AS Chemistry Unit 1

• Created by: Elena
• Created on: 29-04-14 14:49
Relative Molecular Mass, Mr
The average mass of a molecule on a scale where Carbon-12 is 12
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Relative Atomic Mass, Ar
The average mass of an atom of an element on a scale where Carbon-12 is 12
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Relative Isotopic Mass
The mass of an atom of an isotope on a scale where Carbon-12 is 12
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First Ionisation energy
Energy required to remove 1 mole of electrons from 1 mole of a gaseous atom to form 1 mole of gaseous +1 ions in standard conditions
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Isotope
Same number of protons, different number of neutrons, same chemical properties, different physical properties
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Accuracy
How close the results are to the true value
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Reliability
How replicable the results are
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Atom economy
How efficient the reaction is - Molar mass of desired product / molar mass of all products x 100
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Percentage yield
Tells you how wasteful the process is (how much product is lost) = Actual / Theoretical x 100
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Atom Economy of substitution and addition reactions
Addition = 100% as there is only one product, however substitution = lower atom economy as some atoms from one reactant are swapped with atoms from another reactant - results in at least 2 products (desired and by-product)
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Enthalpy Change
The heat energy transferred in a reaction at constand pressure. Kjmol-1
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Exothermic
Give out energy. -ve
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Endothermic
Absord energy. +ve
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Preparing a salt
Mix, leave to evaporate, filter, wash with distilled water and then dry
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Standard enthalpy change of reaction
Enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation, under standard conditions
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Standard enthalpy change of formation
The enthalpy change when one mole of a compound is formed from it's elements under standard conditions
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Standard enthalpy change of combustion
Enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
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Standard enthalpy change of neutralisation
Enthalpy change when 1 mole of water is formed from the neautralisation of hydrogen ions by hydroxide ions under standard conditions
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Standard enthalpy change of atomisation
Enthalpy change when 1 mole of gaseous atoms is formed from the element in it's standard state
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How to calculate enthalpy change
E(j) = m c /\T
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What kind of errors can occur in an experiment?
SYSTEMATIC- repeated every time experiment is carried out & always affects your results in the same way - due to experimental set-up, or limitations of the equipment. RANDOM ERRORS - no pattern to them, but they always happen! Reduced by repetition
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Hess's Law
The total enthalpy change is independent of the route taken
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What way do the arrows face in a combustion Hess cycle? up or down?
Down
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What way do the arrows face in a formation Hess cycle? up or down?
Up
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Bond dissociation enthalpy (bond enthalpy)
Amount of energy needed per mole to break bond. The smaller the bond enthalpy, the faster the reaction will be at room temp
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Mean bond enthalpy
The energy needed to break 1 mole of bonds in the gas phase, averaged over many different compounds. Always positive as bond breaking is endothermic. Add bond values and divide by the number of values
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The stages in Mass Spectrometry
1.Vapourisation 2.Ionisation 3.Acceleration (electric field) 4.Deflection (magnetic field) 5.Detection
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What is Mass Spectrometry used for?
Carbon dating, pharmacautical industry identifies compounds in possible drugs, testing athlete's urine for banned substances (steroids), probes to Mars to check for signs of life
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What shapes are the s and p orbitals?
s orbitals are spherical and p orbitals are dumbbell-shaped.
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How many orbitals do the s, p and d sub-shell have? And how many electrons can each sub-shell hold?
No. of orbitals: s has 1, p has 3 and d has 5. No. of electrons: s holds 2, p holds 6 and d holds 10.
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Factors affecting ionisation energy
1.Nuclear charge-the more protons there are in the nucleaus, the sronger the attraction. 2.Distance from nucleus-attraction lowers rapidly with distance. 3.Shielding- As no. of electrons between nucleus and outer electrons increases = less attraction
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First Ionisation Energy trends
Decreases down the group but increases across the period
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Second Ionisation Energy
Energy needed to remove 1 mole of electrons from 1 mole of gaseous 1+ ions to form 1 mole of gaseous +2 ions
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Successive Ionisation Energies
Increases because electrons are removed from an increasingly positive charge - less repulsion and held more strongly by nucleus. Big jump in ionisation energy happens when a shell is broken into - electron being removed from a shell closer to nucleus
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Decreases across a period - As no. of protons increases, +ve charge of nucleus increases so electrons pulled closer so atomic radius decreases.
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Trends in melting point - metals and simple molecular substances
