Chem Flashcards
Definitions of relative isotopic mass
Relative atomic mass
Relative molecular mass
Relative istopic mass: is the mass of one ISOTOPE compared to one twelfth of the mass of one carbon atoms of carbon-12
Relative atomic mass:is weighted mean mass of one ATOM compared to 1/12th of the mass of one atoms carbon 12
Relative molecular mass:is the AVERAGE mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
Hydrated salt- practical
Weigh and empty clean dry crucible and lid.Add 2g of hydrated salt .Heat strongly with Bunsen burner.Let it cool and weigh again.reheat and re weigh.
Making A Solution
Ideal gas equation
PV=nRT
Pascal
M3
Mol
8.31 for R
Temperature +273 from C* to K
Avogradros constant
6.02 * 10^23
No of particles=moles * avogradore
Other formulas
Density
Percentage yield
Atom economy
Density= mass/ volume
Percentage yield= actual yield /theoretical yield *100
Atom economy=mass of useful products/mass of all reactant *100
Acids and Bases
Acids release H+ ions in aqueous solutions e.g. HCl,H2SO4,HNO3, CH3COOH
Bases neutral is acids.Alkalis are soluble bases and release OH- ions. NaOH,KOH,NH3 aq
REDOX
Oxidation is the process of electron loss
Oxidation number increases
Reduction is electron gain
Oxidation number decreases
Oxidation numbers
H 1
F -1
Cl,Br,I -1
O -2
Reactions of acid with metal
Acid + metal——> salt + H2
Sub energy levels
S holds 2 spherical
P holds 6 dumbbells
D holds 10
F holds 14
What are some exceptions to the rules of sub shells
4s fills up before 3d
The elements Cr and Cu are exceptions to the rule.
Each electron occupies one orbital before pairing to prevent repulsion between each other.
Ionic bonding
Ionic bonding is the electrostatic force of attraction between oppositely charged ions formed by electron transfer.Its stringer and have higher melting points when the ions are smaller/ have higher charges, e,g,MgO Mg+2 O-2.These form giant ionic lattices
High m.p
Non conductor of electricity when solid- only when molten or in solution
Usually soluble
Covalent Bonding
Covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Dative covalent bond is when the shared pair comes from only one of the bonding atoms.
Structure:simple molecular (only used the words molecules and intermolecular forces when taking about simple molecular substances)
Comparison giant ionic and molecular
Giant ionic has high b.p and m.p. Due to strong forces
Molecular has low due to weak i.m. Forces
Giant ionic are usually soluble
Molecular usually poorly soluble
Conductivity is poor for molecular
General description:Gina ionic and crystalline solids
Molecular are mostly gases & liquids
Shapes of molecules
Linear : 2 bonding 180*
Trigunal planar:3 bonding 120*
Tetrahedral: 4 bonding 109.5
Trigunal pyramidal 3 bonding 1 lone 107*
Non-linear 2 bonding 2 lone 104.5
octahedral 6 bonding 90*
Electronegativity
Electronegativity is the relative tendency of an atom in a covalent bond in a molecule to attract electrons in a covalent bond to itself.
Factors:increases across as proton no. Increases and atomic radius increases as the electrons are pulled in more
It decreases down a group because distance between the nucleus and outer electron increases and the shielding increases
Dipole
Polar covalent bonds have unequal distribution of electron and produces a charge separation (dipole) ends. S+ and S-
Intermolecular bonding
Induced dipole-dipole interactions:All molecular substances (not in ionic).In any molecule the electrons are moving randomly and constantly this causes electron density to fluctuate adn parts of the molecule becomes more or less negative .These temporary dipoles induces dipoles in neighbouring molecules,called induced dipoles.The more electrons,the stronger.
Permanent dipole-dipole:polar molecules,stronger,higher b.p.,they occur in addition to London forces.
Hydrogen bonding
Occurs between hydrogen attached to nitrogen,oxygen or fluorine, with a lone pair.
Ice:when in solid state molecules are held further apart which explains lower density.
Iodine:crystal contains regular arrangement of weak London forces. I2
Periodicity
Is a repeating pattern across different period
First Ionisation Energy
Is energy needed to remove an electron from each atom in one mole of gaseous atoms
H(g)——> H+(g) + e-
Factors affecting:
Attraction of the nucleus,the more protons the more attraction
The distance of electrons from nucleus:the bigger atom,the further ,the weaker the attraction
Shielding :outer electrons are repelled by inner electrons
Pattern of period 2 elements
He has highest f.i.e, shell closest to nucleus,no shielding,has one more proton than H.
F.i.e decrease down a group bcs outer electron around in shells further from nucleus and more shielding
F.i.e increases across a period same shielding effect,electron are added proton increases decreasing atomic radii.
