full custy notes Flashcards
definition of a standard solution
a standard solution is one of known concentration
how can a standard solution can be prepared
accurately weigh out the mass of a solute by weighing by difference, transfer the solute into a beaker and add deionised water.
to dissolve the solute.
then pour the mixture into a standard flask , using a funnel
then rinse the beaker and funnel with deionised water, using a pipette make the solution up to the graduation mark with deionised water, then invert the flask several times
characteristics of a primary solution
extremely high purity
examples of suitable primary standards
sodium carbonare
sodium chloride
draw a calculation graph
absorbance at side and concentration at the bottom
what is atomic emission
atomic emission absorption are used to identify and quantify elements present in a sample. this is done by exciting electrons and producing absorption/emission
what is empirical formula
empirical formula is the simplest ratio of atoms in a compound
what is equilibrium constant
the equilibrium constant has the symbol k, (k has no units). the general equation for k is
aA + bB ->
difference between homogeneous equilibrium and a heterogeneous mixture
homogeneous equi: all species in equation are same state
heterogeneous equi: species in equation are different states
how do you write an expression for k when it is a heterogeneous equilibrium
when writing an expression for k in a heterogenous equilibrium, pure solids and liquids are emitted as their concentration is taken as constant and given value 1
what does the value of k tell us about the position of equilibrium
if k=1 neither products/reactants are favoured k>1 => products are favoured, k<1 => reactants are favoured
what effect does pressure have on k
this will change equilibrium position, the value of k does not change
what effect does a catalyst have on k
not change equilibrium position. value of k does not change
what effect does temp have on k
- if endothermic, an increase in temp products, and product/ reactant ratio increases. therefore k increases
- if exothermic, increase in temperature favours reactants and so ratio product/reactant decreases. therefore k decreases
what effect does concentration have on k
it will change equilibrium position, however value of k does not change
equation for parts per million
ppm=grams of solution x 1,000,000
what is 1ppm equal to
1ppm=1mgkg-1.
1ppm=1mgl-1
be able to draw skeletal formulas
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rough procedure for a back titration
a back titration allows the concentration of an unknown solution to be determined by reacting it with a known excess of a reagent. the quantity of the excess reagent is determined by titration of/with a second reagent
why is a back titration carried out
a back titration is used for substances that are not a primary standard, therefore a standard solution cannot be prepared
what is the formula for calculating dilution factor
df= final volume/initial volume
what is the procedure for diluting a solution
calculate the dilution factor, the initial volume required and final volume. then add using a pipette, the required volume of solution to a standard flask of required volume. then make the solution up to the graduation mark by using deionised water and a pipette.
what are drugs - medicines
drugs are designed as substances that can alter the biochemical processes in the body medicines are those drugs that have a beneficial effect
different classifications of medicines
most medicines can be defined as agonist or antagonist according to the response they trigger when bound to a receptor
what’s an agonist
an agonist mimics the natural compound and binds to the receptor molecule to produce a response similar to the natural active compound
what’s an antagonist
an antagonist prevents the natural compound from binding to the receptor, and blocks the natural response from occurring
what is the section of a drug that binds to a protein receptor
the section of a molecule that binds to a protein receptor is called the pharmacophore
what are amines
amines are nitrogen containing organic compounds derived from ammonia in which one or more hydrogen atoms have been replaced by alkyl groups
typical shape of amines
pyramidal shape, because a lone pair in place of bonding pair, which exerts a stronger force, bond angle is 107 degrees between
how are they classified
- primary amines have one r group attached to nitrogen atom
- secondary amines have two r groups attached to nitrogen atoms
- tertiary amines have 3 r groups attached to nitrogen atom
rules for naming amines
practice some
what is the skeletal structure for phenyl group
draw
what do amines react with
primary and secondary amines contain polar n-h bond. so have H bonding between molecule. no such bond occurs in tertiary because no H bond directly with nitrogen. p + s have high bp whereas tertiary has lower bp
- amines with lower mass are soluble in water because they can form H bonds (including tertiary)
general structure of ethers
structure`; r-o-r, where r is alkyl group. an ether can be regarded as an alkane with an alkoxy group attached
rules for naming ethers
congest carbon chain gives parent name. ‘oxy’ also used instead.
