Paper 3A Part 1 Flashcards
Definition of Relative Atomic Mass (Ar)
Weighted mean mass of an atom relative to 1/12th the mass of an atom of carbon 12
Definition of Relative Formula Mass (Mr)
The term used when working out the calculation for compounds with giant structures
Name 3 types of giant structures
Giant IonicGiant CovalentGiant Metallic
Definition of Relative Molecular Mass
The term used when working out the calculation for compounds that are simple molecules
Name a type of simple molecular structure
Covalent Compounds
What is the formula for finding out how much of a compound is made up of a particular element?
% of element = ((number of atoms of element x relative atomic mass of the element) / relative formula mass of compound) x 100
What is the molar mass?
.The mass per mol of a substance in g mol^-1.Same number as Mr
What is the amount of substance + unit?
.A means of counting the number of particles in a substance.Unit is the mol
What is Avogadro’s Constant?
(NA) 6.02x10^23 mol-1
What is everything measured relative to?
Carbon-12
Define the mole
The amount of any substance containing as many elementary particles as there are carbon atoms in 12 grams of carbon-12 (6.02x10^23) particles
number of mols (mol) =
mass (g) / molar mass (g mol-1)
Smallest mass of an atom
1.67x10^-27
The largest mass of an atom
4.52x10^-25
What do we use the smallest mass of an atom to do?
Produce a relative scale called the unified atomic mass unit ‘u’ = 1.67x10^-27
If hydrogen-1 = 1u, what does carbon-12 =?
12u
Define relative isotopic mass
The mass of an atom of an isotope relative to 1/12th the mass of a carbon 12 atom
What is 1/12th the mass of a carbon-12 atom?
1u
Define relative atomic mass
The relative atomic mass is the ‘weighted mean’ mass of an atom relative to 1/12th the mass of a carbon-12 atom
formula to find out relative atomic mass/weighted mean?
((mass x abundance) + (mass x abundance)) / 100
Define molecular formula
The number and type of atoms of each element in a molecule
Define empirical formula
Shows the simplest whole number ration of atoms of each element in a compound
State the steps for finding the empirical formula
- find the mass2. calculate the moles3. divide all the results by the smallest value to get the ration4. adjust the ratio to get whole numbers5. workout the empirical formula
What is water of crystallisation?
Water molecules that are bonded into a crystalline structure of a compound
What doe solid compounds formed from aqueous solutions have trapped in their crystal structures?
The crystals that are formed have water molecules trapped in the crystal structure
What does copper sulphate exist as?
Blue crystals
How does copper sulphate lose its water?
Heat
What colour is anhydrous copper sulphate?
White
What is the formula of copper sulphate?
CuSO4.xH2Ox = number of water molecules
Anhydrous definition
Contains no waters of crystillisation
Hydrated definition
A crystallised compound containing water molecules
Where is the water in copper sulphate?
Water forms part of the crystal sturcture
Four steps of the hydrated and anhydrous practical
- Weigh an empty crucible2. Add the hydrated salt into the weighed crucible, weigh the crucible and the hydrated salt3. Using a pipe clay triangle, support the crucible containing the hydrated salt on a tripod. Heat the crucible and contents gently for about one minute. Then heat it strongly for a further three minutes.4. Leave the crucible to cool. Then weigh the crucible and anhydrous salt
What is a binary compound?
Binary compounds contain 2 elements only
How to name a binary compound with one example
To name it, take the first element then change second elements name to –ide (for ionic compounds the metal always comes first) for example magnesium oxide (MgO), sodium chloride (NaCl), Calcium sulphide (CaS)
What is a polyatomic ion?
Ions comprised of more than one atom
What are brackets in formulas used for?
Polyatomic ions need to go into brackets
What is a redox reaction?
When reduction and oxidisation happen at the same time
What is OILRIG
OxidisationIsLossReductionIsGain
What assumptions were made during the copper sulphate anhydrous and hydrated salt experiment? Any extra infomation (how to prevent/any problems that could arise)
.That all the water has been lost – could heat the mass then weigh and repeat till it stays the same to counteract this.No further decompositions – copper oxide might have been made if we heated it too much
When are you allowed to use half values for equation balancing?
In combustion equations, specifically on the oxygen
In what order do you balance combustion equations (hydrocarbons)?
Carbon first then the hydrogen before finally the oxygen
What does aqueous mean?
Dissolved in water
Equipment needed for the determination of the formula for magnesium oxide practical
.access to balance accurate to two decimal places.Crucible and lid.bunsen burner.Tripod stand.heat-proof mat.clay pipe triangle.Tongs
Health and Safety for the determination of the formula for magnesium oxide practical
.Wear eye protection at all time (safety goggles).Take care not to touch any apparatus that is hot.Take particular care at steps 3 and 4, do not look at any bright light given off by the reacting magnesium while it is being heated.Do not place the magnesium ribbon directly in the Bunsen flame
Method for the determination of the formula for magnesium oxide practical
- Measure the mass of crucible and lid2. Put the magnesium ribbon to the crucible. You will need to coil the magnesium so that it fits. Reweigh the crucible and lid.3. Arrange the equipment with a tripod on a heatproof mat, a clay pipe triangle on the tripod, a crucible in the triangle and a bunsen burner under it. Raise the crucible lid slightly using tongs to control the reaction4. When the reaction is nearly complete, place the crucible lid on the heatproof mat and heat the crucible strongly for 5 minutes. During this time, tap the magnesium oxide gently with tongs to break up the residue5. Allow the crucible to cool and reweigh the crucible, its contents, and lid
What is molar gas volume?
The molar gas volume is the volume per mole of gas molecules at the stated temperature and pressure
What are the conditions at RTP?
Conditions: RTP, Room temperature and pressure20’C101KPa (1atm) pressure
At RTP what does 1 mole of gas have a volume of?
24dm^3 (24000cm^3)
What is the volume and molar gas volume equation?
amount n (mol) = Volume V / molar gas volume V
How is a gas a ‘perfect’ or ‘ideal’ gas?
If it obeys the ideal gas equation
When is a gas most close to obeying the ideal gas equation and why?
real gases obey the equation very closely at low pressure (no more than atmospheric pressure) and high temperature (room temperature). Under these conditions a gas is most like a gas and least like a liquid.
What 5 assumptions does the kinetic theory make about gas molecules?
• The particles are moving in straight lines at random.• We can neglect the volume of the particles themselves in comparison with the total volume of the gas (occupy negligible volume).• The particles do not attract one another (exert no force on one another).• The kinetic energy of the particles is proportional to the temperature of the gas.• No energy is lost in collisions between particles.
What is the ideal gas equation?
pV = nRT
In the ideal gas equation what is ‘p’ and what is it measured in?
Pressure, measured in Pa
In the ideal gas equation what is ‘n’ and what is it measured in?
Amount of gas, measured in mol
In the ideal gas equation what is ‘T’ and what is it measured in?
Temperature, measured in K
In the ideal gas equation what is ‘V’ and what is it measured in?
Volume, measured in m^3
In the ideal gas equation what is ‘R’ and what is it measured in?
Ideal gas constant, measured in J/mol/K
What is the ideal gas constant?
8.31 J/mol/K
How to convert from cm^3 to m^3
x10^-6
How to convert from dm^3 to m^3
x10^-3
How to convert from ‘C to K?
