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Chemistry > Unit 3 -PPQ > Flashcards

Unit 3 -PPQ Flashcards

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1
Q

Explain why enthalpy of hydration is always exothermic [2]

A

bonds form between polar water molecules and charged ions

- reduces kinetic energy of system of which is given out as heat

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2
Q

Why is lattice energy of Mg(OH)2 more exothermic than that of Ba(OH)2? [3]

A

atomic radius of Ba2+&raquo_space; radius of Mg2+

  • strength of ionic bonding in Mg(OH)2 is greater as ions in lattice are closer together
  • as lattice forms, more energy released
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3
Q

HCOOH + H20 ⇌ H3O+ + HCOO-

Explain how this, with sodium methanoate acts as a buffer solution [4]

A

on adding acid: added H+ ions mopped up by available HCOO- ions. Eqm shifts to left. [H+] remains fairly constant, as does pH.
on adding alkali: added OH- reacts w/ H+ to form water. Eqm shifts to right. More HCOOH dissociates to replace H+ ions removed. [H+] remains fairly constant, as does pH

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4
Q

Reaction is exothermic. State the effect, if any, on Kp of increasing the temperature at constant pressure [1]

A

Eqm shifts in endothermic direction, favouring reactants, decreasing Kp

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5
Q

Give 2 equations to show how PbO exhibits amphoteric character [2]

A

PbO(s) + 2HNO3(aq) -> Pb(NO3)2(aq) + H2O(l)

PbO(s) + 2NaOH(aq) -> Na2Pb(OH)4(aq)

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6
Q

Give an equation to show why solutions of CO2 in water are acidic [1]

A

CO2 + H2O⇌ H2CO3⇌2H+ + CO32-

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7
Q

When a metal is placed in a solution of its ions, the electrode potential set u between metal and solution can’t be measured without using a reference electrode. Explain why this is so [1]

A

It’s not possible to make electrical contact between ions in solution and voltmeter

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8
Q

State how metallic character of G4 elements change with an increase in atomic number. jUstify your answer [2]

A

Metallic character increases down group

  • Carbon: diamond (electrical insulator)
  • Lead: Metallic lattice (electrical conductor)
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9
Q

Stability of +2 oxidation state increases down G4. What’s the reason for this?

A

An increasing tendency for outer pair of s electrons not to become involved in bonding i.e. only pair of p electrons involved. +2 state becomes more stable

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10
Q

CCl4 and SiCl4 behave in different ways when added to water. State how each chloride behaves and explain the difference [5]

A

CCl4: no hydrolysis occurs. 2 immiscible liquid layers form. C has filled outer quantum shell of electrons. No vacant orbitals that can be attacked by lone pairs of O on H2O
SiCl4: rapid hydrolysis occurs. Evolution of misty white fumes + formation of faint white suspension occurs. Has empty 3d orbitals into which lone pairs from H2O can donate to
SiCl4 + 2H2O -> SiO2 + 4HCl

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11
Q

What types of bonding exist in Al2Cl6? [2]

A

Single covalent bonding between 1x Al and 3xCl
Dative covalent bonding between 1x Al and 1x Cl
Van der Waals beween Al2Cl6 dimer units

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12
Q

Give the expression for the ionic product of water [1]

A

Kw= [H3O+][OH-]

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13
Q

When HCl is added to aqueous ammonia, explain why a buffering effect occurs where a mixture of NH3(aq) and NH4Cl(aq) is present [3]

A

NH4+ ⇌ NH3 + H+
NH3 reacts w/ added acid to form NH4+
NH4+ dissociates as H+ reacts w/ added alkali

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14
Q

State the function performed by the salt bridge in an electrochemical cell [2]

A

completes circuit between electrode solutions

allows movements of ions without mixing of solution

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15
Q

Explain why the 2H+ + 2e- ⇌ H2 electrode has an electrode potential of 0 [1]

A

used as a standard

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16
Q

State 1 disadvantage of using hydrogen fuel cells to power vehicles [1]

A

difficult to store enough hydrogen

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17
Q

State 1 advantage of using hydrogen fuel cells compared to combustion of petrol [2]

A

Doesn’t release CO2 which is a greenhouse gas

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18
Q

Both BN and C form hexagonal graphite-type structures. Explain why:
BN and C both adopt same hexagonal structure
Both exhibit lubricating properties
C is an electrical conductor by BN is an insulator at room temp [6]

A

BN and C = isoelectronic; can form 3 bonds w/ 1 unbounded p orbital
Both have layer structures; weak VdW forces allow slippage of layers
In C, delocalisation of electrons allows for conduction of electricity; in BN each N has full unbounded p orbital whereas each b has empty unbounded p orbital; N is more electronegative than B, so electron density not evenly spread

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19
Q

Explain why most Cu2+ compounds are coloured in presence of water [4]

A

3d orbitals split by water ligands into high energy doublet and low energy triplet
electrons absorb energy allowing for d-d transition
blue colour due to non-absorbed frequencies

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20
Q

Explain why most Cu+ compounds are colourless/white [1]

A

3d sub-shell is full

- d-d transition can’t occur

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21
Q

Explain why lead forms solid chloride PbCl2 but CCl2 and SiCl2 are too unstable to exist [2]

