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Yr 12 Chemistry > Industrial Chemistry > Flashcards

Industrial Chemistry Flashcards

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1
Q

identify & discuss issues associated with the increased need for a natural resource that is not a fossil fuel and evaluate the progress currently being made to solve the problems identified

A

increasing population means greater demand for natural resources, yet these are in finite supply. massive demand for rubber in WWII (tyres) could not be met by the natural supply of rubber trees, & therefore synthetic products were required. synthetic rubber –> styrene-butadiene-rubber (SBR) is a useful replacement for natural rubber beacuse: -SBR is less likely to deteriorate than natural rubber. -extremely efficient and low cost to produce -styrene & butadeine are byproducts of petroleum refining SBR is mainly used for tyres

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2
Q

what are the advantages and disadvantages of synthetic rubber?

A

Advantages over natural rubber: -Better aging and weathering -Greater resistance to oil, solvents, oxygen, ozone and certain chemicals -Resilience over a wider temperature range disadvantages: not as much resistance to tearing when hot, compared to natural rubber

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3
Q

What are 3 uses of sulfuric acid?

A

-used to to make fertilisers (superphosphate & ammonium sulfate) -dilute H2SO4 used in the production of ethanol as a catalyst -Used in pigments for paints, plastics & paper. in particular titanium dioxide (TiO2) which is a white pigment

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4
Q

What are the properties of sulfur that allows its extraction?

A

-low melting point: 113 C, meaning superheated water (160 C) easily melts it -low density –> water sulfur emulsion has low density meaning that compressed air can lift it to surface -insoluble in water, meaning that after cooling sulfur easily separates from the water.

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5
Q

What are the steps in the Frasch Process?

A
  1. Superheated water (160C) is pumped down a pipe into the sulfur deposit 2. A second pipe transfers conmpressed air into the mixture of molten sulfur and water 3. The sulfur water emulsion is forced to the surface through a third pipe, rising easily due to Sulfur’s low density, as well as being aerated. 4. At the surface: air escapes, . When the mixture cools, solid sulfur separates from water with 99.5% being obtained.
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6
Q

What are the environmental issues of the Frasch process?

A

sulfur is chemically inert in the environment however: -some superheated water can cause thermal pollution in water ways h2s and so2 are harmful pollutant gases causing asthma and other health problems -some sulfur vapour can escape to form sulfur dioxide, forming acid rain -habitat destruction -the cavern remaining after sulfur has been removed is prone to collapse so subsidence over the area is v dangerous

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7
Q

ways in which the production of sulfuric acid can be maximised?

A
  1. using catalyst with a large SA (porous vandium oxide) 2.Using high pressure (however is expensive & often avoided) 3. Using a compromise temperature, that isn’t too low because the reaction is exothermic 4.Having excess oxygen
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8
Q

What are the main steps in the Solvay process?

A
  1. Brine is purified to be suitable for use in the process 2. Sodium Hydrogen carbonate formation 3. Decomposition of sodium hydrogen carbonate to sodium carbonate 4. Ammonia is then recycled
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9
Q

What is step 1. in the solvay process?

A

Brine is purified to be suitable for use in the process PURIFICATION: -calcium salts are precipitated by adding sodium carbonate Ca3+ + CO32- –> CaCO3 (s) -NaOH added to precipitate Mg, Fe & other heavy metals Mg2+ + 2OH- –> Mg(OH)2 (s) Fe3+ + 3OH- –> Fe(OH)3 (s) -after flocculation brine is then filtered

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10
Q

Where is brine obtained from in the solvay process?

A

saltwater stores, rock salt deposits & sea water

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11
Q

What is step 2. in the solvay process?

A

Sodium hydrogen carbonate formation -the purified, saturated brine solution is saturated with ammonia. -it passes through carbonators (at the top of solvay towers), where CO2 from the lime kiln is bubbled through

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12
Q

What happens in the formation of sodium hydrogen carbonate

A

-CO2 dissolves in water –> carbonic acid carbonic acid (weak acid) reacts with ammonia (weak base) –> NH4+(aq) + HCO3-(aq) -Na+ ions form a precipitate with HCO3- ions –> NaHCO3 (sodium hyfrogen carbonate)

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13
Q

what is the overall process/reaction for the formation of sodium hydrogen carbonate?

A

NaCl + CO2 +NH3 +H2O ———> NaHCO3(s) +NH4Cl (aq)

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14
Q

What is step 3. in the solvay process?