273
How to convert from KPa to Pa?
x10^3
Max number of electrons in the first shell?
2
Max number of electrons in the second shell?
8
Max number of electrons in the third shell?
18
Max number of electrons in the fourth shell?
32
What is an electron shell?
A group of atomic orbitals with the same principal quantum number, n
What’s the principal quantum number?
Represented as n, a number representing the overall energy level of the orbital. The bigger the number, the further the distance between the energy level and the atomic nucleus
Formula to work out how many electrons in the shell?
2(n^2)
What is an orbital?
A region of high probability within an atom that can hold 2 electrons with opposite spin
What are shells made up of?
Orbitals
What did Pauli discover in 1924?
.Orbitals only hold 2 electrons.Electrons carry a negative charge.Spin on-axis - generate a magnetic field.Spin clockwise or anti-clockwise, represented by arrows.Electrons in the same orbital must spin in different directions
What does an s-orbital look like?
A sphere
Which shells have s-orbitals?
From n=1 onwards, each shell contains one s-orbital (max two electrons)
What does a p-orbital look like?
Dumbbell shaped, like a balloon squashed in the middle
Which shells have p-orbitals?
From n=2 onwards, each shell contains three p-orbitals (max 6 electrons)
Which shells have d-orbitals?
From n=3 upwards, each shell has 5 d-orbitals (max 10 electrons)
Which shells have f-orbitals?
From n=4 onwards, each shell has 7 f-orbitals (max 14 electrons)
What does each part of the notation 1s^2 represent?
1 = energy levels = type of orbital2 = number of electrons in orbital
What is Aufbau’s principle?
Electrons fill the lowest energy orbitals in sequence
What is the order that the orbitals fill up?
1s 2s 2p 3s 3p 4s 3d 4p 5s
What is an electron energy level made up of?
An electron energy level is made up of atomic orbitals with the same principal quantum number
What is a sub-shell?
Within each shell, orbitals of the same type are grouped together as a sub-shellsEach sub-shell is made up of only one type of orbital only, so there are s, p and d sub-shells
What is Hunds Rule
Electrons singly occupy orbitals before pairing up
When ionising, using the orbital model, which electrons are lost?
The ones in the outer shell, so even if 3d has electrons in it they will be lost from 4s when ionising
Which two elements don’t follow Aufbau’s principle?
Copper and Chromium
How does Copper not follow Aufbau’s principle?
copper steals a 4s electron to gain a full 3d orbitalIt’s actually 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
How does chromium not follow Aufbau’s principle?
chromium steals a 4s electron to be able to put an electron in every 3d orbitalIt’s actually 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
How do copper and chromium gain stable structures?
Cr and Cu get stable structures from full and half full 3d sub shells
What do the big numbers in equations show?
The molar ratio
What are atoms trying to achieve when they bond?
A full outer shell
4 key things about ionic bonding
Between metals and non-metalsIts to do with the loss and gain of electronsMetals form positive chargesNon-metals form negative charges
How does an atom gain a positive charge?
It loses electrons, therefore there are more protons than electorns
How does an atom gain a nagative charge?
It gains electrons, therefore there are less protons than electrons
What is an ion?
A charged particle
How do ionic bonds stay together?
The electrostatic attraction between the positive and negative ions
What do you use the crosses and dots for on ionic bonding diagrams?
use crosses for the metals electrons and dots for the non-metals electrons
What is a lattice?
A lattice is a regular repeated three-dimensional arrangement of atoms, ions, or molecules in a metal or other crystalline solution.
What is the structure of ionic compounds like?
A giant ionic lattice, the attraction between the oppositely charged ions acts equally in all directions, which leads to the formation of a giant ionic lattice in three dimensions
Moles equation with concentration and volume
Mol = (cm^3 x moldm^-3) / 1000
Rearrange the moles equation with concentration and volume for concentration =
moldm^-3 = (mol x 1000) / cm^3
What are almost all ionic compounds at room temperature?
solids
Why are almost all ionic compounds solid at room temperature?
At room temperature there is insufficient energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions in the giant ionic lattice, high temperatures are needed to provide this energy
Why is the melting points higher for ionic lattices containing ions with greater ionic charges? What else does ionic attraction depend on?
The melting points are higher for lattices containing ions with greater ionic charges, as there is a stronger attraction between ions.The ionic attraction also depends on the size of the atom
Melting point of NaF
993’C
Melting point of CaF2
1423’C
Melting point of Na2O
1275’C
Melting point of CaO
2614
What do many ionic compounds dissolve in?
Polar solvents like water
Why might an ionic compound not be soluble?
.Polar water molecules break down the lattice and surround each ion in the solution.But in a compound made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure, and the compound will then not be soluble
Solubility of NaCL at 20’C
6.1 mol dm^-3
Solubility of CaCl2 at 20’C
0.67 mol dm^-3
Solubility of Na2CO3 at 20’C
2.0 mol dm^-3
Solubility of CaCO3 at 20’C
1.3x10^-4 mol dm^-3
What 2 processes does solubility require?
.The ionic lattice must be broken down.The water molecules must attract and surround the ions
What does the solubility of an ionic compound in water depend on?
on the relative strengths of the attractions within the giant ionic lattice and the attractions between ions and water molecules
As the solubility decreases in ionic compounds…
ionic charge increases
When does and when doesn’t an ionic compound conduct electricity?
.In the solid state, an ionic compound does not conduct electricity.But once melted and dissolved in water the ionic compound does conduct electricity
Describe an ionic compounds electric properties in solid state
.The ions are in a fixed position in the giant ionic lattice.There are no mobile charge carriers, as the ions cannot move.An ionic compound is a non-conductor of electricity in the solid state
Describe an ionic compounds electric properties in a liquid or dissolved state
.The solid ionic lattice breaks down.The ions are now free to move as mobile charge carriers.An ionic compound is a conductor of electricity in liquid and aqueous states
Summarise the properties of ionic compounds
Most ionic compounds – .Have high melting and boiling points.Tend to dissolve in polar solvents such as water.Conduct electricity only in the liquid state or aqueous solutions
What is the main component in teeth, bones and tooth enamel
hydroxyapatite, Ca5(PO4)3OH
What allows tooth decay?
Acid conditions, from food, break down enamel and allow tooth decay
What does saliva do?
Salvia helps to neutralise acidic food and also to replace ions
How do fluoride ions help teeth?
.Fluoride ions help to replace lost ions by forming fluoropatite, Ca5(PO4)3F, which is stronger than hydroxyapatite and more resistant to acid conditions
What do most toothpastes and some water sources contain?
Most toothpastes contain fluoride as sodium fluoride, your water may also contain fluoride depending on where you live
What is the theoretical yield?
The maximum possible amount that can be made
Why is the theoretical yield never achievable?
.The reactions may have not gone to completion.Other reactions (side reactions) may have occurred.Purification of the product may have resulted in loss of product
Percentage yield % =
(actual yield mol / theoretical yield mol) x 100
Describe the use of aqueous barium chloride in qualitative analysis
Test for sulphate ions
What is atom economy?
A measure of the proportion of reactants included in the final useful product
What happens in an ideal reaction, in terms of atom economy?
All reactant atoms end up within the useful product molecule, no waste produced!
What do inefficient reactions have in terms of atom economy?
They are wasteful and have a low atom economy
What do efficient reactions have in terms of atom economy?
