Definitions Flashcards
Standard électrode potential
The e.m.f. of a half-cell compared with a standard hydrogen half cell measured at 298K with solution concentrations of 1mol dm-3 and a gas pressure of 100kPa
Standard conditions
100kPa
298 K
1 moldm-3
End point
The point in a titration where the indicator changes colour
Indicates when the reaction is just complete
Equivalence point
The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution
Transition element
A d-block element that can form at least one stable ion with an incomplete d sub-shell
Why do transition elements have variable oxidation states?
The energy levels of the 4s and 3D sub shells are very close to each other
Why do transition elements and their compounds make good catalysts?
They can change oxidation states
What happens when you mix transition metal ions with aqueous sodium hydroxide or aqueous ammonia?
A coloured hydroxide precipitate forms
Colour change for copper II
Pale blue solution to a blue precipitate
What does [Cu(OH)2(H2O)4] s form when reacted in excess ammonia?
[Cu(NH3)4(H2O)2]2+ aq
Dark blue
What colour solution does iron II form?
Pale green solution to green ppt
Colour change for iron III
Yellow solution to an orange ppt
Manganèse II colour change
Pale pink solution to a pink ppt
Chromium III colour change
Green solution to grey-green precipitate
What happens to the green-grey chromium III precipitate in excess NaOH?
It forms an aqueous dark green coloured solution
Cr(OH)6 3-
What happens to what happens to the green grey ppt on excess ammonia?
It forms a purple coloured solution
Complex ion
A metal ion surrounded by coordinately bondés ligands
Coordinate bond
A covalent bond in which both electrons in the shared pair come from the same atom
Ligand
An atom, ion or molecule that donates a pair of electrons to a central metal atom/ion
Coordination number
The number of coordinate bonds that are formed with the central metal atom or ion
What must a ligand have?
At least one line pair of electrons
When does optical isomerism occur in complex ions?
Occurs in complex ions with three bidentate ligands attached to the central ion
What shaped ligands can show cis/trans isomerism?
Square planar and octahedral complex ions that have at least two pairs of ligands
What do cis isomers have?
The same groups on the same side
What do trans isomers have?
The same groups on opposite sides
What is cis-platin an example of?
An anti-cancer drug
What ligands can be found on cis-platin?
Two chloride ligands and two ammonia ligands
Which ligands on cis-platin are easy to replace?
The two chloride ligands
What are the chloride ligands on cis-platin replaced with?
Two nitrogen atoms on the DNA molecule of the cancerous cell causing the cell to die
What is a disadvantage of cis-platin?
It prevents normal cells from reproducing
What does ligand substitution usually cause?
A colour change
What happens to the coordination number in ligand substitution reactions if ligands are the same size?
It stays the same
What happens if the ligands in à ligand substitution are different sizes?
There’s a change in coordination number and a change in shape
What type of ion does haemophilia contain?
Fe 2+
How many coordinate bonds do iron II ions form?
6
Where do four of the lone pairs in the haemoglobin come from?
The nitrogen atoms in the haem group
Where does the fifth line pair come from in haemoglobin?
A nitrogen atom on a protein (globin)
Where does the final lone pair come from in haemoglobin?
The water ligand
What happens to the haemoglobin in the lungs?
The oxygen concentration is high so the water ligand is substituted for an oxygen molecule.
What is haemoglobin called when it contains oxygen?
Oxygaemoglobin
What is carboxyhaemoglobin?
Haemoglobin with a CO ligand instead of water
Why is carboxyhaemoglobin bad?
It is a string ligand so no the haemoglobin can no longer exchange oxygen anymore
How is Fe 2+ oxidised to Fe 3+?
Acidified potassium manganate (VII)
How is Fe 3+ reduced to Fe 2+?
By iodide ions
How can the Cr 3+ ion in [Cr(OH)6] 3- be oxidised to chromate (VI) solution and what is the colour change?
