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Chemistry OCR B A LEVEL > Elements from the Sea > Flashcards

Elements from the Sea Flashcards

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1
Q

Draw a simple diagram showing apparatus involved in electrolysis

A
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2
Q

Oxidation occurs at………

Reduction occurs at ………

A

Anode

Cathode

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3
Q

Cations migrate to………..

Cathode is…………….

A

cathode

positive

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4
Q

Cations migrate to ……

Anions migrate to …….

A

Cathode

Anode

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5
Q

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?

A

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.

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6
Q

Electrolysis of Copper

Products at Cathode:

Products at Anode:

Observation to CuSO4 solution

A
  • Cu
  • Cu2+
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7
Q

Equation for reduction of H2O at Cathode:

Equation for the oxidation of water at Anode:

A
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8
Q

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

A

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

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9
Q

What is oxidation(3)

A

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

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10
Q

Displacement rxns:

What happens during a halogen displacement rxn?

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

A
  • A more reactive halogen displaces a less reactive halide ion
  • Disproportionation
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11
Q

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

A

Most positive side

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12
Q

What 3 species can you add when balancing ionic equations?

A
  • e- to balance charge
  • H2O to balance oxygen
  • H+ to balance hydrogen
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13
Q

What is the systematic name of the following compounds:

KMnO4

ClO-

ClO4-

KNO3

A

Potassium manganate(VII)

Chlorate(I)

Chlorate(VII)

Potassium nitrate(V)

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14
Q

What is the strongest oxidising halogen? Most reactive halogen?

A

Fluorine (F2) Fluorine(F2)

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15
Q

Oxidising power trend

A

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

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16
Q

Electronegativity trend

A

-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 .

17
Q

Iodine-Sodium Thiosulphate Titrations:

Explain the 2 stages involved:

A
  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.
18
Q

What happens during an Iodine-Sodium Thiosulfate titration?

A
  • Acidic potassium iodine added so iodate(V) oxidise some of the iodide ions to iodine.
  • Iodine solution reacts with thiosulphate to make iodide ions.
19
Q

Colours involved in Iodine-Sodium Thiosulfate titrations:

  • Start colour of solution
  • Colour of iodine towards end point
  • Adding ‘indicator’
  • Endpoint
A
  • Brown solution
  • fades to pale yellow near endpoint
  • Dark blue
  • Colour disappears
20
Q

Titration Accuracy:

  • What can be done to get very accurate results?(3)
A
  • 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
21
Q

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

A

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

22
Q

The trend in boiling points Group 7

A

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

23
Q

Are anions smaller or larger than atoms?

A

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

24
Q

What halide ions does chlorine oxidise/displace?

A

-Bromide ions -iodide ions

25
Q

Colours of halogen in standard state:

F2

Cl2

Br2

I2

A

F2= pale yellow gas

Cl2= yellow green gas

Br2= red/brown liquid

I2= shiny grey solid

26
Q

Colours of halogens in water:

Cl2

Br2

I2

A

Cl2= colourless

Br2= yellow/orange

I2= Brown

27
Q

Colours of halogens in organic solvents:

Cl2

Br2

I2

A

Cl2= colourless

Br2= orange/red

I2= violet

28
Q

Why do halogens get less reactive down the group?

A
  • Down grp atoms get larger, outer electrons further from nucleus, more shielding, making it harder for larger atoms to attract electrons.
29
Q

Products of hydrogen halides thermal decomposition

and

describe the trend in thermal stability

A
  • 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.
30
Q

Do HX disolve in water?

Write an equation for the reaction if a HX with ammonia:

A
  • Yes HXs are very water soluble.
  • HX(g) + NH3(g) –> NH4X(s) a white solid
31
Q

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.?

A
  • 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
32
Q
A
  • 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
33
Q

Atom economy:

  • Equation
  • What is measured?
A
  • (mr of useful products/total mr of products)X 100
34
Q

Equilibria: see notes#

  • State le chanteliers principle
  • How does increasing conc of reactant affect this?
  • How can conc be decreased?
A
  • 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
35
Q
  • How does increasing pressure affect the point of equilibrium?
  • How does decreasing temp affect the point of equilibrium?
A
  • POE shifts to side with fewer moles of gas increasing yield of side with fewer moles.
  • POE shifts to the exothermic side.
36
Q

Kc values:

  • Equation
  • Kc of > 1 means
  • Kc of < 1 means
A
  • 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)

Chemistry OCR B A LEVEL (4 decks)

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