AQA Chemistry A level

What makes transition metal characteristics

incomplete d sub-level in atoms or ions

4 main characteristics of Transition metals

complex formation, formation of coloured ions, variable oxidation state, catalytic activity

what is a complex

a central metal ion surrounded by ligands

what is a ligand

An atom, ion or molecule which can donate a lone electron pair

what is a coordinate bond

Co-ordinate bonding is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms

what is coordination number

The number of co-ordinate bonds formed to a central metal ion

why is carbon monoxide toxic

CO is toxic to humans as CO can from a strong coordinate bond with haemoglobin. This is a stronger bond than that made with oxygen and so it replaces the oxygen attaching to the haemoglobin

what is the chelate effect

The substitution of monodentate ligand with a bidentate or a multidentate ligand leads to a more stable complex. This chelate effect can be explained in terms of a positive entropy change in these reactions as more molecules of products than reactants

type of isomerism shown in square planar/octahedral complexes

E-Z

isomerism shown only in octahedral complexes

Complexes with 3 bidentate ligands can form two optical isomers (non-superimposable mirror images)

how do transition metals show colour

Colour arises from electronic transitions from the ground state to excited states: between different d orbitals.

A portion of visible light is absorbed to promote d electrons to higher energy levels. The light that is not absorbed is transmitted to give the substance colour.

what is the equation which links the colour and frequency of the light absorbed with the energy difference between the split d orbitals

E = hv.

v = frequency of light absorbed (unit s-1 or Hz) h= Planck's constant 6.63 × 10-34 (J s)

E = energy difference between split orbitals (J)

how can you change colour of transition metals

Changing a ligand or changing the coordination number will alter the energy split between the d- orbitals, changing E and hence change the frequency of light absorbed

describe the method of spectroscopy

•Add an appropriate ligand to intensify colour •Make up solutions of known concentration (dilution series)

•Measure absorption or transmission

•Plot graph of absorption vs concentration •Measure absorption of unknown and compare

general trend of variable oxidation states

- Relative stability of +2 state with respect to +3 state increases across the period

- Compounds with high oxidation states tend to be oxidising agents e.g MnO4--Compounds with low oxidation states are often reducing agents e.g V2+ & Fe2+

four colour and symbol stages of Vanadium

VO2+ Oxidation state +5 ( a yellow solution)

VO2+ Oxidation state + 4 (a blue solution)

V3+ Oxidation state + 3 (a green solution)

V2+ Oxidation state + 2 (a violet solution)

YOU BETTER GET VANADIUM

what is used to reduce vanadium

Addition of zinc to the vanadium (V) in acidic solution will reduce the vanadium down through each successive oxidation state, and the colour would successively change from yellow to blue to green to violet

what is used in testing for aldehydes

[Ag(NH3)2]+ is used in Tollen's reagent to distinguish between aldehydes and ketones . Aldehydes reduce the silver in the Tollen's reagent to silver

why are dark colours of solutions difficult to measure

The purple colour of manganate can make it difficult to see the bottom of meniscus in the burette.

what acid is used for manganate titrations

Only use dilute sulphuric acid for manganate titrations.

Insufficient volumes of sulphuric acid will mean the solution is not acidic enough and MnO2 will be produced instead of Mn2+.

Using a weak acid like ethanoic acid would have the same effect as it cannot supply the large amount of hydrogen ions needed (8H+).

It cannot be conc HCl as the Cl- ions would be oxidised to Cl2

what is a heterogenous catalyst

in a different phase from the reactants

what is a homogenous catalyst

in the same phase as the reactants

what are standard conditions for heterogenous catalysts

Heterogeneous catalysts are usually solids whereas the reactants are gaseous or in solution. The reaction occurs at the surface of the catalyst.

how do heterogenous catalysts work

Adsorption of reactants at active sites on the surface may lead to catalytic action. The active site is the place where the reactants adsorb on to the surface of the catalyst. This can result in the bonds within the reactant moleculesbecomingweaker,or themoleculesbeingheldin a more reactive configuration. There will also be a higher concentration of reactants at the solid surface so leading to a higher collision frequency.

how does the strength of adsorption help to determine the effectiveness of the catalytic activity.

