Chem5 Exam Q's

Front 1

how does a catalyst speed up a chemical reaction?

Back 1

Alternative route (forms intermediate species)

of lower activation energy

Front 2

Characteristic property of transition metals that enables them to act as catalysts?

Back 2

Variable oxidation state

Front 3

Suggest one reason why poisoning reduces the effectiveness of a heterogenous catalyst.

Back 3

Poison attaches to surface/blocks active site/reduces surface area

Front 4

Suggest how poisoning of a catalyst can be minimised?

Back 4

Purify reactants/remove impurities

Front 5

State why the electrode potential for standard hydrogen electrode is 0V

Back 5

By definition

Front 6

Other than cost, why platinum electrodes are made by coating a porous ceramic material

Back 6

Increases the surface area (so reaction faster

Front 7

Suggest why the emf of a fuel cell is the same in alkaline and acidic conditions.

Back 7

Same overall reaction

Front 8

Other than lack of pollution, main advantage of fuel cell over rechargeable cell

Back 8

hydrogen and oxygen supplied continously/recharged quickly

OR

operated without stopping to recharge

Front 9

Give one reason why fuel cell might not be carbon neutral.

Back 9

Hydrogen made using energy source that isnt carbon neutral

Front 10

Explain why the bond enthalpy of a Cl-Cl bond is greater than Br-Br bond.

Back 10

Bonding pair closer to nucleus/bond is shorter/Cl is smaller atom;

Attraction to bond pair is stronger

Front 11

Why is the electron affinity of chlorine exothermic?

Back 11

Net attraction between chlorine nucleus and electron/Chloride ion is more stable

Front 12

Explain the meaning of perfect ionic model?

Back 12

Ions are perfect spheres/point charges/no polarisation;

only electrostatic attraction/no covalent interaction

Front 13

Why is lattice enthalpy of silver chloride greater than silver bromide?

Why is enthalpy of CaF2 > CaCl

Back 13

Chloride ion smaller;

attracted more strongly

flouride ion smaller;

electrostatic attraction stronger/more energy to separate ions/ionic bonding stronger

Front 14

Suggest why practical value of lattice enthalpy is greater than theoretical

Back 14

Covalent character;

forces stronger than pure ionic bonding/stronger bonding/additional bonding

Front 15

Explain why entropy increases with temp from 0?

Back 15

Particles VIBRATE more

Front 16

Why is there a large entropy change during boiling?

Back 16

liquid to gas;

big increase in disorder/much mroe random movement

Front 17

State and explain one risk associated with cisplatin.

Back 17

kills or causes damage to normal cells/hair loss;

may attach to DNA in normal cells

Front 18

What shape is Co2+ in water?

Back 18

octahedral

Front 19

Explain why ethanediamine complex is more stable than aqua complex

Back 19

entropy change is positive;

4 moles reactants form 7 moles products

Front 20

Explain why chloride ion complex co-ordination number is diff to CoCl2

Back 20

Chloride ion ligand too big to fit more than 4

Front 21

State and explain the trend in electronegativities across Period 3 from sodium to sulfur. (4)

Back 21

increases;

increase in proton number;

same number of electron shells/same radius/shielding of outer electrons remains the same;

attraction of bond pair to nucleus increases

Front 22

Explain why Ti(III) compounds are usually coloured but Ti(IV) compounds are colourless

Back 22

Ti(III) has a d electron that can be excited to a higher energy level;

absorbs one colour of light from white light;

Ti(IV) has no d electron so no electron transition with energy equal to that of visible light

Front 23

2 reasons why a spectrometer is the most appropriate method for measuring conc of coloured ions in an experiment.

Back 23

Rapid determination of conc/easy to take many readings;

does not interfere with reaction/does not use up reagent/can measure very low conc

Front 24

Explain the shape of the autocatalysis curve

Back 24

Negative ions collide high activation energy;

autocatalyst formed;

MnO4- ions used up

Front 25

Suggest what happens to the electrons in flourite when UV light is absorbed and when visible light is given out.

Back 25

UV absorbed: electrons move to higher energy levels/excited;

visible out: fall back down/move to lower energy levels

Front 26

What property of silicon dioxide can be deduced from teh fact that it reacts with NaOH not Hcl?

