AQA A LEVEL Chemistry

Relative atomic mass

Relative atomic mass

The average mass of an atom of an element, relative to 1/12th of the mass of an atom of Carbon-12

Relative molecular mass

Average mass of a molecule compared to 1/12th of the mass of a carbon-12 atom

The Avogradro constant

the number of particles in a mole

ideal gas equation

pV = nRT

empirical formula

the simplest whole number ratio of atoms of each element in a compound

percentage atom economy

(Mass of desired product/total mass of reactants) x 100

ionic bonding

the electrostatic attraction between oppositely charged ions in a lattice

covalent bond

a shared pair of electrons between non-metal elements

co-ordinate bond

a shared pair of electrons where both electrons are supplied by one atom

repulsion in shapes of molecules

Lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair

electronegativity

the power of an atom to attract the pair of electrons in a covalent bond

hess' law

Total enthalpy change for a reaction is independent of the route chosen

mean bond enthalpy

The energy required to break a covalent bond into gaseous atoms averaged over different molecules

Bonds broken - bonds made

activation energy

The minimum amount of energy needed to start a chemical reaction

catalyst

A substance that increases the rate of a chemical reaction without being changed by providing an alternative reaction pathway by lowering activation energy

Le Chatelier's principle

When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to oppose the change.

oxidising agents

electron acceptors

reducing agents

electron donors

Enthalpy of formation

Enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions in their standard states

Enthalpy of atomization

The energy required to produce one mole of gaseous atoms from an element in its standard state

Electron affinity

the enthaply change when one mole of gaseous atoms forms one mole of -1 ions

Lattice enthalpy of formation

Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase

Lattice enthalpy of dissociation

Energy change when 1 mol of an ionic lattice dissociates to its gaseous ions.

standard electrode potential

298K
100kPa
1.00moldm-3

Electrode reactions in lithium cell
(positive electrode)

Li+ + CoO2 + e- → Li+[CoO2]-

Electrode reactions in lithium cell
(negative electrode)

Li → Li+ + e-

Electrode reactions in hydrogen-oxygen fuel cell in acidic conditions
(positive electrode)

02 + 4H+ +4e- -> 2H20

Electrode reactions in hydrogen-oxygen fuel cell in acidic conditions
(negative electrode)

H2 -> 2H+ + 2e-

Brosted- lowry Acid

proton donor

Brosted- lowry base

proton acceptor

weak acids

partially dissociate in aqueous solution

what is an acidic buffer made of?

weak acid and its salt

what is an basic buffer made of?

weak base and its salt

spontaneous reactions

when enthalpy is negative and entropy is positive ( spontaneous at all temperatures)

when enthalpy is positive and entropy is negative (not spontaneous at any temp)

Stereoisomerism

Molecules with the same structural and molecular formula but have a different spatial arrangement

Enthalpy change

Heat energy change at constant pressure

Oxidation of primary alcohols

Aldehyde
(Alcohol in excess + product distilled off immediately) Carboxylic acid (oxidising agent in excess + Under reflux )

Oxidation of secondary alcohols

Ketones
No further oxidation

Oxidation of tertiary alcohols

Can't be easily oxidised as they do not have two hydrogen atoms directly attached to he carbon that is bonded to the OH group but can be oxidised by hot nitric acid

Oxidising agent for oxidation of alcohols

Acidified potassium dichromate

Orange (Cr2O7 2-) to green(Cr 3+)

What happens when an unsymmetrical alcohol undergoes and elimination reaction

A mixture of isomeric products are produced

Biofuel

Any fuel made from living organisms or their waste

Carbon neutral

No net annual emissions of carbon dioxide into the atmosphere

Line with largest m/z ratio on a mass spectrum of a compound

Molecular ion (a molecule which had lost an electron)

High resolution spectrometry

Used to distinguish between compounds and can measure relative atomic masses to 4 decimal places

Finger print region

The area of the spectrum below the 1500cm-1, it is unique to the molecule

Molecular formula

The actual number of stones of each element imma compound

Functional group isomer

Compounds with the same molecular formula but different functional group

Positional isomer

Isomers with the same carbon chain and the same functional group but attached at different points of the carbon chain

