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Chemistry A level > chap 8- oceans > Flashcards

chap 8- oceans Flashcards

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1
Q

what can prevent substances from dissolving

A

if the bonds to be broken are stronger than those that will be formed

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2
Q

why do ionic substances not dissolve in non polar solvents

A

the non polar solvents don’t interact strongly enough with ions to pull them away from an ionic lattice. the electrostatic forces between the ions are way stronger than any bonds that can form

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3
Q

why do covalent substances only dissolve in non polar solvents

A

IM bonds between covalent molecules tend to be pretty weak so can be broken by non polar solvents. don’t dissolve in polar substances because H bonds are stronger than the bonds that would form between the water and non polar solvent

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4
Q

what is the difference between hydration and solvation

A

hydration is the process of ions being surrounded by water molecules to become hydrated ions. if the solvent isn’t water though this process is called solvation

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5
Q

what is standard lattice enthalpy

A

the enthalpy change when one mole of an ionic lattice is formed from its gaseous ions under standard conditions

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6
Q

what is the enthalpy change of hydration

A

the enthalpy change when one mole of aqueous ions is formed from gaseous ions

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7
Q

what is the enthalpy change of solution

A

the enthalpy change when one mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution

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8
Q

how can you measure enthalpy change of a solution using an experiment

A

put reactants in a container, stick a themometer in and measure temp change (use polystyrene beaker and lid) then use Q=mc T

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9
Q

what is charge density of an ion

A

charge / radius

higher charge density means its better at attracting ions of the opposite charge

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10
Q

what is entropy

A

measure of the number of ways that particles can be arranged and the number of ways energy can be shared out between particles

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11
Q

why do particles try to increase entropy

A

substances like disorder and they’re more energetically stable when there’s more disorder

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12
Q

how does energy affect entropy

A

the more energy quanta a substance has the more ways they can be arranged and the greater the entropy

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13
Q

how does number of moles affect entropy

A

entropy increases as number of moles increases because there are more particles and so more ways their energy can be arranged

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14
Q

how do you calculate the total entropy change of reactants and products

A

entropy change of system + entropy change of surroundings

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15
Q

how do you calculate the total entropy change of a system

A

entropy of products - entropy of reactants

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16
Q

how do you calculate entropy change of the surroundings

A

-enthalpy change (Jmol-1) / T

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17
Q

what is a feasible reaction

A

one that once started will carry on to completion without any energy being supplied to it

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18
Q

what does a reaction need in order to be feasible

A

for the entropy change to be positive or 0

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19
Q

what is a saturated solution

A

a solution where the water has dissolved as much of the solid as it can hold and you can add extra solid but none will dissolve

20
Q

what is solubility

A

the maximum amount of solid that will dissolve in a certain solvent (changes with temperature)

21
Q

what is a sparingly soluble solid

A

only dissolves a little bit to give 30-100 parts solvent to 1 part solute (10-30 g dm-3 in water)

22
Q

how do you work out solubility in moldm-3 from solubility in gdm-3

A

divide by the molar mass (M)

23
Q

what is the difference between acids and bases in terms of protons

A

acids release protons and bases accept protons

24
Q

whats a bronsted lowry acid

A

a proton donor that releases hydrogen ions when mixed with water and combine with the water to form hydroxonium ions (H3O+)

25
Q

whats a bronsted lowry base

A

a proton acceptor that grabs hydrogen ions from water molecules

26
Q

what is a conjugate pair

A

an acid and a base where the base accepts the proton from that acid and the acid donates its proton to that base

27
Q

what is a neutral solution

A

one where H+ and OH- concentrations are equal

28
Q

how do you work out pH from H+ conc

A

pH = -log10 (H+)

29
Q

what is a monoprotic acid

A

each mole of acid produces one mole of hydrogen ions

30
Q

how can you work out (H+) if you know the pH

A

10^-pH

31
Q

what is Kw

A

a constant called the ionic product of water. units are always mol2dm-6. always has the same value for an aqueous solution at a given temperature

32
Q

how do you calculate Kw

A

(H+)(OH-)

33
Q

what is the Kw value for an aqueous solution at 298K

A

1x10-14 mol2dm-6

34
Q

what is the value of Kw in pure water and why

A

Kw= (H+)^2 because in pure water there is always one H+ ion for every OH- ion

35
Q

what are the units of Ka

A

mol dm-3

36
Q

what is the general expression for Ka

A

Ka= (H+)2 / (HA)

37
Q

what does pKa =

A

-log10 Ka

38
Q

how do you work out Ka if you know pKa

A

10^-pKa

39
Q

what is a buffer

A

a solution that resists changes in pH when small amounts of acid or base are added or its diluted

40
Q

what is an acidic buffer

A

pH of less than 7 made by mixing a weak acid with one of its salts. Ethanoic acid and sodium ethanoate is a good example (CH3COO-Na+)

41
Q

how are buffers used in respiration

A

blood needs to be kept at pH 7.4. its buffered using carbonic acid (H2CO3) and levels are controlled by respiration

42
Q

what does the sun emit electromagnetic radiation as

A

visible light, UV radiation and infrared radiation

43
Q

what happens when the suns radiation reaches the earths atmosphere

A

most of the UV and infrared is absorbed by atmospheric gases and some radiation is reflected back into space from clouds

44
Q

3 main greenhouse gases

A

water vapour, carbon dioxide, methane

45
Q

how do greenhouse gases transfer energy

A

they absorb IR radiation to make the bonds in the molecule vibrate more. the extra vibrational energy is passed on to other molecules in the air by collisions (transfers kinetic energy and heat)

Chemistry A level (10 decks)

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