Back 26

Lewis acid

Front 27

Suggest why ions from s block elements do not usually act as catalysts.

Back 27

only exist in one oxidation state

Front 28

Why is the activation energy for S2O82- and I- high?

Back 28

both negative charge/repel each other

Front 29

State how an element can be classified as a transition element.

Back 29

partially filled/incomplete d sub-shell/orbital

Front 30

Explain the meaning of the term complex ion.

Back 30

Has ligand(s);

linked by coordinate bonds

Front 31

Explain why an aqueous solution of cobalt sulfate has a red colour

Back 31

Light is absorbed from incident white light;

due to electrons moving to higher energy levels;

remaining light transmitted is colour observed

Front 32

Explain why CO is toxic

Back 32

bonds to the iron/haemoglobin/greater affinity for haemoglobin;

displaces oxygen/prevents transport of oxygen

Front 33

2 reasons why extraction of copper using scrap iron is environmentally friendly.

Back 33

Less CO2 released;

less mining of copper ore;

lower energy consumption

Front 34

entropy and enthalpy are negative. explain why the reaction is not feasible at higher temp?

Back 34

G = H-TS;

G>0;

at high temp, -TS (is positive and greater than)H

Front 35

One reason why methanol, synthesised from CO2 and hydrogen, may not be carbon-neutral

Back 35

CO2 produced during H2 manufacture

Front 36

Describe a standard hydrogen electrode.

Back 36

H2 gas/bubbles;

1.0moldm^-3 HCl/H+;

298K and 100kPa;

platinum

Front 37

2H+(aq) + 2e- ----> H2(g) 0.00V

Fe3+(aq) + e- -----> Fe2+ (aq) +0.77V

suggest what happens when hydrogen gas is bubbled into a solution of Fe2+ and Fe3+ ions.

Back 37

Fe3+ reduced to Fe2+;

E(Fe3+/Fe2+)> E(H+/H2)

/Fe3+ better oxidising agent/cell emf 0.77V

Front 38

Define the term enthalpy of lattice dissociation.

Back 38

Enthalpy change when 1 mole of a (solid) ionic compound/lattice is dissociated/separated into ions;

ions in their gaseous state

Front 39

Why is the first electron affinity of oxygen exothermic?

Back 39

Attractive force between the nucleus of an O atom and an external electron

Front 40

Despite negative free energy change, why is a sample of magnesium oxide stable in air at room temp.

Back 40

Barrier of MgO/protective layer;

or acitvation energy too high/rate too slow

Front 41

For formation of MgO from magnesium and oxygen, why is entropy change negative

Back 41

1 mole of solid and 0.5 mole of gas reactants and 1 mole of solid products

system becomes more ordered

Front 42

Explain why enthalpy change is positive for melting of water.

Back 42

Hydrogen bonds between water molecules;

energy required to break bonds

Front 43

Freezing of water is exothermic. One reason why temp of water stays constant when freezing?

Back 43

Heat escapes

Front 44

pH of NaOH?

Back 44

14

Front 45

pH of H3PO4?

Back 45

0

Front 46

2 reasons why platinum electrode?

Back 46

Inert;

conducts electricity/allows electron flow

Front 47

2 reasons why KNO3 is a suitable solution for salt bridge?

Back 47

Ions can move (conducts electricity/carries charge);

does not react with solution in either electrode

Front 48

State why it's possible to use a spectrometer to measure the conc of manganate ions in this reaction mixture.

Back 48

Manganate ions are coloured (purple)

Other reactants and products not coloured

Front 49

Give the meaning of the term autocatalyst and explain how the above curve indicates that the reaction is autocatalysed.

Back 49

Catalyst of the reeaction is a reaction product;

starts off slow/gradient slower;

gets faster/gradient steeper

Front 50

2 other characteristic properties (aside from catalyst and compelex) and an example

Back 50

Variable oxidation state;

Fe(II) and Fe(III);

Coloured ions;

Cu2+ (aq)/[Cu(H2O)6]2+

Front 51

Define Lewis base

Back 51

electron pair donor

Front 52

An excess of dilute ammonia is added to aqueous iron(II) and left to stand for some time. State and explain observations

Back 52

Start with green solution;

green ppt of Fe(H2O)4(OH)2;

changes to brown solid;

Iron(II) hydroxide oxidised by air to iron(III) hydroxide

Front 53

Why is white phosphorous stored under water?

