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OCR A-Level Chemistry > Module 5 - Physical Chemistry and Transition Elements - Exam Questions > Flashcards

Module 5 - Physical Chemistry and Transition Elements - Exam Questions Flashcards

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1
Q

A proposed mechanism for a reaction takes place in several steps. Suggest two reasons why the reaction couldn’t take place in one step (2)

A

Stoichiometry in rate equation does not match stoichiometry in overall equation
Collision unlikely with more than 2 ions/species/particles

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2
Q

What is meant by the half life of a reaction? (1)

A

Time for concentration of reactant to fall to half of the original value

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3
Q

How can a concentration against time graph for a reactant be used to work out order of reaction? (2)

A

Show two half-lives on graph
Zero - half life decreases
First - half life is constant
Second - half life increases

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4
Q

If concentration is altered, is the half life effected on a first order reactant? (1)

A

No

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5
Q

What effect on Kc does using a smaller container for the reaction have? (1)

A

No effect

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6
Q

What effect does adding a catalyst have on Kc? (1)

A

No effect

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7
Q

State three large scale uses of hydrogen (3)

A 
Choose three from:
Extraction of some metals from ores
Fuel cells
Hydrogenation of alkenes
Haber process
Making HCl
Making methanol
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8
Q

The forward reaction is exothermic, if the temperature is raised, what effect is there on Kc? (1)

A

Kc is smaller

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9
Q

2 mols LHS, 2 mols RHS, if pressure is increased, what effect is there on Kc? (1)

A

Kc is same

Kc is not changed by pressure

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10
Q

4 mols LHS, 3 mols RHS, forward reaction exothermic. A chemist increases the temperature and pressure, explain why it can be difficult to predict the change to equilibrium position (2)

A

Increased temperature shifts to the left
Increased pressure shifts to the right as fewer moles of gas on RHS
Difficult to predict relative contributions of two opposing factors

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11
Q

Define Brønsted-Lowry acid (1)

A

Proton donor

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12
Q

Define weak acid (1)

A

Partially dissociates

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13
Q

What name is given to Kw? (1)

A

Ionic product of water

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14
Q

What is the expression for Kw? (1)

A

Kw = [H+(aq)] [OH–(aq)]

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15
Q

What is meant by the rate-determining step? (1)

A

The slowest step

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16
Q

What information is provided by Ka values? (1)

A

Strength of acid

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17
Q

H2PO4(-) can act as an acid or a base. Why can Ca(H2PO4)2 in water act as a buffer solution, using equations? (3)

A

H2PO4- produced from Ca(H2PO4)2
H2PO4(-) + H(+) H3PO4
H2PO4(-) H(+) + HPO4(2-)

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18
Q

State what is meant by a buffer solution (1)

A

A solution that minimises pH changes

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19
Q

Suggest a chemical that could be added to methanoic acid to prepare a buffer solution. Explain (2)

A 
HCOONa
Supplies HCOO(-)
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20
Q

What factors determine the pH of a buffer solution? (2)

A

Ka

Temperature

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21
Q

Write an equation for the reaction of nitric acid with limestone (2)

A

2HNO3 + CaCO3 -> Ca(NO3)2 +CO2 + H2O

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22
Q

Why is the pH scale a more convenient measurement for measuring acid concentrations than [H+]? (1)

A

pH makes numbers manageable

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23
Q

Define a strong acid (1)

A

Completely dissociates

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24
Q

A solution mixes NaOH and CH3COOH (less moles of NaOH than CH3COOH), why is it a buffer solution? (2)

A

Solution is a mixture of CH3COOH and CH3COONa

Has an excess of acid

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25
Q

A solution mixes NaOH and CH3COOH (same number of moles), why is it not a buffer solution? (2)

A

Contains only CH3COONa

Therefore it’s neutral

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26
Q

The pH of water at 25°C is 7.0, and 6.7 at 40°C. What does this show about water’s tendency to ionise with temperature? (2)

A

[H+] increases
H2O H+ + OH-
Equilibrium moves to the right

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27
Q

Why is second electron affinity an endothermic process? (2)

A

Negative ion repels electron being added

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28
Q

Suggest why the entropy of water is zero at 0K (1)

A

Particles are in maximum state of order

29
Q

Why is the entropy change of liquid to gas, bigger than that of solid to liquid? (2)

A

Increase in disorder is bigger

30
Q

Define feasible reaction (1)

A

ΔG =< 0

31
Q

Why might a reaction be feasible at all temperatures? (3)

A

ΔG=ΔH-TΔS
ΔH negative and -TΔS is negative
Hence ΔG is always negative

32
Q

2SO2(g) + O2(g) 2SO3(g)

Why is there a decrease in entropy of the system? (2)

A

Fewer moles of gas

More order in system

33
Q

State what is meant by enthalpy change (2)

