U1 unknowns Flashcards

1
Q

what happens in emission spectroscopy?

A
  • the sample is heated to a high temperature
  • electrons are excited
  • the electrons then drop to lower energy levels
  • photons are emitted and measured
  • an emission spectrum is produced
  • the intensity of light at each wavelength
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2
Q

how do electrons behave like waves in an atom?

A

they behave as standing (stationary ) waves in an atom. these are waves that vibrate in time but do not move in space.

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3
Q

what is an orbital in terms of waves?

A

different sizes and shapes of standing waves possible around the nucleus, known as orbitals

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4
Q

under non-standard conditions, any reaction is feasible…

A

if ∆ G is negative

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5
Q

how can industrial systems be effective

A

by the removal of the product which ‘forces’ the equilibrium in the desired direction.

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6
Q

the reaction 2Al(s) +11/2 O2 → Al2O3(s)
has a large difference between the values of ΔG
and ΔH. Suggest a reason for this
difference

A
  • not much energy is required to break down the intermolecular forces (LDF) within the elements.
    but lots of energy is required to make strong covalent bonds in Al2O3.
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7
Q

conditions for a spontaneous reaction?

A
  • ∆ G is negative
  • there’s a decrease in enthalpy ie. ∆H is negative
  • there’s an increase in entropy ∆S is positive (3rd law of thermodynamics)
  • the activation energy is low enough to be overcome at standard conditions.
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8
Q

how can ions absorb energy in the visible part of the electromagnetic spectrum?

A

d orbital splitting causes a gap in energy between the d orbitals. this means that electrons can be promoted across the gap absorbing a photon of light. the wavelength of light absorbed corresponds with the size of the energy gap.

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9
Q

explain how water and hydroxide can act as a ligand?

A

ligands are substances with a negative charge or a lone pair of electrons that are capable of binding to a transition metal ion forming a complex.
they do this via dative covalent bonding to the central metal ion. dative covalent bonding is a covalent bond in which both electrons are donated by the same atom.

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10
Q

It is more difficult to remove a proton (H+) from [Fe OH(OH2)5] 2+ than from [Fe(OH2)6]3+. Explain why this is so.

A

this is because removing a proton from[Fe(OH2)6]3+ will be easier since it has a bigger positive charge and so it is less reluctant to hold onto electrons in comparison to {FeOH(OH2)5] 2+ which has a smaller positive charge of +2.
also because[Fe(OH2)6], 3+ has effectively already lost a proton to form OH and so losing another one will be more difficult.

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11
Q

how many electrons can occupy an orbital at any one time?

A

2 due to the Pauli exclusion principle

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12
Q

what is chemisorption?

A

the process by which heterogeneous catalysts work:

  • TM can form intermediate complexes
  • reactant molecules are therefore absorbed onto the active sites of the catalyst
  • the bonds within the reactant molecules are therefore weakened.
  • this allows the reactants to be held in a more favourable conformation and so intermediate complexes are formed.
  • the products can then be desorbed from the surface of the catalyst and it can be reused.
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13
Q

what does the presence of unpaired electrons or unfilled d orbitals allow?

A

the formation of intermediate complexes

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14
Q

a good example of homogenous catalysis?

A

the oxidation for Rochelle salt (potassium sodium tartrate) by hydrogen peroxide. the reaction progresses very slowly without a catalyst with only a few bubbles of gas being released. almost immediately on the addition of pink cobalt (II) chloride solution, vigorous effervescence is observed. a colour change is also seen as the cobalt changes from pink to green. when the reaction finishes the effervescence stops and the pink colour returns. in terms of oxidation states, the cobalt has changed from +2 (pink) to =3 (green) and then back to +2 (pink).
Co2+ (aq) -> Co 3+ (aq) -> Co 2+ (aq)
pink -> green -> pink

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15
Q

what is meant by the term diprotic?

A

an acid which is able to produce two H+ ions from each molecule. eg. sulfuric acid

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16
Q

What is the first law of thermodynamics?

A

conservation of energy:

energy cannot be destroyed merely changed from one form to another.

17
Q

Explain why the lines in an emission spectrum become closer and closer together as they converge towards the high energy end of the spectrum of an element?

A

as the principal quantum number increases, the energy levels become closer and closer together

18
Q

what is meant by the term monoprotic acid?

A

an acid that produces just one H+ ion from each molecule eg. nitric acid

19
Q

describe the relationship between the temperature of pure water and its pH

A

as the temperature increases, the ionic product of water increases so the pH decreases.

20
Q

what is the oxidation state of hydrogen in metal hydrides?

A

-1

21
Q

what is the oxidation state of oxygen in peroxides?

A

-1