Back 53

Prevent it coming into contact/reacting with air/oxygen

Front 54

Suggest why phosphorous(V) oxide is represented by P4O10 rather than P2O5.

Back 54

One molecule contains 4P and 10O/P4O10 is molecular formula

Front 55

Explain why the use of an excess of NaOH to neturalise phosphoric acid solution might lead to environmental problems in the lake

Back 55

NaOH will make the lake alkaline/toxic/kill wildlife

Front 56

Explain the meaning of the term electron affinity.

Back 56

Enthalpy change when one mole of gaseous atoms;

form one mole of gaseous negative ions (with a single charge)

Front 57

Explain why the electronegativity of flourine is greater than the electronegativity of chlorine.

Back 57

Flourine atom is smaller/shielding is less/outer electrons closer to nucleus;

bonding pair of electrons more strongly attracted to nucleus

Front 58

Explain why the hydraition enthalpy of the flouride ion is more negative than the hydration enthalpy of the chloride ion.

Back 58

Flouride ion is smaller/higher charge density;

attracts water more strongly

Front 59

Suggest why entropy change for dissolving AgF is positive.

Back 59

Increase in number of particles/more disorder

Front 60

The free energy for the reaction to form NO from N2 and O2 stays constant at diff temp. why?

Back 60

no change in number of moles of gases;

so entropy/disorder remains relatively constant/very small/S=0/TS=0

Front 61

One environmental advantage of rechargeable cell compared with non rechargeable cell

Back 61

metal compounds are re-used/supplies not depleted/cell not used;

no landfill problems;

less waste;

less mining;

less energy to extract metals

Front 62

Suggest why ethanol is carbon-neutral

Back 62

CO2 released by combustion;

taken up in photosynthesis

Front 63

Suggest, in terms of electrons, why the colours of the complex ions [Cr(H2O)6]3+ and [Cr(H2O)5Cl]2+ are different.

Back 63

energy levels/gaps of the d electrons are different;

diff wavelength/energy of light absorbed (when d electron excited)

OR

diff wavelength transmitted/reflected

Front 64

Explain why [Cr(H2O)6]3+ behaves differently than [Cr(H2O)6]2+ when sodium carbonate is added

Back 64

Cr(III) is acidic and forms H+ ions;

because it polarises water (more polarising power in book)

Front 65

Co2+ is a catalyst for the reaction between sulfate(IV) ions with oxygen to form sulfate (VI) ions. Suggest why the reaction is faster in the presence of Co2+ ions

Back 65

Activation energy is lower;

oppositely charged ions attract

Front 66

Define bond dissociation enthalpy as applied to chlorine

Back 66

Enthalpy change to break the bond in 1 mole of chlorine molecules;

to form two moles of gaseous chlorine atoms/free radicals

Cl2(g) ---> 2Cl(g)

Front 67

Explain why the enthalpy of atomisation of chlorine is exactly half the bond dissociation enthalpy of chlorine.

Back 67

Only one mole of chlorine atoms formed/half the amount of molecules involved

Front 68

Explain why the enthalpy of formation of ClF3(g) is likely to be different from a data book value

Back 68

Cl-F bond is different in different compounds

Front 69

Explain why magnesium ions attract water molecules.

Back 69

Water is polar/O in water has slightly negative charge.

Magnesium ion/positive ion attracts O on a water molecule/attracts lone pairs

NOT H BONDING

Front 70

Explain why the evaporation of water is spontaneous even though this change is endothermic.

Back 70

Molecules become more disordered/more random when water changes from a liquid to a gas;

positive entropy/entropy increases;

TS>H

G is negative

Front 71

State the type of bonding in basic oxides.

Explain why this type of bonding causes these oxides to have basic properties.

Back 71

Ionic;

contains O2- ions;

accept protons to form OH-

Front 72

Why does sulfur dioxide form a weakly acidic solution?

Back 72

Reaction with water is equilbrium/lies far to the left/partially ionised/dissociated

Front 73

Give one reason why impurities in the reactants can cause problems in processes that use heterogenous catalyst

Back 73

poison the catalyst/block the active sites/

adsorb onto the catalyst AND reduce surface area

Front 74

Give the meaning of term heterogenous.