Metals - melting point increases across period because metal-metal bonds get stronger. Simple molecular substances - melting point depends on strength of london forces between (weak & easily overcome) so these elements have low melting points
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What are compounds? And what are the 2 main types?
Atoms of different elements bonded together. Two main types: ionic and covalent.
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What is ionic bonding?
Then ions are stuck together by electrostatic attraction.
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What are anions, cations, anodes and cathodes?
Anion = -ve ion. Cation = +ve ion. Anode = +ve electrode. Cathode = -ve electrode.
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Ionic crystals
are Giant Lattices of ions - lattice is just a regualr structure and it's 'giant' because it's made up of the same repeated basic unit
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Evidence of ionic bonding from physical properties
High melting points = stronge attraction. Soluble in water but not in non-polar solvents = particles are charged (pulled apart by polar molecules). Don't conduct electricity when solid = fixed in position by strong ionic bonds
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Ions and atoms; which is bigger for metals and non-metals?
Metals - ion smaller than atom. Non-metals - atom is smaller than ion
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Evidence for existances of ions
1. Migration of ions on wet filter paper. 2. Electron density maps
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Born-Haber cycles
Show enthalpy changes when a solid ionic compound is formed from it's elements in their standard states.
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What are standard states?
298K, 100 kPa (1atm), 1.00 mol
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How to work out theoretical Lattice Energies
Based on the ionic model - Assume all ions are spherical and have their charge evenly distributed around them - purely ionic lattice. Then work out how strongly the ions are attracted to one another based on their charges & distance between them
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Why are small cations very polarising?
Small cations + large charge = high charge density- positive charge is concentrated in ion so cation can pull electrons towards itself. Large anions = polarised more easily than small anions because electrons are further from nucleus
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How to work out charge density
Charge / volume = how polarising a cation is (charge density)
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What are molecules?
Groups of atoms bonded together - Atoms can be the same or different. Molecules are held together by covalent bonds which are strong - 2 atoms share electrons so both have a full outer shell. +ve nuclei attracted electrostatically to shared electrons
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What do Electron density maps give evidence for?
Covalent bonding - Area of high electron density between 2 atoms which shows they're sharing electrons.
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Sigma and Pi bonds
2 s orbitals overlap in a straight line to form a sigma bond (single covalent bond) Pi bond is formed when 2 p orbitals overalp - one above and below nuclear axis = less tightly bound so they're weaker than sigma bonds. pi bonds = more reactive
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Dative covalent bonding (coordinate)
Where both electrons come from one atom (ammonium ion, NH4+)
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How does evidence for covalent bonding come from giant structures?
All insoluble in polar solvents (water) = don't contain ions. Form hard crystals with high melting points = very stronge covalent bonds. Don't conduct electricity = bonding electrons used to form covalent bonds and contain no charged particles
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Metallic bonding
Outermost shell of electrons is delocalised (free to move) - leaves +ve metal ion which is attracted to delocalised -ve electrons - Form a lattice of closely packed +ve ions in a sea of delocalised electrons
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How does metallic bonding explain properties of metals?
Delocalised electrons can pass kinetic energy = good thermal conductor. Electrons can carry current = good electrical conductors. Insoluble = strength of metallic bonds. No bonds holding ions together - slide over each other = malleable and ductile
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General formula
An algebraic formula that can describe any member of a family of compounds
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Empirical formula
Simplest ratio of atoms of each element in a compound (cancel numbers down if possible)
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Molecular formula
Actual number of atoms of each element in a molecule, with any functional group indicated
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Structural formula
Shows atoms carbon by carbon, with the attached hydrogens and functional groups
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Displayed formula
Shows how all atoms are arranged, and all bonds between them
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Skeletal formula
Shows bonds of carbon skeleton only, with any functional group. H and C atoms aren't shown.
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Nomenclature
Naming organic compounds
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Homologous compounds
Same general formulas - same functional group but differs by -CH2- in it's carbon chain. E.g Methanol, Ethanol, Propanol, Butanol...etc.
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Prefix or Suffix of alkanes, branched alkanes, alkenes, halogenalkanes, alcohols
Alkanes = -ane. Branced alkanes = alkyl-. Alkenes = -ene. Halogenalkanes = chloro-/bromo-/iodo-. Alcohols = -ol.
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Alkanes
Saturated hydrocarbons. CnH2n+2. Every carbon has 4 single bonds. Cycloalkanes - a ring of carbon atoms with 2 H attached to each - CnH2n = still saturated
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Structural isomers
Different arrangements of the same atoms - atoms connected in different ways. Same molecular formula. Chain isomers: some are straight and some are branched chains = diff carbon skeleton
