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chem A2 > paper 4 physical > Flashcards

paper 4 physical Flashcards

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1
Q

Suggest why ΔHhyd of Mg2+ ion > ΔHhyd of Ca2+ ion

A

(ΔHhyd depend on cd)
- The size of Mg2+ is smaller and the charge density is
larger than Ca2+ ion
- The FOA btw Mg2+ ion and WATER molecules is stronger

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2
Q

Why is it impossible to determine the ΔHhyd of oxide ion, O2-

A

O2- reacts water H20 to form OH-

O2- + H20 –> 2OH-

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3
Q

Suggest 1 reason why CO is produces in addition to CO2 in some internal combustion engines

A

Incomplete combustion of hydrocarbon fuels

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4
Q

Why lattice energy represents an exothermic change

A

Because it is forming an ionic bond

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5
Q

Trend of Thermal Stabilities of Grp 2 CO32- / NO3-

A
  • TS of grp 2 carbonates ↑ down the grp
  • When going down the group, size of +ve metal ion ↑
  • Charge density + Polarising power of M2+ ↓
  • e- cloud of CO32- ion is less polarized
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6
Q

Use the data booklet to explain why NiCO3 will decompose more/less readily than CaCO3

A
  • Radius of Ni2+ is 0.07nm, radius of Ca2+ is 0.099nm
  • Charge density of Ni2+ is > Ca2+, polarizing power is >
  • e- cloud of CO32- ion in NiCO3 is more polarized than
    in CaCO3
  • Therefore, NiCO3 will decompose more readily than
    CaCO3
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7
Q

Describe in detail what you would observe when crystals of Mg(NO3)2•6H20 are heated in a boiling tube, gently at first and then more strongly.
Write eqns for any reactions

A

Mg(NO3)2•6H20 –> Mg(NO3)2 +6H2O,
Mg(NO3)2 –> MgO + 2NO2 + 1/2O2
- When crystals are heated, the solid will dissolve and
turn to liquid.
- Condensation takes place in the tube.
- When it is heated more strongly, a white sild is formed
- Brown gas is released. Colourless gas formed relights
a glowing splint

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8
Q

Write eqn for the decomposition of AgNO3

A

AgNO3 –> Ag + NO2 + 1/2O2

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9
Q

Write eqn for the prep of Ca(NO3)2 by an acid-base reaction

A

CaO + 2HNO3 –> Ca(NO3)2 + H2O

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10
Q

MgCl (s) + aq –> Mg2+ (aq) + 2Cl-(aq)
Describe in terms of bond breaking and bond making, what happens to solid ionic lattice when an ionic compound dissolves in water.

A
  • Ionic bond btw Mg2+ and Cl- breaks

- FOA btw ions and H2O will be formed

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11
Q

Describe and Explain how the solubility of the grp 2 sulfates down the grp

A
  • Solubility ↓ down the grp
  • When going down the group, the lattice energy and
    hydration energy ↓
  • The rate of ↓ of Hyd E is faster than the rate of
    ↓ of LE
  • The enthalpy change of solution becomes more endothermic
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12
Q

Describe and Explain how the solubility of the grp 2 hydroxides down the grp

A
  • Solubility ↑ down the grp
  • When going down the group, LE and Hyd E ↓
  • The rate of ↓ of LE is faster than the rate of ↓ of
    Hyd E.
  • The enthalpy change of solution becomes more
    exothermic
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13
Q

Notes - solubility of OH and SO42-

ΔHsol = - LE + HydE

A

-ve ΔHsol = soluble

+ve ΔHsol = insoluble

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14
Q

Why is there a diff btw the LE of ZnBr2 and ZnCl2

A
  • The size of Cl- is smaller than Br- ion.
  • Charge density of Cl- is greater,
  • The electrostatic FOA btw Zn2+ and Cl- is stronger
    compared to the FOA btw Zn2+ and Br-
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15
Q

Why is there a diff btw the LE of ZnCl2 and ZnO

A
  • The size of O2- is smaller than Cl-
  • Charge density of O2- is greater,
  • The electrostatic FOA btw Zn2+ and O2- is stronger than
    btw Zn2+ and Cl- ions
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16
Q

Explain why LE of CaO is more exo than LE of LiF

A
  • Ca2+ and O2- have higher charge density compared to
    Li+ and F-
  • The electrostatic force btw Ca2+ and O2- is stronger
    than Li+ and F-
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17
Q

ΔS for addition polymerization

A

-ve, because many monomers combine to form a large polymer

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18
Q

ΔS for condensation polymerization - ester

A

+ve, because each pair of monomer molecules join tgt, 2 water molecules will be produced

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19
Q

Suggest and explain the trend of electron affinity of grp 17

A
  • e- affinity becomes more positive when going down
    group 17
  • e- affinity depends on the distance between the nucleus
    and outermost e- ,
  • which increases down grp 17
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20
Q

Describe and Explain what happens to the entropy of a gas when temp is increased

A
  • when T ↑, particles gain more energy and move faster
  • entropy of the system ↑ because
  • the amount of disorder will ↑
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21
Q

Explain the origin of colour in transition element complexes.