.High atom economy.Important for sustainable development.Conserve natural resources and create less waste
What is a bonding pair?
A pair of electrons in a covalent dot n cross diagram that are being used in the reaction
What is a lone pair?
A pair of electrons in a covalent dot n cross diagram that are not being used in the reaction
How is a sigma bond formed?
The head-on overlap of orbitals
In hydrogen what happens in covalent bonding, in terms of orbitals
The two 1s orbitals overlap and they become a molecular orbital
How is the octet rule broken in Boron trifluoride?
It becomes an electron deficient molecule
How can the octet rule be broken in sulphur hexafluoride?
3rd shell of S can hold 18 electrons, octet rule can be broken
What is NH4 ^+
Ammonium ion, a type of molecular ion
What is a dative covalent bond?
A bond formed when both electrons in the share are donated by one atom
For an exam question what should you do?
READ IT ALL AND DO EVERYTHING IT TELLS YOU
Properties of simple covalent molecules
.Low melting and boiling points.Weak intermolecular forces.Not soluble in polar solvents – only in other non-polar liquids.Molecules are not charged so they don’t conduct electricity (no mobile charges).Weak and soft when solid
What does VSEPR theory stand for?
.Valence.Shell.Electron.Pair.Repulsion.Theory
What is the shape of a molecule or ion determined by?
The shape of a molecule or ion is determined by the number of electron pairs in the outer shell of the central atom, more specifically the number of electron pairs repelling as far away from each other as possible (maximum repulsion).
What is the valence shell?
The outer shell
the bond angle of a linear molecule
180’
the bond angle of a triangular planar shape
120’
the bond angle of a tetrahedron
109.5’
the bond angle of an octahedron
90’
Molecular formula of hydrochloric acid
HCl
Molecular formula of sulphuric acid
H2SO4
Molecular formula of nitric acid
HNO3
Molecular formula of ethanoic acid
CH3COOH
Molecular formula of sodium carbonate
Na2CO3
Molecular formula of sodium hydroxide
NaOH
Molecular formula of pottasium hydroxide
KOH
Molecular formula of phosphoric acid
H3PO4
Define hydrogen ion
An ion with no electrons and 1 proton
Define acid
In water an acid releases hydrogen ions into the solution
Define strong acid
Releases all of its hydrogen ions into the solution and completely disassociates, this is irreversible
Define weak acid
Only releases a small number of its hydrogen ions into the solution and partially disassociates, this is reversible
How is sulphuric acid both a strong and weak acid?
Sulphuric acid is both strong and weak, it can form 2H+ and SO42- or H+ and HSO4-
Define a base
A compound that neutralises an acid, by accepting a hydrogen ion to form a salt – for example ammonias, hydroxides, carbonates and metal oxides
Define an alkali
A type of base that dissolves in water to form hydroxide ions
Define a salt
The product of a reaction in which the H+ ions from the acid are replaced by the metal or ammonium ions
Describe and explain the conductivity of sodium Na, chlorine Cl2, and sodium chloride NaCl (6 marks)
.Sodium is a metal and conducts as both a solid and liquid.Free moving delocalised electrons to carry the charge.Chlorine is a small simple molecule that does not conduct.No free moving delocalised electrons to carry the charge.Ionic bond between sodium and chlorine to form sodium chloride, conducts as molten or aqueous but not when solid.Free moving ions when molten and aqueous so can conduct as they carry the charge
Why is the shape of PCl5 special?
Trigonal bi-pyramidBond angles of 120’ and 90’
Describe and explain the shape of a NH3 molecule
3 bonding pairs + 1 lone pair = 4 electron pairsSo repels to corners of tetrahedronDon’t see the lone pair so therefore the shape is pyramidal
Bond angle of NH3
107’
Why do lone pairs of electrons have greater repulsion
not attracted by nuclei unlike bonding pairs
What is the order of repulsion?
LP:LP > LP:BP > BP:BP
By how much does one LP in a tetrahedron reduce the bond angle by?
2.5’
Bond angle of H2O and why?
109.5 – 2.5 – 2.5 = 104.5’2 x LP’s so (– 2.5’) 2 times to the bond angle on a tetrahedron (109.5)
Why is CO2 linear?
C has 2 electron regions (2 BP’s) so it is linear
Define electronegativity
a measure of the tendency of an atom to attract a bonding pair of electrons within a covalent bond.
Where are the electrons positioned when both atoms in a bond are identical?
When the 2 atoms are identical, the electrons are shared equally and stay in the middle
What did Linus Pauling invent and when?
Linus Pauling – invented the Pauling scale in 1932 which measures electronegativity on an atom
Why does it get more reactive as you go down group 1?
More reactive as you go down the groupLess nuclear attraction to the outer electronEasier to loseThe nucleus is being shielded by the electrons in-betweenSo the electron feels less nuclear attraction
Across a period what happens to the electronegativity?
increases
Down a group what happens to the electronegativity?
decreases
Why does electonegativity increase across a period?
.Size roughly equal across period with same shielding by 2, 8.Nuclear charge increases across period therefore greater nuclear attraction so electronegativity increases
Why does electonegativity decrease down a group?
.Down group size of atom increases.Shielding of outer shell increases.This reduces the nuclear attraction and electronegativity
In a bond, what happens if one atom is more electronegative than the other? Example.
.The more electronegative atom will have a greater share of the electrons.Take H and Cl as an example.H = 2,1, Cl = 3.0.Cl more electronegative so the electrons are attracted more towards it
What does delta +/- mean?
means it has a slight positive or negative charge now
When H reacts with Cl what happens to its electron density?
.H has lost a small amount of electron density – becomes s+
What type of molecule is H-Cl?
Polar
Why is H2O a polar molecule?
the dipoles act in the same direction
Why is Carbon Dioxide a non-polar molecule?
Symmetrical dipoles will cancel each other out, so CO2 is non-polar
What atom gets the delta- charge?
The more electronegative atom will take the s- charge
Can you predict bonds from eletronegativity?
Yes
If there is no difference between electronegativity there is what sort of bond?
non-polar covalent bond
If there is a small difference (0 to 1.8) between electronegativity there is what sort of bond?
polar covalent bond
If there is a large difference (>1.8) between electronegativity there is what sort of bond?
ionic
metal + hydrochloric acid –>
metal chloride + hydrogen
Metal + sulphuric acid –>
metal sulphate + hydrogen
Metal + nitric acid –>
Metal nitrate + hydrogen
Metal + phosphoric acid –>
Metal phosphate + hydrogen
Metal oxide + acid –>
Salt + water
Metal hydroxide + acid –>
salt + water
Metal carbonate + acid –>
salt + carbon dioxide + water
Ammonia + acid –>
ammonium salt
Where to observe the meniscu
eye level
What is weighing by difference?
With weighting boat – used weighing boat = mass
What is an intramolecular force?
strong bonds inside molecules
What is an intermolecular force?
act between different molecules, weak compared to covalent bonds
What are intermolecular forces caused by?
Intermolecular forces are caused by weak attractive forces between very small dipoles in different molecules
3 types of intermolecular forces and their relative strength if ionic and covalent are 1000
Hydrogen Bonds 50Dipole-dipole forces 10London forces 1
What is a dipole dipole force?
permanentA weak attractive force between permanent dipoles in neighbouring polar molecules
Explain HCl as an example of dipole dipole intermolecular force
Take HCL, H is s+ and Cl s-, these charges weakly attract opposite charges in neighbouring molecules
In London forces as the number of electrons increase …
so does the strength of the London Forces due to larger instantaneous dipoles created.
