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Chem C4-C6 > ✅C6.1 (1) - fertilisers, haber + contact processes > Flashcards

✅C6.1 (1) - fertilisers, haber + contact processes Flashcards

c6.1.1 - c6.1.4

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1
Q

why are nitrogen, phosphorus and potassium compounds important in agricultural production?
- what happens without them

A

without them, quality and yield of food would be reduced

- as they would be mineral deficient

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2
Q

how do fertilisers help plants?

A

replace the elements used by plants as they grow

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3
Q

what form must elements be in in order for plants to absorb them?
- and name them for each element

A 
- water soluble (ie. ions) 
NPK
- NO3- (nitrate ions), or NH4 +(ammonium ions)
- PO43- (phosphorus ions)
- K+ (potassium ions)
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4
Q

what do NPK fertilisers do?

A

provide plants with nitrogen, potassium and phosphorus in water soluble compounds

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5
Q

what is the importance of the Haber process in agricultural production?

A

it produces ammonia from nitrogen and hydrogen

MS:
Endless supply of starting materials / no need to use solid raw materials to make fertilisers (1)
Ammonia used to make fertilisers which increase crop yield (1)

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6
Q

why is ammonia important in agricultural production?

A

is a large source of nitrogen, and so is used to make nitrogen based fertilisers

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7
Q

how is nitrogen obtained for the Haber process?

A

fractional distillation of liquefied air

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8
Q

how is hydrogen produced for the Haber process?

A

reacting natural gas (ie. methane) with steam

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9
Q

in terms of processes, what happens in a fertiliser factory?

A

several different processes are inegrated using a variety of raw materials

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10
Q

how do you manufacture ammonium nitrate?

A

1) react methane + air + water

2) react ammonia + nitric acid

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11
Q

how do you manufacture ammonium sulfate?

A

1) methane + air + water
(produces ammonia)

2) ammonia + sulfuric acid

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12
Q

why and how is phosphate rock treated?

A
  • because it cannot be used directly as a fertiliser
  • is treated with nitric acid/sulfuric acid
  • to produce a soluble salt
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13
Q

what are the 3 differences between the industrial and lab production of fertilisers?

A 
LAB 
- use ammonia solution/sulfuric acid (bought from chemical manufacturer) 
- small scale 
- only few stages
titration -> crystallisation

INDUSTRY

  • use raw materials + purify them (ie. to make ammonia)
  • large scale
  • many stages needed
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14
Q

describe the process of making potassium sulfate in the lab

A

1) dilute potassium hydroxide solution into conical flask
2) add drops of phenolphthalein indicator

3) perform titration with sulfuric acid
(colour changes from pink to colourless)

4) add activated charcoal
(attracts phenolphthalein indicator)

5) filter mixture (removes charcoal + indicator)
6) warm filtrate to evaporate water + leave behind potassium sulfate salt. You must not heat this to dryness.

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15
Q

what are the three ‘main’ processes when making potassium sulfate salt?

  • and what is each for?
A

1) titration (neutralise acid)
2) filtration (get rid of indicator)
3) crystallisation (obtain salt from solution)

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16
Q

describe the process of making ammonium sulfate - there’s another card later w/ full process

A

1) dilute ammonium solution with methyl orange indicator

2) titration
add dilute sulfuric acid (H2SO4, from a burette or dropping pipette) (until indicator changes from yellow to red)

3) once end-point reached, add a little extra ammonia solution to ensure reaction is complete
(excess released as ammonia gas//any remaining ammonia will be lost during evaporation)

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17
Q

difference between lab and industrial process (in terms of solutions)

A

LAB = dilute solutions (as they can be dangerous)

IND = concentrated solutions (so they have a higher yield)

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18
Q

dangers while making fertilisers through lab processes?

- when making ammonium sulfate and potassium sulfate

A
  • do not inhale fumes (ammonia gives off an irritating sharp smell)
  • ammonia solution and potassium hydroxide solution are alkaline

(Googled: , wouldn’t worry - just remember the fumes)

  • potassium hy = contact can severely irritate and burn the skin and eyes leading to eye damage. ► Contact can irritate the nose and throat
  • amm sol = corrosive injury including skin burns, permanent eye damage or blindness.
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19
Q

what is the purpose of the experiments to produce a fertiliser?

A

to produce the salt

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20
Q

what are the three conditions needed for the haber process?

