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

Question 1

why are nitrogen, phosphorus and potassium compounds important in agricultural production?

Answer 1

whithout them, quality and yielf of food would be reduced

- as they would be mineral deficient

Question 2

how do fertilisers help plants?

Answer 2

replace the minerals used by plants as they grow

Question 3

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

Answer 3

• water soluble (ie. ions)
  NPK
• NO3- (nitrate ions)
• PO43- (phosphorus ions)
• K+ (potassium ions)

Question 4

what do NPK fertilisers do?

Answer 4

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

Question 5

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

Answer 5

it produces ammonia from nitrogen and hydrogen

Question 6

why is ammonia important in agricultural production?

Answer 6

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

Question 7

how is nitrogen obtained for the Haber process?

Answer 7

fractional distillation of liquefied air

Question 8

how is hydrogen produced for the Haber process?

Answer 8

reacting natural gas (ie. methane) with steam

Question 9

how do you manufacture ammonium nitrate?

Answer 9

1) react methane + air + water

2) react ammonia + nitric acid

Question 10

how do you manufacture ammonium sulfate?

Answer 10

1) methane + air + water
(produces ammonia)

2) ammonia + sulfuric acid

Question 11

why and how is phosphate rock treated?

Answer 11

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

Question 12

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

Answer 12

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

Question 13

describe the process of making potassium sulfate

Answer 13

bad wording but gist is there

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

Question 14

describe the process of making ammonium sulfate in the lab - bad answer icl

Answer 14

1) dilute ammonia solution with methyl orange indicator

2) titration
add sulfuric acid (until indicator turns yellow to red)

3) add a little more ammonia solution to ensure reaction is complete
(excess released as ammonia gas)

Question 15

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

Answer 15

LAB = dilute solutions (as they can be dangerous)

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

Question 16

dangers while making fertilisers through lab processes?

Answer 16

do not inhale fumes (one contains ammonia)

Question 17

what are the three conditions needed for the haber process?

Answer 17

• 200 atmosphere pressure
• 450 degree celcius
• iron catalyst

Question 18

write out the symbol equation for the haber process

Answer 18

N (g) + 3H (g) ⇌ 2NH (g)

2 2 3

Question 19

is the haber process endothermic or exothermic?

Answer 19

exothermic

(-93kj/mol) - the triangle thing

Question 20

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

• and why or why not would you use it

Answer 20

• increases the equilibrium yield 4 vs 2 mol
• increases rate of reaction
• would not use it as it is dangerous (at high pressure, for the containers)
• and would be expensive

Question 21

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

• and why or why not would you use it?

Answer 21

• 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 okay yield, but high enough for rate of reaction
• cost: somewhat okay at this compromise (450*C)

Question 22

give 2 reasons why the haber process is not carried out at a low temperature?

Answer 22

• the iron catalyst works more efficient above 400 degrees celcius
• lower rate of reaction

Question 23

how is the overall yield improved in the haber process? (apparatus)

Answer 23

the mixture of gases leaving vessel are cooled
- so ammonia liquifies (higher boiling point)
- but unreacted nitrogen and unreacted hydrogen remain as gases (as they have lower boiling points)

• and are recycled
  (yield to around 97%)

Question 24

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

Answer 24

high pressure does not justify the additional costs

Question 25

what is the purpose of the contact process?

Answer 25

produce sulfuric acid

Question 26

what is sulfuric acid used for?

Answer 26

paints, fertilisers, oil refining, metal extraction

Question 27

what are the three raw materials to produce sulfuric acid?

Answer 27

sulfur, air, water

Question 28

where are the raw materials of the haber process obtained from?

Answer 28

nitrogen (fractional distillation from air)

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

Question 29

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

Answer 29

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

Question 30

explain stage 1 of the contact process in more detail

and give symbol equation

Answer 30

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

S(s) + O (g) -> SO (g)
2 2

Question 31

explain stage 2 of the contact process in more detail (and give the corresponding symbol equations)
and the factors:
- energy change
- temp
- pressure
- which catalyst

Answer 31

• exothermic REVERSIBLE reaction
• uses 2 atmospheres pressure
• 450 degrees celcius
• vanadium(V) oxide catalyst

2SO (g) + O (g) ⇌ 2SO (g)
2 2 3

Question 32

describe stage 3 of the contact process in more detail

and give correspondning symbol equations

Answer 32

2 STAGES

1) sulfur trioxide reacts with water to make oleum
SO3 (g) + H2O (l) -> H S O (l)
2 2

2) oleum added to water
H S O (l) + H O (l) -> 2H SO (aq)
2 2 7 2 2 4

Question 33

why is stage 3 of contact process carried out in two steps?

Answer 33

as it is very exothermic (produces a hazardous acidic mist)

• and as oleum already contains water, it would not react as violently

Question 34

what factors determine the pressure chosen in the contact process?

Answer 34

• would increase the yield
• but yield is already very high (so 2 atmospheres is enough)
• a slightly higher yield does not justify a drastic increase in cost + danger

Question 35

how would a higher temperature affect the contact process?

Answer 35

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

Question 36

symptoms of nitrogen deficiency in plants (2)

Answer 36

• poor growth
• yellow leaves

Question 37

symptoms of potassium deficiency in plants (2)

Answer 37

• poor fruit growth
• discoloured leaves

Question 38

symptoms of phosphorous deficiency in plants (2)

Answer 38

• poor root growth
• discoloured leaves