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CfE AH Chemistry > Unit One > Flashcards

Unit One Flashcards

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1
Q

Why do we say that electromagnetic radiation has a dual nature?

A

It can be considered as both a stream of photons and as waves with characteristic properties such as wavelength and frequency.

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2
Q

What is atomic emission spectrum?

A

An Atomic emission spectrum is a unique spectrum of light emitted by an element when electricity is run through it or when it is viewed through a prism.

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3
Q

What causes an atomic emission spectrum?

A

When energy is transferred to atoms the electrons within them may use the energy to move to a higher energy level. These electrons have become excited and can move back to lower energy levels by losing energy. The energy lost from atoms in this way is released in the form of photons (these are the lines that can be seen). These spectra provide evidence of quantised energy levels in atoms.

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4
Q

Definition of an atomic orbital

A

The volume in space where the probability of finding and electron is greater than 90%.

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5
Q

Define degenerate orbitals

A

Orbitals that have the same energy

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6
Q

What is the maximum number of electrons an orbital can hold?

A

2

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7
Q

What is the shape of the s and p orbitals?

A

S orbitals are spherical and p orbitals are dumb bell shaped.

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8
Q

What is the Aufbau Principle?

A

Electrons fill orbitals in order of increasing energy

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9
Q

What is Hund’s Rule?

A

When degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts

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10
Q

What is the Pauli Exclusion Rule?

A

No two electrons in the one atom can have the same set of four quantum numbers (basically the two electrons in the same orbital must spin in opposite directions)

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11
Q

Order of Orbitals and number in each shell

A

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p
1 s orbital in each shell
3 p orbitals in each shell
5 d orbitals in each shell

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12
Q

What is VSEPR?

A

Valence shell electron pair repulsion and it is responsible for the shapes of molecules and polyatomic ions.

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13
Q

What are lone pairs of electrons?

A

Pairs of electrons occupying an orbital in an atom or molecule and not directly involved in bonding

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14
Q

What has greatest repulsion:
Lone-pair to lone pair
Lone-pair to bonding pair
Bonding pair to bonding pair

A

Lone pair to lone pair is strongest repulsion and Bonding to bonding is weakest.

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15
Q

What is a transition metal?

A

A transition metal forms one or more stable ions with incompletely filled d-orbitals.

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16
Q

Why is the electronic configuration of chromium and copper out with the aufbau principle?

A

There is a special stability associated with half-filled or completely filled d-orbitals.

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17
Q

Why are zinc and scandium not always considered to be transition metals?

A

They do not form stable ions with incompletely filled d orbitals.

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18
Q

What can oxidation and reduction be considered as?

A

Oxidation can be considered as an increase in oxidation number and reduction can be considered as a decrease in oxidation number.

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19
Q

What do compounds containing metals in high oxidation states tend to be?

A

Oxidising Agents.

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20
Q

What do compounds with metals in low oxidation states tend to be?

A

Reducing Agents.

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21
Q

What do transition metal complexes consist of?

A

A central metal ion surrounded by ligands.

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22
Q

What is a ligand?

A

Negative ions or molecules with non- bonding pairs of electrons which they donate to the central metal atom/ion forming dative covalent bonds.

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23
Q

What is a dative covalent bond?

A

They are like any other covalent bond but one atom has donated both electrons.

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24
Q

What are the definitions of monodentate and bidentate ligands?

A

Monodentate ligands donate one pair of electrons to the central metal ion e.g. Cl- and H2O.
Bidentate ligands donate two pairs of electrons to the central atom e.g.. 1,2-diaminoethane and ethanedioate ion.

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25
Q

What is the coordination number?

A

The total number of bonds from the ligand to the central metal ion.

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26
Q

What are the anion names for Iron, Copper, Tin and Lead?

A

Ferrate, Cuprate, Stannate and Plumbate.

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27
Q

What happens to the d orbitals of a transition metal when a ligand bonds and why?

A

The d orbitals lose their degeneracy and split and this is due to repulsion between the electrons in the metal and the electrons in the ligand.

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28
Q

When the d orbitals are split what affects how big the energy gap is?