physical properties of ethers
low bp because no h bonds. they can join h bond with water molecules, ie soluble in water
ethers are volatile and highly flammable
they are used as solvents. being volatile there solvents are removed by distillation
what is ems
electromagnetic radiation includes x rays and tv signals, different types of ems make up the ems
what produces ems waves
waves are produced by electrically charged particles
what are photons
electromagnetic radiation can be absorbed, when this occurs electromagnetic radiation behaves more like a stream of particles than as a wave. these particles caked photons. therefore say that electromagnetic raduatuin has a dual nature; wave motion and streams of photons
fromula to calc energy of 1 photon
e=hf
what is atomic process that produces atomic emission spectrum
when an atom gains energy it gets promoted to a higher energy level. When the excited electron drops back down to the lower energy level a photon is emitted.
Definition of transition metal
A transition metal has a partially filled d-sub shell in at least one of its valencies, ie when it is an ion
Why are zn and sc not considered a transition metal
Sc has an empty 3D orbital so doesn’t fit the tm definition
Zn has a full d orbital so doesn’t fit the tm definition
Electron configuration within a trans metal
(Fe) => [AR] 4s3 3d6.
As there is special stability, associated with half-filled/ completed filled d orbitals when transition metals atoms form ions electrons form the 4s orbitals are lost first
Oxidation state of a transition metal
Ox state is a change on an ion. TM’s show variable valency. Ie ionisable oxidation states/numbers
The preferred ox state depends on the stability of the ion
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Why is Fe3+ the preferred ox state of iron
Fe3+ is the most stable as it is half filled
Rules for determining oxidation number of a trans metal
- all free elements have an ox number = 0
- for montomic ions, the ox number is the same as the charge on the ion
- in compounds oxygen has an oxidation number of 2
- hydrogen has an oxidation number of …
- in polyatomic ions the sun of all the oxidation number is equal to the overall charge of the ion
What is oxidation / reduction
Oxidation is an increase I. Oxidation number
Reduction is a decrease in oxidation number
What compounds tend to be ox/reduce agents
Compounds containing metals high oxidation states tend to be good oxidising agents as rhe ions are easily reduced to lower oxidation states, compounds containing metals in low oxidation states tend to be reducing agents
What is a trans metal complex
A TM complex consists of a central metal ion surrounded by ligands, the metal ion is positive and acts as an electrophile
What is a Ligand
Ligands are negative ions with one or more lone pair of electrons that they can donate to the central metal ion, forming dative covalent bonds. A dative covalent bond is one in which both electrons in a bond are donated by one of the atoms.
What are the most common types of ligands
H20 - aqua
Nh3 - ammine (double m)
Fluorine - Flurido
Chlorine - chlorido
Different types of ligands
Monodentate ligands attach to the TM at one point. (Ie donate one pair of electrons)
A bidentate attaches at two points
Hexadentate at 6
Formula for a TM complex
Practice drawing
Rules for naming a TM metal
- number of ligands
- name ligand (if more than one then alphabetical order)
- TM
- oxidation state of TM
Practice negative TM complexes
Sound but x
What is the coordination number
The number of bonds formed to the TM by ligands is called the coordination number, TMs commonly have a coordination number of 2,4,6
What causes a line in the emission spectrum
An exited electron returns to ground state, emitting energy difference as visible light of a specific wavelength
Why do the lines converge as they reach the continuum
The energy gaps between energy levels decrease with increasing energy. Ie the higher energy levels get closer and closer together
what does the shape of a tm depend on
the shape depends on the coordination number
why d orbitals in a tm are no longer degenerate
in TM complexes the ligands approach the central metal ion along the x,y,z axis. the electrons in d-orbitals if the metal ion are repelled by the electrons of the approaching ligands, there d-orbitals therefore have higher energy then the d-orbitals that lie between axes. the d-orbitals are no longer degenerate. this is known as the splitting of d-orbitals
what are strong/weak field ligands