In terms of intermolecular forces what can and cant dissolve in water
If no permanent dipoles it can’t dissolve in water, London forces don’t count as they are temporary dipoles
How do London forces work?
.Movement of electrons produces a changing dipole in a molecule.At any instant, an instantaneous dipole will exist, but its position is constantly shifting.The instantaneous dipole induces a dipole on a neighbouring molecule.This induced dipole induces further dipoles on neighbouring molecules, which then attract one another
How to find uncertainty?
Half the smallest possible unit you can make
Percentage uncertainty =
(uncertainty of equipment/size of measurement) x 100
What anomalous properties does water have?
Elevated melting and boiling points Ice floats (solid is less dense than the liquid)relatively high surface tension and viscosity
Why does water have an elevated melting and boiling point?
due to strong H bonds between molecules
Why does ice float?
as liquid water freezes the molecules arrange themselves in a more open, regular lattice structure
What is a hydrogen bond?
A strong dipole-dipole attraction between .An electron-deficient hydrogen atom on one molecule (O-HS+ or N-HS+)and .A lone-pair of electrons on a highly electronegative atom on a different molecule (H-OS- or H-NS-)
Why does water have relatively high surface tension and viscosity?
The hydrogen bonds
In what compounds are hydrogen bonds useful?
organic compounds containing O-H and N-H bonds (alcohols, carboxylic acid etc)
What are hydrogen bonds responsible for the shape of?
They are responsible for shape of proteins and even DNA
New concentration equation
New conc = (original volume / new volume) * original conc
Define oxidation number
A measure of the number of electrons that an atom uses t bond with an atom of another element. Oxidation numbers are derived from a set of rules.Also known as an element’s oxidation state
What is the oxidation number of a neutral element?
zero
What is the oxidation number of a monatomic ion?
The same as the charge of the ion
What is the sum of all oxidation numbers in a neutral compound?
zero
What is the sum of all oxidation numbers in a polyatomic ion equal to?
the charge on the ion
What is the oxidation number of groups 1-3 in compounds
In compounds the elements of:Group 1 have an oxidation number of +1Group 2 have an oxidation number of +2Group 3 have an oxidation number of +3
What is the oxidation state of hydrogen in a compound? What if it is in a binary metal hydride? What is a binary metal hydride?
The oxidation state of hydrogen in a compound is usually +1. If the hydrogen ion is part of a binary metal hydride (compound of metal and some hydrogen), then the oxidation state is -1.
What is fluorines oxidation number in compounds?
Fluorine has an oxidation number of -1 in compounds.
What is the oxidation state of oxygen usually? What is its oxidation state in a peroxide? What is its oxidation state when bonded to fluorine?
The oxidation number of oxygen in a compound is usually -2. If, however, the oxygen is in a class of compounds called peroxides (like hydrogen peroxide), then the oxygen has n oxidation number of -1. If the oxygen is bonded to fluorine, the number is +2.
What happens with transition metals oxidation numbers?
In transition metals, the oxidation number can vary.
What are chlorine, bromine, and iodines oxidation numbers? What is the exception?
Chlorine, Bromine and iodine usually have numbers of -1, except when it is in a compound with oxygen.
In compound names with roman numerals, what does the roman numeral refer to?
The oxidation number of the element that is joined in name to the oxygen, but not the oxygen (for example in element(1) element(2)ate (Roman Numeral) then the roman numeral refers to the element (2))
In potassium manganate(VII), what does the VII refer to?
The oxidation number of manganese
In equations, if an elements oxidation state increases what has it undergone?
Oxidation
In equations, if an elements oxidation state decreases what has it undergone?
Reduction
What is a disproportionation reaction?
when the same element is both oxidised and reduced at the same time in a reaction
Rules for writing ionic equations
1) Re-write out the equation showing the separate ions present in each substance.2) Look for ions that change state and/or form non-ionic compounds and underline them3) Cross out spectator ions 4) Rewrite the equation leaving out the spectator ions. 5) Make sure your equation still balances
How does developing chemical processes with high atom economy benefit sustainability?
Less environmental waste as a high percentage of atoms are being used in useful products
Alkene general formula
CnH2n
Does an alkene exist with 1 carbon?
no
Are alkenes saturated or unsaturated?
Unsaturated
What is the test for alkenes?
bromine water is decolourised (orange to colourless)
What is a pi bond?
these are formed by the sideways overlap of the two adjacent p orbitals
Chemical formula of limonene
C10H16
What is limonene responsible for?
The smell and flavour of lemons and oranges
What happens in an alkene addition reaction?
The double bond opens up and allows two atoms to join to it
What happens in a hydrogenation of an alkene?
Addition reaction with hydrogen
Conditions for hydrogenation of alkene
nickel catalyst and 150’C
Why does the Z isomer have a lower boiling point?
It cant pack as closely together
What happens with hydration of alkenes?
.Alkenes will react with steam, H2O, in the presence of phosphoric acid, H3PO4, to produce alcohols
What does bromine water test for?
Unsaturation
Why is HBr polar?
Br is more electronegative
Explain how electrophilic addition works using HBr as an example
HBr is polar due to electronegative BrThe pi electrons attracted towards the Hs+, i.e. pi bond breaksHs+ acts as an electrophile (accepts a pair of electrons)H-Br bond breaks via heterolytic fission
What is an electrophile?
‘electron loving’, able to accept a pair of electrons
What is a nucleophile?
‘nucleus loving’, able to donate a pair of electrons
Why is Br2 non-polar?
Both Br atoms have the same electronegativity
How does Br2 react with an alkene?
Bromine is none polar due to each atom having the same electronegativityBut as bromine approaches the pi bond on the alkene, it repels the electrons in the bond and pushes them away, giving the bromine atoms slight chargesThe pi electrons induce a dipole in the non-polar Br2 molecule as it approaches the bondThis means electrophilic addition can ensue
In electrophilic addition, in the stage between the adition of the electrophile and the addition of the other atom, what is the alkene called? Why?
A carbocation (or carbonium ion) as it has a positive charge
What forms of carbocations are there?
Primary, secondary and tertiary
How do +I affects increase stability?
Carbon centres have a positive inductive effect (+I). This pushes electron density towards the C+ and helps to stabilise it.
The more +I effects,
the more stable the carbonium ion
The more stable ions are,
more favourable
Which product of electrophillic thing is more favourable?
Major product
What is markownikoffs rule?
The major product is produced when the negative part of the molecule joins to the carbon with the least number of attached H (hydrogen) atoms within the double bond.
What is the order of carbonium ion stability? Why?
Primary carbonium ions are less stable than secondary, which are less stable than tertiary, because:- Primary = 1 x +I- Secondary = 2 x +I- Tertiary = 3 x +I
Draw the electrophillic mechanism for HCl and CH3CH=CH2
Check notes from 29.1.20
Define acid
dissociates in water and releases H+ ions
Define alkali
dissociates in water to release OH- ions
Neutralisation equation
H+ + OH-1 H2O
Bronsted Lowry Acid:
Proton donor
Bronsted Lowry Base:
Proton acceptor
pH = 1 (x 10 the concentration of H+ ions) pH =
2
What makes an acid strong?