A
  • 200 atmospheres pressure (20MPa)
  • 450 degree celcius
  • iron catalyst
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21
Q

write out the symbol equation for the haber process

A

N (g) + 3H (g) ⇌ 2NH (g)

2 2 3

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22
Q

is the haber process endothermic or exothermic?

A

exothermic

🔺H = -93kj/mol

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23
Q

how does a higher pressure affect the haber process?
(think about the equation)

  • and why or why not would you use it
A
  • increases the equilibrium yield 4 vs 2 mol
  • would not use it as it is hazardous (at high pressure, for the containers)
  • and would be expensive
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24
Q

how does a higher temperature affect the haber process? (equation)

  • and why or why not would you use it?
A
  • decreases equilibrium yield (shifts position to left)
    is exothermic
  • but not too low, or else rate of reaction is too low
    COMPROMISE
  • low enough for reasonable yield, but high enough for rate of reaction
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25
Q

give one more reason why the haber process is not carried out at a low temperature?

A

as the iron catalyst works more efficient above 400 degrees celcius

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26
Q

how is the overall yield improved in the haber process?

A

the mixture of gases leaving vessel are cooled
- so ammonia liquifies (lower boiling point)

  • but unreacted nitrogen and unreacted hydrogen remain as gases
  • and are recycled
    (yield to around 97%)

In English:
The mixture of gasses leaving the reaction vessel is cooled so that the ammonia is liquefied.
This allows the ammonia to be removed, and unreacted nitrogen and hydrogen to be recycled.
This improves the overall yield to around 97%.

27
Q

give another reason why a high pressure is not used for the haber process (to produce ammonia)

A

high pressure does not justify the additional costs

28
Q

what is the purpose of the contact process?

A

produce sulfuric acid

29
Q

uses of sulfuric acid (4)

A
  • to make fertilisers

- Oil refining, metal extraction, making paints and polymers

30
Q

what are the three raw materials to produce sulfuric acid?

A

sulfur, air, water

31
Q

where are the raw materials of the haber process obtained from?
- one of them has two ways of being obtained

A

nitrogen (fractional distillation from air)

hydrogen (electrolysis of water or by reacting natural gas with steam)

32
Q

how does an iron catalyst increase the rate of reaction for the haber process?
- why

A
  • iron filings have a high surface area

- so gases can be absorbed on the surface

33
Q

what are the 3 stages in the contact process (and give a brief description of each one)

A

1) BURNER
burn sulfur powder in air to produce sulfur dioxide

2) CONTACT PROCESS
sulfur dioxide reacts with oxygen to produce sulfur trioxide - REVERSIBLE (so has specific conditions)

3) HYDRATION
sulfur trioxide converted into sulfuric acid (using oleum) - 2 STAGES

34
Q

explain stage 1 of the contact process in more detail

and give symbol equation

A
  • an exothermic reaction
  • sulfur powder just burned in air + reacts with oxygen

S(s) + O2 (g) -> SO2 (g)

35
Q

explain stage 2 of the contact process in more detail (and give the corresponding symbol equations)
- and the factors

A
  • sulfur dioxide reacts with oxygen
  • exothermic REVERSIBLE reaction (-144kJ/mol)
  • equilibrium yield = 96%
  • uses 2 atmospheres pressure (200kPa)
  • 450 degrees celcius
  • vanadium(V) oxide catalyst (V2O5)

2 SO2 (g) + O2 (g) ⇌ 2 SO3 (g)

36
Q

explain stage 3 of the contact process in more detail

(and give correspondning symbol equation) + state symbols

A

2 STAGES

1) sulfur trioxide passed through sulfuric acid (made previously) to make oleum
H2SO4 (l) + SO3 (g) -> H2S2O7 (l)

2) oleum added to water
H2S2O7 (l) + H2O (l) -> 2H2SO4 (aq)

37
Q

why is stage 3 carried out in two steps?

A

The reaction between sulfur trioxide and water is very exothermic. It would produce a hazardous acidic mist.

  • and as oleum already contains water, it would not react as violently (not sure about this one AD)
38
Q

what factors determine the pressure chosen in the contact process?

A
  • would increase the yield

- but yield is already very high (so 2 atmospheres is enough)

39
Q

how would a higher temperature affect the contact process?

