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Chemistry A level > Oceans > Flashcards

Oceans Flashcards

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1
Q

What are positive ions called?

A

Cations

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2
Q

What are negative ions called?

A

Anions

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3
Q

What is the structure of NaCl? and why?

A

Each Na+ ion is surrounded by 6 Cl- ions.
Each Cl- ion is surrounded by 6 Na+ ions
Because each oppositely charged ions attract and similarly charged ions repel. Overall attractions are stronger than the repulsions so the lattice holds together.

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4
Q

What happens when NaCl is dissolved in water?

A

The ions separate from each other randomly.

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5
Q

What must happen to allow the ionic lattice to separate? What is this called?

A

The electrical attraction between the oppositely charged ions has to be over come.
This is the lattice enthalpy

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6
Q

What is lattice enthalpy?

A

This is the enthalpy change when one mole of solid is formed by the coming together of separate ions.
It is the energy released when gaseous ions bond to form a solid product.

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7
Q

Are all lattice enthalpies negative or positive?

A

They are all negative

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8
Q

How is a lattice broken? (in terms of energy)

A

Energy must be put into the lattice equal to the lattice enthalpy.

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9
Q

Atoms with the highest charge density…

A

Have the highest lattice enthalpy

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10
Q

How does an ionic lattice become hydrated?

A

The ions in the lattice become separated from the lattice by the polar water molecules. Cations (positive) are attracted to the partially negative oxygen in the water. Anions are attracted to the partially positive hydrogen in the water molecule.
Water surrounds the ion and this separates it from the lattice.

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11
Q

What does extensively hydrated mean?

A

This is the amount that the water is attracted to an ion.

The higher the charge the more water molecules become attracted to it.

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12
Q

How is the energy supplied to break the lattice?

A

Energy is released when the water forms a bond with the ion. this energy is used to break the lattice

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13
Q

What is the enthalpy change of hydration?

A

This is a measure of the strength of attraction between ions and water molecules

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14
Q

What value is the enthalpy change of hydration always?

A

It is always a negative value

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15
Q

What affects the enthalpy change of hydration?

A 
The size of the radii (smaller the better)
The charge (Greater the better and this also has the greatest impact on the enthalpy change of hydration)
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16
Q

What is the enthalpy of solvation?

A

This is the same as the enthalpy of hydration however it involves a solvent (such as ethanol) not water.

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17
Q

What is the enthalpy change of solution?

A

This is the enthalpy change when one mole of solute dissolves in water to form a very dilute solution.
It is also the difference between the enthalpy change of hydration and the lattice enthalpy.

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18
Q

What is the equation for enthalpy change of solution?

A

ΔsolutionH = ΔhydH(cation) + Δhyd(anion) - ΔleH

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19
Q

What is a non-polar solvent? and what are its properties

A

This is when a solvent is non polar and doesn’t form a dipole between a solute and solvent. It struggles to dissolve because it cannot interact with the solute.
The enthalpy change of solution is too large to overcome

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20
Q

What is emitted when things get hot? What does the temperature affect?

A

They emit electromagnetic radiation and the temperature changes the frequency of the radiation emitted

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21
Q

What happens to light from the sun that shines onto the earths surface?

A

The light is absorbed by the earths surface but because the earth is much cooler than the surface of the sun, it reradiates a much lover frequency of electromagnetic radiation (in the infrared spectrum).

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22
Q

What do greenhouse gasses do to the reemitted radiation?

A

The greenhouse gasses absorb some of the radiation and prevent it from being reemitted into space. This causes the earth to heat up

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23
Q

What does absorbed infrared radiation do to carbondioxide molecules?

A

It increases the vibrational energy which can be transferred to other molecules heating the atmosphere
Some of this radiation is then reemitted by the carbon dioxide molecules back into space or down to earth

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24
Q

Talk about the wavelengths of infrared radiation absorbed by water vapor

A

Water vapour is the most abundant greenhouse gas and it does NOT absorb all the frequencies of infrared radiation. The frequencies it allows to escape is called the IR window. This fact allows to balance the temperature of the earth.

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25
Q

What happens if there is more water vapour or carbon dioxide in the atmosphere?

A

More carbon dioxide: Increases the earths temperature by absorbing more infrared radiation and reemitting it back to earth.
The increased temperature causes more water to evaporate into the atmosphere
More water vapour: absorbs more radiation and heats up the atmosphere and makes the problem of global warming worse

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26
Q

What is the definition of an acid?

A

It is a substance that donates an H+ ion in a chemical reaction

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27
Q

What is the definition of a base?

A

It is a substance that accepts an H+ ion in a chemical reaction.

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28
Q

What is the bronsted-lowery theory?

A

This is the theory about H+ ions being donated and accepted. An H+ ion is just a proton and so we can refer to it as protonation and deprotonation

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29
Q

What is a conjugate acid?

A

This is the acid that is formed when a base disociates

NH3(aq) + H+ ==> NH4+ (conjugate acid)

30
Q

What is a conjugate base?

A

This is the base that is formed when an acid disociates

HA(aq) ==> H+(aq) + A-(aq)(Conjugate base)

31
Q

What can water act as when combined with an acid or a base?

A 
It can become an acid or a base.
e.g: 
HCl + H2O ==> H3O+ + Cl-
or
NH3 + H2O ==> NH4+ + OH-
32
Q

What is the pH a scale of?

A

It is a scale based off the concentration of H+ ions in a solution.
pH 0 has 1 mol of H+ ions / dm3.
pH 14 has 1x10-14 mol of H+ ions / dm3

33
Q

How many H+ ions and OH- ions per dm3 when there is a pH of 6?

A

H+: 1x10-6

OH-: 1x10-14 / 1x10-6 = 1x10-8

34
Q

How do you work out the concentration of OH- with the H+ concentration?