strong field ligands are ligands which cause a large difference in energy between the d-orbitals, weak field ligands cause a small difference in energy between d-orbitals (ie orbitals are split less)
what is the spectrochemical series
ligands can be placed in order of their ability to split d-orbitals, this is the electrochemical series
why do TM absorb light
light is absorbed when electrons in a lower d-orbital are promoted to a d-orbital of higher energy. if light of one colour is absorbed, the complimentary colour will be observed
explain why TM are used as catalysts
TMs are used as catalysts because unpaired d electrons or unfilled d orbitals allows intermediate complexes to occur. twos weal’s the covalent bonds inside the reactant molecules, this can provide reaction pathways with lower EA. another reaction is because TM have variable oxidation states, this allows TM to provide an alternative reaction pathway with lower Ea
what is a homogeneous/hetergeneous catalyst
homogeneous catalysts are in the same physical state as the reactants,
the heterogeneous catalysts are in a different physical states to reactants
what is the valency shell electron pair Repulsion rule
VSEPR
states that a molecule will adapt the shape that results in the minimum repulsion between the valency electrons. bonds space out as far as possible from each other to give minimum repulsion forces.
what is the hierarchy of repulsion between electron pairs
LP:LP>LP:BP>BP:BP
what are the rules when working out the shape of a molecule that has no lone pairs
- write formula
- workout how many valency electrons the central atom and other atoms contribute to bonding
- divide by 2 to get the number of bonding pairs
- decide on the basic shape of the molecule.
draw a table showing different shapes of molecules
memorise table
what happens to the shape of molecules when there are lone pairs.
when lone pairs are inverted, the basic shapes are modified because the LP. has greater repulsion than the BP. where all the positions are not equal the LP goes to the site with the least repulsion, ie in the trigonal bipyrimdal this is the equational position. when there is more than one LP they try to get as far apart as possible from each other.
when calculating PH, if its sulfuroc acid you have to divide your answer by two as sulphuric acid is dibasic.
h2so4
(2 hydrogens)
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calcium hydroxide formula ca(oh)2
for calcium hydroxide if ph u double the concentration as oh is 2 moles worth
optical isomer
non-superimposable mirror images of each other
In the reaction of but-1-yne with hydrogen, but-1-ene is formed. Explain why but-1-ene has no geometric isomers.
swapping any of the groups on the C=C results in the same structure.
State how transition metals can act as catalysts.
empty/half-filled/incomplete d orbitals/subshell
if it says binds to a receptor then its a pharmacophore
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if delta h/s/g has a dot it means standard conditions and so the temperature is deemed to be 298k
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What is standard enthalpy of combustion
Standard enthalpy of formation, H, is defined as the enthalpy change involved when one mole of a substance is formed from its elements in their standard states. Standard state of a substance is its most stable form at a pressure of 1 atom and a temp of 298k
How can standard enthalpy of formation be used to calculate the enthalpy change for a reaction
Delta H= products - reactants
What is entropy
Energy of a substance is a measure of the amount of disorder within that system, the larger the entropy the greater the amount of disorder. The symbol is s. Units KJ mol-1
Solid,liquid, gas (which has highest entropy)
Gas highest to solid lowest
Effect of temp on entropy
Higher temp means a higher degree of disorder (higher entropy) at the melting/boiling point of a substance there is a large increase in entropy
What effect does an exothermic reaction have on the entropy of surroundings
Exothermic increases the entropy of surroundings as heat energy released
What effect does an endothermic reaction have on the entropy of surroundings
Endothermic decreases entropy of surroundings heat energy released
What is standard entropy of a substance
S, is the energy of 1 mol of the substance at temp 298K
Third law of thermodynamics how is standard entropy calculated
The entropy of a substance (perfect crystal) at 0K is zero, because particles in a solid are no longer interacting at a perfectly absorbed 0K.
