A-level OCR B Salters Chemistry - Oceans

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what do ionic substances dissolve in

polar solvents - non polar solvents not strong enough to pull ions out of their lattice - electrostatic forces too strong

what do covalent substances dissolve in

non polar solvents - as im bonds are weak and can ve broken easily

What are ion-dipole bonds?

formed between H20 and dissolved ions with delta charges

hydration

process of ions being surrounded by h20 molecules

hydrated ions

when ions are surrounded by h2o molecules - name of ions

solvation

same as hydration just with a different solvent e.g ethanol

ion dipole bonds

strong enough to pull ions from lattice therefore ionic solids dissolve in h20

Standard lattice enthalpy

The enthalpy change when one mole of ionic lattice is formed from its gaseous ions under standard conditions- always exothermic as bonds are broken and energy is released

enthalpy change of hydration

when one mole of aqueous ions are formed from gaseous ions - always endothermic as bonds between ions and h20 are made

enthalpy change of solution

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

how to work out enthalpy change of solution

• LE + (HYD CATION AND ANION)

How to measure enthalpy change of solution

q=mcT and h=q/n

higher charge density - LE

better attracting each other in ionic lattices - stronger ionic bonds - more energy released when bonds are made - more exothermic lattice enthalpy

higher charge density - hydration

better at attracting water molecules with lower charge densities - stronger im bonds - more energy released when breaking bonds - more exothermic enthalpy

entropy

a measure of the disorder of a system

factors affecting entropy

physical state

how does physical state affect entropy

solid to gas - more ways to arrange particles - more disorder more positive entropy

hows does energy affect entropy

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

how does number of particles affect entropy

more no of moles greater entropy - more ways energy can be rearranged

how to calculate total entropy change

entropy change of system + entropy change of surroundings

entropy change of system

products - reactants

entropy change of surroundings

• enthalpy change / temp (K)

feasible

total entropy change greater than zero

for a reaction to occur

total entropy must be positive

if entropy change in system is negative

change is surrounding must be positive and as large as syst to be feasible

equilibrium

the total entropy change is zero there is no net change in either direction

small and postive total entropy

feasible

large total entropy

spontaneous reaction

solubility

the minimum amount of solid that will dissolve in a certian solvent moldm-3

gdm-3

divide moldm-3 by mr

saturated

adding extdra solid doesnt affect rate of reaction

Ksp

when a sparingly soluble solid is dissolved in H2O to give a saturated solution

if Ksp > the ions multiplied together

ions stay in solution

if Ksp given < ions multiplied together

precipitate is formed

Ksp units

moldm-3 same as Kc and other constants

Bronsted-Lowry acid

proton donor

Bronsted-Lowry base

proton acceptor

strong acids/bases

almost completely dissociate in H20 release a lot of H+

weak acids/ bases

Dissociate partially in water/solution forms equilibrium which lies for to the left

conjugate acid-base pair

consists of two substances related to each other by the donating and accepting of a single hydrogen ion

conjugate acid

the particle formed when a base gains a hydrogen ion

conjugate base

the particle that remains when an acid has donated a hydrogen ion

neutral solution

[H+] = [OH-]

pH calculation

pH=-log[H+]

acid-base titration

add standard solution of base to known acid volume and use indicator

Ka for strong acids assumptions

H+ = OH-

Kw

ionisation product of water 1x10-14

kw calculation

[H+][OH-]

pKa

-logKa

Ka

10^-pKa

[H+]

10^-pH

The lower the pKa

the ____ the acid

The higher the pKa

the the acid.

the higher the Ka _

stronger acid

Buffer

A solution that resists changes in PH when small volumes of acids or alkali are added or is diluted

Buffer Calculations

Ka =. [H+] x salt/acid

adding small amounts of acid

equaliibrium shifts to the left reducing [H+] as OH- reacts with extra acid

small amounts of base

removes H+ as H+ reacts with extra OH to form water therefore removing H+ so equilibrium shifts to the right to allow further dissociation

adding H20

salt / acid ration increases by the same amount therefore no change in equilibrium position

greenhouse effect

Natural situation in which heat is retained in Earth's atmosphere by carbon dioxide

what happens when molecules absorb IR

increase in vibrational energy

what radiation does the sun emit

EM mainly as visible light

molecules remit

IR radiation in all directions back to earth keeping the earth warm

some IR trapped by greenhouse gases

provides and insulation layer

IR window

range of IR frequencies not absorbed by atmospheric gases