It fully dissociates
As a Strong acid fully dissociates, pH of a strong acid can be calculated from
concentration of acid
pH =
-log10[H+]
Sulphuric acid is dibasic, what does this mean?
H2SO4 2H+ + SO42-
[H+] =
10-pH
Weak acids form an acid dissociation constant called
Ka
Ka =
[products] / [reactants]
[H+] = for weak acids
root([HA] Ka)
[HA] is what?
concentration of weak acid
How can we test for acids?
We can test for acids using universal indicator paper which turns red or orange depending on the strength of the acidBlue litmus paper also turns red in the presence of an acid
HCl + H2O –>
H3O+ + Cl-
What is H3O+
A hydronium ion, also known as an oxonium ion
What is water acting as in the equation:HCl + H2O H3O+ + Cl-
a base
What is a bronsted-lowry base?
A Bronsted Lowry base is a substance which accepts protons in solution
What is a bronsted-lowry acid?
A Bronsted Lowry acid is a substance which releases or donates protons in solution
What does a bronsted-lowry acid-base reaction involve?
the transfer of a proton from one base to another
What does ammonia do in water? include equation
Ammonia, in water, accepts a protonNH3 + H2O NH4+ + OH-
In the equation,NH3 + H2O NH4+ + OH-, what is water acting as?
An acid
For a bronsted-lowry base, what is the pH of an acid?
So for the Bronsted Lowry theory, a base does not need to have a pH>7
What are substances that can act as either a base or an acid called?
Substances that can act as either an acid or a base are amphoteric
What are some old defnitions of acids?
.The definition of acids has developed since the time of the ancient Greeks.Simpler ideas involved substances that had a sour taste, contained hydrogen, hydrogen ions or had a pH lower than 7
.When a chemical reacts with an acid it is the __________ from the acid which is driving the reaction forward
hydrogen ion, H+,
HCl (aq) + NaOH (aq)
NaCl (aq) + H2O (l)
How did the Bronsted-Lowry name come about?
Johannes Nicolaus Bronsted and Martin Thomas Lowry did not work together but both chemists formulated the idea that acids are proton donors and bases are protons acceptors
The Brønsted–Lowry acid–base theory is a development of these earlier ideas and states that:
.An acid is a proton donor.A base is a proton acceptor
.How many protons, neutrons and electrons does a Hydrogen ion, H+ have?
.A hydrogen ion is just a proton
We know that HCl forms a covalent bond between the hydrogen and chlorine so what happens when it dissolves in water to become hydrochloric acid?
.HCl(g) + aq H+(aq) + Cl-(aq)
HCl(g) + aq H+(aq) + Cl-(aq).On closer inspection is?
HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)
.H3O+(aq) is known as the hydronium ion, also known as _______ ion
hydroxonium
.In this equation:HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)what is HCl and H2O acting as?
The HCl is a proton donor (a Brønsted–Lowry acid).The H2O is a proton acceptor (a B-L base)
In the reverse equation of HCl(g) + H2O(l) H3O+(aq) + Cl-(aq) what happens to the roles?
.In the reverse equation, the roles reverse:H3O+(aq) + Cl-(aq) HCl(g) + H2O(l)
once an acid has ‘donated’ a proton it would become able to ‘accept’ a proton back and hence act as a base, what is this called?
We call these pairs of chemicals conjugate acid-base pairs
Give an example of a conjugate acid-base pair?
HCl and Cl- = Acid and conjugate base
What are the acid base pairs in HCl + H2O H3O+ + Cl-
HCl = acid 1Cl- = base 1H2O = base 2H3O+ = acid 2
What are the acid base pairs in CH3COOH + H2O CH3COO- + H3O+?
CH3COOH = acid 1CH3COO- = base 1H2O = base 2H3O+ = acid 2
What are the acid base pairs in NH3 + H2O NH4+ + OH-?
Base 2 Acid 1 Acid2 Base 1
What are the acid base pairs in HCO3- + HCl H2CO3 + Cl-?
Base 2 Acid 1 Acid 2 Base 1
Complete the equation for the conjugate acid-base pair: CH3CH(OH)COOH + CH3CH2CH2COOH
CH3CH(OH)COO- + CH3CH2CH2COOH2+
List the roles of H+ in reactions
spectator ions:Acid + metal salt + hydrogenSolid carbonates and soluble carbonates:Acid + carbonate Water + carbon dioxidebase (metal oxides): Acid + base salt + waterAlkali: H+ + OH- H2O
What did Soren Sorenson do?
introduced simple numbers to represent the colours of indicators using an electrochemical cell to measure the hydrogen content
What did Soren Sorenson find?
.He found the ion concentration had a very large range of values of powers of 10 (10-1 to 10-14)
What is a strong acid? With general equation
.A strong acid is one which completely dissociates into ions in a solutionHA H+ + A-
So for a strong acid, [H+] =
concentration of the acid ([HA])
pH =
-log10[H+]
What does the equation pH = -log10[H+] tell us?
.It tells us the relative hydrogen ion concentration of a given solution
What must we remember with the equation pH = -log10[H+]?
.THIS ONY WORKS FOR STRONG ACIDS
.An increase in H+ x10, it reduces the pH by how much?
1
What is pH of 1M HCl?
0
What is Sorenson’s pH scale?
.The logarithmic scale means that a shift of one pH unit means a 10x change in the acidity and alkalinity of the solution.Theoretically there is no limit to the pH scale
What type of acid is HCl, what does this mean?
monobasic = [H+]
What type of acid is H2SO4, what does this mean?
dibasic = 2[H+]
What type of acid is H3PO4, what does this mean?
tribasic = 3[H+]
[H+] =
10-pH
What is the [HCl] of a solution with pH 1.8?
0.016 moldm-3
What is the [H2SO4] of a solution with pH 1.8?
0.008 moldm-3 as dibasic acid
50cm^3 of 0.1M HCl is diluted to 100cm^3 with water, what is the change in pH?
Before dilution, pH = 10n dilution, HCl conc is halved to 0.05MAfter dilution, pH = 1.30Change = 0.3
What is a strong acid?
A strong acid is one which completely dissociates into ions in a solution
WHat does pH = -log10[H+] only work for?
ONLY WORKS FOR STRONG ACIDS
[H^+] equation for changing concentraation
[H+] = [H+]old x (old volume / new volume)
How are weak acids different to strong ones?
.Weak acids do not dissociate fully like strong acids
What happens when a weak acid dissociates?
An equilibrium is established between the ions and the acid
As an equibrlium is established when weak acids dissociate, what can we calculate?
we can calculate an equilibrium constant Ka (Acids dissociation cons tat)
What does Ka equal for, HA H+ + A-?
Ka = ( [H+] [A-] ) / [HA]
For the Ka equation what two assumptions need to be made?
.A pure acids will split evenly into equal quantities of [h+] and [A-].The concentration of the acid doesn’t change as the equilibrium lies so far to the left it can be considered equal
does [H+] = [H+ aq]?
yes
.A sample of ethanoic acid of concentration 0.04 moldm-3.What is the value of Ka?
2.5x10-9 moldm-3
Steps to calculating pH of weak acid
.Step 1: Calculate [H+] from ka and [HA].Step 2: Calculate pH
Are the approximations for weak acids justified?
