qs i got wrong

Question 1

Chlorine has a low boiling point because the forces between the molecules
are weak.
Explain how these forces arise between molecules of chlorine.

Answer 1

1. random movement of e- in a Cl2 molecule creates a temporary dipole
2. this induces a dipole in neighbouring Cl2 molecule
3. temporary attraction between δ+ and δ–

Question 2

Excess dilute aqueous ammonia is added to the mixture.
Some of the precipitate dissolves and a darker yellow precipitate
remains what does this mean ? give equations

Answer 2

1. NH3 dissolves AgCl leaving yellow ppt AgI
2. AgCl(s) + 2NH3(aq) → Ag(NH3)2
   +(aq) + Cl−
   (aq)

Question 3

Explain why chlorine is added to water even though it is toxic

Answer 3

health benefit outwieghs risk/ only used in small conc

Question 4

Write an ionic equation for the reaction between chlorine and cold dilute
sodium hydroxide solution.

Answer 4

Cl2 + 2HO–> OCl– + Cl– + H2O

Question 5

Why wear gloves to hold tlc plate

Answer 5

To prevent contamination from hands to plate

Question 6

Why solvent depth not more than 1cm in tlc chromatography

Answer 6

If solvent too deep it will dissolve the mixture on the plate

Question 7

Is alllwimg the solvent to rise up the tlc plate to the top essential and why

Answer 7

No as rf value can be calculated even if solvent front does not reach up to top of plate

Question 8

Why allow plate to dry in fume cupboard for tlc

Answer 8

Solvent is toxic

Question 9

Why do amino acids have different rf values

Answer 9

Different polarities. So diff retention on the stationary phase / diff affinities for stat and mobile phases /diff solubility in developing solvent

Question 10

A calc of the Enthalpy of Lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value. Than the experimental data

Answer 10

AgI contains covalent character
Forces / bonds holding the lattice are stronger

Question 11

Degeees to kelvin

Answer 11

0degrees = 273 kelvin

Question 12

Magnesium chloride can absorb some water to form salt MgCl2. 4H2O (s)
Suggest a reason why. Enthalpy change. For this rxn cannot be determined directly using calorimetry

Answer 12

Some mgcl2 dissolves. Not possible to prevent this

Question 13

Describe how to find Enthalpy of solution of using 8g of anhydrous magniusum chloride

Answer 13

1. Using a measuring cylinder weigh out 25cm3 distilled water into polystyrene cup
2. Record initial temp for 3 mins every min
3. At 4th min Add known mass 8g of anhydrous mgcl2 and don’t record temp
4. Record temp at regular time intervals e.g. every min until 8 minutes stir continuously with thermometer
5. Plot graph temp against time and draw lines of best fits for before and after point of addition
6. Extrapolate cooling part of graph to point of addition / lines to when solid added to find temp change
7. Tfinal - Tinitial = triangle T
8. Q= mcdeltaT
9. Amount/ moles = mass/mr
10. Qdivided by 1000 / moles = Enthalpy of solution

Question 14

In terms of electrostatic forces explain why fluorine has a negative value for electron affinity

Answer 14

There’s an attraction btwn nucleus and added electron
energy is released

Question 15

Define Enthalpy of hydrat of an ionion

Answer 15

Enthalpy change when one mole of a gaseous ion is hydrated to form aqueous ions

Question 16

Adv and disadvantage fuel cells

Answer 16

Adv
Don’t need to recharge - just need good supply of hydrogen and oxygen
Only waste product is water- no pollution
More efficient

Disadv
Hydrogen is highly flammable + must be stored and transported correctly
Expensive to store and transport hydrogen in pressured containers
Energy required to make H and O=fossil fuels

Question 17

Electrode chmiecal series

Answer 17

List of electrode potentials in order

Question 18

Adv and disav of regarchable cell

Answer 18

Adv : less waste than non rechargeable/ cheaper
Disadv : still some waste issues

Question 19

Rechargeable cell defin example

Answer 19

Rxns can be reversed by applying external current e.g Lithium cobalt electrodes

Question 20

Non rechargeable cells disadv and adv

Answer 20

Cheap
Waste issues

Question 21

What do u do for discharge eq of e cells
Recharge

Answer 21

Combine the equations /flip if needed regarding where oxidation and reduction occur on rhs/lhs according to +/- emf value

For recharge, flip overall discharge equation

Question 22

Aluminium was rubbed with sandpaper before using as electrode why?

Answer 22

To remove oxide layer on aluminium

Question 23

Salt bridge can be made from dipping filter paper into potassium carbonate why wouldn’t this work for SHE cell

Answer 23

Carbonate ions react with acid in SHE
H+ conc change

Question 24

If cell can’t be recharged then

Answer 24

Cell rxns can’t be reversed

Question 25

In external circuit of copper in coppersukfate cell electrons move via ammeter from right to left why do they move in this direction

Answer 25

Cu2+ is more conc in left hand electrode
Reaction of Cu2+ and 2e- will occur more at left hand electrode

Question 26

Why can recharging lithium cell lead to releasing co2 into atmosphere

Answer 26

Electricity for recharging the cell may come from power stations burning fossil fuels

Question 27

Use the hydrogen oxygen fuel equations to explain how a current is generated

Answer 27

Hydrogen electrode produces electrons
Oxygen electrode accepts electrons

Question 28

Why does. Fuel cell not need to be recharged

Answer 28

Hydrogen / reactants are supplied continuously

Question 29

Solar cells generate an electric current from sunlight. These cells are often used to
provide electrical energy for illuminated road signs.
Explain why rechargeable cells are connected to these solar cells.

Answer 29

Solar cells do not supply electrical energy all the time

Rechargeable cells can store electrical energy for use when the solar cells are
not working

Question 30

Suggest one reason why many waste disposal centres contain a separate section
for cells and batteries.

Answer 30

Prevent pollution of the environment by toxic or dangerous substances

Question 31

Relative atomic mass defin

Answer 31

Average mass of an atom of an element compared to 1/12 mass of an atom of carbon 12

Question 32

Give 2 reasons why necessary to ionise isotopes of chromium before they can be analysed by mass spec

Answer 32

Ions will interact with and be accelerated by electric field
Hit negatively charged plate and create a current

Question 33

Why do some particles have v low energies

Answer 33

Collisions make particles lose energy

Question 34

How can rxn occur

Answer 34

Particles should collide in right orientation with E above activation energy

Question 35

Some carbon particulates are formed how?

Answer 35

Incomplete combustion as co2 and h2O react to form carbon particulates/ carbon monoxide and water

Question 36

Explain why complexes formed from TM ARE COLOURED

Answer 36

1) wavelengths of visible light are absorbed by TM ion complex
2) excites the electrons in d- orbitals
3) complementary wavelengths of light not absorbed are reflected to give colour we see

Question 37

Define transition metal

Answer 37

A metal that can form 1/ more stable ions with an incomplete d sub shell.

Question 38

Which are not transition metals

Answer 38

Zn and Sc

Question 39

Transition metal physical properties

Answer 39

High densities
High mpt/bpt

Question 40

TM chemical properties

Answer 40

1) form coloured ions in sol
2) form metal ion complexes
3) good catalysts
4) variable oxidation states

Question 41

Calc diff in Energy equation when electrons move btwn sub shells

Answer 41

Delta E= hc/ wavelength (m)
Delta E= hv (freq of light absorbed in hertz)

Question 42

Colour of complex ion depends on

Answer 42

Change in ligand
Change in CN
Change in oxidation state

Question 43

Ligand

Answer 43

Atom/ mol/ ion that forms a coordinate bond with a complex metal ion by donating a pair of electrons