Some metals e.g. W have too strong adsorption and so the products cannot be released.

Some metals e.g. Ag have too weak adsorption, and the reactants do not adsorb in high enough concentration.

what is the effect of increasing surface area

Increasing the surface area of a solid catalyst will improve its effectiveness. A support medium is often used to maximise the surface area and minimise the cost (e.g. Rh on a ceramic support in catalytic converters).

contact process equation (manufacture of sulphuric acid)

V2O5 is used as a catalyst in the Contact Process. Overall equation : 2SO2 + O2 --> 2SO3 step1 SO2 +V2O5 --> SO3 + V2O4

step 2 2V2O4 + O2 --> 2V2O5

what are the effects of catalytic poisoning

Poisoning has a cost implication e.g. poisoning by sulphur in the Haber Process and by lead in catalytic converters in cars means that catalysts lose their efficiency and may need to be replaced.

reaction between iodide and persulphate ions

The reaction between I- and S2O82- catalysed by Fe2+

The uncatalysed reaction is very slow because the reaction needs a collision between two negative ions. Repulsion between the ions is going to hinder this - meaning high activation energy.

Both of the individual stages in the catalysed mechanism involve collision between positive and negative ions and will have lower activation energies.

overall S2O82- + 2I- --> 2SO42- + I2

Catalysed alternative route

stage 1 S2O82- + 2Fe2+ --> 2SO42- + 2Fe3+

stage2 2I- + 2Fe3+ --> 2Fe2+ + I2

Autocatalytic Reaction between Ethanedioate and Manganate ions

overall 2MnO4- + 5C2O42- + 16H+ --> 2Mn2+ + 10CO2 + 8H2O

Catalysed alternative route

Step 1 4Mn2+ + MnO4- + 8 H+ --> 5Mn3+ + 4 H2O Step 2 2Mn3+ + C2O42- --> 2Mn2+ + 2 CO2

what is autocatalysis

when the product of a reaction acts as a catalyst

what is a lewis acid

electron pair acceptor (metal ion)

what is a lewis base

electron pair donor (ligand)

colour of hexaaqua iron (II)

green

colour of hexaaqua copper (II)

blue

colour of hexaaqua aluminium (III)

colourless (not a transition metal)

colour of hexaaqua iron (III)

violet

what is a hydrolysis/acidity reaction

addition of water/removal of a hydrogen

[M(H2O)6]2+ + H2O --> [M(H2O)5(OH)]+ + H3O+

why are 3+ ions more acidic than 2+

The acidity of [M(H2O)6]3+ is greater than that of [M(H2O)6]2+ in terms of the greater polarising power (charge/size ratio) of the 3+ metal ion. The greater the polarising power, the more strongly it attracts the water molecule. This weakens the O-H bond so it breaks more easily.

Precipitate of Copper (II) with hydroxide or NH3 (deprotonation acid-base reaction)

blue

Precipitate of Iron (II) with hydroxide or NH3 (deprotonation acid-base reaction)

green

Precipitate of aluminium (III) with hydroxide or NH3 (deprotonation acid-base reaction)

white

Precipitate of Iron (III) with hydroxide or NH3 (deprotonation acid-base reaction)

brown

what happens to Aluminium with excess OH-

With excess NaOH the Al hydroxide dissolves. Al becomes [Al(OH)4]- (aq) colourless solution. This hydroxide is classed as amphoteric because it reacts and dissolves in both acids and bases.

what happens to copper with excess ammonia

With excess NH3 Cu and its precipitate dissolve

deep blue solution

reactions of M2+ ions with carbonates

form solid carbonate salt precipitates (straight precipitation reaction)

what happens with M3+ ions with carbonates

The 3+ ions with carbonate solution form a M(OH)3 ppt and CO2 gas is evolved

why is a carbonate salt not formed with metal 3+ ions

MCO3 is formed with 2+ ions but M2(CO3)3 is not formed with 3+ ions. The difference is explained by the greater polarising power of the 3+ ion due to its higher charge density.

precipitates formed in the carbonate (acidity reactions)

Al forms white ppt of Al(OH)3 (H2O)3 + CO2 Fe(III) forms brown ppt of Fe(OH)3 (H2O)3 + CO2

What is the relative mass and charge on a proton?