A

The transition metal ion, the oxidation state and the ligand.

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29
Q

What is the spectrochemical series?

A

It puts in order the ability of ligands to ‘split’ the d orbitals

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30
Q

What are strong field and weak field ligands?

A

Strong field ligands create a large energy difference and weak field ligands create a small energy difference.

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31
Q

How would you identify strong and weak field ligands using spectroscopy?

A

Strong field ligands cause transitions with energy occurring in the UV region and weak field ligands cause transitions with energy occurring in the visible region

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32
Q

Why do transition metal complexes make good catalysts?

A

The unpaired d electrons and unfilled d orbitals allow intermediate complexes to form providing alternative pathways with lower activation energies compared to the uncatalysed reactions.

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33
Q

Define homogenous and heterogeneous catalysts

A

Homogeneous catalysts are in the same phase as the reacting species and heterogenous catalysts are in a different phase

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34
Q

How do heterogenous catalysts work?

A

Chemical adsorption of the reactants onto the surface increases the chance of favourable collisions taking place.

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35
Q

What is Equilibrium constant stated as?

A

It is stated for a given temperature however it is independent of concentration, pressure or the presence of a catalyst

36
Q

What happens to K if there is an increase in temperature?

A

For endothermic reactions a rise in temperature causes an increase in K while for exothermic reactions a temperature increase causes a decrease in K.

37
Q

What does a high/low value of K mean.

A

A high value of K means that the fraction is top heavy and therefore there is more product so the equilibrium lies to the right. A low value of K means the equilibrium lies to the left.

38
Q

Does a catalyst have an effect on K?

A

No, as it doesn’t affect the position of the equilibrium it will have no effect on K.

39
Q

What concentration is a pure solid or liquid as a solvent given when present in equilibrium

A

1

40
Q

What is meant by the ionic product of water?

A

The equilibrium in water between the water molecules, H+ and OH- ions.

41
Q

What name is given to substances like water that act as both an acid and a base?

A

Amphoteric

42
Q

Is the dissociation of water reaction endothermic or exothermic?

A

Endothermic

43
Q

As the dissociation of water is an endothermic reaction what happens to the pH of water as temperature increases?

A

pH decreases as temperature increases

44
Q

As water is neutral what does this means happens to the neutral pH value as temperature changes?

A

The pH value that is neutral will also change

45
Q

What are strong acids and weak acids? Give examples

A

Strong acids are ones that completely dissociate into their ions in a solution (HCl). Weak acids only partially into ions in a solution (Any carboxylic acid).

46
Q

What are strong bases and weak bases? Give examples

A

A strong base completely dissociates into ions in a solution (NaOH) and weak bases only partially dissociate into their ions in solution (NH3)

47
Q

Why are strong acids and bases good conductors?

A

Ions can carry a current

48
Q

What parents acids and bases will give what pH of salt in a neutralisation reaction?

A

Strong Acid+ Strong Base = Neutral
Weak Acid+ Strong Base= Alkali
Strong Acid+ Weak Base= Acid

49
Q

What is the Bronsted-Lowry Theory?

A

An acid is any substance capable of donating a proton. A base is any substance capable of accepting a proton.

50
Q

What are conjugate acids and bases?

A

The conjugate base of an acid is the particle that remains when a proton is removed from the acid. The conjugate acid of a base is the particle that results when the base receives the proton from the acid.

51
Q

What are indicators usually?

A

Indicators are usually weak acids in which the colour of the acid is different from that of its conjugate base.

52
Q

What does a substance need to be a useful indicator?

A

The colour of the non-ionised form, HIn, must be distinctly different from that of its conjugate base, In-

53
Q

In practice when is the colour change in a titration distinguishable?

A

When concentration of HIn and In- differ by a factor of 10.

54
Q

What are the four quantum numbers and what do they mean?

A 
n= number of shell
l= n-1 and refers to the shape
m= the angular momentum in a s orbital=0 p orbital= -1,0 +1, in a d orbital= -2, -1, 0, 2, 1
S= the spin of the electron and will be 1/2 or -1/2
55
Q

What is the definition of a racemic mixture?