Warm hydrogen peroxide solution in alkaline conditions
Dark green to yellow
What happens when dilute sulfureux acid is added to the chromate (VI) solution?
It produces orange dichromate (VI) solution
How is dichromate (VI) solution reduced to Cr 3+?
Give the colour change
Acidified zinc
Orange to green
How is Cu 2+ reduces to copper (I) iodide?
Give the colour change
Using aqueous iodide ions
Pale blue to off white ppt
What does Cu+ do?
It is unstable and spontaneously disproportionate to produce Cu solid and Cu2+ aqueous
How can you identify transition metal ions with sodium hydroxide?
Ass NaOH solution drop wise from a pipette to a test tube
What colour is the Cu 2+ ion when sodium hydroxide is added?
Blue ppt
What colour are Fe 2+ ions in NaOH?
Green ppt
What colour are Fe 3+ ions in NaOH?
Orange ppt
What colour are Mn 2+ ions in NaOH?
Pink ppt
What colour are Cr 3+ ions in NaOH?
Grey-green ppt
What is the test for a carbonate?
Add nitric acid to the test compound
Bubble any has given off through limewater
What is the observation for the carbonate test?
Limewater turns from clear to cloudy if carbonate is present due to CO2 gas
How do you test for halides?
Add silver nitrate to the test compound
What colour observations do you get when testing for halides?
Chloride gives a white ppt
Bromide gives a cream ppt
Iodide gives a yellow ppt
How do you test for a sulfate ion?
Add barium nitrate or barium chloride
What observation can be seen if a sulfate is present?
White ppt forms
How can you test for ammonium ions?
Add cold NaOH to the test compound and warm
Hold red litmus paper over the solution
What observation can be seen when testing for ammonium ions?
Red litmus paper turns blue in the presence of ammonia
What is in a hydrogen half cell?
H2 (g) at 298K and 100kPa
Platinum electrode
Glass tube with holes to allow H2 gas bubbles to escape
Acid solution containing 1.0 mol dm-3 H+ aqueous
First ionisation energy
The energy required is the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
Factors that affect ionisation energy
Atomic radius
Nuclear charge
Electron shielding
Second ionisation energy
The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole gaseous 2+ ions
First electron affinity
The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions
Why are ionisation energies endothermic?
Energy is required to overcome the attraction between a negative electron and the positive nucleus.
Why are first electron affinities exothermic?
The electron being added is attracted to the nucleus
Why are second electron affinities endothermic?
The negative ion repels the second electron
Energy is needed to force the negatively charged electron into the negative ion
Effect of ionic size on lattice enthalpy
Ionic radius increases down the group
Attraction between ions decreases
Lattice energy less negative
Melting point decreases
Effect of ionic charge on lattice enthalpy
Ionic charge increases
Attraction between ions increases
Lattice energy becomes more negative
Melting point increases
Effect of ionic size on enthalpy of hydration
Ionic radius increases
Attraction between ion and water molecules decreases
Hydration enthalpy less negative
Effect of ionic charge on hydration enthalpy
Ionic charge increases
Attraction with water molecules increases
Hydration energy becomes more negative
Is bond breaking exo or endothermic?
Energy is required to break bonds
Bond breaking is endothermic
Is bond making exo or endothermic?
Energy is released when making bonds
Bond making is exothermic
Covalent bonding
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Ionic bonding
The electrostatic attraction between positive and negative ions
Dative covalent bond
A covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
What electronegativity difference gives an ionic bond?
Greater than 1.8
How does the conjugate base remove acid in the buffer solution?
On the addition of acid, the hydrogen ion concentration increases
The hydrogen ions react with the conjugate base
The equilibrium position shifts to the left, removing most of the hydrogen ions
How does the weak acid in the buffer solution remove added alkali?
The hydroxide ion concentration increases
The small concentration of hydrogen ions reacts with the hydroxide ions to form water
HA dissociates, shifting the position of equilibrium to the right to restore most of the hydrogen ions