.The first approximation assumes that the dissociation from water is negligible.[H+(aq)]eqm = [A-(aq)]eqm - if pH>6 then water dissociates and [H+] from water will be more significant than from dissociation of acid.This approximation breaks down for very weak acids or very dilute solutions.Second approximation assumes that the concentration of the acid [HA] is much greater than the [H+] concentration at equilibrium.[HA]start»_space; [H+]eqm [HA]eqm = [HA]start – [H+]eqm so [HA]eqm = [HA]start.Not valid as acid gets stronger as [H+] becomes more significant and real difference between [HA]eqm = [HA]start – [H+]eqm.Not justified for stronger weak acids / very dilute solutions.
.The value of Ka for weak acids is almost always very small and difficult to compare numbers with negative indices, how do we get around this?
create a scale of more useable numbers we often use the value of pKa, when talking about the aciditing of weak acids
What is pKa often used for?
to compare acids in biological systems
pKa equation
pKa = -log10Ka
What do the values of pKa mean?
The higher the value of pKa, the weaker the acidThe lower the value of pKa, the stronger the acid
How does wine show behaviour of typical dibasic and tribasic acids?
Wines often contain traces of sulphurous acid, H2SO3, added as a preservative.Sulphurous acid is dibasic and its dissociation is shown as:H2SO3 H+ + HSO3 - (pKa = 1.92)HSO3 - H+ + SO3 2- (pKa = 7.18).For the first dissociation, H2SO3, acts as a weak acid.From the pKa values, HSO3, is a far weaker acid than H2SO3.The behaviour is typical of dibasic and tribasic acids
Where strong acids completely dissociate to release all H+ ions into solution, weak acids only partially dissociate, explain this in terms of equations
Strong: HA → H+ + A-Weak: HA ⇌ H+ + A-
As weak acids form an equilibrium their dissociation can be represented by the acid dissociation constant, Ka, whats the equation for this?
Ka = “[H+(aq)][A-(aq)]” /”[HA(aq)]”
Explain why a larger value for Ka means a lower pH
.The larger the value for Ka the more the equilibria lies to the right and so the lower the pH i.e. higher [H+]
What alters Ka?
Temperature
.As the values for Ka are very small it is easier to give their negative logarithm, pKa, instead, what is the equation for this?
pKa = - logKa
pKa = - logKa, what is the inverse equation for this?
The inverse for this equation is: Ka = 10-pKa
This means that the weaker an acid the:._____ Ka._____ pKa
.Smaller Ka.Larger pKa
.The [H+] of a weak acid depends on the value of what?
Ka and [HA]
.The equilibrium concentrations, [ ]eqm, can be used to determine a value for Ka, what is the equation for this?
Ka = “[H+]eqm [A-]eqm” /”[HA]eqm”
There are two approximations that need to be made when calculating Ka, what are they?
.HA dissociation forms equal [H+] and [A-].The change in [HA] is negligible so [HA]eqm = [HA]start
Using the approximations, Ka can be determined by what equation?
Ka = “[H+]eqm 2” /”[HA]start”
How can pH be calculated for a weak acid?
[H+] = √(“Ka x [HA]” ) → pH = -log[H+]
.A value for Ka can be determined experimentally, how?
by using a pH meter to get the pH of a standard solution
.The larger the value for Ka, the greater the _________
dissociation
When calculating values for Ka there are issues with the approximations made, what are these issues?
• At pH values >6 water dissociation is significantTherefore doesn’t work for very weak acids or very dilute solutions• If [H+] concentration is significant there will be a difference between [HA]eqm and [HA]startTherefore doesn’t work stronger weak acids with Ka > 10-2 mol dm-3 or very dilute solutions
All aqueous solutions contain which ions?
H+ and OH- ions
H2O
H+ + OH-
In ____ [H+] > [OH-]In ____ [OH-] > [H+]In ____ [H+] = [OH-]
In acids [H+] > [OH-]In alkalis [OH-] > [H+]Neutral [H+] = [OH-]
For every 500,000,000 H2O molecules, only _ dissociates
1
For every 500,000,000 H2O molecules, only 1 dissociates, what does this mean for the equilbrium?
the equilibrium is on the left hand side
Do the Kc equation for water equilibrium
Kc = ([H+][OH-]) / [H2O]
[H2O] x Kc =
[H+] x [OH-]
[H2O] is such a large excess it can be classed as a ____
constant
What is Kw?
ionic product of water
Kw = [H2O] x Kc, so replace [H2O] x Kc with Kw in the correct equation
Kw = [H+] x [OH-]
At 298K, Kw =
1x10-14 mol2dm-6
Why is the pH of pure water at 298K, 7?
Kw = [H+] x [OH-]1x10-14 = [H+] x [OH-]The concentrations are the same and so it can be written as:1x10-14 = [H+]21x10-7 = [H+]pH = 7
Effect of temperature on Kw
The dissociation of water is endothermicTemperature increase will move the equilibrium to the right, and so Kw will increaseTemperature decrease will move the equilibrium to the left, and so Kw will decreaseWater will always remain neutral at all temperatures, pH may change with temperature, but [H+] = [OH-] all the time and so it is neutral
.Water ionises very slightly, acting as both an acid and as a base – setting up an ________
equilibrium
.Water dissociates a very, very small amount according to the equation – it must do, otherwise it would not _____________
conduct electricity
.1 dm3 (1000g) of water is mainly ________ H2O
undissociated
. [H2O(l)] = 1000/18 = 55.6 mol dm-3 (a constant), why?
.1 dm3 (1000g) of water is mainly undissociated H2O
.If we know the concentration of hydroxide ions we can rearrange Kw to give us the value of what?
[H+]
What is the pH of 0.4 mol dm-3 NaOH?
Kw = [H+][OH-] = 1.00 × 10–14 mol2dm–6 (1.00 × 10_14 )/([0.4])=[H+] = 2.5 x 10-14 mol dm-3 pH = -log10[H+] = -log10[2.5 x 10-14 ] = 13.60
What is the pH of a solution with [OH-] = 2 x 10-2 mol dm-3 at 25oC ?
Step 1 : calculate [H+] from Kw and [OH-] Kw = [H+][OH-] = 1.00 x 10-14 [H+] = Kw = 1.00 x 10-14 = 5.00 x 10-13 mol dm-3 [OH-] 2.00 x 10-2Step 2 : Use calculator to find pH pH = - log [H+] = -log (5.00 x 10-13) = 12.30
What are the concentrations of H+ (aq) and OH- (aq) in a solution of pH 3.25 at 25oC ?
Step 1 : Use calculator to find [H+(aq)][H+] = 10-pH = 10-3.25 = 5.62 x 10-4 mol dm-3Step 2 : Calculate [OH-] from Kw and [H+]Kw = [H+][OH-] = 1.00 x 10-14[OH-] = Kw = 1.00 x 10-14 = 1.78 x 10-11 mol dm-3 [H+] 5.62 x 10-4
For pH values that are whole numbers, it is easy to work out the [H+] and [OH-] concentrations as the indices add up to what?
