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Chem - A level (units 1 -10) > Oceans - Unit 8 > Flashcards

Oceans - Unit 8 Flashcards

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1
Q

Describe arrangement of NaCl?

A

Each Na surrounded by 6 Cl and each Cl is surrounded by 6 Na

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2
Q

What determines the solubility of ionic lattices?

A
  • Sub with large lattice enthalpies are insoluble
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3
Q

What type of process is the dissolving of ions?

A

Endothermic ( as bond breaking endo)

Ions in sol then hydrated in exothermic process (as bond making exo)

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4
Q

Define lattice enthalpy?

A

The enthalpy change when one moles of solid is formed by the coming together of the separate ions

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5
Q

Will the lattice enthalpy be positive or negative?

A

Always exo

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6
Q

Will the enthalpy change of hydration be positive or negative?

A

Always exo

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7
Q

Will the enthalpy change of solution be positive of negative?

A

Exo or endo

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8
Q

What determines the size of the lattice enthalpy?

A

Stronger ionic attractions = large lattice enthalpy

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9
Q

What makes lattice enthalpies more negative?

A

Higher charge density of ion:
Higher charge - means ions attract each other more strongly
Smaller radius - ions can come closer together

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10
Q

Attractions between ions and water molecules?

A

ion-dipole interactions

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11
Q

What does it mean for ions to be hydrated?

A

They have water mols bound to them

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12
Q

What determines how hydrated an ion is?

A

How strong it’s bonds are with the water mol.

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13
Q

How many water mols should you should surrounding one ion?

A

4

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14
Q

Define enthalpy change of hyrdation?

A

The enthalpy change for the formation of a solution of ions from one mol of gaseous ions

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15
Q

How does the charge density affect enthalpy change of hydration?

A

Larger charge density = More exothermic
More charged = attract water mols more strongly
Smaller = Get closer to water mols
therefore, greater attraction between ions and water mols

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16
Q

What is the enthalpy change of solution?

A

The enthalpy change when one mole of a solute dissolves to form a very dilute sol.

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17
Q

What is the solubility when the enthalpy change of sol. is negative?

A

solute normally dissolve

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18
Q

What is the solubility when the enthalpy change of sol. is positive?

A

solute doesn’t insoluble

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19
Q

Solubility of ionic lattice in non-polar solvents (hexane)?

A

No soluble

the mols in solvent not charged so unable to interact with ions

20
Q

Describe global warming?

A

1 - UV + Visible light radiation from sun hits earth, heating it
2 - This is re-emitted by earth as IR
3 - This IR is absorbed by greenhouse gases causing vibrations of bonds within mols
4 - These gases then transmit vibrational E to neighboring mols
5 - Some IR remitted to earth, heating it
6 - Causes global warming

21
Q

What happens to the Infared energy once it’s absorbed by greenhouse gases?

A

1 - Increase vibrational E of molecules so bonds vibrate more.
- The vibrational E can then be transferred to other mols by collisions
- This increases mols KE, increasing T of air
2 - Some infrared emitted to earth or into space

22
Q

What is the IR window?

A

The wave length of infrared radiation that water vapour does not absorb

23
Q

How does water vapour regulate earth’s temp?

A

1 - Less infrared radiation absorbed

2 - More emitted to space

24
Q

issue with Co2?

A

1 - Absorbs infrared at same WL as the IR window
- Therefore infrared radiation that would have passed through atmosphere now absorbed
2 - CO2 raises temps
- therefore more water vapour
- therefore more radiation absorbed

25
Q

What is the Bronsted Lowry theory of acids and bases?

A

Acids proton donors

Bases proton acceptors

26
Q

Conjugate acid-base pair?

A

Conjugate base = ion of an acid that acts as a base + accepts H+ to form the acid
Conjugate acid = acid formed from this

27
Q

How can the position of an equilibrium tell you about the strength of an acid?

A

further to right = stronger acid

28
Q

What buffer?

A

A solution which resists a change in pH for small additions of acid/alkali

29
Q

How do buffers work?

A

1 - Weak acid reacts with OH-, preventing sol. becoming more alkaline
2 - Salt reacts with H+, preventing sol. becoming more acidic

30
Q

What is a buffer sol. made of?

A

Weak acid + it’s salt

Weak base + it’s salt

31
Q

=What are the two assumptions made in order to describe how a buffer works?

A 
Assumption 1:
- All A- ions come from salt 
- The Weak acid, HA, supplies very few A- compared to salt 
Assumption 2:
- Almost All HA remains unchanged
32
Q

Why is a weak acid and a salt needed in a buffer sol?

A

weak acid - acts as source of H+

salt - acts as a sink for H+ ions

33
Q

What happens when alkali added?

A

1 - Alkali removes H+
2 - H+ regenerated from HA
3 - pH re-established

34
Q

What do the conc. of the acid and alkali need to be in buffer?

A

Similar, so can equally resist addition of acid/alkali

35
Q

How does water effect buffer?

A

1 - conc. of acid and salt equally reduced therefore ph not effected

36
Q

What kind of gas is CO2?

A

Acidic

37
Q

What is Ksp?

A
  • Constant which describes the solubility of a product

- The solubility product

38
Q

Two outcomes regarding Ksp when ions are mixed together?

A
  • The value of the ions concentration multiplied is greater than Ksp = then compound will precipitate out of sol
  • The value is less/equal to Ksp = ions will remain in sol (are soluble)
39
Q

What is entropy?

A

A measure of the number of ways of arranging molecules and distributing energy

40
Q

When is entropy change positive vs negative?

A 
Positive = products more disordered than reactants (e.g solid --> gas) (therefore products have higher entropy than reactants)
Negative = reactants more disordered than products (e.g gas --> solid)
41
Q

How does state of a substance link to the entropy?

A

Gases + more complex mols = highest entropy
Liquids = 2nd highest
Solids + Giant covalent/lattice = Lowest entropy

42
Q

Units of entropy?

A

JK-1mol-1

43
Q

What is the chemical system?

A

products and reactants

44
Q

What increases entropy change of system?

A

Increasing temp

45
Q

Entropy of mixture compared to two separate things?

A

1 - entropy mixture higher

Chem - A level (units 1 -10) (14 decks)

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