Specific heat capacity

Energy required to raise the temperature of 1g of a substance by 1 degrees

Solvents used for nmr

CCL4, CDCL3

Do not cause peak on h nmr but causes known peak on carbon nmr

Carboxylic acid + carbonates

Salt, carbon dioxide + water

Carboxylic acid + alcohol

Ester + water

Uses for esters

Food colouring, perfumes, solvents and plasticisers

Uses for sulfur dioxide

Bleach, food preservatives

Acid hydrolysis of esters

Acid and alcohol

Base hydrolysis of esters

Carboxylate ion and alcohol

Hydrolysis of oils and fats using NaOH

Glycerol, soap (salt if long chain carboxylic acid)

How are biodiesel made

Reacting vegetable oils with methanol and KOH


Makes glycerol and methyl esters

Uses for quaternary ammonium salts

Fabric cleaners, hair products

enthalpy of hydration

Enthalpy change when 1 mole of gaseous ions becomes aqueous ions

intial rate of reaction

The rate of reaction at time t = 0 s. Used to compare the effect on the rate of changing the independent variable.

rate determining step

The slowest step in a reaction mechanism

equivalence point

The point during a titration when the number of H+ ions and OH- ions are equal. This is at the middle of the steepest part of the titration curve.

buffer

A solution that resists changes in pH when small amounts of acid or base are added.

autocatalyst

Catalyst that is a reaction product

transition metal

elements that form colored ions in solution and have multiple oxidation states

ligand

an ion or molecule with at least one lone pair of electrons that can form a coordinate bond to a metal atom or ion

complex

a central metal ion or atom surrounded by ligands

co-ordination number

Number of lone pairs bonded to the metal ion

hemoglobin

protein structure containing four haem groups bonded to four flobular proteins - used for gas exhange

chiral carbon

A carbon atom attached to four different atoms or groups of atoms.

hetregenous catalyst

A catalyst that is in a different phase from that of the reactant substances.

homogenous catalyst

A catalyst that is in the same phase as all the reactants and products in a reaction system

enantiomers

Non-superimposable mirror image

race mate/ racemic mixture

50/50 mixture of left and right enantiomers

immiscible

liquids that are not soluble in each other

condensation polymers

polymers formed from when monomers join together and eliminate a small molecule such as water or hydrogen chloride

addition polymers

polymers madenfrom alkenes in an addition reaction

zwitterion

dipolar ion formed when amino acids undergo an internal acid-base reaction

mobile phase

from chromatography, the liquid or gas used to move the sample up the stationary phase

stationary phase

The phase that does not move in chromatography

perfect ionic model

Ions which are perfect spheres with no covalent character

isotopes

atoms with the same number of protons but different number of neutrons

Alkali

a soluble base

First ionisation energy

the enthaply change when one mole of electrons is remoeved fromone mole of gaseous atoms to form one moles of gaseous ions with a single positive charge

Dative covalent bond

When an electron pair donated by one molecule is shared between two molecules

Activation energy

the minimum amount of energy required to start a chemical reaction

Disproportionation

when a substance is oxidised and reduced in a reaction to produce two different products

Anion

A negatively charged ion

Cation

A positively charged ion

atom economy

molecular mass of the desired product/ sum of the molecular masses of all reactants x100

Dynamic Equilibrium

a equilibrium where both the forward and reerse reactions are occuring a the same rate and the concentrations of the reactants and products remain constant

Enthalpy of combustion

the enthalpy chang when one mole of of a substance if burned completley in excess oxygen with all reactants and products in their standard stases under standard conditions

Homologous series

series of compounds with the same general formula

Percentage yield

actual yield/theoretical yield x100

reflux

the continuous boiling and condensing of a mixture

structural isomerism

compounds that have the same molecular formula but differnet structural formula

Time of flight mass spec stages

1.Electrospray Ionization
sample vaporized and put into a small capillary tube and high voltage is applied causing the atoms to lose an electron and making the sample a mononuclear gas

2.Acceleration
Ions accelerated by an electric field, smaller ions travel faster

3.ion drift
ions have a constant speed and kinetic energy and enter region of no electric field (flight tube)
Smaller ions move faster

4.Detection
Smaller ions reach detector first as they travel faster

5.Data analysis
time and mass of the ins are recorded by a computer and analyzed to make a mass spectrum

concordant results ins titrations

similar results to the neares 0.1cm3