C15. Using Our Natural Resources Flashcards
🟢 Why do plants need nitrogen
Plants need nitrogen to grow and make proteins.
🟢 How do plants take in nitrogen
Plants take in nitrogen in the form of soluble nitrate ions from the soil, through their roots.
🟢 Why is nitrogen not being replaced in the soil by natural cycling?
As the farmer harvests the plants, so most of the plants are not allowed to rot back into the soil, so the nitrogen absorbed from the soil during growth is not replaced by the natural cycling of nitrogen.
🟢 Why can most plants not ‘fix’ nitrogen directly from the air, given that it is 80% nitrogen?
Nitrogen gas is insoluble in water, and most plants can only absorb a soluble form of nitrogen, meaning they can’t just take in nitrogen from the atmosphere. Turning nitrogen gas from air into nitrogen compounds that plants can absorb in solution through their roots is called ‘fixing’ nitrogen.
🟢 Ammonia NH3 (g)
- Structure Type
- Bonding Within Molecule
- Bonding Between Molecules
Structure Type:
- Simple Molecular
Bonding Between Molecules:
- Covalent Bonds
Bonding Between Molecules:
- Weak intermolecular forces
🟢 Ammonia
- Stick Diagram
- Dot and Cross Diagram
Stick Diagram:
H - N - H
|
H
Dot and Cross Diagram:
The Nitrogen will havs 7 ‘x’s round it, with 3 hydrogens around each side with one circle each.
🟢 Balanced Chemical Equation of the Haber Process (Making Ammonia)
N2 (g) + 3H2 (g) ⇌ (iron catalyst) 2NH3
🟢 Given that ammonia molecules have strong covalent bonds, explain why ammonia has a very low melting point?
Ammonia molceules have strong covalent bonds, but very weak intermolcular forces holding each of the separate molecules together. With the intermolecular forces being so weak, little energy is needed to overcome the forces, meaning it has such a low boiling points.
🟢 Flow Chart/Stages of the Haber Process to get Ammonia (from raw materials to liquid ammonia)
Stages:
Raw Materials:
- Methane
- Steam
Reactants:
- Hydrogen, H2
- Nitrogen,N2
Reactor Conditions:
- Pressure: 200 atm
- Temperature: 450°C
- Catalyst: Iron Filings
-NH3 removed by cooling it to liquid ammonia
- (Reversible Reaction can take place sending the reactants back to the reactor and reaction conditions)
- (Unreacted Nitrogen and Hydrogen is recycled and sent back to the reactor)
- Product:*
- Liquid ammonia (NH3) is made
🟢 What temperature are hydrogen and nitrogen reacted at to make Ammonia (in the reactor)
450°
🟢 What pressure are hydrogen and nitrogen reacted at to make Ammonia (in the reactor)
200 atm
🟢 What catalyst is used when reacting hydrogen and nitrogen to make Ammonia (in the reactor)
Iron Filings
🟢 Temperature at 450° when reacting hydrogen and nitrogen to form ammonia:
- Effect on Yield
- Effect on Rate
- Effect on Cost
Effect on Yield:
It decreases the yield of ammonia, as the forward reaction is exothermic
Effect on Rate:
It increases the rate of the reaction
Effect on Cost:
The cost increases as it costs money to to keep the reaction heated, but it’s a good comprimise as the it keeps the reaction rate high
🟢 Pressure at 200 atm when reacting hydrogen and nitrogen to form ammonia:
- Effect on Yield
- Effect on Rate
- Effect on Cost
Effect on Yield:
It increases the yield of ammonia, as ammonia has less molecules
Effect on Rate:
It doesn’t affect the rate of reaction
Effect on Cost:
Generating the pressure costs money, but having equipment that maintains the pressure well also costs money. It increases the yield and is not super, super costly, so it’s a good compromise
🟢 Catalyst of Iron Filings when reacting hydrogen and nitrogen to form ammonia:
- Effect on Yield
- Effect on Rate
- Effect on Cost
Effect on Yield:
Does not affect the yield
Effect on Rate:
It increases the rate of the reaction, as the catalyst allows for a lower activation energy
Effect on Cost:
As there’s a lower Activation Energy, it means less energy needs to be used to make the ammonia, making it more cost effective
🟢 Is the reaction to make Ammonia an endothermic reaction or an exothermic reaction?
The reaction to make ammonia is an exothermic reaction.
🟢 Why does higher temperature lead to higher rates if reaction?
Faster rate of reactant particles have more energy so more energetic collisions and more collisions have energy greater than the activation energy
🟢 What is the Neutralisation Reaction between ammonia solution and phosphoric acid
Ammonia + Phosphoric Acid —> Ammonium Phosphate
3NH3 (aq) + H3PO4 (aq) —> (NH4)3PO4
🟢 What colour does litmus paper turn in alkali and acid
Acids:
- Litmus paper will turn red
Alkali:
-Litmus paper will turn blue
🟢 What elements/nutrients to crops need to grow
As well as nitrogen, N, crops also need significant amounts of the nutrients phosphorus, P, and potassium, K, for healthy growth. Farmers can buy fertilisers that provide compounds of nitrogen, phosphorus and potassium.
Therefore, bags of NPK fertilisers contain formulations of compounds to provide all 3 of the ‘macro-nutrients’
🟢 What are sources of phosphorus rock
The sources of phosphorus are deposits of phosphate-containing rock, which is dug or mined from the ground. It cannot be used directly on the soil, as it it is insoluble in water, so the rock is treated with acids to make fertiliser salts.
🟢 How is Phosphate rock treated?
Phosphate rocks are treated:
- With nitric acid to produce phosphoric acid, H3PO4, and calcium nitrate Ca(NO3)2. Then the phosphoric acid is neutrakised with ammonia to produce ammonium phosphate, (NH4)3PO4
- With sulphuric acid to produce single superphosphate, a mixture of calcium phosphatw, Ca(PO4)2, and calcium sulphate, CaSO4
- With phosphoric acid to produce triple superphosphate, which is calcium phosphate, Ca(PO4)2.
🟢 The student adds a 0.13 mol/dm3 solution of sulfuric acid from a burette to 25 cm3 of the ammonia solution contained in a conical flask.
She finds that exactly 26.4 cm3 of the sulfuric acid solution is needed for neutralisation.
Calculate the mass of ammonium sulfate the student should make.
Relative atomic masses, Ar values: H = 1, N = 14, O = 16, S = 32
0.13 x (26.4/1000) = 3.432x10^-3
Mr of (NH4)2SO4 = (2x14) + (8x1) + (1x32) + (4x16) = 132
3.432x10^-3 x 132 = 0.453024
🟢 Stages in the Haber Process
- Hydrogen and nitrogen gases are pumped into the vessel
- The nitrogen/hydrogen mixture is compressed to a pressure of 200atm and heated to 450°C.
- It then put into a reaction vessel containing an iron catalyst.
- The mixture of gases emerging from the reactor is cooled; ammonia liquifies and is separated.
5, the unreacted nitrogen and hydrogen are returned to the reaction vessel via the compressor.
🟢 State the sources of the raw materials used in the Haber process
Nitrogen is taken from the atmosphere, while hydrogen is taken natural gas.