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Burning alkanes
Burn completely in oxygen - Give Carbon Dioxide and Water. Combustion happens between gases so liquid alkanes vapourised first - burn more easily.
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Free-radical substituion - Alkanes + Halogens --> halogenalkanes
H atom is substituted by chlorine or bromine in photochemical reaction (started by UV radiation). Free-radical substitution reaction.
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1. Initiation - free radicals produced. 2.Propogation - Free radicals used up and created in chain reaction. 3.Termination - Free radicals mopped up (got rid of)
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Fractional distillation
Separates crude oil into more useful fractions. Crude oil vaporised - into fractionating column and rises up through trays (largest hydrocarbons don't vaporise at all). Vapour gets cooler and condenses at diff temps (diff chain lengths).
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Cracking
Light fractions are in demand so heavier fractions can be 'cracked' (breaking long-chain alkanes into smaller hydrocarbons - involves breaking c-c bond). Two types: thermal and catalytic
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Thermal Cracking
High temp & high pressure. Produces a lot of alkenes which are used to make valuable products such as poly(ethene)
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Catalytic Cracking
Makes mostly motor fuels and aromatic hydrocarbons. Uses a zeolite catalyst at a slight pressure and high temp - cuts costs because lower temp and pressure. Catalyst also speeds reaction up = time is money
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Uses of alkanes
Methane used in central heating & cooking in homes, alkanes with 5-12 carbon atoms used in petrol, kerosene used in jet fuel and Diesel is made of a mixture of alkanes with 15-19 carbon atoms
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What harmful emissions does buring fossil fuels cause?
sulfur oxides from power stations, carbon monoxide and hydrocarbon particles from incomplete combustion and nitrogen oxides from vehicle engines
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Greenhouse gases
Keep planet warm enough to support life by absorbing infra-red radiation and then re-emitting some of it towards Earth. e.g CO2, water vapour, methane.
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Global warming and climate change
Too much greenhouse effect = global warming. CO2 from burning fossil fuels which enhances greenhouse effect causing earth to warm up = polar ice caps melt, sea levels rise, floods and food shortages due to climate change
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Alkenes
Unsaturated hydrocarbons, CnH2n, all have at least 1 C=C bond. More reactive than alkanes due to Pi bond
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Alkene + hydrogen --> Alkane
Ethene reacts with H to produce ethane - needs nickel catalyst and 150 temp
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Double bond opens up and another atom is added to each carbon. Double bond has plenty of electrons so is attacked by electrophiles and double bond is nucleophilic so attracted to places with not enough electrons.e.g alkene + bromine --> dibromoalkane
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Electrophiles
electron-pair acceptors - attracted to areas with lots of electrons. E.g positively charged ions and polar molecules
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Risk Assessment
Help to make lab work safer. Looks at hazards of all reactants, products and procedures& consider how to makes risks as small as possible
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Hazard
Anything that could cause harm
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Risk
The chance that what you're doing will cause harm
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Using bromine water
Tests for double C=C bonds. Orange --> colourless.
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What oxidises alkenes?
Acidified potassium manganate (VII). Purple --> decolourised (makes a diol) = another test for a double bond
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What causes E/Z isomerism?
The restricted rotation around the C=C double bond
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E-isomer/Trans
When the same groups are across the double bond, above and below the carbons
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Z-isomer/Cis
On Z same side - When the same groups are both above or both below the double bond
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When alkenes join up, what do they form?
Addition polymers - Double bonds in alkenes open and join together to make long chains (polymers) - unreactive (lost double bond). small alkanes are monomers
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Burying of plastics
Not biodegradable - bury it = landfill site, compact it and then bury it.
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Problems with a landfill site
Amount of waste we generate is becoming more and more of a problem -need to reduce landfill as much as possible
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Recycling of plastics
Plastics made from finite resourse (crude oil) - have to be sorted into different types first - some plastics can be melted and remoulded, some can be cracked into monomers
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Burning of plastics
Plastics burnt to be used to generate electricity - carefully controlled to reduce toxic gases - waste gases passed through scrubbers (neutralise gases) to allow them to react with a base
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Decompose quickly in right conditions - organisms can digest them - made from materials such as starch - produced from renewable raw materials or from oil fractions.
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Advantages of using renewable raw meterials
Raw materials aren't going to run out like oil will. CO2 is produced when polymers biodegrad. Some plant-based polymers save energy
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Other cards in this set

Card 2

Front

Relative Atomic Mass, Ar

Back

The average mass of an atom of an element on a scale where Carbon-12 is 12

Card 3

Front

Relative Isotopic Mass

Card 4

Front

First Ionisation energy

Isotope