Mass 1

charge +1

What is the relative mass and charge on a neutron?

Mass 1

Charge 0

What is the relative mass and charge on an electron?

Mass 1/2000

Charge -1

What is the mass number?

The total number of protons and neutrons in the nucleus of an atom

What is the Atomic (proton) number?

This is the number of protons in the nucleus of an atom and is used to identify an element

What are Ions?

Ion have different numbers of protons and electrons. Negative ions have more electrons than protons and positive ions have fewer electrons than protons.

What are isotopes?

Isotopes of an element are atoms with the same number of protons but different numbers of neutrons

describe Thomson's model of the atom.

Thomson's model of the atom was like a 'plum pudding' with a positively charged pudding (solid sphere) that contained negatively charged particles (electrons).

What was found in Rutherford's gold foil experiment?

When alpha particles were fired at a thin gold sheet, most of them passed straight through with a very small number deflected straight back.

What was Rutherford's new nuclear model for the atom?

A tiny positively charged nucleus at the centre, surrounded by a cloud of negative electrons. Most of the atom is empty space.

What did Bohr's atom model show?

Electrons only exist in fixed orbits and not anywhere in between.

Each Shell has a fixed energy.

When an electron moves between shells, electromagnetic radiation is emitted or absorbed.

Because the energy of the shells is fixed, the radiation will have a fixed energy.

What difference is found between the original Bohr atom model and the refined Bohr model?

Scientists discovered that not all electrons in a shell have the same energy, so it was refined to include sub shell's.

What is relative atomic mass?

The average mass of an atom of an element compared to one twelfth of the mass of an atom of carbon 12.

What is relative isotopic mass?

Relative isotopic mass is the mass of an atom of an isotope of an element on a scale where an atom of Carbon-12 is exactly 12.

Calculating relative atomic mass

relative atomic mass = isotopic masses x percentages/total percentage

What is relative molecular mass?

The average mass of an entity compared to one twelfth of the mass of an atom of carbon 12.

What is the equation used to calculate the number of moles of any substance?

Number of moles = mass(g)/ mass of one mole (mol)

What are the 5 stages in mass spectrometery?

vaporisation, ionisation, acceleration, deflection, and detection

What happens during the vaporisation stage of mass spectrometry?

The sample is turned into a gas using an electrical heater in a vacuum.

What happens during the ionisation stage of mass spectrometry?

An electron gun fires a beam of high energy electrons which bombards the gaseous particles, knocking off electrons leaving a positive ion

What happens during the acceleration stage of mass spectrometry?

The positive ions are attracted by negatively charged plates in an electric field which accelerates the ions and focuses the beam.

What happens during the deflection stage of mass spectrometry?

The fast moving ions pas into a string magnetic field, deflecting the ions into a curved path. The degree of deflection depends on the Mass/charge ratio (m/z). Ions with with a high m/z ratio are deflected the least (they're heavier). The strength of the magnet is gradually increased so that ions with different m/z ratios are deflected towards the detector.

What happens during the detection stage of mass spectrometry?

The positive ions hit an electrically charged plate/ the current produced is then amplified and recorded as a 'peak'. Each peak is a measure of the relative abundance of each ion.

What is the general ionisation equation?

X(g) => X+ = e-

What does a mass spectrum chart show?

Each line represents a different isotope of an element. the height of each peak gives the relative isotopic abundance (the amount of it). For a molecular substance the peak with the greatest m/z ratio corresponds to the Mr.