What is a feasible reaction
Delta s= products-reactants
What is the standard free energy change
A feasible reaction is a reaction that tends towards the products rather than the reactants
What can be said about the reaction if the change in energy between reactants and products is negative
2nd law states that for a reaction to be feasible, total entropy for a reaction system and the surroundings must be positive for a spontaneous reaction, the total entropy and surroundings always increases
How can degrees be converted to celsius
To convert degrees to kelvin, add 273
Explain formation of molecular orbitals
In atoms electrons occupy atomic orbitals, electrons in molecules occupy molecular orbitals. Molecular orbitals are generated by combining atomic orbitals. The number of orbitals formed is equal to the number of atomic orbitals that combine. Each molecular orbital can hold two electrons.
What are bonding molecular orbitals/antibonding molecular orbitals
One of the molecular orbitals is law and energy than either of the Tomich orbitals that combined to produce it, this is called a bonding molecular orbitals. The other molecular orbital is known as an anti bonding molecular orbital and is of higher energy than either of the atomic orbitals that combined to produce it.
Difference between the bonding molecular orbital is polar/non-polar molecules
In a nonpolar molecule, the molecular orbital will be symmetrical around the two atoms. In a polar molecule, the molecular orbital will be asymmetric around the two atoms.
Sigma bonds and their formation
Molecular orbital is formed by an Overlap of (atomic) orbitals along the axis of the bonds. I.e. a covalent bond, called a sigma bond. This is usually referred to as an end on overlap.
Pi bonds
To parallel P atomic orbitals that are perpendicular to the axis of the bond can overlap laterally or side on to form a pi bond. The overlap of atomic orbitals is much less effective than the end on overlap. Pie bonds are weaker than Sigma bonds.
What is hybridisation of orbitals
Hybridisation is the process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. Which are degenerate
Hybridisation of alkanes
In alkanes the four sp3 orbitals on each carbon atom will overlap and end on with four other orbitals, i.e. then the hydrogen ___ orbitals and one sp3 orbital on the other carbon atom. Four sigma bonds will be formed and they will adapt a tetrahedral arrangement.
Hybridisation of alkenes
In alkenes, the 3 sp2 orbitals adapt a trigonal planar arrangement. In Ethene each carbon atom uses its three sp2 orbitals two form Sigma bonds with two hydrogen atoms and with other carbon. The unhybridized 2p orbital left on the carbon atoms overlaps the side to form a pi bond.
Hybridisation of alkynes
In alkynes the 2 sp2 orbitals in each carbon form sigma bonds with the other carbon atom. The unhybridized 2p orbitals overlap side on to form pi bonds
Hybridisation of benzene
In benzene, c6h6, each carbon atom is sp2 hybridised and the 3 half-filled sp2 orbitals form sigma bonds with a hydrogen aion and the two neighbouring carbon atoms. This leaves an electron occupying a p-orbital on each carbon atom. Each of there p-orbitals overlap side on with p orbitals on neighbouring carbon atoms, a pi electron bond is formed
What is a chromophore
A chromophore is a group of atoms within a molecule which is replicable for absorption of light. Chromophores Exist in molecules, with conjugated system brackets attract double bonds. Delocalised electrons between atoms are conjugate system has alternating sigma and pi bonds
Why some organic molecules appear coloured
Absorption of electromagnetic energy can cause electrons to be parallel from the highest occupied molecular orbital ‘homo’ to the coho. If the wavelength of light absorbed lies in the ems then the color observed will be complementary to that absorbed
Why most organic molecules are colourless
Most organic molecules are colourless as the gap between the homo and lumo is large, this means that light from uv region is absorbed and so molecule appears colourless
What happens to the frequency of light absorbed when the conjugated system contains more atoms?
If there are more atoms in the conjugated system then there is a smaller energy gap between homo/lumo. Therefore lower frequency and lower energy is absorbed.
Geometric isomers:
can occur when there is restricted rotation around a carbon-carbon double bond or a carbon-carbon single bond in a cyclic compound
must have two different groups attached to each of the carbon atoms that make up the bond with restricted rotation
can be labelled cis or trans according to whether the substituent groups are on the same side (cis) or on different sides (trans) of the bond with restricted rotation
have differences in physical properties, such as melting point and boiling point
can have differences in chemical properties
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The filling of the d orbitals follows the aufbau principle, with the exception of chromium and copper atoms.
