AS Chemistry 2020 Flashcards
What is relative atomic mass
Mass of an atom compared to 1/12 of an atom of carbon-12
What is avogadro’s number
6.02x10^23
Volume of 1 mol of gas at r.t.p
24dm^3
What is mass spectrometer for
to determine masses of isotopes and their relative abundance
What is an orbital
A region of space where there is a high probability of finding an electron
What is Hund’s rule
Orbitals of the same energy remain singly occupied before pairing up
what are the 2 exceptions to the aufbau principle
Chromium: 4s1,3d5 NOT 4s2,3d4
Copper: 4s1,3d10 NOT 4s2,3d9
Define Ionisiation energy
Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous cations.
Ionisation energy ______ across a period and ______ down a group
increases, decreases
Successive ionisation energies are always _____ than the previous one
greater
4 types of chemical bonds
ionic
covalent
dative covalent
metallic
3 types of physical bonds
Van der waals forces - weakest
dipole-dipole interaction
hydrogen bonds - strongest
Properties of giant ionic lattice:
High M.P and B.P Solid does not conduct Liquid does conduct well They are hard The dissolve in water (to an extent) They are brittle
Properties of metals
Conduct electricity High M.P and B.P Shiny High density Insoluble in most solvents Malleable Ductile
Definition of electronegativity
The attractive force of the nucleus of an atom on a shared electron pair in a covalent bond
Properties of non polar molecular solids
Strong intramolecular forces Weak intermolecular forces Very low M.P and B.P Do not conduct electricity Soluble in non-polar solvents
What is polar covalent bonding
Bonds in which positive nuclei are both attracted to the negatively charged electron pair between them creating a permanent dipole.
Formed between atoms with high, but slightly different electronegativities.
Properties of polar molecular solids
Strong intramolecular forces. Strong intermolecular forces. Low M.P and B.P Do not conduct electricity Soluble in polar solvents.
Properties of macromolecular solids
Very hard.
Do not conduct electricity
High M.P and B.P
Insoluble in all solvents.
What is a sigma bond
When electrons pair to occupy a single orbital that spreads over both atoms
What is a pi bond
electrons pair to occupy an orbital that has 2 lobes
Linear bond angle
180
trigonal planar bond angle
120
tetrahedral bond angle
109.5
trigonal pyramidal bond angle
107
V-shaped bond angle
105
Octahedral bond angle
90
trigonal bypyramid bond angle
90 and 120
3 conditions of the kinetic model of gases
particles moving in rapid and random motion;
particles are independant of eachother - no forces between them;
The volume occupied by the particles is negligible compared with the volume of the container.
What is Boyle’s law
At constant temp, for a given gas, volume is inversely proportional to pressure
What is Charles’ law
Volume of a given gas at constant pressure is proportional to its absolute temperature
What is the ideal gas law formula
PV = nRT
Definition of atomic radius
half of the average distance between the nuclei of 2 covalently or metal-bonded atoms
From top to bottom of a group, atomic radius _______
increases
From left to right of a period, atomic radius _______
decreases
3 Factors influencing first ionisation energy:
Size of the positive nuclear charge (larger size means stronger attractive force so higher I.E;
Distance of the electron from nucleus (further away electrons are easier to remove)
The shielding effect by electrons in the inner shells
Define organic compound
A compound consisting of carbon and any other elements
Define functional group
The site at which reactions take place in an organic molecule
Define homologous series
The family of compounds all having the same functional group and general formula
Define saturated compound
A compound with no double or triple bonds, incapable of undergoing addition reactions
Define catenation
The ability to form bonds between atoms of the same element
What are chain or branched chain isomers
Same number and type of atoms with different carbon skeletons
What are positional isomers
Molecules that have a substituent in different positions on the same carbon skeleton
What are functional group isomers
When molecules belong to different homologous series
What is sterioisomerism
Different spacial arrangement of atoms in a molecule
What is an addition reaction
When atoms are introduced to an unsaturated molecule
What is an elimination reaction
When new double or triple bonds are made between carbon atoms with the elimination of a small molecule such as hydrogen
What is a substitution reaction
When one atom is exchanged for another. There are 2 products formed
What is a condensation reaction
When two large molecules combine, discarding a small molecule, often H2O or HCl
What is a redox reaction
Reaction involving both oxidation and reduction half reactions
What is hydrolisis
Decomposition or alteration of a chemical substance by water
What is homolytic fission
The breaking of a covalent bond leaving both atoms in the bond with 1 electron each
What is initiation stage
The step producuing free radicals
What is propagation
Steps which produce products and more free radicals
What is termination
Steps where free radicals turn into molecules
4 Physical properties of alkanes
Non polar - do not mix with water
do not conduct electricity
M.P and B.P of branched chain alkanes lower than unbranched
2 chemical reactions of alkanes
Halogenation
Combustion
Physical properties of alkenes
Non-polar
B.P increases with increased molar mass
What is hydration
The addition of water to alkenes. Requires heat and dilute H2SO4 catalyst
What is hydrogenation
The addition of hydrogento alkenes. Requires catalyst of platinum, nickel or palladium
What is combustion
Alkenes burn in a smokier flame than the corresponding alkane to produce H2O, CO2, CO and some carbon
What is used to oxidise alkenes, and what are the results in different conditions
Potassium permanganate.