Back 74

In a different phase to the reactants

Front 75

Explain the meaning of the term ligand and bidentate.

Back 75

Ligand is an electron pair donor;

bidentate donates two electron pairs (to a transition metal ion) from different atoms/two atoms in the same molecule

Front 76

Explain why CoCl4 and Co(H2O)6 have different colours

Back 76

D electrons/orbitals have different energies/d splitting is different;

light energy is absorbed causing electrons to be excited;

diff wavelength absorbed/reflected/transmitted

Front 77

Explain the value for the enthalpy of hydration for the chloride ion is more negative than that for the bromide ion

Back 77

Chloride ions smaller;

force of attraction between water and chloride ions stronger;

chlroide ions attract slightly positive H/electron deificnet H on water

Front 78

Explain why G for the dissolving of KCl is negative even though the enthalpy change is positive.

Back 78

Entropy change is positive/entropy increases;

as 1 mol (solid) forms 2 moles aquous ions/number of particles increases/aqueous ions more disordered;

TS>H

Front 79

Explain in terms of molecules why the entropy is 0 when temp is 0K

Back 79

Molecules are stationary/not moving/not vibrating;

no order/perfect order/max order

Front 80

Explain why the magnitude of G decreases as T increases

Back 80

TS gets bigger/entropy change is positive

Front 81

Outline a simple experiment to demostrate that MgO has ionic bonding

Back 81

Melt it;

conducts electricity

Front 82

Suggest why SiO2 is insoluble.

Back 82

Macromolecular;

covalent bonding;

water cannot supply enough energy to break the covalent bonds/hydration enthalpy

Front 83

Explain why the melting point of phosphorous oxide is less than silicon dioxide

Back 83

Molecular with covalent bonding;

weak vdW between molecules/little energy to break

Front 84

Explain how the salt bridge provides an electrical connection between two electrodes.

Back 84

Has mobile ions

Front 85

Electrochemical cell, 2 coppe electrodes, 1.0 moldm CuSO4(aq) on left, 0.2moldm CuSO4(aq) on right.

Suggest why KCl is not a suitable salt bridge.

Suggest why electrons move from right to left.

Explain why current falls to 0 eventually.

Back 85

Cl- ions react with copper ions to form CuCl4;

Cu2+ ions on left more conc;

so reduction of copper ions favoured on left/left hand electrode positive;

Copper ions at same conc in both electrodes

Front 86

What factors affect the colour of a transition metal ion?

Back 86

Ligand;

coordination number/shape;

type of ion;

oxidation state

Front 87

Explain why a cobalt compound is able to act as a catalyst for

2CH3CHO + O2 ----> 2CH3COOH

Back 87

Has variable oxidation states;

can act as an intermediate that lowers the activation energy

Front 88

Explain in terms of the chelate effect, why the complex ion formed from cobalt and ethane-1,2-diamine is formed in preference to [Co(H2O)6]2+.

Back 88

Number of particles increases;

so increase in diorder/entropy

Front 89

Why does enthalpy change for electron affinity of flourine have a negative value?

Back 89

Attraction between the nucleus and the added electron;

energy is released/product is more stable/lower energy/reaction is exothermic

Front 90

Explain why the theoretical value for lattice enthalpy of AgF is different from experimental.

Back 90

Experimental lattice enthalpy allows for covalent interaction/distorted ions/polarisation

OR AgF has covalent character;

Theoretical assumes only ionic interaction/point charges/perfect spheres

OR AgF not perfectly ionic

Front 91

Define enthalpy of hydration.

Back 91

Enthalpy change when 1mole of a gaseous ion forms aqueous ions

Front 92

Suggest why hydration of chlorine is exothermic.

Back 92

Water is polar has positive H;

Cl- attracts the H in water

Front 93

Describe what you would observe when magnesium is heated above 373K in absence of air with water.

Back 93

Brilliant white flame;

white powder/solid/smoke

Front 94

Explain why magnesium has a higher melting point than sodium.

Back 94

Magnesium has a higher charge/has more delocalised electrons/greater charge density;

attracts delocalise/sea of electrons more strongly/stronger metallic bonding

Front 95

Physical properties of macromolecular structures.