What are the steps in calculating relative atomic mass?

Step 1: For each peak multiply the relative isotopic abundance by the relative isotopic mass.

Step 2: Add up these totals.

Step 3: Divide by 100

How many orbitals do each-sub shell contain?

s - 1

p - 3

d - 5

f - 7

What are four rules for electronic arrangement notation?

1: Each principle and subsidiary level fills up before the next one

2: When the 3p energy level is full, the 4s level fills before the 3d

3: When an atom or ion has 3d electrons, the 4s is written after the 3d

4: Atoms that have 3d electrons always lose the 4s electrons first while forming ions

What is the first ionisation energy?

The first ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

How does nuclear charge affect ioniation energy?

The more protons that are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons

How does distance from the nucleus affect ionisation energy?

Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away.

How does shielding affect ionisation energy?

As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge. This lessening pull of the nucleus by inner shells of electrons is called shielding.

What is the second ionisation energy?

The second ionisation energy is the energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions.

What is the trend in ionisation energy down group 2?

First ionisation energy decreases down Group 2. This provided evidence that electron shells really do exist.

What is the trend in ionisation energy across periods?

As you move across a period the general trend is for the ionisation energy to increase, it gets harder to remove an electron. This is because the number of protons is increasing which means a stronger nuclear attraction.

There are small drops between groups 2 and 3 due to sub-shell structure, the electron is in a new sub-shell so further away from nucleus, more electron shielding

There is a drop between groups 5 and 6 due to electron repulsion. the repulsion between two electrons in an orbital means that the electrons are easier to remove from shared orbitals.

What is molar mass?

The mass of one mole of something, the same as relative molecular mass but the units are g mol-1

What is the equation linking the number of moles to concentration and volume?

number of moles = concentration x volume (in dm3)

What is the ideal gas equation?

pV=nRT

p = pressure in pascals

V = Volume in m3

n = number of moles

R = 8.31 the gas constant

T = temperature measured in kelvin

What is a neutralisation reaction?

When an acid reacts with an alkali and a salt and water is produced.

What is an empirical formula?

The empirical formula gives the smallest whole number ratio of atoms in a compound.

What is the molecular formula?

The molecular formula gives the actual numbers of atoms in a molecule.

What is the theoretical yield?

The theoretical yield is the mass of the product that should be formed in a chemical reaction. It assumes no chemicals are 'lost' in the process.

What is percentage yield and what is its formula?

For any reaction the actual mass of the product (actual yield) will be less than the theoretical yield.

percentage yield = actual yield / theoretical yield x 100

What is Atom economy?

Atom economy is a measure of the proportion of reactant atoms that become part of the desired product (rather than by-products) in the balanced chemical equation.

What is the formula for Atom economy?

% atom economy = mass of desired product / total mass of reactants x 100

What is electrostatic attraction?

Electrostatic attraction holds positive and negative ions together - it is very strong.

What is ionic bonding?

Ionic bonding is bonds that have electrostatic attraction. When oppositely charged ions form an ionic bond you get an ionic compound.

What are giant ionic lattices?

A lattice is just a regular structure. Ionic crystals are giant lattices of ions. Different ionic compounds have different shaped structures but they're all still giant lattices.

What is the electrical conductivity of an ionic compound?

Ionic compounds conduct electricity when they're molten or dissolved - but not when they're solid. The ions in a liquid are free to move and carry a charge. In a solid they're in a fixed position by the strong ionic bonds.

What is the melting point for ionic compounds?

Ionic compounds have high melting points. The giant ionic lattices are held together by strong electrostatic forces. It takes lots of energy to overcome these forces, so melting points are very high.

What is the solubility of ionic compounds?

Ionic compounds tend to dissolve in water. Water molecules are polar - part of the molecule has a small negative charge and the other bits have small positive charges. The water molecules pull the ions away from the lattice and cause it to dissolve.