AQA A Level Chemistry Year 12 content

define disproportionation

in a redox reaction, where the oxidation states of atoms of the same element increase for some and decrease for others

why is chlorine added to drinking water?

forms ClO- ions which kill microorganisms, health benefits outweigh the risk

Are alkanes polar?

no, because only C and H which have similar electronegativity

Define activation energy

the minimum energy that particles must collide with for a reaction to occur

Why does increasing temperature increase the rate of reaction?

higher proportion of particles have greater energy than the activation energy so there are more frequent successful collisions

Why does increasing concentration/ pressure increase rate of reaction?

there are more particles in a given volume so more frequent successful collisions

How do catalysts work?

they provide an alternative reaction pathway with a lower activation energy, so more particles have sufficient energy and successful collisions are more frequent

What must particles do in order to react?

collide with sufficient energy and the correct orientation

Describe metallic bonding

layers of positive metal ions in a sea of delocalised electrons

How does the strength of metallic bonds change across periodic table?

increases because ther is a higher charge on the ions, so more delocalised electrons and stronger forced of attraction between them

Describe the structure of graphite

covalent macromolecular arranged in layers, with each C atoms bonded to 3 others, delocalised electrons between layers

What is ionic bonding?

strong electrostatic forces of attractionbetween oppositely charged ions held in a giant lattice

What is macromolecular covalent bonding?

lattice of many atoms held together by strong covalent bonds

What is simple molecular covalent bonding?

strong covalent bonds between atoms arranged as molecules with weak intermolecular forces

Describe the structure of diamond

3D tetrahedral structure of C atoms each covalently bonded to 4 other atoms

Define percentage yield

the percentage of a product produced by a reaction compared to the theoretical maximum

Define atom economy

the percentage of amount of reactants made into useful product

What is the ideal gas equation?

PV = nRT

Define empirical formula

the simplest whole number ratio of atoms in a compound

How do you calculate concentration?

concentration = moles/ volume

How do you calculate moles?

moles = mass/ Mr

What substance is used in flue gas treatment?

CaO or CaCO3

6 bonding pairs, 0 lone pairs

octahedral, 90°

5 bonding pairs, 0 lone pairs

trigonal bipyramid, 90°/ 120°

4 bonding pairs, 0 lone pairs

tetrahedral, 109.5°

3 bonding pairs, 0 lone pairs

trigonal planar, 120°

2 bonding pairs, 0 lone pairs

linear, 180°

5 bonding pairs, 1 lone pair

square pyramid, \~89°

4 bonding pairs, 1 lone pair

see saw, \~89°/ \~119°

3 bonding pairs, 1 lone pair

trigonal pyramid, 107°

2 bonding pairs, 1 lone pair

bent, \~118°

4 bonding pairs, 2 lone pairs

square planar, 90°

3 bonding pairs, 2 lone pairs

t-shaped, 90°/120°

trigonal planar 120°

2 bonding pairs, 2 lone pairs

bent, 104.5°

What is the ideal gas equation?

PV=nRT

What group is paired with carboxylic acids in functional group isomerism?

esters

What group is paired with alkenes in functional group isomerism?

cyclic alkanes

What group is paired with aldehydes in functional group isomerism?

ketones

What are the conditions for production of ethanol by fermentation?

35°C, yeast enzyme, aqueous, anaerobic

What are the conditions for production of ethanol by hydration of ethene?

300°C, 70atm, concentrated phosphoric acid

What are the conditions for thermal cracking?

900°C, 70 atm, no catalyst

What are the products of thermal cracking?

alkenes

What are the conditions for catalytic cracking?

450°C, 1-2 atm, zeolite catalyst,

What are the products of catalytic cracking?

cycloalkanes, aromatic hydrocarbons, branched alkanes (motor fuels)

What are the equations for the depletion of ozone?

Cl• +O3 → ClO• + O2

ClO• + O3 → 2O2 + Cl•

2O3 → 3O2

Titration steps

* Use pipette to add reactant 1 into conical flask
* Add reactant 2 to burette, record initial volume
* add few drops of indicator to conical flask
* Open burette tap, swirl
* Once colour change occurs, record final volume
* Repeat until get concordant results

What are concordant results?

