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Chemistry > transition metals > Flashcards

transition metals Flashcards

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1
Q

what is a transition metal

A

an element that forms at least one stable ion with a partially filled d sub shell

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2
Q

what 4 key features do transition metals display

A

1) form complex ions
2) coloured ions- transition metal compounds are diffrent colours
3) catalytic properties- transition elements and compounds formed from transition events can act as catalysts
4) variable oxidation states
transition elements form compounds in which the metal can have different oxidation states

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3
Q

what is a coordinate bond

A

shared pared of electrons that come from the same ion

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4
Q

what is a ligand

A

an ion or molecule with a lone pair of electrons that can from a coordinate bong

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5
Q

what is a bidentate ligand

A

2 coordinate bonds in a ligand

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6
Q

coordination number

A

number of coordiante bonds

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7
Q

what is a complex ion

A

centeral atom surrounded by ligands

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8
Q

multi dente ligand

A

2 or more coordinate bonds formed

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9
Q

name 5 monodente ligands

A

water H2O:
ammonia :NH3
hydroxide -:OH
chloride Cl:-
cynaide -:CN

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10
Q

name two bidentate ligands

A

ethane-1,2-diamine
:NH2CH2CH2NH3:

ethanedioate ion
C2O4-2

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11
Q

why does chloride ligands only fit 4 around

A

relatively large

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12
Q

how many coordinate bonds can EDTA4- form

A

6
2 form N atoms
4 from O atoms

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13
Q

when does the chelate effect occur

A

when a monodente ligand is substituted by and bidente ligand or multi dente ligand
AND THERE IS A LARGE INCREASE IN ENTROPY

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14
Q

explain why ligand substation reactions are feasible

A

more moles of products then reactants
so increase in entropy/disorder
same amount of bonds broken as formed
^H IS APPROXIMATELY ZERO
^G is less then or exalt to zero making reaction feasible

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15
Q

how is suffocation caused by coordinate bonds

A

O2 forms a coordinate bond to Fe2+
in hameoglobin enabling oxygen to be transported in the blood
CO is toxic because CO bonds more strongly to Fe2+ in hameglobin
this prevents O2 from forming bonds causing suffocation

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16
Q

want is a stereoisomer

A

same structural formula but a diffrent arrangement in space

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17
Q

trans isomer

A

2 ligands arranged opposite to each other

18
Q

what is a cis isomer

A

two ligands arranged next to each other

19
Q

why is Cis platin an anti cancer drug

A

binds to the DNA in cancer cells and stops cell replication
preventing growth and spread of cancer cells

20
Q

how do you find out which optical isomer is present

A

optical isomers rotate a plane of polarised light in opposite directions

21
Q

describe the energy of diffrent colours of light

A

ROY -low energy
G
BIV- high in energy

22
Q

why do transition metal compounds appear coloured

A

they have partially filled 3d subshells
in a transition metals all d orbitals are equal in energy (GROUND STATE)
the presence od other atoms causes the d orbitals to have slightly diffrent energies
this enables electrons to be excited from one d subshel to another
when an electron moves from a low energy subshel to a higher one the energy needed to make the transition is taken from white light
the colour of the light absorbed is then missing from the light which is reflected
the colours are transmitted give the compound is colour

23
Q

change in E can be found using what formula

A

^E=hv
^E is change in energy gained by the excited electron
h is planks constant
v is frequency of light

24
Q

explain big E BIV absorption

A

large increase in energy between d sub shells
high energy light absorbed to excite electrons
red orange yellow reflected
so looks red orange

25
Q

what things can alter the colour of a compound

A

change in
ligands
oxidation state
coordination number
shape of a complex

26
Q

what does colorimetry do

A

determine the unknown concentration of transition metal ions
by measuring the amount of lights transmitted threw a sample

27
Q

describe the experimental method

A

an appropriate ligand is added to solution in order to intensify colour

a range of solutions of same complex ion are made of known concentrations

one at a time they are tested in a colorimeter the transmission is measured

a graph is plotted of conc vs transmission and line of best flirt drawn

the transmission of unknown solution is measured in a colorimeter and it’s concentration is determined by a reading off the calibration curve

28
Q

what affects the amount absorption in the experimental method of measuring absorpion

A

length of container the solution is in
diluted
filters used in the colorimeter which allows one colour of light threw the sample

29
Q

how do you calibrate in order to measure absorption of unknown solution

A

cuvette is filled with water and put in the colorimeter and set to zero
this ensure accuracy and negated absorbsnce due to solution

30
Q

what is a catalyst

A

a substance that increases the rate of a chemical reaction without being used up

31
Q

how does a catalyst work

A

provides an alternative reaction pathway with a lower activation energy

32
Q

what is a heterogeneous catalyst

A

diffrent phase to reactant

33
Q

what is a homogeneous catalyst

A

same phase an the reactants

34
Q

how do heterogenous catalysts work

A

reactants ADsorb onto the surface of the catalyst on an active site
reaction occurs on the surface of the catalyst
products DEsorb from the surface of the catalyst

35
Q

how do you make a catalyst most effectent

A

increase surface area
spread the catalyst over an inert support medium

36
Q

how can poison of catalyst occur

A

impurities blocking the active sites
prevents the reactants from adsorbing
purifying the reactants in the best way to prevent poisoning

37
Q

name 3 heterogeneous catalyst examples

A

making ammonia in the haber process
catalysed by solid iron

making sulfuric acid in the contact process
catalysed by solid vandium oxide

manufacturing of methanol
catalysed by solid chromium oxide

38
Q

why can transition metals act as catalysts and group 1 metals can’t

A

they have variable oxidation states

39
Q

example of homogenous catalyst you must no

A

peroxodisulfate ions oxsdise iodide ions to iodine
the uncatalyzed reaction has high activation energy as the 2 negative ions repel each other

Fe2+ catalyses it in a 2 step process
S2O8 + 2Fe2+ -> 2SO42- + 2Fe3+
2I- + 2Fe3+ -> I2 + 2Fe2+

both steps then are between positive and negative ions
in the second step the catalyst is regenerated

40
Q

what is an autocatalyst

A

a homogeneous catalyst where one of the products of the reaction actually catalyses the reaction as it proceeds further

e.g oxidation of ethanedioic acid and managaate ions

41
Q

describe the oxidation of ethanedioic acid by magnate ions

A

the rate starts of slow as there is no catalyst intially
the 2 negatively charged reactants collide with a very high Ea
then as some Mn2+ is formed the rate increases as the reaction is being increasingly catalysed
the rate then decreases and levels off as the reactants get used up

42
Q

why is the titration of Fe2+ and MnO4 self indicating

A

as the MnO4- reactants to form Mn2+ it turns from deep purple to colourless
as the MnO4- is added to the Fe2+ solution it decolourises as it reacts
as soon as all the Fe2+ is reacted the reaction mixture will start to turn pale pink as the MnO4- has nothing to react with

purple (MnO4-) + (Fe2+) pale green

goes pink Fe3+ ?

Chemistry (24 decks)

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