A

Internal energy change measured at constant pressure

34
Q

How is entropy changed when water freezes and why? (1)

A

Decreases

State changes to more ordered one

35
Q

Define lattice enthalpy (2)

A

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions

36
Q

Describe and explain the factors that affect the values of lattic enthalpies (3)

A

Decreases in ionic size makes it more negative
Increase in ionic charge makes it more negative
Greater attraction between ions gives more negative LE

37
Q

Why is enthalpy change of hydration of chloride ions exothermic? (1)

A

Hydration involves bond forming

38
Q

Explain why enthalpy change of hydration of Mg ions is more exothermic than Ca ions (2)

A

Magnesium ion is smaller

Mg2+ has a stronger attraction to H2O

39
Q

Define enthalpy change of solution (2)

A

The enthalpy change that takes place when one mole of a solute dissolves in a solvent

40
Q

Define enthalpy change of hydration (2)

A

The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

41
Q

Define standard entropy (2)

A

The entropy of one mole of a substance, under standard conditions

42
Q

Discuss two advantages and two disadvantages of using fuel cells for energy rather than using fossil fuels (4)

A 
Advantages:
Only H2O formed
Greater efficiency
Disadvantages:
H2 difficult to store
H2 difficult to manufacture initially
43
Q

Define standard electrode potential (3)

A

Emf of electrochemical cell comprising a half cell combined with a standard hydrogen electrode at 1 atm, 298K and solutions of 1 mol/dm^3

44
Q

Give one use of chromium metal and state the property that makes it suitable (1)

A

Stainless steel

Corrosion resistance

45
Q

When given the cell potentials of redox systems, how can the most powerful oxidising agent be identified? (1)

A

LHS of most positive cell potential

46
Q

What is used for the electrode and solution in the H2 half cell? (2)

A

Platinum electrode

H+ at 1 mol/dm^3

47
Q

What is the direction of electron flow in a cell circuit? (1)

A

Most positive solution to most negative solution, along the wire

48
Q

Define transition element (1)

A

Has at least one ion with a partially filled d-orbital

49
Q

Define complex ion (1)

A

A central metal ion surrounded by ligands

50
Q

Define ligand (1)

A

Molecule with a lone pair(s) of electrons capable of forming dative bonds to a metal ion

51
Q

NaOH(aq) is added to Fe2+(aq), what would be observed, and what is the ionic equation? (2)

A

Green precipitate
Fe2+(aq) + 2OH–
(aq) → Fe(OH)2
(s)

52
Q

In octahedral complex ions, what kind of stereoisomerism is shown? (1)

A

Optical and geometric isomerism

53
Q

In square planar complex ions, what kind of stereoisomerism is shown? (1)

A

Geometric isomerism

54
Q

In tetrahedral complex ions, what kind of stereoisomerism is shown? (1)

A

Optical isomerism

55
Q

Which reagent should be chosen for converting [Ru(H2O)6]3+ to [Ru(H2O)5Cl]2+? (1)

A

Concentrated HCl

56
Q

What name is given to changing the molecules that form dative covalent bonds with metal ions? (1)

A

Ligand substitution

57
Q

How is the end point of a titration involving iodine identified? (1)

A

Starch added is decolourised

58
Q

Suggest why a cyanide ion can act as a ligand (1)

A

Has a lone pair of electrons that can be donated

59
Q

NaOH(aq) is added to Fe3+(aq), what would be seen and write an ionic equation (2)

A

Brown precipitate
Fe3+(aq) + 3OH–
(aq) → Fe(OH)3
(s)

60
Q

Define bidentate ligand (2)

A

Ligand able to donate two lone pairs to form dative covalent bonds

61
Q

Describe a test to show the presence of Fe3+ ions in a solution of FeSO4.7H2O (1)

A

Adding NaOH(aq) will give a brown precipitate

62
Q

[Cu(H2O)6]2+ is reacted with conc HCl, describe the observations made (1)

A

Blue to yellow solution

63
Q

Describe the bonding within [CuCl4]2– (2)

A

Lone pair on chloride ions donated to copper(II) ion

64
Q

Define co-ordination number (1)

A

Number of dative covalent bonds formed with the transition metal

65
Q

How does cisplatin help with cancer treatment? (2)

A

Binds with DNA

Prevents tumour growth

66
Q

State two typical properties of compounds of a transition element (2)

A

Form complexes

Act as catalysts

67
Q

Explain why the H-O-H bond angle in a water ligand is 107 not 104.5 (3)

A

Water molecule 2 lone pairs and 2 bond pairs
Water ligand 1 lone pair and 3 bond pairs
Lone pairs repel more than bond pairs

68
Q

Which metals are present in brass? (1)

A

Copper and zinc

69
Q

Give a common use for brass and state the property responsible (1)

A

Coins

Corrosion resistance

OCR A-Level Chemistry (34 decks)

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