In cold dilute solution, the alkene forms a diol.
In hot concentrated solution, the diol is split into fragments are further oxidised into ketones or carboxylic acid
What is a catalytic converter and what is it’s catalyst.
Used in cars to remove pollutant gases from the exhaust using platinum/rhodium catalyst on a ceramic block.
What is the balanced equation for the reduction of NO2 in a catalytic converter.
2NO + 2CO -> N2 + 2CO2
What is oxidation number
Shows the relative state of oxidation or reduction of an element. Change in number means a redox reaction has occured.
What is the trend in electronegativity going down group 17 and why
Decreases going down because atomic radius increases meaning there is less attraction to outer electrons and shared electrons.
What is the trend in oxidising ability from top to bottom of group 17
Decreases from top to bottom, however all are strong oxidising agents - become reduced easily.
What is the trend in vigour of reactions with hydrogen going down group 17
Decreases going down.
Describe reaction of fluorine with hydrogen
explosive reaction as F-F bond is easy to break
Describe reaction of chlorine with hydrogen
explosive reaction, only in the presence of sunlight
Describe reaction of bromine with hydrogen
reacts only on heating with platinum catalyst
Describe reaction of iodine with hydrogen
Very slow reaction, even on heating
What is the trend in thermal stability of hydrogen halides going down group 17
Thermal stability decreases going down as H-Halogen bond energy decreases
What is the appearance and solubility of hydrogen halides
all colourless gases and all very soluble in water
When treated with a silver nitrate solution, what can be observed from Cl-,Br-,I-
Cl- ions form white ppt. soluble in dilute ammonia soln.
Br- ions form cream ppt. insoluble in dilute ammonia soln, but soluble in concentrated ammonia soln.
I- ions form a yellow ppt. insoluble in concentrated ammonia solution
Are halogenoalkanes soluble in water? Why
No because they are non-polar
As the molar mass of halogenoalkanes increases, solubility _______ and B.P ________
decreases, increases
Why do branched chain result in lowered B.P?
The intermolecular forces are weaker between branched molecules.
Why are alkyl flourides relatively unreactive
The C-F bond is strong
What are the reagents and conditions in the formation of nitriles
Reagent: aqueous, alcoholic KCN or NaCN
Conditions: Reflux in aqueous alcoholic soln.
What are the reagents and conditions for formation of primary amines
Reagent: alcoholic ammonia
Conditions: Reflux in alcoholic solution, pressure.
What is the inductive effect?
When a halogen draws electrons towards itself
Why do alcohols have relatively high B.P and M.P compared to alkanes?
Because of the presence of hydrogen bonds in their molecules. The -OH group makes part of the molecule polar.
What products are formed by oxidising primary alcohols?
first to aldehydes, then further oxidised to carboxylic acids
What products are formed by oxidising secondary alcohols?
Ketones
What products are formed by oxidising tertiary alcohols?
Tertiary alcohols are not oxidised by common oxidising agents
What is the Lucas test used for? What are the positive results?
To distinguish between water soluble alchohols.
Tertiary alcohols go cloudy immediately;
Secondary alcohols go cloudy in a few minutes.
Primary alcohols do not go cloudy until very long.
How are alcohols dehydrated to alkenes? What catalyst is used?
By elimination of a water molecule using an acid catalyst
How are esters formed from carboxylic acids? What catalyst is used?
By eliminating a water molecule using a concentrated H2SO4 catalyst
What is the main difference between aldehydes and ketones?
Aldehydes have a single hydrogen atom bonded to the carbonyl atom while ketones always have two alkyl groups.
6 Physical properties of carbonyl compounds
Colourless liquids at R.T.P
Higher M.P and B.P than alkanes of similar mass
Less volatile than corresponding alkanes
More volatile than corresponding alcohols
Cannot form hydrogen bonds
Aldehydes and Ketons with <5 carbon atoms are soluble in water.
How are aldehyes formed.
By oxidation of primary alcohols then distillation.
How are ketones formed.
By oxidation of secondary alcohols then distillation.