-14
.The pH of weak bases can be calculated via a similar method to that used for ______
weak bases
.In an aqueous solution, there will always be both H+ (aq) and OH- (aq) ions present such that ________
[H+ (aq)][OH- (aq)] = Kw
.A solution is ______ when [H+ (aq)] > [OH- (aq)] .A solution is ______ when [H+ (aq)] = [OH- (aq)].A solution is ______ when [OH- (aq)] > [H+ (aq)]
.A solution is acidic when [H+ (aq)] > [OH- (aq)] .A solution is neutral when [H+ (aq)] = [OH- (aq)].A solution is alkaline when [OH- (aq)] > [H+ (aq)]
.So a solution that is acidic will still contain __ ions, it is just that there are more __ions (and vice versa in an ______ solution)
OH-H+Alkaline
.The value of Kw controls the ______ of each ion
Concentrations
• Kw can also tell us the pH of ______
pure water
• As the water splits into equal concentrations of OH- and H+ ions we can make what assumption?
Kw = [H+][OH-] = 1.00 × 10–14 mol2dm–6 = [H+]2 = 1.00 × 10–14 = [H+] = 1.00 × 10–7 pH = -log10[H+] = -log10[1.00 x 10-7 ] = 7
When is neutral not neutral?
.A neutral solution is defined by a equal number of moles of H+ ions and OH- NOT by a pH of 7 as you may have been taught.Whilst this value is 7 at approximately 298K, the value of Kw increases with temperature
.The pOH scale measures what?
the concentration of hydroxide ions
.Therefore you can solve fpr pH, pOH and [OH-] given just ___
[H+]
pH + pOH =
14
.Kw = [H+][OH-] =
1x10-14
H2O(l) H+(aq) + -OH(aq)
Water slightly ionises, what equation will show this?
[H+][-OH] / [H2O]`
Ka of :H2O(l) H+(aq) + -OH(aq)=
Kw
Ka x [H2O] =
[H+][-OH]
Kw =
Kw is the ionic product of water, at 25’C it equals 1x10-14 mol2dm-6
What is Kw?
What is a buffer?
a solution that minimises pH change when a small amount of acid or alkali is added
What two types of buffers are they?
Weak Acid and Salt of Weak AcidExcess Weak Acid and Strong Base
Suggest and explain a Weak Acid and Salt of Weak Acid buffer
Weak Acid – Ethanoic Acid – CH3COOH(aq) CH3COO-(aq) + H+(aq)Salt of Weak Acid – Sodium Ethanoate – CH3COONa(s) + (aq) CH3COO-(aq) + Na+(aq)¬Buffer Contains – CH3COOH(aq) CH3COO-(aq) + H+(aq)When add H+, H+ reacts with conjugate base, equilibrium will move to the left to reduce the amount of H+, pH is constantAdding –OH (alkali) –-OH + H+ H2OConc of H+ decreases, equilibrium moves to the right to increase the conc of H+, pH is constant
Suggest and explain an excess Weak Acid and strong base buffer
CH3COOH(aq) + NaOH(aq) –> CH3COONa(aq) + H2O(l)CH3COONa(aq) CH3COO-(aq) + Na+(aq)CH3COOH(aq) CH3COO-(aq) + H+(aq)When add H+, H+ reacts with conjugate base, equilibrium will move to the left to reduce the amount of H+, pH is constantAdding –OH (alkali) –-OH + H+ H2OConc of H+ decreases, equilibrium moves to the right to increase the conc of H+, pH is constant
Excess methanoic acid is reacted with potassium hydroxide, explain how a buffer solution is produced and how pH is controlled when 5cm3 of HCl is added.
The solution now contains HCOOK(aq) HCOO- (aq) + K+(aq) and HCOOH(aq) HCOO-(aq) + H+ equilibriums in solution – the buffer. When 5cm3 of HCl is added, it dissociates into H+ and Cl-, the H+ ions increase the concentration of the H+ already in the solution, so the HCOOH(aq) HCOO-(aq) + H+ point of equilibrium moves to the right – decreasing the conc of H+ in solution, and so keeping the pH constant.
Ka x ( [HA]/[A-] ) = ? what does each part mean?
[H+] = Ka x ( [HA]/[A-] )[HA] = concentration of weak acid[A-] = concentration of conjugate base
50cm3 of 1.2M NaOH reacts with 250cm3 of ethanoic acid (1M), Ka = 1.74x10-5, what is the pH?
CH3COOH CH3OO- + H+CH3COOH + NaOH CH3COO- + Na+ + H2O1. Moles weak acid = 250x1 / 1000 = 0.25mol2. Moles NaOH = 50x1.2 / 1000 = 0.06mol3. Moles A- = 0.06mol4. Moles HA = 0.19mol5. [H+] = Ka ([HA] / [A-]) = 1.74x10-5 x (0.19/0.06) = 5.51x10-56. pH = 4.26
Blood must contain a pH of what?
Blood must contain a pH of 7.40 +- 0.05
What is the most important buffer in blood?
the carbonic acid – hydrogencarbonate
Carbonic acid dissociation equation
H2CO3 H+ + HCO3-
If blood becomes too acidic (acidosis), what presents?
fatigue, shortness of breath, shock, death
If blood becomes too alkaline (alkalosis), what presents?
spasms, light-headed, nausea
What happens if the body produces more acidic products?
.The H+ concentration in the blood will increase, the equilibrium of the hydrogencarbonate dissociation will shift to the left, the H+ ions will be used up to form more hydrogencarbonate, the H+ concentration will return to normal, the pH will have had minimal change.If the acid level continued to rise, fatigue, shortness of breath, shock, or death would eventually set in.This would occur when we have ran out of HCO3- ions
Carbon dioxide dissolves in water to form what? What is the equation for this?
carbonic acid:CO2 + H2O H2CO3
Inhalation of high levels of CO2 means what?
Inhalation of high levels of CO2 mean that the equilibrium in the blood must shift to the right to form more H2CO3, this means that the level of H2CO3 in the blood increase, so in the equilibrium H2CO3 H+ + HCO3- the equilibrium shifts to the right to counter this, this forms more H+ ions in the blood, making it more acidic, and resulting in acidosis which would lead to fatigue, shortness of breath, shock, and eventual death. Increased [H+] means enzymes would also be denatured.
Draw the titration curve for when HCl is added to NaOH
check notes
Draw the titration curve for when NaOH is added to HCl
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Draw strong acid strong base titration curve
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Draw strong acid weak base titration curve
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Draw weak acid strong base titration curve
check notes
Draw weak acid weak base titration curve
check notes
The shape of the titration curve depends on what?
- Substance being titrated i.e. acid or base- Type of acid or base i.e. strong or weak
Describe and explain parts of titration curve
- Excess of base: pH decreases as acid added2. Vertical section: acid base concentration similar, pH alters rapidly3. Excess of acid: pH decreases slightly as acid is added4. The equivalence point: halfway up the vertical section
What is the equivalence point?
The point halfway between the two horizontal lines on the titration curveThe equivalence point is the volume required to have completely reacted the acid and base toetehr, stoichiometric volumesThe pH at the equivalence point depend son the type of acid and base
Where is the equivalence point on each titration curve?
Equivalence point = 7 on SA-SBEquivalence point < 7 on SA-WBEquivalence point > 7 on WA-SBNo equivalence point on WA-WB
Why is the equivalence point 0 on SASB titration curves?
- H+ ions completely neutralised by OH- ions, so only water and salt present, neutral
Why is the equivalence point < 7 on SAWB titration curves?
- A weak base, like NH3, will have a strong conjugate acid, NH4+ , which will react with water to produce H3O+ so the pH is less than 7
Why is the equivalence point > 7 on WASB titration curves?