A

1x10-14 / [H+ conc] = [OH- conc]

35
Q

What is a strong acid?

A

It is an acid that fully dissociates in water

36
Q

What is a weak acid?

A

It is an acid that doesn’t fully dissociate in water

37
Q

What is the concentration of a H+ ions in a 0.02moldm-3 solution of HCl?

A

Concentration of H+ ions: 0.02moldm-3

38
Q

What type of reaction is it when a weak acid dissociates?

A

It is an equilibrium reaction and has an equilibrium constant.

39
Q

How do you convert between concentration of H+ or OH- and pH?

A

H+: pH = -Log10([H+ conc])

OH-: pH = -Log10(1x10-14 / [OH- conc])

40
Q

What is the acidity constant?

A

It is a measure of the position of equilibrium of a weak acid. It measures how far it dissociates.

41
Q

What is the equation to measure the acidity constant?

A

Ka = [H+ conc][A- conc] / [HA conc]

42
Q

What are the two assumptions that are made when regarding the acidity constant equation?

A
  1. That there is an equal amount of H+ and A- ions made

2. The amount of HA at equilibrium is equal to the amount put into solution

43
Q

How can the acidity constant equation be arranged to find the concentration of H+ ions?

A

√Ka x [HA conc] = [H+ conc]

44
Q

How is pKa calculated?

A

pKa = -Log10(Ka)

45
Q

What is Kw and what is its value?

A

It is the ionisation product of water

At 298K Kw = 1x10-14

46
Q

What is the equation of the ionisation product of water?

A

Kw = [H+ conc][OH- conc]

47
Q

What is a buffer?

A

It is a solution that can resist the change in pH in a solution

48
Q

How does a buffer work?

A

It reacts with the acid or alkali and removes it from the solution

49
Q

What are buffers made from?

A

Either:

  • A weak acid and one of its salts
  • A weak base and one its salts
50
Q

What are the assumptions made with buffers? x2

A

HA <=> H+ + A-
Stalt ==> Negion + posion
1. The number of A- from the weak acid is far smaller than the amount from the buffer.
2. Almost all of the HA molecules remain unchanged

51
Q

What happens when H+ ions (acids) are added to a buffer solution?

A

The negative ions from the buffers salt which has dissociated reacts with the H+ ions from the added acid to from a weak acid that isn’t dissociated. This counteracts the change.

52
Q

What is the equation of Ka for a buffer solution?

A

Ka = [H+ conc] x ( [Salt] / [Acid])

53
Q

Where does the value of Ka often lie?

A

pH 4 and pH 10

54
Q

What is solubility equilibria?

A

It is the position of equilibrium when a salt dissolves. No salt is insoluble or completely soluble

55
Q

What does Ksp mean?

A

Ksp is the solubility product constant and is a measure of the position of equilibrium when something dissolves in water

56
Q

What is the equation for Ksp?

A

Ksp = [prod1 conc][prod2 conc] / [reactant conc]
so for: CaCO3 <=> Ca 2+ + CO3 2-
Ksp = [Ca2+ conc][CO32- conc] / [CaCO3 conc]

57
Q

How can Ksp be used to predict to see if a precipitate will form?

A

If the concentration of the two parts of the salt when multiplied are greater than the Ksp of that salt then a precipitate will form.
e.g.
[Ca2+ conc]x[CO32- conc] > Ksp of CaCO3

58
Q

What is disorder?

A

This is what causes substances and reactions to occur spontaneously. Atoms want to spread apart and distribute evenly and randomly.

59
Q

What is entropy?

A

It is a measure of the randomness of a system. It is a measure of how many ways atoms can be arranged in a system and is given the symbol S

60
Q

What is entropy?

A

It is a measure of the randomness of a system, how atoms are arranged and distributed and how energy is distributed in a system. It is given the symbol S

61
Q

What is the unit of entropy? and at what conditions are values given?

A

JK-1mol-1

298K 100kpa

62
Q

How do you find the total entropy change for a process?

A

The entropy of the system and the surrounding needs to be added together.
ΔtotalS = ΔsysS + ΔsurrS

63
Q

What does total entropy change tell you about a reaction?

A

A reaction is only feasible if the entropy change is positive

64
Q

Can we work out the entropy of each individual substance in a system?

A

No, it is impossible to know exactly how energy has been shared out

65
Q

What is a system?

A

It is a substance in its surrounding environment

66
Q

What factors affect entropy?

A 
The amount of substance
Temperature
Pressure
The size of the molecule (e.g. H2 vs Cl2)
The state of the substance
67
Q

What happens when alkali is added to a buffer solution?

A

H+ ions from the acid buffer reacts with the OH- from the added alkali to from water and this moves the position of equilibrium for the acid buffer to the right so more H+ ions are produced.

68
Q

What is another form of ΔtotalS = ΔsysS + ΔsurrS?

What does this form say about ΔsurrS ?

A

ΔtotalS = ΔsysS + (-ΔH / T)

The change in entropy to the surroundings is equal to the energy transferred divided by temperature

69
Q

Why does limestone break down when it is next to laval but not when it is on the earths surface at surface temperature?

A

Because at higher temperatures, near hot lava, the entropy change would be positive and the reaction could occur because the energy would spread out and cause disorder. Decomposition of limestone would result in a large entropy decrease if it was at atmospheric conditions

70
Q

Talk about the position of equilibrium with regards to entropy and ice at different temperatures.

A

The total entropy wants to increase.
When the air is 10C ice melts because the entropy is increasing.
When the air is -10C ice does not melt because entropy would then be negative which is not favorable.
When the change in entropy is 0, there is not change .

71
Q

Does entropy explain reaction rates?

A

No

Chemistry A level (13 decks)

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