Titres within 0.1cm3 of each other

What is avogadro’s constant?

number of particles in one mole of a substance (6.022 x10^23)

Define relative atomic mass

Average mass of all isotopes of an element relative to the mass of 1/12th of a 12C atom

What are the 2 types of ionisation in mass spectrometry and when is each one used?

electron impact (low formula mass) and electrospray (high molecular mass)

When is electron impact ionisation used?

molecules with low molecular mass

When is electrospray ionisation used?

molecules with higher molecular mass

How are ions detected in mass spectrometry?

The positive ions gain electrons at the negatively charged plate, causing flow of current, the size of the current is proportional to the proportion of that ion

Define ionisation energy

the energy required to remove 1 mol of electrons from 1 mol of gaseous atoms

what is the trend in ionisation energy along a period?

ionisation energy increases because nuclear charge increases and atomic radius decreases

what is the trend in ionisation energy going down a group?

ionisation energy decreases, because shielding increases

What happens to the first ionisation energy as you go down group 2?

decreases because; shielding increases, atomic radius increases,

How

What are the units for pressure in the ideal gas equation?

Pa

What are the units for volume in the ideal gas equation?

m cubed

What are the units for temperature in the ideal gas equation?

K

What affects the strength of metallic bonds?

nuclear charge

Define electronegativity

The ability of an atom to attract the electron density of a covalent bond

What affects electronegativity?

* nuclear charge
* atomic radius
* electron shielding

When do polar bonds occur?

when the atoms in a covalent bond have different electronegativities

What is the strongest type of intermolecular force?

hydrogen bonding

Why are Van der Waals forces stronger in larger molecules?

they have more electrons

Describe Van der Waals forces

temporary dipole from electron movement induces dipole in neighbouring molecule, opposite charges cause attraction

Describe dipole-dipole attraction

there are forces of attraction between dipoles in adjeacent molecules

What is dative covalent bonding?

when an electron deficient atom accepts a lone pair of electrons from n atom with the lone pair

What 3 bonds can cause hydrogen bonding?

O-H, N-H, F-H

Define enthalpy change

Energy change of a system at a constant pressure

What energy change is associated with breaking bonds?

endothermic , positive enthalpy change

How do you calculate enthalpy change from experimental data?

Q=mcAT

How can simple calorimeters be made more accurate?

add draught screens, add lid, add mineral wool around beaker

How can you more accurately calculate enthalpy change from experimental data?

use a cooling curve

What energy change is associated with making bonds?

exothermic, negative enthalpy change

Define standard enthalpy of formation

The enthalpy change when one mole of a compound is formed from its constituent elements in standard conditions with all reactants and products in their standard states

Define standard enthalpy of combustion

The enthalpy change when one mole of a substance is burned completely in oxygen in standard conditions with all reactants and products in their standard states

What is Hess’ Law?

The enthalpy change of a reaction is the same regardless of the route taken

Define bond dissociation enthalpy

The energy required to break a covalent bond with all species in the gaseous state

Define mean bond enthalpy

The average bond dissociation enthalpy of a specific bond ,averaged across all molecules

Why may experimental values for enthalpy change be inaccurate?

heat loss, not in standard conditions, incomplete reaction

Why does increasing temperature increase the rate of reaction?

higher proportion of particles have the activation energy so more frequent successful collisions

Why does increasing concentration/ pressure increase the rate of reacction?

larger number of particles in a given volume so more frequent successful collisions

Define dynamic equilibrium

the rate of the forward and reverse reaction are equal

What is Le Chatelier’s principle?

If a change in condition occurs the system in equilibrium will shift the position of equilibrium to oppose the change

What effect does a catalyst have on the position of equilibrium?

no effect

How does reactivity with water change as you go down group 2?

increases, because atomic radius increases so electrons are lost more easily

Does Mg react with water?

not liquid water but does react with steam

What is the trend in hydroxide solubility down group 2?

increases down the group

What is the trend in sulphate solubility down group 2?

decreases down the group

what is the trend in melting point down group 2?

decreases, atomic radius increases so delocalised electrons are further from positive ions and forces of attraction are weaker

What is Mg(OH)2 used for?

antacid for indigestion

What is Ca(OH)2 used for?

neutralises soil

what is BaSO4 used for?

barium meal to outline gut in X-rays, safe because it’s insoluble

What is the trend in boiling point down group 7?

increases, because more electrons so van der waals forces are stronger

What is the trend in electronegativity down group 7?

decreases, greater atomic radius so forces of attraction between nucleus and electron pair is lower

What condition will affect the value of Kc?

temperature