- A weak acid, HA, will have a strong conjugate base, A-, which can react with water to produce OH- ions, so the pH is more than 7
What are acid-base indicators?
Acid-Base indicators are weak acids that have different coloured conjugate basesIn acidic conditions the indicator equilibrium is shifted towards the weak acid (HIn)As the system becomes more basic the equilibrium shifts towards the conjugate base (In-), altering the colour
What is the end point?
The end point is when equal [HIn] and [In-] are present, the colour will therefore lie between both extremesEach indicator will have a different pH value for the end point as they each have different ka values
HIn
H+ + In-
How is an acid-base indicator chosen?
The indicator required for a titration must have a colour change that lies within the vertical section of a titration curve
Draw an aldehyde group
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Draw an ester group
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Draw a haloalkane group
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Draw an alcohol group
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Draw an alkene group
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Draw a carboxylic acid group
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Draw a ketone group
google it
Draw an amine group
google it
What are aromatic hydrocarbons?
Aromatic hydrocarbons are when some or all of the carbons are found in a benzene ring
What are aromatic hydrocarbons also called?
Arenes
What is an alkyl group?
An alkyl group has a hydrogen group removed from the alkane chain
What are compounds with one substituent group?
.These are aromatic compounds with one substituent group that is mono-substituted on to a benzene ring
.If the substituent group is: An alkyl group (e.g. CH3), halogen (e.g. Br, Cl), or a nitro group (NO2).Then …
the parent group is classed as the benzene ring and the group added is considered the prefix
If the substituent group is: amine or an alcohol, then …
the parent group is classed as the functional group and benzene is classed as the prefix
What is the prefix for benzene?
phenyl
Draw Benzene carboxylic acid
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Draw Benzaldehyde
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Some molecules may contain more than one substituent group, so it may have ___ substituents bonded to it.
two
We number the benzene ring like you would a ____ chain
carbon
The substituent groups are listed in _____ order and using the ________ possible number.
alphabetical smallest
Draw 2-chloro methylbenzene
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Draw 3-methylphenylamine
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When was Benzene discovered? and by who?
Discovered in 1825 by Michael Faraday
what is the percentage make up of benzene found by faraday? relative formula mass, and empirical formula
.92% carbon, 8% hydrogen.It has a relative formula mass of 78.Empirical formula found to be CH
What was weird about benzene when discovered?
.The structure was difficult to define
Who proposed the first structure of Benzene, what was it and did it work?
.Kekule’s proposed structure for benzene.It was planar, cyclic with alternating double and single bonds which had 120’ bond angles.But there were problems with this structure
What was the chemical evidence against Kekule’s benzene?
.Benzene would not react with bromine, hydrogen bromide, and sulfuric acid.This tells us there are no double bonds in the molecule.The molecule does not undergo electrophilic addition reactions
What was the bond length evidence against Kekule’s benzene?
.A carbon-carbon single bond length is 0.153nm.A carbon-carbon double bond length is 0.134nm.So you would expect benzene to be an irregular hexagon.In 1922, Kathleen Lonsdale used x-ray diffraction to measure the bond length in benzene.She found it had a regular shape.She found that all the carbon-carbon bonds were the same length – 0.14nm.Each bond is an intermediate between a single and double bond
What was the thermochemical evidence against Kekule’s benzene?
.The enthalpy of hydrogenation is defined as the change in enthalpy when 1 mole of unsaturated compound reacts with an excess of hydrogen to become fully saturated.The molecule had an enthalpy of -208, Kekule’s model in theory should have had -360.So it’s bonds are more stable than cycloalkenes, as it is less exothermic than expected
Describe the declocalised model of benzene
.Each carbon atom has 3 σ (normal) bonds.This leaves a spare electron in 2p orbital.120’ bond angle between carbon atoms.Planar hexagonal molecule.2p orbitals overlap above and below the ring.To form pi bonds.The electrons in the pi bonds are delocalised
Draw the delocalised model of bezene
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Draw Kekule’s benzene model
Check notes or google
What is an electrophile?
An electrophile is an electron acceptor and can have a positive charge
What must an electrophile have to attack the stable benzene ring?
An electrophile has to have a strong positive charge to be able to attack the stable benzene ring, most compounds just aren’t polar enough
What does an electrophile need when attacking a benzene ring?
Needs a halogen carrier – iron, iron halides (e.g. FeCl3) or aluminium halides (e.g. AlCl3)
Br-Br: + AlBr3
AlBr4- + Br+
In an electrophilic substitution reaction with benzene, what does the halogen carrier do?
The halogen carrier accepts a lone pair of electrons from a halogen atom, as the lone pair is pulled away from the polarisation increases forming a strong electrophile
What is halogenation?
when a hydrogen atom is substituted for a halogen on a benzene ring
Give an example of halogenation
bromine is substituted onto a benzene ring to make bromobenzeneC6¬H6 + Br2 AlBr3 C6H5Br + HBr
WHat is the mechanism to a halogenation?
Step 1 – creating the electrophile with the halogen carrier catalystStep 2 – electrophile accepts a long pair of electrons from the benzene ring to form a dative covalent bond, this forms as unstable intermediate, the intermediate breaks down to form the organic productStep 3 – the catalyst is regenerated
Draw the halogenation of benzene with Br2 with the AlBr3 catalyst
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Benzene reacts with nitric acid at what speed?
slowly
How can we increase the rate of reaction of benzene and nitric acid?
by using sulphuric acid as a catalyst and 50’C
What happens when benzene reacts with nitric acid?
The H atom is substituted for a nitro (NO2) group
C6H6 + HNO3 H2SO4
C6H5NO2 + H2O
Draw the mechanism for benzene and nitric acid
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Describe the steps of the mechanism for benzene and nitric acid
Step 1: Creating the electrophile with the sulphuric acidStep 2: Electrophile accepts a lone pair of electrons from the benzene ring to form a dative covalent bond, this forms an unstable intermediate – the intermediate breaks down to form the organic productStep 3: The catalyst is regenerated
Why is the reaction between benzene and nitric acid kept at 50’C?
so that only 1 nitro group attaches
What is alkylation?
.This is when a hydrogen atom is substituted for an alkyl group on a benzene ring.Called the Friedel crafts reaction
In alkylation, what does the alkyl group need to be attached to?
a halogen
Give an example of alkylation
a methyl group is substituted onto a benzene ring to make methyl benzene
For alkylation, the halogen in the catalyst has to be what?
the same as the halogen the alkyl group is attached to
Draw the mechanism for attaching a methyl group to benzene
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What is Acylation?
.This is when a hydrogen atom is substituted for an acyl chloride group on a benzene ring.Also called the Friedel crafts reaction
Draw the acyl chloride group?
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In an acylation reaction, Ethanoyl chloride reacts with benzene to make what?
phenylethanone
Draw the mechanism for benzene becoming phenylthanone
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What are phenols?
Phenols are a type of organic chemical containing a hydroxyl group (-OH) functional group directly bonded to an aromatic ring
The simplest member of the phenols is ?
Phenol
Draw phenol
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.Any compound that has an OH (hydroxyl) group bonded directly to a benzene ring is a what?
phenol
.If the compound doesn’t have a OH bond directly but still has an OH group it is classed as an ______, not a ______
alcohol, not a phenol
.Phenol is less soluble in water than alcohols, why?
due to its non-polar benzene ring