2 Main differences in chemical reactivity of aldehydes vs ketones
Aldehydes are more reactive towards nucleophilic addition;
Aldehydes are more easily oxidised
How are hydroxy nitriles produced
Addition of HCN to aldehydes/ketones
What is produced by addition of hydrogen to aldehydes/ketones?
Aldehydes - first degree alcohols
Ketones - Second degree alcohols
What is produced by reacting ketones/aldehydes with 2,4-DNPH?
Hydrazones
What is observed when aldehydes react with Tollen’s reagent?
Silver mirror
What is observed when ketones react with Tollen’s reagent?
No reaction
What is observed when aldehydes react with Fehling’s solution or Benedict’s solution?
Red-brown ppt.
What is observed when ketones react with Fehling’s solution or Benedict’s solution?
No reaction
As size of carboxylic acids increases, B.P ________. Why?
increases due to increased van der waals forces
What are the products of hydrolysis of esters? What catalyst must be used?
Products: Alcohol + Carboxylic acid
Catalyst: Any dilute acid or alkali
Does exothermic reaction have positive or negative enthalpy change?
Negative
Does endothermic reaction have positive or negative enthalpy change?
Positive
What are the standard conditions of reaction
100kPa Pressure
25*C or 298K Temp
Concentration of 1mol/dm^3 for aqueous soln
If energy released making bonds > energy used to break bonds is reaction endothermic or exothermic
Exothermic
If energy released making bonds < energy used to break bonds is reaction endothermic or exothermic
Endothermic
Equilibrium is reached when there is__________
No overall change (i.e. pressure and amount of reactants is constant)
Why does the rate of reaction of a dynamic equilibrium decrease over time?
As the reaction proceeds the reactants get used up and the rate of reaction slows.
What are 4 characteristics of a system in equilibrium
- system is closed
- no observable change in temp, pressure or ratio of reactants to products
- Both reactants and products are present together
- Both forward and reverse reactions are occuring at same rate.
If concentration of reactants is increased in reaction which way will the equilibrium move?
Towards products
If pressure is increased in an equilibrium which way will equilibrium shift?
Towards the larger number of gaseous molecules.
If temperature of an equilibrium reaction is increased which way will equilibrium shift?
Exothermic: Towards reactants
Endothermic: Towards products
Does a catalyst affect the position of an equilibrium?
No, only affects the speed at which the equilibrium is attained
What are the reactants and conditions and catalyst for the Haber process?
3:1 Ratio of hydrogen:nitrogen gas.
Pressure: 350atm
Temp: 450*C
Catalyst: Iron
Where are the reactants sourced for haber process?
Natural gas supplies hydrogen, nitrogen found in air.
What is the contact process?
Industrial preparation of sulfuric acid,
What are the 3 stages of contact process?
1) Sulfur is burned in air to make sulfur dioxide
2) The SO2 is further reacted with O2 over a vanadium pentoxide catalyst to make SO3
3) The SO3 is reacted with H2SO4 to from H2S2O7 (oleum) which then reacts with water to form sulfuric acid.
An acid is a proton ____
donor
What are 4 points of the collision theory
- particles msut collide for a reaction take place
- not all collisions lead to a reaction
- reactants must possess a minimum amount of energy
- particles must approach eachother with a certain orientation.
What are group 2 metals known as
Alkaline earth metals
The atomic radius of group 2 elements _____ from to to bottom
increases
Why is the third ionisation energy of group 2 elements so much higher than 1st and 2nd?
They have to remove a valence shell which requires more energy
Ionisation energy of group 2 metals ______ from top to bottom
decreases
Group 2 metals become _____ reactive going down the group
more
Flame colour of Mg
Bright white
Flame colour of Ca
Brick red
Flame colour of Sr
Red
Flame colour of Ba
Green
Group 2 nitrates become _____ thermally stable going down the group.
More
Group 2 carbonates become ______ thermally stable going down the group
More
Hydroxides of group 2 metals become _____ soluble going down the group
More
Sulfates of group 2 metals become _____ soluble going down the group
Less
Carbonates of group 2 metals become _____ soluble going down the group
Less
Hydroxides of group 2 metals become _____ soluble going down the group
More
What shape is the Ammonium ion
tetrahedral
What is the oswald process
Production of nitric acid from ammonia
What are the 3 stages of the oswald process
1) Ammonia is heated in air and passed over a heated catalyst of rhodium and platinum
2) Resulting mixture is cooled and more air is added.
3) More air is added and reactants are mixed with water
What is eutrophication?
When nitrogen fertilisers enter waterways algae grows on surface of water blocking out light, so plants underwater die and oxygen is used up so water animals die