A
  • The d-orbitals split into 2 diff E levels by repulsion of
    approaching ligands.
  • When e- absorb the freq or wavelength of light, it
    will be promoted from a lower E level to a higher E level
  • The colour observed is complementary to the colour
    absorbed
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22
Q

Y - [CuCl4]2- , yellow
Z - [Cu(H20)6]2+ , blue

Explain why complexes Y and Z are coloured and why their colours are different.

A
  • The d-d orbitals are split into 2 sets of E levels of
    different E
  • when wavelength or freq of photon is absorbed, e- will
    be promoted from a lower E level to a higher E level
  • the colour observed is complementary to the colour
    absorbed
  • Since the energy gap d-d is different for Y and Z, diff
    freq or wavelength of light is absorbed
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23
Q

Explain why the colours of the two complex ions are different

A
  • The d-d energy gap is different, different
    freq/wavelength of light is absorbed.
  • So different colour will be reflected
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24
Q

The reaction is 1st order with respect to H2(g)

Use data from graph to confirm this statement

A
  • The half-life is at 46s.
  • From 8 moldm-6 to 4 moldm-6 , half-life is 46s
  • From 4 moldm-6 to 2 moldm-6 , half-life is 46s
  • Sice half-life is constant, the reaction is 1st order with
    respect to H2
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25
Q

State whether the LE of CaCl2(s) is more or less exothermic than the LE if MgF2(s)

A
  • CaCl2 is less exo bcuz both Ca2+ and Cl- ions are larger
    than Mg2+ and F- ions,
  • The electrostatic btw Ca2+ and Cl- is weaker than Mg2+
    and F-
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26
Q

Give 2 names of solutions that could be mixed to form BaSO4

A
  • Barium nitrate solution

- Sodium sulphate solution

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27
Q

write eqns to show how a buffer solution consisting a mixture of HA(aq) and NaA(aq) controls pH when an acid or alkali is added

A

when acid is added, H+ + A- –> HA

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28
Q

suggest why Cu(I) salts are usually white

A

all orbitals are fully filled

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29
Q

suggest 2 functional grps present in a molecule of a drug named chloramphericol

A
  • amine / amino
  • benzene/ phenyl ring
  • alcohol/ hydroxy
  • chloro
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30
Q

methylamine is a base,

write eqn to show how methylamine dissolves in H2O to give an alkaline solution

A

CH3NH2 + H2O ⇆ CH3NH3+ + OH-

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31
Q

Suggest how the △H(vap) of I2 would compare to Br2. Explain

A
  • More ENDOTHERMIC because the VDW btw I2 molcules

is stronger than Br2

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32
Q

Suggest why the △H(hyd) of Br- is more exo than that of I-

A
  • Br- has a smaller ionic size with stronger ion-dipole attraction with water molecules
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33
Q

explain why polyamides (R-NH2) biodegrade more readily than polyalkenes (C-C)

A
  • Polyamides can be broken down by hydrolysis

- C-C bonds are non-polar and cannot be hydrolysed

34
Q

Suggest why △H(latt) of CaBr2 is more EXO than that of KBr

A
  • Ca2+ has a higher charge
  • higher charge density and stronger electrostatic FOA
    btw Ca2+ and Br- compared to K+ and Br-
35
Q

A second chromatogram of the same mixture is taken using a more POLAR solvent
Predict the effect on the Rf values of amino acids, explain

A
  • Greater Rf values bcuz amino acids are more stable in

solvent / forms more HB w the solvent

36
Q

H2NCH2COOH + HCL –>

H2NCH2COOH + NaOH –>

A

Cl-H3N+CH2COOH

H2NCH2COO-Na+

37
Q

Explain why Cr metal cannot be obtained by the electrolysis of dilute aq Chromiun(II) sulfate. Include data fr data booklet

A
  • Cr2+ + 2e ⇆ Cr E= -0.91V , 2H+ + 2e ⇆ H2 E=0.00V
  • H2 gas is formed bcuz E of hydrogen is more +ve than
    Cr2+/Cr.
  • Hydrogen ion will be reduced to form h2 gas
38
Q

Equation for Sr with cold water

A

Sr(s) + 2H2O(l) –> Sr(OH)2 (aq) + H2(g)

39
Q

Describe and Explain the trend in reactivity observed in the reactions of these group 2 metals w cold water

