8 - Oceans (O)

Question 1

Factors determining the relative solubility of a solute in aqueous and non-aqueous solvents?

Answer 1

-Temperature
-Polarity
-Molecular size

Question 2

Define hydrated ions

Answer 2

Ion surrounded by water molecules in a spherical-shaped shell

Question 3

Define enthalpy change of solution

Answer 3

The enthalpy change that occurs when one mole of ionic solid dissolves in water to form one mole of aqueous ions under standard conditions

Question 4

Define lattice enthalpy

Answer 4

The enthalpy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions
Exothermic

Question 5

Define enthalpy change of hydration

Answer 5

The enthalpy change when one mole of gaseous ions are completely hydrated by water to form one mole of aqueous ions under standard conditions

Question 6

Define charge density

Answer 6

The charge per unit volume/surface area/length

Question 7

How are lattice enthalpy and enthalpy change of hydration affected by charge density of the ions?

Answer 7

Greater charge density means:
-More exothermic lattice enthalpy (more electrostatic attraction)
-More exothermic hydration enthalpy (more attraction of water molecules)

Question 8

Define entropy

Answer 8

Measures the number of ways that molecules and their associated energy quanta can be arranged - the measure of disorder in a system

Question 9

How can the sign of entropy change be predicted?

Answer 9

-Increases from a solid to a liquid to a gas, then positive
-More gaseous products than reactants = increase in entropy, so positive

Question 10

What is total entropy change equal to?

Answer 10

Total entropy change =
Entropy change of the system +
Entropy change of the surroundings

Question 11

Equation for the entropy change of the surroundings

Answer 11

-Enthalpy change of reaction /
Temperature (K)

Question 12

When is a reaction feasible?

Answer 12

When total entropy change is positive

Question 13

How do you calculate the entropy change of the system?

Answer 13

Entropy of products - entropy of reactants

Question 14

What is the disorder if the entropy change of the system is positive?

Answer 14

More disordered

Question 15

What is the disorder if the entropy change of the system is negative?

Answer 15

Less disordered

Question 16

Define solubility product

Answer 16

K[sp] is an equilibrium constant for a solid dissolving in aqueous solution

Question 17

What does a high K[sp] value mean?

Answer 17

The more soluble a substance is and hence the more solute that dissolves

Question 18

How to calculate K[sp]?

Answer 18

For reaction
aA 9(s) ⇌ cC (aq) + dD (aq),
Ksp = [C]^c [D]^d

Question 19

Define Brønsted-Lowry acid

Answer 19

Proton donor

Question 20

Define Brønsted-Lowry base

Answer 20

Proton acceptor

Question 21

What is the proton donor and acceptor in this reaction?
HNO2 + H2O —> H3O+ + NO2-

Answer 21

Donor: HNO2
Acceptor: H2O

Question 22

Define conjugate acid-base pair

Answer 22

Contains 2 species that can easily be converted by transferring a proton

Question 23

Define strong acid

Answer 23

Completely dissociates in solution

Question 24

Define strong base

Answer 24

Completely dissociates in solution

Question 25

Define weak acid

Answer 25

Only partially dissociates in solution

Question 26

What is the acid dissociation constant?

Answer 26

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

Question 27

Equation for pK[a]

Answer 27

pK[a] = -logK[a]

Question 28

Why are pK[a] values sometimes used instead of K[a] values?

Answer 28

More manageable than K[a] values and makes it easier to compare the strengths of solutions

Question 29

Define pH

Answer 29

Easier way of measuring hydrogen concentration

Question 30

How can you measure the pH of a solution?

Answer 30

-pH probe -pH scales with a suitable indicator

Question 31

How to calculate the pH of a strong acid?

Answer 31

pH = -log[H+]

Question 32

How to calculate the pH of a strong base?

Answer 32

Kw = [H+] [OH-] so, pH = -log(Kw / [OH-])

Question 33

How to calculate the pH of a weak acid

Answer 33

Ka = [H+]^2 / [HA] so, pH = -log(√Ka [HA])

Question 34

What assumptions are made in a weak acid calculation?

Answer 34

[H+] = [A-]

Question 35

Define buffer

Answer 35

A system that minimises pH changes on addition of small amounts of an acid or base

Question 36

How do buffers work for the reaction CH3COOH ⇌ CH3COO- + H+

Answer 36

Addition of acid: More H+ ions present in the solution and combine with CH3COO- to form CH3COOH - shifts equilibrium left Addition of base: More OH- ions present in solution and combine with H+ to form H2o - shifts equilibrium to the right

Question 37

Define weak acid buffer

Answer 37

A mixture of a weak acid and its conjugate base

Question 38

How do you calculate the pH of a buffer solution made by partial neutralisation?

Answer 38

-Calculate the number of moles of each compound reacted and at equilibrium and hence their concentration -Sub into the Ka expression and rearrange for [H+] -pH = -loh[H+]

Question 39

Define greenhouse effect

Answer 39

-Sun produces UV, visible and IR radiation which is partially reflected back into space when it reaches the Earth -Some is absorbed by the Earth's surface causing it to heat up -IR radiation emitted by the Earth can be absorbed by gases in the troposphere and become trapped -IR radiation is then re-emitted in all directions, some towards the Earth, causing a heating effect

Question 40

Why does the absorption of IR by greenhouse gas molecules increase the atmosphere's temperature?

Answer 40

-Absorbing IR causes the bond to vibrate more as it has more energy -This energy is transferred to other surrounding molecules via collisions -This increases the E[k] and therefore temperature of the molecules