A

The decomposition of sodium hydrogen carbonate -filtered sodium hydrogen carbonate from step 2, is heated to form sodiumcarbonate THERMAL DECOMPOSITION: NaHCO3 (s) –> Na2CO3(s) +CO2(g) + H2O(g) (Carbon dioxide is recycled back into the carbonators to save $$)

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15
Q

What is step 4. in the solvay process?

A

-The filtrate recovered from hydrogen carbonate contains ammonium chloride, salt and water. -Ammonia is recovered by heating it with slaked lime. LIME COMES FROM limestone decomposition process in the lime kiln that generates CO2 -Lime decomposition: CaCO3(s) –>CaO(s) +CO2(g -calcium oxide is converted to CaOH solution the slaker: CaO(s) +H2O –> Ca(OH)2(aq) -Ammonia is recovered: Ca(OH)2(aq) + 2NH4Cl(aq) –> CaCl2(aq) +2H20 +2NH3(g) the ammonia formed is recycled to save $$

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16
Q

What is the overall reaction for the Solvay process?

A

2NaCl(aq) + CaCO3(aq) —(ammonia)—> Na2CO3(s) +CaCl2(aq)

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17
Q

What are the enviromental issues to do with the Solvay process?

A

-calcium chloride needs to be disposed of, thermal pollution, ammonia loss, disposal of solid wastes (unburnt cacl, sand and clay)

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18
Q

issues with the disposal of Cacl in the solvay process?

A

-limited uses for calcium chloride: -drying agent in industry -de-icing roads -additive in soil treatment and concrete mix BUT more is produced can be used -plants located near the sea dilute the Cacl and pump it into the ocean -Cacl can’t be disposed of into lakes s it increases the Cl- conc. to unacceptable levels. -Inland plants evaporate the Cacl to dryness and dispose of the solid wastes in appropriate locations but this is costly.

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19
Q

issues with thermal pollution in the solvay process?

A

there are some exothermic and endothermic reactions in the solvay process yet it is difficult to make use of this. -plants near the sea can effectively discharge the heated water , dissipating over a large volume of sea water causing minimal disruption to the environment. -Inland plants must release water slowly into lakes or pump into cooling ponds before being discharged into the environment

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20
Q

Issues with ammonia in the Solvay process?

A

-during certain stages in the solvay process ammonia loss inevitably occurs. -this is an issue because ammonia is an atmospheric pollutant, and also plant profits decrease with the amount of ammonia needing to be replaced as it is extremely expensive. Therefore ammonia recovery is also crucial!)

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21
Q

Issues with the disposal of solid wastes in the Solvay process?

A

Unburnt calcium chloride, sand and clay from the kiln. This solid waste isn’t toxic however hundreds of tonnes are produced daily. -It forms an unsightly sludge and the massive quantities make it difficult to aesthetically dispose of. -It could be used in bricks, landfill and road base if made commercially viable.

22
Q

What are the 3 methods of extracting sodium hydroxide?

A

-mercury cell -diaphragm cell -membrane cell

23
Q

What is reduced at the cathode in the mercury cell?

A

sodium ions are reduced at the cathode

Na+(aq) + e- + Hg(l) ———–> Na(l)(dissolved in Hg)

24
Q

What is reduced at the cathode in the diaphragm and membrane cell?

A

water is reduced at cathode 2H2O(l) +2e- –>H2(g) + 2OH- (aq)

25
Q

What is oxidised at the anode in all 3 types of mercury, diaphragm and membrane cells?

A

chlorine 2Cl- (aq) ————> Cl2(g) +2e-

26
Q

In the mercury cell is NaOH produced with brine or in separate chambers?

A

Brine & NaOH form in separate chambers

27
Q

In the Diaphragm cell is NaOH produced with brine or in separate chambers?

A

Brine & NaOH mix and have to be separated

28
Q

In the Membrane cell is NaOH produced with brine or in separate chambers?

A

Brine and NaOh do not mix, as the membrane wont let Cl- & OH- through

29
Q

in the Mercury cell is NaOH and H2 made in an electrolysis cell or in separate chambers?

A

NaOH & H2 are made in separate chambers (the decomposer) so H2 and Cl2 are kept apart: 2Na(l) + H2O(l) —————> 2NaOH(aq) +H2(g)

30
Q

What is the mercury process?