A
  • Reactivity increases down the group

- as ionisation energies decreases down the group

40
Q

The reaction between OH- ions and CH3Br is first order to [OH-] and first order with respect to [CH3Br].
CH3Br + OH- –> CH3OH + Br-
Suggest a practical method that would confirm that the reaction is 1st order wrt [OH-] and 1st order wrt CH3Br

A
  • Excess of CH3Br is used. Temp is controlled
  • An experiment is carried out with known initial conc of
    OH-
  • Measure the t taken for reaction to complete anf find the
    conc of OH- by sample and titrate
  • Plot a graph with the conc oh OH- against t
  • Determine the half life
  • If half life is constant, this indicated that the reaction is
    first order wrt conc of OH-
41
Q

NH4+ ⇆ NH3 + H+
i) Explain, with aid of EQN, how this solution can behave
as a buffer when a small amount of strong ACID is
added
ii) Explain, with aid of EQN, how this solution can behave
as a buffer when a small amount of strong BASE is
added

A

i) when acid is added, NH3 + H+ –> NH4+

ii) when base is added, NH4+ + OH- –> NH3 + H2O

42
Q

Describe fully the observations
Mg + O2
Sr + O2

A

Mg: white flame/white solid
Sr: red flame

43
Q

Describe the benefit of adding Ca(OH)2 or CaCO3 to soil

A
  • they both neutralises the pH of the soil
44
Q

Why is butylamine basic,

hence write an eqn to show butylamine reacting as a base

A
  • Nitrogen has a lone pair which can accept proton

- C4H9NH2 + HCL ⇆ C4H9NH3+ + Cl-

45
Q

State 2 of the ↑ oxi states of Cr commonly seen in its compounds

A

Cr3+ and Cr6+

46
Q

WHy does Na2O has a ↑ mp

A
  • giant ionic structure

- strong electrostatic FOA btw Na+ & O2-

47
Q

Explain why Na2O + H2O produces an alkaline solution. Use Bronsted-Lowry theory to explain

A
  • Reaction btw Na2O and H2O produces NaOH

- The OH- ions in NaOH can accept proton

48
Q

NO acts as catalyst in the oxidation of atmospheric SO2.

Give 2 eqn to describe how NO acts as catalyst

A
  1. NO + 1/2O2 –> NO2

2. NO2 + SO2 –> NO + SO3

49
Q

MgCO3 was heated in an open test tube. It was difficult to see whether a thermal decomposition reation took place. Explain why (2)

A
  • The gas produced is colourless (CO2)
  • The appearance of solid does not change (white s –>
    white s)
50
Q

An alternative method is used to show the rxn is 1st w.r.t H2. This method uses large excess of ICL(g) and measures how the concentration of H2(g) varies with time

i) Describe 2 ways of using these results to show that
the reaction is 1st order w.r.t. [H2(g)]

A
  • Plot graph with conc of H2 against time.
    1. Determine the half life.
      The constant half life indicates that the rxn is 1st order
      w.r.t. H2
    2. Draw 2 tangents and determine both of it’s gradients
      If the conc 1 at time 1 is equal to gradient 1, this
      indicates 1st order w.r.t. H2
    3. Plot graph of rate of H2 against conc of H2. A straight
      line through origin indicates 1st order w.r.t. H2
51
Q

What property of transition elements allows them to act as catalysts?

A
  • they have variable oxidation states
52
Q

Complete the equation

C4H4O6(2-) + 3[O] –>

A

2HCO2- + 2CO2 H2O

53
Q

Nane 1 example of each of the following types of polymer.

  1. synthetic polyamide
  2. synthetic polyester
  3. conducting polymer
  4. non-solvent based adhesive
A
  1. synthetic polyamide - nylon
  2. synthetic polyester - terylene
  3. conducting polymer - polyethyne
  4. non-solvent based adhesive - superglue
54
Q

At rt, Kstab is 2.34 x10^5

Explain what this value indicates about the equilibrium and the stability of complex Z (product)

A
  • Complex Z is stable.

- equilibrium shifts to RHS, due to large kstab value

55
Q

Cu(+) and Ag(+) salts are colourless, suggest why.