A

In PbCl2, Pb2+ ion stabilised due to inert pair effect
CCl2 and SiCl2 instable because:
- +4 oxidation state more stable that +2 at top of G4
- covalent bonding more stable than ionic at top of group and 4 bonds needed for outer octet

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22
Q

State what is meant by amphoteric [1]

A

Reacts with both acids and bases

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23
Q

Aluminium chloride is a compound of amphoteric Al whilst magnesium chloride contains non-amphoteric Mg. Explain how NaOH can be used to distinguish between these 2 solutions [3]

A

add NaOH drop-wise until there’s excess
white ppt forms w/ Mg but doesn’t redissolve
white ppt forms w/ Al which redissolved in excess

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24
Q

Explain why 2 AlCl3 monomers join together [2]

A

Al is electron deficient and Cl has lone pairs which it donates, to form dative covalent bond

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25
Q

2N2O5(g) -> 4NO2(g) + O2(g)
colourless brown colourless
Suggest 2 methods of studying kinetics of this reaction [2]

A

colorimetry
- measure intensity of brown colour over time
measure pressure/volume over time

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26
Q

State what is meant by transition metal [1]

A

partially filled d orbitals in atom/when they form ions

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27
Q

Write the overall equation when ion is extracted from Fe2O3 in blast furnace using CO [1]

A

Fe2O3 + 3CO -> 2Fe + 3CO2

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28
Q

Explain why CO can be used as a reducing agent but PbO can’t [2]

A

Stable oxidation state of C is +4 but for Pb it’s +2

- due to inert pair effect becoming more significant down group

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29
Q

What is meant by strong acid [1]

A

Completely dissociates to release H+

30
Q

State the role of the Pt electrodes in a cell [1]

A

inert electrode used to carry charge

31
Q

4H+ + 4I- + O2 ⇌ 2I2 + 2H2O
Use Le Chatelier’s principle to suggest a reagent you could add, apart from H2O to decrease amount of yellow iodine present. Explain your choice [2]

A

Add small amount of NaOH
OH- reacts w/ H+ to form H2O
Increases [H2O]
Shifts position of eqm to left

32
Q

Describe what is seen when solid NaI is added to conc H2SO4 [2]

A 
purple vapour (I2)
steamy white fumes (HI)
yellow solid (S)
33
Q

Give equations for reaction of Cl2 w/ NaOH

A

Cl2 + 2NaOH -> NaCl + NaOCl + H2O

34
Q

Shape and colour of:

  • [CuCl4]2-
  • [Cu(NH3)4(H2O)2]2+
A
  • Tetrahedral - yellow

- octahedral - dark blue

35
Q

State and explain how ΔfH⦵ values give an indication of G4 oxide’s stability [2]

A

more negative the ΔfH⦵ value, more stable the oxide

36
Q

Give 2 reasons why transition elements and their compounds can act as catalysts [2]

A

variable oxidation states

partially filled 3d orbital

37
Q

Describe reaction to show that both Al3+ and Pb2+ exhibit amphoteric character [4]

A

Add NaOH dropwise into each
white ppt of Al(OH)3 and Pb(OH)2 seen
- in excess OH-, ppt dissolves giving colourless solution

38
Q

Describe what is seen when iodide ions are added to Pb2+, giving an ionic equation for the reaction [2]

A

Yellow ppt

Pb2+ + 2I- -> PbI2

39
Q

Describe and explain the shape of curve when aqueous ammonia is added to aqueous nitric acid [3]

A

HNO3 = strong acid w/ pH <2
As NH3 added, pH slowly increases until pH~3
Rises rapidly
At pH 8-9, rails off slowly because NH3 is a weak base

40
Q

State what is meant by a Lowry-Bronsted acid [1]

A

Proton donor

41
Q

Define pH [1]

A

-log[H+]

42
Q

Describe the factors that affect pH [4]

A

low pH corresponds to high [H+]
strong acid is totally dissociated whilst weak acid is partially dissociated
need to consider concentration of acid as well as strength

43
Q

Why can transition elements form compounds with variety of oxidation states [1]

A

energies of d orbitals are similar

44
Q

State one use for c-BN structure [1]

A

Wear resistant coatings

45
Q

Write the equation for the reaction of chlorine with cold aqueous sodium hydroxide [1]

A

Cl2 + 2NaOH -> NaCl + NaClO + H2O

46
Q

Write the equation for the reaction of chlorine with hot aqueous sodium hydroxide [1]

A

3Cl2 + 6NaOH -> 5NaCl + NaClO3 + 3H2O

47
Q

Classify the reaction of chlorine with NaOH [1]

A

Disproportionation

48
Q

Explain why Phosphorus forms two chlorides, PCl3 and PCl5, but nitrogen only forms NCl3 [2]

A

P can expand normal octet by using 3d orbitals

N cannot do this since it’s in the second period and 3d orbitals aren’t available for it

49
Q

What are the 2 enthalpy changes which are the factors affecting solubility and enthalpy change of solution of an ionic compound? [2]

A

Enthalpy of hydration (exothermic)