A

The mercury process uses electrolytic process to convert sodium chloride into:

-sodium hydroxide,

-chlorine gas

-hydrogen gas

31
Q

How does the mercury cell work/equipment/

A
  • Mercury flows across a sloping floor which has the voltage source terminals immersed into it
  • The mercury amalagum then flows to a second tank which contains water and a reaction produced sodium hydroxide
32
Q

What is the anode and cathode in the mercury cell?

A

Anode: Positive titanium rods which experience oxidation

Cathode: liquid mercury

33
Q
A
34
Q

What are the advantages of the mercury process?

A
  • produces very pure NaOH
  • produces pure Chlorine gas which could be sold
  • doesn’t use asbestos
35
Q

What are the techinical disadvantages of the mercury process?

A
  • process requires high voltage, making it expensive to run compared to other processes
  • v pure brine is required to start the process which is $$$ to obtain
  • lots of heat is produced at the decomposer which must be cooled
  • NaOH is very corrosive, must be stored safely
36
Q

What are the environmental issues associated with the mercury cell?

A
  • ALthough it produces v pure NaOH, some mercury can escape in nearby waterways
  • Mercury is bioaccumulative neurotoxin that is poisonous to all life
  • Chlorine gas is a strong oxidising agent, so care must be taken with its release into the enviro
37
Q

What is the over all cell reaction for the mercury cell?

A

2Na+(aq) + 2Cl- (aq) ——–> Cl2(g) +2Na(l) (Dissolved in Hg)

38
Q

What is the diaphragm process?

A

A concentrated aquous solution of sodium chloride is electrolysed to produce sodium hydroxide and hydrogen at the cathode and chlorine at the anode

39
Q

What is the anode and cathode of the diaphragm cell?

A
  • Anode: titanium anode (to withstand attack from the Cl formed)
  • Cathode: iron mesh
40
Q

What is the diaphragm cell process?

A
  • The asbestos diaphragm that lines the iron mesh cathode prevents the products from mixing
  • The asbestos allows water and sodium chloride to flow between the electrodes but separates the chlorine and hydrogen gas and helps to prevent the hydroxide ions from flowing towards the positive anode
41
Q

What is the overall cell reaction for the diaphragm cell?

A

2Na+(aq) + 2Cl-(aq) +2H2O(l)

—–>

Cl2(g) + H2(g) +2Na+(aq) + 2OH-(aq)

42
Q

What are the advantages of the diaphragm cell?

A
  • produces large quantites of NaOH and chlorine (lowest purity of all the cells tho)
  • has low voltage requirements, therefore low costs!
43
Q

What are the disadvantages of the diaphram cell (technical)?

A
  • process isn’t as effective as it produces lower purity products than the mercury process (always a small amount of chlorine in the NaOH)
  • Hypochlorite (strong oxidising agent CIO-) is present in brine and must be removed before brine is discharged into enviro
  • the need to keep chlorine and H2 gases separated, since they may react quite vigorously in contact.
44
Q

What are the environmental issues associated with the diaphragm process?

A
  • asbestos was used in early cells –> significant health and environmental issues as there are small losses of asbestos, which is a highly toxic respiratory irritant
45
Q

What is the anode and cathode for the membrane cell?

A
  • Anode: titanium rods/plates
  • cathode :iron mesh
46
Q

What is the membrane process?

A
  • anode and cathode compartments are separated by an ion-permeable membrane from synthetic polymers such as teflon.
  • The membrane only allows ions in solution to pass through, blocking out molecules
47
Q

What is the basic chemistry and process of the membrane cell?

A
  • purified brine is acidified with HCl and is passed into the anode compartment
  • Water flows through the cathode compartment, where it is reduced to OH-
  • The special membrane allows sodium ions to pass through, but not hydroxide or chloride ions
  • This prevents contamination of sodium hydroxide with sodium chloride
48
Q

What is the overall reaction for the membrane cell?

A

2NaCl(aq) + 2H2O(l)

——->

2NaOH(aq) +Cl2(g) + H2(g)

49
Q

What are the advantages of the membrane cell?

A

compared to the mercury and diaphragm cells, the main advantages are:

  • lower energy consumption
  • minimal enviro impact (no toxic waste products)
  • Produces a pure product similar to mercury cell, and more than the diaphragm cell, without the need for evaporation of excess water
50
Q

What are the disadvantages of the membrane cell?

A

No immediate environmental or health issues,

but the membrane is non-biodegradable –> long term issues

Yr 12 Chemistry (11 decks)

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