A
  • The d-orbitals are full
  • No e- will be promoted, no colour will be absorbed,
    hence no colour is reflected
56
Q

Explain how the choice of indicator is linked to the pH curve

A

pH range of indicator matches the vertical range of the graph

57
Q

State change in entropy and explain

i) freezing of water

A

i) Entropy ↓ bcuz particles in solid have lower KE and are
more orderly than in liquid. There is an overall reduction
in number of possible arrangements of particles

58
Q

Suggest the trend in the first e- affinity of the elements in Group 17. Explain your answer

A
  • when going down grp 17, electron affinity ↓
  • when going down the group, DISTANCE btw nucleus
    and outermost e- ↑,
  • nuclear attraction ↓
  • less E required to accept e-
59
Q

Catalysts used for:

i) manufacture of NH3 in the Haber process
ii) removal of nitrogen oxides from car engines
iii) Oxidation of SO2

A

i) Fe
ii) Platinum / Rhodium
iii) V2O5

60
Q

△H(r3) : Ba(OH)2 (aq) + 2CO2 (g) —> Ba(HCO3)2 (aq)
△H(r4) : Ca(OH)2 (aq) + 2CO2 (g) —> Ca(HCO3)2 (aq)

How would you compare the △H for reaction 3 and 4? Explain

A
  • △H(r3) will be identical to △H(r4) bcuz reaction is the
    same
  • the metal ions remain as sepctator ions
  • 2OH- (aq) + 2CO2 (g) —> 2HCO3- (aq)
61
Q

Suggest and explain a reason why Na2CO3 is more stable to heat than MgCO3

A
  • Na+ has a smaller charge and larger ionic radii than
    Mg2+
  • The CO32- anion is less polarized by Na+ than by Mg2+
62
Q

State the relationship btw pKa and the strength of acid

A

the smaller the pKa value, the stronger the acid

63
Q

Suggest why transition elements often show variable oxidation states in their compounds, but typical s-block elements do not

A
  • close similarity of E of the 4s and 3d sub-shells
64
Q

Kpc of benzophenone, C6H5COC6H5, btw octan-1-ol and H2O is diff than that of in Kpc of benzoic acid.
Explain Why

A
  • Kpc is greater in benzophenone bcuz it is more soluble in octan-1-ol

(benzophenone- more polar, more soluble in octan-1-ol, less soluble in H2O)
(bonzoic acid - hb; soluble in h2o)

65
Q

Describe and explain how the density and mp of Co compare to those of Ca

A

density of Co: higher than Ca
explanation: Co has larger relative atomic mass, Ar and smaller atomic size compared to Ca

mp of Co: higher than Ca
explanation: Stronger electrostatic FOA btw cation and sea of deloacalised e- , due to higher no. of delocalised e- in Co than in Ca

66
Q

Explain why some polymers are biodegradable

A
  • they are esters and can undergo hydrolysis
67
Q

Suggest why this polymer conducts electricity

A
  • it contains delocalised e- in the double bonds
68
Q

By ref to a chemical/physical property, suggest one adv of a conducting polymer when compared w metals

A
  • polymers are less dense
69
Q

Entropy is a measure of the disorder of a system

Describe and explain what happens to the entropy of a gas when the temp is increased

A
  • when t ↑, particles gain KE and move faster

- entropy ↑ bcuz amount of disorder ↑

70
Q

Explain the principles of the separation of amino acids by electrophoresis

A
  • Direction of movement related to charge of amino acids

- Distance travelled depends on the Mr of amino acids

71
Q

Ca(s) + 2HCL (aq) –> CaCl2(aq) + H2(g)
Ca(s) + HNO3 (aq) –> Ca(NO3)2 (aq) + H2(g)

How would the enthalpy change compare for these 2 reaction where HCL is replaced HNO3

A
  • enthalpy changes should be similar as both HCL and HNO3 are strong acids which fully ionises
72
Q

Name a polymer that is non-biodegradeble

A

PVC

73
Q

Explain how amino groups in CH2NH2CH2NH2 allow the molecules to act as a Bronsted-Lowry base

A
  • N contains LP of e- and can accept proton
74
Q

State 1 environmental consequence of raised levels of

  • CO
  • CO2
A
  • CO: this gas is toxic

- CO2: this gas contributes to global warming

75
Q

Describe the reactions, if any, that occur when separate samples of SnO2 and PbO2 are heated in air
Include observations and eqns

A
  • SnO2 = no reaction
  • PbO2 = black to yellow
    PbO2 –> PbO + 1/2O2
76
Q

Explain why NMR spectroscopy can detect hydrogen atoms in molecules

A
  • Nucleus of H atom consists a single proton that has spin
77
Q

Explain why H atoms are invisible to X-rays

A
  • H doesn’t have enough e-
78
Q

How to confirm that the gas is CO2

A
  • Pass the gas using delivery tube into limewater

- Limewater turns cloudy confirms the presence of CO2 gas

79
Q

Chemical Properties of transition compounds

A
  • forms coloured compounds
  • can act as catalysts
  • have variable oxi states
80
Q

fuel cell :
eqns
ads / disads

A

anode : 2H2 + 4OH- —> 4H2O +4e
cathode : O2 + 2H2O +4e —> 4OH-

ads: can be recharged, less pollutant as H2O is produced
disads: expensive since large amounts of Pt required, ↑T

81
Q

carrier gas used in gas chromatography

A
  • H2
  • He
  • N

chem A2 (4 decks)

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