OCR AS Chemistry
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- Created on: 09-10-18 18:15
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- OCR AS Chemistry
- 1- Atoms and Moles
- Made up of 3 sub-atomic particles: PROTON (+1) NEUTRON (0) ELECTRON (-1)
- RAM - Average mass of an atom on a scale where 1/12th of Carbon-12 is exactly 12
- Relative Isotopic Mass - Average mass of an atom of an isotope compared to 1/12th of the mass of Carbon-12
- Relative Molecular Mass - Average mass of a molecule compared to 1/12th of the mass of Carbon-12
- Relative Formula Mass - Average mass of a formula unit compared to 1/12th of the mass of Carbon-12
- The Mole - unit used to measure number of particles in a sample - uses Avagadro's Constant - 6.022x10^23
- Used to calculate mass, Mr, number of particles present, volume of solutions, volume of gases and concentrations
- No. of particles present / Avagadro's = MOLES
- Mass / Mr = MOLES
- Vol. (aq/l) x Conc. = MOLES
- Vol. (g) / 24 (dm^3) = MOLES
- Gas Volume can also be Calculated using the IDEAL GAS EQUATION
- pV=nRT
- Gas Volume can also be Calculated using the IDEAL GAS EQUATION
- Used to calculate mass, Mr, number of particles present, volume of solutions, volume of gases and concentrations
- 2- Formulas and Equations
- There are two types of formulae in chemistry - EMIPIRICAL and MOLECULAR
- EMPIRICAL - smallest whole number ratio of atoms of each element in a compound
- MOLECULAR - actual number of atoms of elements in a compound
- Equations must be balanced
- IONIC EQUATIONS - reactions involving ions in solution - only reacting particles included i.e. H+ + OH- -> H2O
- Calculations - use MOLES equations depending on info provided
- There are two types of formulae in chemistry - EMIPIRICAL and MOLECULAR
- 3- Reactions and Calculations
- Acids, Bases and Salts
- ACID - proton donor -releases H+ ions when mixed with water i.e. HCl
- Strong Vs Weak - Strong Acid/Base FULLY dissociates in water - Weak PARTIALLY dissociates in water
- SALT - product of neutralisation reaction
- Neutralisation can occur in many ways
- Metal + Acid => Salt + Hydrogen
- Metal Oxide + Acid => Salt + Water
- Acid + Metal Hydroxide => Salt + Water
- Metal Carbonate + Acid => Salt + Carbon Dioxide + Water
- Acid + Base => Salt + Water
- Hydrated and Anhydrous - Hydrated = contains water of crystallisation - Anhydrous = doesn't contain water of crystallisation
- Calculating formula of Hydrated Salts - 1) mass of anhydrous - mass of hydrated 2) Find moles of water lost 3) Calculate number of moles of anhydrous produced 4) work out ratio of moles of anhydrous to moles of water
- Neutralisation can occur in many ways
- Titrations - allow us to see how much acid is needed in order to neutralise an alkali
- Indicators used in order to identify end point and point of neutralisation
- i.e. methyl orange, phenolphthalei-n
- Precision - mass - reset balance + make sure all solid is transferred solution - volumetric flasks and pipette
- Standard Solutions - solution that has a precisely known concentration - known amount of solid dissolved in known amount of water to create known concentration
- Indicators used in order to identify end point and point of neutralisation
- BASES - proton acceptor - remove H+ ions and release OH- ions i.e. NaOH - soluble bases = alkalis
- Concentrated Vs Dilute - Concentrated Acid/Base has more H+/OH- ions - Diluted has less H+/OH- ions
- ACID - proton donor -releases H+ ions when mixed with water i.e. HCl
- Strong Vs Weak - Strong Acid/Base FULLY dissociates in water - Weak PARTIALLY dissociates in water
- ACID - proton donor -releases H+ ions when mixed with water i.e. HCl
- Concentrated Vs Dilute - Concentrated Acid/Base has more H+/OH- ions - Diluted has less H+/OH- ions
- ACID - proton donor -releases H+ ions when mixed with water i.e. HCl
- actual yield / theoretical yield x 100 = % yield
- theoretical yield = mass/Mr to find moles and then multiply moles by molar mass