A

One that has equal amounts of left and right handed enantiomers of a chiral molecule.

56
Q

What decreases as an acid is diluted?

A

The concentration of H+ ions

57
Q

What is the equation to find the concentration of Hydrogen Ions of a solution?

A

[H+]= 10^-pH

58
Q

What is the equation that links Ka, H3O+ and c?

A

Ka= [H3O+]^2/ c

59
Q

What is the dissociation constant for an acid given by?

A

Ka= [H3o+] [A-] / [HA]

60
Q

What is a buffer solution?

A

One in which pH remains fairly constant when small amounts of acid, base or water are added.

61
Q

What does an acid buffer usually consist of?

A

A weak acid and one of its salts.

62
Q

What does a basic buffer usually consist of?

A

A weak base and one of its salt.

63
Q 
What are the suitable indicators for:
Strong acid- strong base
Strong acid- weak alkali
Strong alkali- weak acid
Weak acid- weak alkali
A
  • pH 3-10
  • pH 3-7
  • pH 7-10
  • No indicator
64
Q

What is the definition of the standard enthalpy of formation?

A

The enthalpy change involved when one mole of a substance is formed from its elements in their standard states.

65
Q

What is the enthalpy of formation of an element?

A

Zero

66
Q

What are standard conditions?

A

298K (25 C) and pressure of 1atm and the standard state of a substance is the most stable state of the substance under standard conditions.

67
Q

What will happen to the total entropy of an isolated system over time?

A

It will increase

68
Q

What is the definition of a spontaneous reaction?

A

Reactions that do not require an outside source of energy to proceed.

69
Q

What is entropy?

A

The measure of the amount of disorder in a system.

70
Q

What happens to entropy when temperature increases?

A

It increases.

71
Q

State five instances when entropy would increase?

A
  • When changing state from solid to liquid to gas.
  • As the moles of vibration increase (basically as molecules become more complex)
  • When many substances dissolve to form solution
  • When a mixture is formed.
  • With increased number of moles.
72
Q

What is the entropy of a perfect crystal at absolute zero

A

zero

73
Q

What must the total entropy change be for a reaction to be feasible?

A

Positive.

74
Q

What does Gibbs Free energy tell you about a reaction?

A 
Negative = reaction is feasible
Zero= reaction is at equilibrium
Positive= reverse reaction will occur
75
Q

What reactions are spontaneous at all temperatures?

A

Positive entropy and negative enthalpy

76
Q

What reactions are non spontaneous at all temperatures?

A

Negative entropy and positive enthalpy.

77
Q

If a reaction has positive enthalpy and entropy when will it be spontaneous ?

A

At higher temperatures

78
Q

If a reaction has a negative enthalpy and entropy when will it be spontaneous?

A

At lower temperatures.

79
Q

What tells you the order of a reactant?

A
  • If doubling R, has no effect on the rate then R has zero order
  • If doubling R, doubles the rate, R is first order
  • If doubling R, quadruples the rate, R is second order
  • If doubling R, octuples the rate, R is third order
80
Q

What are the units of k?

A 
If overall order = 0 then mol l-1 s-1
If 1 then s-1
If 2 then mol-1 l s-1
If 3 then mol-2 l2 s-1 
If 4 then mol-3 l3 s-1
81
Q

What is the slowest step in the reaction mechanism called and what does it do?

A

Rate-determining step and it governs the overall rate of the reaction.

82
Q

What is the difference between the equivalence point and the end point of a titration?

A

Equivalence point is when the solutions have been mixed in exactly the right proportions according to the equation. The end point is when the indicator changes colour.

83
Q

If a reaction vessel is not sealed why can you not find the value of K?

A

There is no equilibrium in an open system

84
Q

Explain why transition metal complexes are coloured?

A

Light is absorbed when electrons in a lower energy d orbital are promoted to a d orbital of a higher energy.

85
Q

What are soaps?

A

Salts of a weak acid and strong base so they dissolve in water to form an alkaline solution

CfE AH Chemistry (3 decks)

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