Back 95

High melting and boiling points;

hard;

brittle/not malleable;

insoluble;

non-conductor

Front 96

One reason why cell is not recharged?

Back 96

Cell reaction cannot be reversed/zinc cannot be regenerated/danger of gas/oxygen/hydrogen produced;

Front 97

How is an electric current generated?

Back 97

One electrode produces electrode;

one accepts electrons

Front 98

Explain why a fuel cell does not need to be recharged.

Back 98

Reagents continously supplied;

concentration of reagents constant

Front 99

Suggest advantage of using hydrogen in a fuel cell as opposed to in an internal combustion engine.

Back 99

More efficient/a greater prop of energy available converted into useful energy

Front 100

Identify major hazard of fuel cell in an engine.

Back 100

hydrogen flammable/H+ and OH- corrosive/hydrogen explosive

Front 101

Explain why complexes with different ligands are different colours.

Back 101

different energies of d electrons/different splitting of d electron energy levels/different energy gap of d electrons/different d orbital energies;

different wavelength of light absorbed by electrons;

different wavlength transmitted

Front 102

Explain why the reaction of diaminoethane occurs with cobalt complex.

Back 102

increase in number of particles/4 particles form 7;

increase in disorder/entropy;

enthalpy change is small/no net change in bond enthalpies (same number and type of bonds broken and formed);

G is negative

Front 103

Suggest how the risk associated with cisplatin could be minimised.

Back 103

small amounts/short bursts/target the application/monitor the patient

Front 104

One property of impurity in a sample that would cause the calculated mass of the sample (that reacted with dichromate) to be greater than the actual.

Back 104

Reducing agent/reacts with dichromate/not fully hydrated;

for given mass impurity would react with more dichromate than similar mass of actual sample

Front 105

Define enthalpy of atomisation.

Back 105

Enthalpy change for the formation of 1 mole of gaseous atoms;

from the element in its standard state

Front 106

Explain why entropy of nitrogen is much greater than carbon (graphite)?

Back 106

Nitrogen is a gas compared with solid carbon;

nitrogen more disordered/random

Front 107

State the type of reaction between sodium oxide and phosphorous oxide.

Back 107

Acid-base/neutralisation

Front 108

Explain why the melting point of lithium oxide is greater than sodium oxide?

Back 108

Lithium ion is smaller/hsa higher charge dnesity;

attracts oxide ion more strongly;

Front 109

Suggest what is done to a heterogenous catalyst to maximise efficiency?

Back 109

SA increased;

use of poweder/granules/finely divided/spreading out on mesh/support

Front 110

Give the meaning of the term multidentate.

Back 110

Forms more than one co-ordinate bond/two or more

Front 111

Give a reason why a vitamin with a cyanide ion as a ligand is not toxic.

Back 111

Ion strongly bound to transition metal by coordinate bond

Front 112

Explain interactions between water and flouride ions during hydration.

Back 112

Water is polar/H is electron-deficient/;

F ions attract water/H

Front 113

Suggest why enthalpy change from mean bond enthalpies is different from practical?

Back 113

mean bond enthalpies taken over a range of diff compounds;

differ from those in a single compound

Front 114

Observation when sulfur reacts with oxygen?

Back 114

Blue flame;

fumes/pungent/choking gas

Front 115

Suggest why a thin layer of aluminium oxide prevents corrosion in moist air.

Back 115

Insoluble/imperable to air/water/oxide is inert

Front 116

Why does X react with Y?

Back 116

Electrode potential more positive/greater than;

so reduces/oxidises;

as more power ful agent

Front 117

One reason why a cell cannot be electrically recharged.

Back 117

Reaction not reversible

Front 118

Give one reason why emf of lead acid cell changes over time.

Back 118

Reagents/ions used up/concentration decreases

Front 119

Explain why voltage remains constant in a fuel cell.

Back 119

reagents/fuel supplied continously;

conc of reagents remains constant.

Front 120

Explain the meaning of the term complex.

Back 120

transition metal ion surrounded by one or more ligands;

by coordinate bonds

Front 121

What is E in the E=hv equation?

Back 121

Energy gained by hte excited electrons

Front 122

Explain why iron(III) is more acidic than iron(II)

Back 122

Higher charge and greater charge density

increases polarisation of coordinated water/weakens O-H bond