A
  • decrease the yield (is exothermic)
  • but temp must be high enough for rate of reaction
  • and vandium oxide catalyst only works above 380 degrees celcius
40
Q

Nitrogen, N - typical symptoms of deficiency

A

Poor growth, yellow leaves

41
Q

Phosphorus, P - typical symptoms of deficiency

A

Poor root growth, discoloured leaves

42
Q

Potassium, K - typical symptoms of deficiency

A

Poor fruit growth, discoloured leaves

43
Q

How do plants obtain mineral ions?

A

As plants grow, they absorb mineral ions from the water in the soil through their root hair cells

44
Q

What does the Haber process reach

A

A dynamic equilibrium

45
Q

It is expensive to achieve very high pressures: Why - 2

A

It is expensive to achieve very high pressures:

  • stronger equipment is needed
  • more energy is needed to compress the gases
46
Q

How to obtain:

Sulfuric acid

A

Sulfur

47
Q

How to obtain:

Phosphoric acid

A

Phosphate rock + sulfuric acid

48
Q

How to obtain:

Ammonia

A

Natural gas, air, water

49
Q

How to obtain:

Ammonium sulfate

A

Sulfuric acid + ammonia

50
Q

How to obtain:

Nitric acid

A

Ammonia

51
Q

How to obtain:

Ammonium phosphate

A

Phosphoric acid, ammonia

52
Q

How to obtain:

Ammonium nitrate

A

Nitric acid, ammonia

53
Q

How to obtain:

Potassium nitrate

A

Ammonium nitrate, potassium chloride

54
Q

Batch process?

A

The lab preparation of ammonium sulfate is a ‘batch’ process. A small amount of product is made slowly at any one time, and the apparatus cleaned ready to make another batch.

55
Q

Continuous process?

A

The industrial production of ammonium sulfate is a ‘continuous’ process. The product is made quickly all the time, as long as raw materials are provided.

56
Q

Substances in lab vs industrial processes - where obtained

A

In lab, you start with pure substances brought from a chemical manufacturer.
.
Fertiliser factories start with raw materials (substances obtained from the ground, air, or sea). These must be purified before use, or the product must be purified at the end.

57
Q 
……………………………… |Batch Process|Continuous process
Rate of production 
Relative cost of equipment
Number of workers needed
Shut-down periods
Ease of automating the process
A

……………………………… |Batch Process|Continuous process

Rate of production - low|high
Relative cost of equipment - low|high
Number of workers needed - large|small
Shut-down periods - frequent|rare
Ease of automating the process - low|high
58
Q

Full proper method, making ammonia sulfate in lab

A

Here is an outline of one way to make ammonium sulfate in the lab. Eye protection must be worn.

  1. Put some dilute sulfuric acid into a beaker.
  2. Add a few drops of methyl orange indicator.
  3. Add dilute ammonia solution drop by drop, stirring in between.
  4. Continue step 3 until the colour permanently changes from red to yellow.
  5. Add a few more drops of dilute ammonia solution. — This is to make sure that all the dilute sulfuric acid has reacted. During heating at stage 6, any excess ammonia gas leaves the evaporating basin, so only ammonium sulfate solution is present.
  6. Pour the reaction mixture into an evaporating basin, and heat carefully over a boiling water bath.
  7. Stop heating before all the water has evaporated and leave aside for crystals to form.
  8. Pour away excess water and leave the crystals to dry in a warm oven, or pat dry with filter paper

(weird to have the acid in the beaker and alkaline in burette - textbook other way round - therefore would be yellow to red also)

59
Q

Both Haber and Contact processes are at same temperature?

A

Yes, 450 degrees

60
Q

Making potassium sulfate vs ammonium sulfate

A

Potassium sulfate - activated charcoal, phenolphthalein (pink to colourless)

Ammonium sulfate -
Methyl orange (yellow to red, alkaline - acid)
61
Q

Difference in catalyst - Haber vs contact

A

Haber:
Iron catalyst - works MORE EFFICIENTLY above 400 degrees

Contact:
Vanadium(V) oxide catalyst - ONLY works above 380 degrees

62
Q

Describe the Haber process.

A

the purified gases are passed over a catalyst of iron at a high temperature (450 degrees Celsius) and a high pressure - 200 atmospheres. Some of the hydrogen and nitrogen react to form ammonia. On cooling the ammonia liquifies and is removed. Unused gases are recycled

63
Q

CONTACT PROCESS - REAL STEP 3

A

H2O + SO3 -> H2SO4

64
Q

Continuous vs batch table

A

Chem C4-C6 (19 decks)

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