being in their standard states

69
Q

Enthalpy change of reaction is the…

A

enthalpy change when the number of moles of reactants as specified in the balanced equation react together

70
Q

The standard enthalpy change of neutralisation is the…

A

enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water.

71
Q

Hess’s law states that…

A

total enthalpy change for a reaction is independent of the route by which the chemical change takes place

72
Q

errors in Calorimetric method…

A

• energy transfer from surroundings (usually loss)
• approximation in specific heat capacity of solution. The method assumes all solutions have the heat capacity of water.
• neglecting the specific heat capacity of the calorimeter- we ignore any energy absorbed by the apparatus.
• reaction or dissolving may be incomplete or slow.
• density of solution is taken to be the same as water.

73
Q

The mean bond enthalpy is…

A

the enthalpy needed to break the covalent bond into gaseous atoms, averaged over different molecules

74
Q

The Activation Energy is defined as…

A

the minimum energy which particles need to collide to start a reaction

75
Q

How can a reaction go to completion if few particles have energy greater than EA?

A

Particles can gain energy through collisions

76
Q

At higher concentrations(and pressures) there are…

A

more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of effective collisions.

The curves will be higher, and the area under the curves will be greater because there are more particles

77
Q

At higher temperatures the energy of the particles…

A

increases.
They collide more frequently and more often with energy greater than the activation energy. More collisions result in a reaction.
As the temperature increases, the graph shows that a significantly bigger proportion of particles have energy greater than the activation energy, so the frequency of successful collisions increases

78
Q

Increasing surface area will cause…

A

successful collisions to occur more frequently between the reactant particles and this increases the rate of the reaction.

79
Q

A heterogeneous catalyst is in a…

A

different phase from the reactants

80
Q

A homogeneous catalyst is in the..

A

same phase as the reactants

81
Q

Environmental benefits of catalysts?

A
  • Catalysed reactions can occur at lower temperature so less fuel needed and fewer emissions from fuels.
  • Catalysed reaction enables use of an alternative process with higher atom economy so meaning fewer raw materials needed and less waste products are produced
82
Q

Dynamic equilibrium occurs when…

A
  • forward and backward reactions are occurring at equal rates.
  • The concentrations of reactants and products stays constant and the reaction is continuous.
83
Q

Le Chatelier’s principle states that…

A

if an external condition is changed the equilibrium will shift to oppose the change (and try to reverse it)

84
Q

If temperature is increased the equilibrium will shift to oppose this and move in the…

A

endothermic direction to try to reduce the temperature by absorbing heat.

85
Q

If temperature is decreased the equilibrium will shift to oppose this and move in the…

A

exothermic direction to try to increase the temperature by giving out heat

86
Q

Low temperatures may give a higher…

A

yield of product but will also result in slow rates of reaction.
- Often a compromise temperature is used that gives a reasonable yield and rate

87
Q

Increasing pressure will cause the equilibrium to shift towards the side with…

A

fewer moles of gas to oppose the change and thereby reduce the pressure.

88
Q

Decreasing pressure will cause the equilibrium to shift towards the side with…

A

more moles of gas to oppose the change and thereby increase the pressure

89
Q

If the number of moles of gas is the same on both sides of the equation then changing pressure will have what effect on the position of equilibrium?

A

no effect on the position of equilibrium

90
Q

Increasing pressure may give a higher…

A

yield of product and will produce a faster rate.
- Industrially high pressures are expensive to produce (high electrical energy costs for pumping the gases to make a high pressure) and the equipment is expensive (to contain the high pressures)

91
Q

A catalyst has what effect on the position of equilibrium?

A

A catalyst has no effect on the position of equilibrium, but it will speed up the rate at which the equilibrium is achieved. It does not affect the position of equilibrium because it speeds up the rates of the forward and backward reactions by the same amount.

92
Q

Kc only changes with…

A

temperature.
- It does not change if pressure or concentration is altered.
- A catalyst also has no effect on Kc

93
Q

The larger the Kc the greater the….

A

amount of products

EDEXCEL AS Chemistry (13 decks)

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