- Atom economy - mass of desired (Mr)/mass of reactants (Mr)
- Oxidation Numbers
- Shows total number of electrons an element has accepted or donated
- Uncombined = 0 - Simple ions = same as charge Molecular ions = overall charge = overall oxidation number Neutral compound = 0 H = +1 F = -1
- Redox = gain in electrons - reducing agent donates electrons and gets oxidised
- Oxidation no. will increase by 1 for every electron lost and it will decrease by 1 for every electron gained
- Redox = gain in electrons - reducing agent donates electrons and gets oxidised
- Uncombined = 0 - Simple ions = same as charge Molecular ions = overall charge = overall oxidation number Neutral compound = 0 H = +1 F = -1
- Shows total number of electrons an element has accepted or donated
- Acids, Bases and Salts
- 4- Electrons, Bonding and Structure
- Bonding
- Ionic
- Electrostatic forces of attraction between positive and negative ions
- Conduct electricity when molten or in solution - ions carry charge and are free to flow when in liquid form
- High MP and BP due to large amount of energy needed to overcome electrostatic forces of attraction
- Soluble in water due to polar water molecules being able to separate ions
- Covalent Bonding
- Shared pair of electrons between 2 atoms
- Dative covalent bonding - one atoms provides both of the shared electrons
- Strength - depends on AVERAGE BOND ENTHALPY - energy required to break a covalent bond
- Shapes of Molecules
- Electron Repulsion Theory - lone pairs repel more than bonding pairs
- Linear - 180 2 bonds - CO2 Trigonal planar - 120 3 bonds - BF3 Tetrahedral 109.5 4 bonds - NH4 Trigonal pyramidal - 107 3 bonds - NH3 Non-linear - 104.5 2 bonds - H2O Trigonal Bipyramidal - 120, 90 5 bonds - PCl5 Octahedral - 90 6 bonds - SF6
- Polarisation
- Electronegativi-ty - ability of and tom to attract bonding electrons in covalent bond
- Polar Bonds - bonding electrons pulled towards more electrone-gative atom
- In a polar bond, difference in electronegativi-ty causes a permanent dipole which is the difference in charge between 2 atoms caused by shift in electron density in the bond
- Polar molecules have an overall dipole - arrangement of polar bonds determines whether it will have an overall dipole or not
- In a polar bond, difference in electronegativi-ty causes a permanent dipole which is the difference in charge between 2 atoms caused by shift in electron density in the bond
- Non Polar Bonds - atoms have equal electronegativi-ty
- Ionic
- Electrons - Subatomic particles with -1 charge
- Has sub-shells - s, p, d, f - can be used to identify certain elements i.e. s-block elements = alkali metals
- Intermolecular forces
- Forces between molecules - weaker than covalent, ionic or metallic
- Induced dipole interactions - cause all atoms to be attracted to eachother - they are temporary - they are constantly being created and destroyed due to constantly moving electrons
- Permanent dipole interactions - cause weak electrostatic forces of attraction between molecules - happen in addition to induced
- Hydrogen bonding - only happens when H is covalently bonded to O,N or F - molecules with H bonding usually have OH or NH groups
- Forces between molecules - weaker than covalent, ionic or metallic
- Bonding
- 5- The Periodic Table
- Modern Periodic table goes up in atomic mass (no. of protons)
- 1st ionisation energy
- The energy needed to remove 1 mole of electrons from one mole of gaseous atoms
- Nuclear charge, atomic radius and shielding affect ionisation energy
- Metals
- Metallic bonding - cations in a sea of delocalised electrons
- Allows metals to have high MP and BP due to more energy being required to over come bonds - they are also malleable and ductile due to the same size atoms sliding over each other - electrons carry current which allows them to conduct electricity - insoluble except for liquid metals
- Group 2 Alkali Metal - down group, they react more due to shielding and radius (ionisation energy decreases) - used for neutralisation i.e. Ca(OH)2 or as antacids
