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Biosciences > Chem 2a Q > Flashcards

Chem 2a Q Flashcards

1
Q

Explain why an incorrect value for the number of moles of iron(II) chloride would have been obtained if the original solution had been titrated with potassium manganate(VII)

A

KMnO4 would oxidise Cl- as well as Fe2+, so titration value would be too large.

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2
Q

In what way does the NH3 behave as a Brønsted–Lowry base?

A

Proton acceptor

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3
Q

In what way does the NH3 behave as a Lewis base?

A

Electron pair donor

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4
Q

State and explain the effect of a catalyst on rate in a reversible reaction.

A
  • Increases the rate at which eqm .is reached
  • Catalyst provides alternative reaction route w/ lower Ea
  • More particles have this Ea so the reaction is faster
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5
Q

State and explain the effect of a catalyst on eqm. yield in a reversible reaction.

A
  • No effect on eqm yield

- Forward & backward reaction rate speeded up equally.

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6
Q

Reactions for Fe2+ as a homogenous catalyst for the reaction of I- and S2O8(2-).

A

2Fe^(2+) + S2O8^(2–) –> 2SO4^(2–) + 2Fe^(3+)

2Fe^(3+) + 2I– –> 2Fe^(2+) + I2

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7
Q

Ligand

A

Electron pair donor

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8
Q

Complex ion

A

Central metal atom or ion surrounded by ligands attached by coordinate bonds

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9
Q

Co ordinate number

A

The number of coordinate bonds made by a metal atom or ion to the ligands

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10
Q

A ligand substitution reaction which occurs with no change in the co-ordination number but a change in the charge on the complex ion.

A

[Fe(H2O)6]^(2+) + 3C2O4^(2–) –> [Fe(C2O4)3]^(4–) + 6H2O

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11
Q

Explain why the pH of a solution of iron(II) chloride is higher than that of a solution of iron(III) chloride of the same concentration.

A

The charge density on Fe2+ is less than on Fe3+ so it is less polarising to the water ligands and fewer H+ ions are released

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12
Q

State the origin of the colour of transition-metal complexes

A

Movement of electrons within the d sub-level orbitals

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13
Q

Give three changes to a transition-metal complex which result in a change in colour

A

Oxidation state
Coordination number
Ligand substitution

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14
Q

Coordinate bond

A

Where one of the atoms involved donates both electrons to the shared pair

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15
Q

Bidentate ligand

A

One which uses two lone pairs to link onto a metal atom or ion.

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16
Q

Suggest why the enthalpy change for a reaction may be close to zero

A

Because the bonds formed are approximately the same strength as those broken

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17
Q

Zwitterion in acidic conditions

A

NH2 becomes NH3+

COOH becomes COO-

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18
Q

Why can Vanadium(III) catalyse the reaction between S2O8^(2-) and I- but Mg(II) can’t?

A

Vanadium(III) can be oxidised to a higher state whereas Mg(II) cannot.

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19
Q

Why is the complex formed when a copper aq ion reacts with EDTA^(4-) more stable than the Cu aq ion?

A

Large increase in entropy as 2 particles form 7 - increases stability.

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20
Q

Reagent needed to carry out

CrO4^(2–) (aq) → Cr2O7^(2–) (aq)

A

Strong acid like HCl

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21
Q

Reagent needed to carry out

VO^(2+) (aq) → [V(H2O)6]^(2+) (aq)

A

Zn metal and HCl

22
Q

Reagent needed to carry out

[Ag(NH3)2]^(+)(aq) → Ag(s)

A

Aldehyde

CH3CHO

23
Q

chelate

A

A central metal ion complexed with a multidentate ligand forming a more stable complex

24
Q

Give one reason why sulphur dioxide gas may be found in the exhaust gases of cars.

A

Sulphur present in petrol

25
Q

Give one reason why sulphur dioxide is considered to be a pollutant.

A

Gives acid rain

26
Q

3 characteristics of a homologous series

A
  • Can be displayed by a general formula
  • Vary by constant amount
  • Show a gradation in properties
27
Q

Molecular formula

A

Actual number of each type of atom in one molecule of a substance

28
Q

Cracking

A

T - 400-900˚C

The breaking of a long alkane chain into smaller alkanes and alkenes

29
Q

What is a fraction

A

A part of crude oil with a specific boiling range

30
Q

Economic value of cracking

A

Use up low demand fractions/Produce commercially favoured fractions like petrol

31
Q

functional group isomerism.

A

Where the atoms of one functional group can be rearranged to produce one or more other functional groups.

32
Q

Empirical formula

A

Simplest whole number ratio of atoms in a compound

33
Q

Structural isomer

A

Same molecular formula but different structural formulae

34
Q

Position isomer

A

Where a particular functional group could be placed in more than one position in the carbon chain

35
Q

Stereoisomers

A

Same molecular and structural formulae, different spatial arrangement.

36
Q

Identify the type of reactive intermediates formed during thermal cracking and explain how they are produced.

A

Free-radicals

the C-C bonds split homolytically

37
Q

Why are polymers solid at room temperature?

A

the long polymer chains are connected by very many van der Waal’s forces
these take a lot of energy to separate - high m.p.

38
Q

Name the type of polymerisation which occurs when ethene is converted into poly(ethene).

A

Addition

39
Q

Explain why ethene is able to react with bromine in an electrophillic addition reaction, given that bromine molecules are non-polar.

A

Induced dipole in the bromine molecule

attack by δ+ on one Br

40
Q

Conditions for nucleophillic substitution

A

Aqueous

Warm

41
Q

Condtions and reagent for an elimination reaction

A

Alcoholic solution

KOH

42
Q

Why is an elimination reaction of CH3CH2Br with OH- not used to produce ethene in industry

A

Alternative reaction produces ethanol and reduces yield

43
Q

State four essential conditions for the conversion of glucose into ethanol

A

Yeast
temp. around 37˚C
Water
Anaerobic conditions

44
Q

Identify a catalyst which could be used in the acid-catalysed dehydration of ethanol

A

H2SO4

45
Q

Give one advantage of the use of propanoyl chloride instead of propanoic acid in the laboratory preparation of methyl propanoate from methanol.

A

Faster reaction

better yield

46
Q

Give one advantage of the use of propanoic anhydride instead of propanoyl chloride in the industrial manufacture of methyl propanoate from methanol.

A

Cheaper reagent
Less toxic
Less violent reaction
Safe

47
Q

Conditions for reducing aldehyde/ketone

A

NaBH4

Water

48
Q

Conditions for esterification

A

Aldehyde + ketone

conc. H2SO4

49
Q

In the industrial manufacture of aspirin, ethanoic anhydride is used as an acylating agent rather than ethanoyl chloride. Give two reasons why ethanoic anhydride is preferred.

A

Cheaper reagent
Less toxic
Less violent reaction
Safer

50
Q

Reaction to distinguish between ethanoic anhydride and ethanoyl chloride

A

Add water
ethanoic anhydride - no initial reaction
ethanoyl chloride - violent exothermic reaction

Biosciences (24 decks)

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