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Oxidation can be defined as an increase in oxidation number. Reduction can be considered as a decrease in oxidation number.
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for chromium and copper do not include the 4s orbital
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what is an isomer
An isomer is a molecule with the same molecular formula but different structural formula
What is a stereoisomers
A stereoisomer is when the order of bonding in each atom is the same but the spatial arrangement of the atom is different in each bond
What are geometric isomers
A geometric isomer occurs when the arrangement of the atom is different in each isomer
Under what circumstances do geometric isomers occur
Occur when there is rotation around a carbon to carbon double bond, also there must be two different groups attached to each of the carbon atoms that make up the bond
What is meant by cis and trans
Cis is groups on the sdame side of the double bond, trans is groups on opposite side of the double bond
How do properties of geometric isomers differ
Geometric isomers can have different physical properties
What are optical isomers
They contain the same number and kinds of atoms and bonds, they are non-super imposable mirror images
When do optical isomers occur
When four different groups are arranged tetrically around a central carbon atom (chiral carbon)
How do properties of optical isomers occur
Identical but on light
Effect of enantiomers on polarise light
One enantiomer will rotate light in one direction and the other enantiomer in the opposite direction by the same difference. as there is an equal amount of each enantiomer, the rotation would cancel
What is a racemic mixture and why are they described as being optically inactive
A racemic mixture is an equal mixture of enantiomers, of a chiral molecule
how does mass spectroscopy work
- a small sample of an organic-compound is bombarded by high-energy electrons
- this removes electrons from the organic molecule generating positively charged, molecular ions known as parent ions
- these molecular ions break into smaller positively charged ion fragments
State what is meant by a dative covalent bond.
Both electrons come from the same atom
What is infrared spectroscopy used for
Its used to identify specific functional groups in organic molecules
Explain how infrared spectroscopy works
Infrared spectroscopy intakes infrared at organic molecules which causes their bonds to vibrate in different ways. The wavelengths which are absorbed depend on the type of chemical bondand the atoms at the end of these bonds
What is the general rule regarding the weight of atoms and bond strength
Lighter atoms are converted by stronger bonds (higher energy radiation absorbed), heavier atoms are connected by weaker bonds (lower energy radiation absorbed)
What is nass spectroscopy used for
Mass spectroscopy is used to determine the accurate molecular mass and structural features of a compound
How does mass spectroscopy work
A small sample of an organic compound is bombarded by high energy electrons. This removes electrons from the organic molecule generating positively charged molecular ions known as parent ions. These molecular ions then break into smaller positively charged ion fragments
Explain how proton nmr spectroscopy works
Nuclei of atoms behave like tiny magnets and in a strong magnetic field some align with the field (lower energy) whilst the rest align against it (higher energy). The absorption of radiation in the radio frequency of the electromagnetic spectrum causes the 1h nuclei to flip from the lower to higher energy alignment. As they fall back from higher to lower energy alignment emitted radiation is detected and plotted on a spectrum
How are proton environments identified
The fragments
upper case or lower case k for equilibrium
upper (capital K for equilbrium
upper or lower case k for rate constant
lower case k for rate
vacuum filtration can be used to speed up the seperation of a filtrate
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why heat under reflux?
to prevent vapours escaping
Explain in detail why vitamin A appears yellow, whereas β-carotene appears orange.
Beta-carotene has greater conjugation so the HOMO-LUMO gap is smaller (1), light of a higher wavelength (lower energy) is absorbed (1), colour we see is the opposite of this so orange (1)
Explain fully how colour arises in these dye molecules.
Electrons move from HOMO to LUMO. (1)
Absorption of light (from the visible part of the spectrum) means that light of the complementary colour is seen.
Explain how ligands bond to metal ions to form complexes.
Ligands) donate (lone/non-bonding) pairs of electrons (to the metal ion)