- Metallic bonding - cations in a sea of delocalised electrons
- Halogens - they form group 7
- Boiling point down group increases due to increased strength of induced dipole interactions
- Displacement reactions occur - more reactive at top of group
- Testing for ions
- CO3 + acid = bubbles
- SO4+Ba(NO3)2 = white precipitate
- Halide + AgNO3 = precipitate
- NH4+/NH3 = red litmus turns blue
- 6- Physical Chemistry
- Enthalpy
- Heat transferred in a reaction in standard conditions with all substances in standard states
- Types include: reaction, formation, combustion and neutralisation
- q=mc(delta)T
- Hess's Law
- Reaction's enthalpy change is the same regardless of the route taken
- Rate
- Maxwell-Boltzmann
- Temp. = particles have higher KE = more frequent and successful collisions = higher rate
- Conc. = more particles = more frequent and successful collisions = higher rate
- Catalysts - HOMO (same state) HETERO (different state) not used up themselves
- Reduce costs - increase rate due to lower Ea
- Enthalpy
- 7- Basic Organic Concepts and Hydrocarbons
- Alkanes - branched or unbranched - un have lower BP/MP - no double bond
- Substitution reactions - initiation, propagation and termination
- Free radicals involved - OZONE
- Substitution reactions - initiation, propagation and termination
- Combustion - incomplete and complete
- CO poisoning
- Alkenes - double bond (unsaturated)
- E/Z and cis and trans are stereoisomers
- Electrophilic addition
- Curly arrow mechanism with ELECTROPHI-LE i.e. Br
- Forms haloalkane
- Electrophilic addition
- Can be used to make polymers
- Reactions of alkenes
- Hydrated, 300C and H3PO4 catalyst that is solid
- Add bromine water to test for saturation - decolourises if is alkene
- Markownikoff's rule - more stable carbocations form i.e. + charge is on 2nd C in propene
- E/Z and cis and trans are stereoisomers
- Alkanes - branched or unbranched - un have lower BP/MP - no double bond
- 8- Alcohols and Haloalkanes
- Alcohols
- General formula is CnH2n+1OH
- Polar due to electronegativ-e OH - alcohol + water = HYDROGEN BONDS FORM
- Undergo substitution reactions to form haloalkanes - requires H2SO4 as catalyst
- Undergo nucleophilic substitution which results in the halogen being substituted in the molecule
- Curly arrow mechanism
- Undergo elimination reactions - water is eliminated = alkene
- Undergo nucleophilic substitution which results in the halogen being substituted in the molecule
- OXIDATION - P = aldehydes by distillation using H2SO4 and K2Cr2O7 and then carboxylic acids by reflux
- S = ketones only using acidified dichromate
- Undergo substitution reactions to form haloalkanes - requires H2SO4 as catalyst
- Polar due to electronegativ-e OH - alcohol + water = HYDROGEN BONDS FORM
- They can be Primary, Secondary or Tertiary
- P - OH attached to C that is attached to 1 other C
- S - OH attached to C that is attached to 2 other C
- T - OH attached to C that is attached to 3 other C
- General formula is CnH2n+1OH
- Haloalkanes
- Alkane with at least one halogen group
- CFCs - C, F and Cl only - Cl radicals break down ozone layer in free radical substitution
- C-halogen bond is polar due to electronegativ-e nature of halogens
- Can be identified by using AgNO3
- Undergo nucleophilic substitution which results in the halogen being substituted in the molecule
- Curly arrow mechanism
- Hydrolysis - hydrolysed by warm aqueous alkali NaOH or water in nucleophilic substitution reaction
- Alkane with at least one halogen group
- Alcohols
- 9- Organic Synthesis and Analysis
- IR Spectroscopy
- IR absorbed by organic molecules' covalent bonds resulting in vibration - different bonds vibrate more or less - wavenumber is used
- Can be applied in numerous ways i.e. breathalysers or pollutant monitors
- Mass Spectrometry
- Mr and empirical formulae can be found with this info from M+ ion peak
- IR Spectroscopy
- 1- Atoms and Moles
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