Elements from the Sea

Question 1

Draw a simple diagram showing apparatus involved in electrolysis

Answer 1

Question 2

Oxidation occurs at………

Reduction occurs at ………

Answer 2

Anode

Cathode

Question 3

Cations migrate to………..

Cathode is…………….

Answer 3

cathode

positive

Question 4

Cations migrate to ……

Anions migrate to …….

Answer 4

Cathode

Anode

Question 5

Electrolysis of (conc)Brine

Why is making Cl2 on-site preferred to transporting it?

What are the products of this electrolysis?

Why is a membrane cell needed during this electrolysis?

Answer 5

A toxic gas so it cannot be contained and bad when inhaled as it is an irritant. Can form chlorinated hydrocarbons which are cancerous.

Cl2 , H2, NaOH all useful

To prevent products from reacting.

Question 6

Electrolysis of Copper

Products at Cathode:

Products at Anode:

Observation to CuSO₄ solution

Answer 6

• Cu
• Cu²⁺

Question 7

Equation for reduction of H₂O at Cathode:

Equation for the oxidation of water at Anode:

Answer 7

Question 8

Appearance and state of Fluorine at rtp Appearance and state of Chlorine at rtp Appearance and state of Bromine at rtp Appearance and state of Iodine at rtp

Answer 8

Pale yellow gas Green gas Reddish-brown liquid Shiny grey/black solid (May sublimate to purple vapour)

Question 9

What is oxidation(3)

Answer 9

-loss of electrons -loss of hydrogen -gain of oxygen

Question 10

Displacement rxns:

What happens during a halogen displacement rxn?

Name given when a species is oxidised and reduced at the same time

Answer 10

• A more reactive halogen displaces a less reactive halide ion
• Disproportionation

Question 11

When balancing half-equations, on which side do you add e-?

Answer 11

Most positive side

Question 12

What 3 species can you add when balancing ionic equations?

Answer 12

• e- to balance charge
• H2O to balance oxygen
• H+ to balance hydrogen

Question 13

What is the systematic name of the following compounds:

KMnO4

ClO^-

ClO^4-

KNO3

Answer 13

Potassium manganate(VII)

Chlorate(I)

Chlorate(VII)

Potassium nitrate(V)

Question 14

What is the strongest oxidising halogen? Most reactive halogen?

Answer 14

Fluorine (F2) Fluorine(F2)

Question 15

Oxidising power trend

Answer 15

-Oxidising power decreases down group -Increasing nuclear charge is overcomed by increasing shielding and increasing radius.

Question 16

Electronegativity trend

Answer 16

-Dereases down group -Increasing nuclear charge due to greater number of protons should attract electrons more but -increasing number of shells so more shielding and less pull on electrons -Increasing atomic radius so attraction decreases as distance increases .

Question 17

Iodine-Sodium Thiosulphate Titrations:

Explain the 2 stages involved:

Answer 17

1. Use a sample of an oxidising agent to oxidise as much iodine as possible. Add acidic potassium iodine to potassium iodate(V)
2. Find out how many moles of iodine have been produced. Titrate with Sodium thiosulphate.

Question 18

What happens during an Iodine-Sodium Thiosulfate titration?

Answer 18

• Acidic potassium iodine added so iodate(V) oxidise some of the iodide ions to iodine.
• Iodine solution reacts with thiosulphate to make iodide ions.

Question 19

Colours involved in Iodine-Sodium Thiosulfate titrations:

• Start colour of solution
• Colour of iodine towards end point
• Adding ‘indicator’
• Endpoint

Answer 19

• Brown solution
• fades to pale yellow near endpoint
• Dark blue
• Colour disappears

Question 20

Titration Accuracy:

• What can be done to get very accurate results?(3)

Answer 20

• Make sure burette is clean and rinse with thiosulfate before start to remove traces of water
• Reduce effect of random errors repeat 3 times and calculate mean value
• Read burette correctly from bottom of the meniscus with eyes level with liquid

Question 21

Colours of halide ions with Silver Nitrate What happens if you add dilute ammonia?

Answer 21

Cl- = White ppt Soluble Br- = Cream ppt Insoluble I- = Pale yellow ppt Insoluble (even in conc NH3)

Question 22

The trend in boiling points Group 7

Answer 22

-Increase in boiling points down group -increased size makes induced dipole-dipole interactions increase -More energy required to separate molecules

Question 23

Are anions smaller or larger than atoms?

Answer 23

-Larger as an extra electron is gained -as repulsion from added electron expands radius

Question 24

What halide ions does chlorine oxidise/displace?

Answer 24

-Bromide ions -iodide ions

Question 25

**_Colours of halogen in standard state:_** **_F2_** **_Cl2_** **_Br2_** **_I2_**

Answer 25

F2= pale yellow gas Cl2= yellow green gas Br2= red/brown liquid I2= shiny grey solid

Question 26

**_Colours of halogens in water:_** **_Cl2_** **_Br2_** **_I2_**

Answer 26

Cl2= colourless Br2= yellow/orange I2= Brown

Question 27

**_Colours of halogens in organic solvents:_** **_Cl2_** **_Br2_** **_I2_**

Answer 27

Cl2= colourless Br2= orange/red I2= violet

Question 28

Why do halogens get less reactive down the group?

Answer 28

* Down grp atoms get larger, outer electrons further from nucleus, more shielding, making it harder for larger atoms to attract electrons.

Question 29

Products of hydrogen halides thermal decomposition and describe the trend in thermal stability

Answer 29

* Only HBr and HI decompose thermally. Into H2 + X2 * Thermal stability decreases down the group as the distance of the outer e- to the nucleus increases down group.

Question 30

Do HX disolve in water? Write an equation for the reaction if a HX with ammonia:

Answer 30

* Yes HXs are very water soluble. * HX(g) + NH3(g) --\> **_NH4X(s) a white solid_**

Question 31

How can we make HXs? How can you collect this? Witch 2 HXs react with the substance used in making HXS? What is the acronym for the side reactions occurring? Alternative substance to make HXs that react with usual conc.?

Answer 31

* react NaX with conc.H2SO4 --\> HX + NaHSO4 * through a gas syringe * HBr and HI * HBr- SOBr meaning SO2 and Br2 + water / HI- HISS meaning H2S(rotten egg smell) + I2 plus water * H3PO4

Answer 32

* HI is the easiest to decompose thermally as it is the largest halogen shared electrons are further from the nucleus. * Bigger so longer bond so easier to break

Question 33

**_Atom economy:_** * Equation * What is measured?

Answer 33

* (mr of useful products/total mr of products)X 100

Question 34

**_Equilibria: see notes#_** * State le chanteliers principle * How does increasing conc of reactant affect this? * How can conc be decreased?

Answer 34

* If a system at equilibrium is disrupted the position of equilibrium will shift to oppose change. * If conc of reactant increases, POE shifts temporarily to forward reaction to oppose this. POE shifts to RHS

Question 35

- How does increasing pressure affect the point of equilibrium? - How does decreasing temp affect the point of equilibrium?

Answer 35

* POE shifts to side with fewer moles of gas increasing yield of side with fewer moles. * POE shifts to the exothermic side.

Question 36

**_Kc values:_** * Equation * Kc of \> 1 means * Kc of \< 1 means

Answer 36

* Equilibrium lies to right hand side * Equilibrium lies to left hand side ( greater than or less than sign looks like an arrow pointing to where equilibrium lies)