Enthalpy of lattice breaking (endothermic)

50
Q

Explain how enthalpy change of solution of a compound and its solubility depend on the balance between enthalpy of hydration and enthalpy of lattice breaking [2]

A

ΔH solution = ΔH lattice breaking + ΔH hydration

If ΔH solution is negative, ionic solid = soluble

51
Q

Write the cell diagram of the cell formed by combining Fe3+, Fe2+ and Ce4+, Ce3+ half cells [1]

A

Pt(s) I Fe2+(aq), Fe3+(aq) // Ce4+(aq), Ce3+(aq) I Pt (s)

52
Q

In an exothermic reaction. what happens to the value of the equilibrium constant, Kc if the temperature is increased [1]

A

Value of Kc decreases since eqm shifts to left

53
Q

State what is meant by a ligand [1]

A

Species with lone pair that can form dative covalent bond to metal atom/ion

54
Q

When excess ammonia is added to a solution containing [Cu(H2O)6]2+ ions, the colour of the solution changes as a new complex ion is formed. Give the formula of the new complex ion and the colour of the solution formed. [2]

A

[Cu(NH3)4(H2O)2]2+ (aq)

Dark navy blue

55
Q

Explain why the standard entropies of CO2 and CO are significantly greater than those of Fe2O3 [1]

A

Gases have higher entropies than solids as molecules have greater degree of disorder

56
Q

ΔG is negative. Explain why this reaction is feasible at all temperatures [2]

A

Reaction is feasible when ΔG is negative

No temp exists where ΔG is positive

57
Q

Many industrial process use high temperatures even when reaction is feasible at low temperatures. Suggest why [1]

A

Higher temperatures increases rate of reaction

58
Q

Explain why B forms compounds with +3 oxidation state alone, but thallium compounds are more stable with +1 oxidation state [2]

A

+1 occurs due to inert pair of s-electrons

Inert pair effect becomes more significant down group

59
Q

Explain the term electron deficient [1]

A

Outer sell of electrons is not full

60
Q

Describe differences between hexagonal BN and graphite in terms of their bonding and structure [3]

A

All atoms the same in graphite but alternate in BN
Within layers, atoms are in register in BN but not in graphite
B-N bonds are polarised but graphite is non-polar
p-electrons in BN are localised by in graphite are delocalised

61
Q

Write an ion-electron half equation for reduction of acidified MnO4- [1]

A

MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O

62
Q

State what is meant by a buffer solution [1]

A

Solution which keeps pH almost constant when small amounts of acid/base are added

63
Q

Write equation for reaction of Cu2+ and I-, clearly identifying the precipitate [2]

A

2Cu2+(aq) + 4I-(aq) -> 2CuI(s) + I2(aq)

64
Q

2H+ + 2l− + H2O2 I2 + 2H2O
Reaction was studied using an iodine clock reaction. Describe the principles of how rate of clock reaction is determined [2]

A

Measure time taken for sudden colour change

Rate = 1/time

65
Q

State the effect of an increase in temperature on a rate constant and a rate equation [1]

A

No affect on rate equation

Increases rate constant

66
Q

Explain what is meant by the rate-determining step [1]

A

slowest step in the reaction

67
Q

NO2 +CO->NO+CO2
rate = k[NO2]2
Write equations to show possible 2-step mechanism for this reaction [2]

A

2NO2 -> 2NO + O2

2NO+ O2 + 2CO -> 2NO + 2CO2

68
Q

Explain the difference between meaning of weak acid and dilute acid [2]

A

Weak acid: partially dissociates in aqueous solution

Dilute acid: small amount of acid dissolved in large volume of water

69
Q

Aqueous ammonia reacts with HCl to form NH4Cl. Give reason why pH value for NH4Cl solution is less than 7 [1]

A

Salt hydrolysis occurs

NH4+ + H2O⇌ NH4OH + H+

70
Q

Copper compounds take part in several different types of reaction including ligand substitution and precipitation. Using copper compounds, give an example for both types of reaction, stating any observations. Give the formula for the copper-containing product for each example. [6]

A

Ligand substitution w/ excess NH3 reacting with [Cu(H2O)6)2+
- forms [Cu(NH3)4(H2O)2]2+
royal blue solution

Ppt reaction:
CuSO4 + NaOH
- pale blue ppt of Cu(OH)2

71
Q

The characteristics of the Group IV elements and their compounds change significantly from carbon to lead. Show how this statement is true by comparing:
• the reactions, if any, of carbon dioxide and lead(II) oxide with acids and alkalis
• the reduction-oxidation properties of carbon monoxide and lead(IV) oxide. [6]

A

Carbon dioxide is acidic while lead(II) oxide is amphoteric
e.g. CO2 + 2NaOH → Na2CO3 + H2O

Pb2+ + 2OH‒ → Pb(OH)2

Pb(OH)2 + 2OH‒ → [Pb(OH)4]2‒

Carbon monoxide is a reducing agent while lead(IV) is an oxidising agent
e.g. CO+CuO→CO2 +Cu

PbO2 + 4HCl → PbCl2 + Cl2 + 2H2O

Chemistry (2 decks)

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