Anomalies in period 2&3 f.i.e
Na has lower f.i.e than Neon because Na is more shielded ,electron easier to remove.
Small drop between Mg and Al because Al is starting to fill up 3p whereas Mg has full 3s?Ekectrons in 3p are slightly easier to remove because 3p electron are higher in energy and shielded .
Small drop from P to S.Sulphur has 4 electron in 3p and 4th electron is starting to pair.When the second electron is added to a 3p orbital there is a slight repulsion between which makes the second electron easier to remove.
Metallic bonding
Is the electrostatic force of attraction between the positive metal ions and the delocalised electrons
Giant metallic lattice ,Li,Be ,Na,Mg,Al
Factors:
Number of protons,the more protons in the stronger
Number of electron per atom,the more the stronger
The smaller the ion the stronger
Macromolecules
Diamond:tetrahedral 4 atoms in covalent bonds
Graphite:planar of C atoms 3 covalent bonds,4th electron delocalised.
B,C ,Si
They have very high melting points
Comparison macromolecules & metallic
High b.p and m.p
Both insoluble in water
Conductivity: poor for diamond,good for graphite.
Good for metallic
Conductivity when molten:poor for macromolecules
General description:solids for macromolecules
Shiny metal,malleable slide over easily for metallic
Group 2
Meltin point decreases as you go down,atomic size increases,ion further away from electron.
Reactivity increases down the group.Atomic radii increased,more shielding,nuclear attraction decreases easier to remove electrons.
MgO is a white solid.MgO will react slowly without a flame.
Reactions of Group 2
Water:mg reacts with steam to MgO or with warm water to Mg(OH)2 .Others reacts with cold water to produce hydroxides+H2
You would observe fizzing,metal dissolving ,heating up,calcium forms white precipitate
Acid:forms salt and hydrogen
Action of water on metal 2 oxides
CaO+H2O——->Ca(OH)2 (aq7 pH 12 bcs it’s quite soluble
It’s also used in agriculture to neutralise soils.If excess soil too alkaline.Aquoues CaOH can be used to test for CO2
MgO+H2O——>Mg(OH)2 (s) pH9 bcs mgOH is slightly soluble.Used in medicine to neutralised excess acid in stomach and treat constipation.Helps with indigestion.Safe to use as its weakly alkaline
Halogens-diatomic
F2-pale yellow gas,very reactive
Cl2-greenish reactive gas,poisonous
Br2-red liquid,gives brown poisonous fumes
I2-shiny grey solids sublimes to purple gas
Higher m.p and b.p as you go down,larger molecules,more electrons,stronger London forces.
A halogen more reactive will displace the less reactive.
Reactivity decreases down as atoms get bigger more shielding so they less attract and accept electrons .
Learn the table for chlorine ,bromine and iodine
Disproportionation
Is the name for a reaction where an element simultaneously oxidises and reduces.
Cl2(g)+H2O——>HClO(aq) +HCl (aq)
Chlorine is used in water treatment to kill bacteria.
Cl2 and cold dilute NaOH .Colour of halogen fades to colourless.NaCl and NaClO is used as bleach and disinfect bacteria
Halide ions and AgNo3 silver nitrate
Add nitric acid (to react with any carbonates present )first and then AgNO3 drop wise .
F does not produce precipitate
Cl white. Br cream. I pale yellow precipitate
Silver chloride dissolves in dilute ammonia
Silver bromide dissolves in con. Ammonia
Silver iodide does not react
Qualitative Analysis
Presence of CO3 carbonate- add dilute acid .Bubble gas through lime water,will turn cloudy.
Presence of SO4 sulfate-acidified (reacts with CO3 impurities that would give false results)BaCl2 solution used as reagent .If +ve white precipitate form.
Sequence is carbonate,sulfate then halife (false positives due to BaCO3 or Ag2SO4)
Ammonium ion NH4+: react with warm NaOH (aq) forming NH3 gas,this will turn red litmus paper blue
Exothermic & endothermic
Exothermic:Energy is transferred from system (chemicals) to surrounding.Products have less energy. change in H is negative
Endothermic:energy transferred from surrounding to chemical.Require an input of energy.H is positive
Activation energy
Minimum energy which particles need to collide to start a reaction
Standard conditions
100 kP
298 K
Solutions at 1 mol dm3
Normal state at room temp.
Enthalpy change of reaction
Is the Enthalpy change that accompanies a reaction in the molar quantities shown in a chemical reaction under standard conditions,with all reactants and products in their standard states.
Triangle Hr central line
Enthalpy change of formation
Enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions,with all reactants and products in their standard states
Enthalpy change of combustion
The Enthalpy change that takes place when one mole of a substance is reacted completely with oxygen under standard conditions with all reactants and products in their standards states
Enthalpy change of neutralisation
Triangle neut H central line
The Enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2P (l) under standards conditions with all reactants and products in their standard states.
Calometry formula
Energy change Q (J) = mass of solution m (g) * heat capacity c (J per g per K) * temperature change T (K)
Calometric method
Errors in calometric method
Energy losses from calorimeter
Incomplete combustion of fuel
Incomplete transfer of energy
Evaporation of fuel after weighing
Heat capacity of calorimeter not included
Measurements not carried out under standard conditions H20 is gas not liquid in here
Average bond Enthalpy
The mean bond Enthalpy us the Enthalpy change when one mole of bonds of us broken.
Bond breaking absorber energy
Bond making releases energy
Collision theory
Reactions can only occur when collisions take place between particles having sufficient energy.
At higher concentration ,there are more particles so frequency of collisions increases.
Reaction rate definition and how to find it
Change in concentration of a substance in unit time. Mole dm3 per seconds.Sodium thiosukftae and HCl see how long it takes for cross to disappear .1/time plot graph.
Catalysts
Increases reaction rates without getting used up.They provide an alternative route or mechanism with a lower a.e.
A heterogeneous is in a different phase from reactants.usually solids
A homogeneous catalyst is in the same phase as reactants.reactions proceeds through intermediate species
Benefits of Catalysts
Lower temp. And pressures ,save energy costs ,fewer CO2 emissions.
Better atom economy with reduced waste,fewer undesired products .
They are often enzymes
Investigate rates of reaction
Change in volume of a gas using gas syringe
Change in mass if gas is involved
Colorimetry if there is a change in colour
Dynamic equilibrium
This occurs when forward and backward reactions are occurring at equal rates in a closed system and the concentration of reactants and products do not change.
Effect of increasing temperature in equilibrium
If temperature increased (decreased) the equilibrium will shift to oppose this and move in the endothermic (exotgermic) direction to reduce (increases)temperature by absorbing heat.
The position of the equilibrium will shift to the …
Giving a lower yield of …..
Effect of pressure in equilibrium
Increasing (decreasing) pressure will cause the equilibrium to shift towards the side either fewer (more)moles of gas to oppose the change and thereby reduce (increase) the pressure .
Position will shift to …
Giving higher/less yield of…
Effect of concentration on equilibrium
I2 + 2OH- <———->I- + IO- + H2O (colourless)
(Brown)
Increasing concentration of OH- ions causes the equilibrium to shift to oppose this and move in the forward direction to remove OH- ions.The position of equilibrium will shift toward the right giving higher yields of I- and OH-.
Adding H+ ions reacts with the OH- ions and reduces their concentration so the equilibrium shifts back to the left giving brown colour.
Uses of equilibrium : Haber process
N2 +3H2 ————> 2NH3
T=450 P=200-1000 atm catalyst=iron
Low temp. Gives good yield but slow rate.high pressure give good yield and good rate.
Uses of equilibrium: contact process
1- S (s) + O2 (g) ————>SO2 (g)
2- SO2 (g) +1/2 O2 (g) <————>SO3
T=450. P=1 to 2 atm. Catalyst =V2O5
Low temp. Compromise moderate temperature used.
Equilibrium: Productions of methanol from CO
CO (g) +2H2 (g) <————>CH3OH (g)
T=400 P=50 atm catalyst=chromium and zinc oxide
Compromise temp. Used
Hydration of ethane to produce ethanol
CH2=CH2 +H2. <—————> CH3CH2OH
T=300 P=70. Catalyst=concentrated H3PO4
Too high pressure would lead to unwanted polymerisation of ethene to poly (ethene)
Equilibrium constant Kc
Kc= C^c * D^d / A^a * B^b
Use concentration
No units
Kc only changes with temperature.
The greenhouse effect-IR
CO2 ,methane,water vapour are greenhouse gases that trap earths radiated infra red energy.infrared radiation is absorbed by c=o,c-h and o-h bonds which contributes to global warming.
IR can be used to monitor gases causing air pollution.Modern breathalysers measure ethanol using infrared spectroscopy l
CFC
Used as aerosols,refrigerants and air conditioning.Has been replaced with HFCs
Ozone layer O3
Filters suns harmful UV radiation.
Ozone formation O2 + UV light > O+O
O+O2>O3
Ozone depletion O3 +Uv>O2 +O
Destruction of Ozone layer
Chlorine free radical catalyse decomposition
Cl+O3>ClO +O2
ClO+O>O2 +Cl*
Basically O3+O*>2O2
Nitrogen oxide
NO+O3>NO2+O2
NO2+O*>O2+NO
overall equation
O3+O*>2O2
