Unit 3 - Topic 4 - Plant Nutrients and Fertilisers Flashcards
Describe the importance of plants
Plants are important to life on the planet as they make food. Plants are eaten for food or animals are eaten which have eaten plants.
As plants grow they make carbohydrates, proteins, vitamins, and oils.
Plants need nutrients from the soil to grow. There are three essential elements required for plant growth. These elements are:
Nitrogen - Nitrogen is the main nutrient element required by plants as all proteins contain nitrogen.
Phosphorous
Potassium
Describe solubility
The nutrients are taken in through the roots of a plant along with water. This means the nutrients must be soluble in water.
What does soluble mean?
The substance dissolves in water.
What is a Fertiliser?
A fertiliser is a substance used to add or replace nutrients in the soil.
Fertilisers can be natural (like manure) or synthetic (man-made).
The main compounds found in fertilisers are ammonium salts, potassium salts, nitrates and phosphates.
Describe man-made fertilisers
Man-made fertilisers can be altered and added to. This means they can be designed to fit the nutrient requirements of specific crops and soils.
Name the compounds found in fertilisers
Ammonium Sulphate Ammonium Phosphate Ammonium Nitrate Potassium Nitrate Potassium Phosphate
Why do Fertilisers Need to be Soluble in Water?
Fertilisers need to be soluble in water so they can be taken into the plant
through the roots.
Describe making ammonia
Nitrate fertilisers are salts of NITRIC ACID (HNO3).
Making nitric acid requires the production of nitrogen dioxide gas (NO2).
Nitric acid is made when nitrogen dioxide gas (NO2) is dissolved in water.
Nitrogen is a very unreactive gas. This is due to the bonding in the nitrogen molecule (N2).
Describe triple covalent bonds
Triple covalent bonds require a large amount of energy to break to allow nitrogen atoms to bond to other atoms.
Describe nitrogen + oxygen
Reacting nitrogen with oxygen to produce nitrogen dioxide is not an economic method as the reaction requires a huge amount of energy and is very slow. Another route to producing nitrogen dioxide was found using ammonia (NH3) as the starting chemical.
Describe preparing ammonia in the lab
Ammonia can be prepared by heating any ammonia salt with an alkali
The experiment detects the presence of the ammonium ion (NH_4^+) in a compound.
The results of this experiment is that it turns wet pH paper blue, indicating ammonia is an alkaline gas.
What happens when ammonia is heated?
When ammonia chloride is heated with sodium hydroxide the products are sodium chloride, water, and ammonia gas.
Describe the appearance of ammonia
Colourless Liquid
Describe the smell of ammonia
Pungent (really strong)
Describe the solubility in water of ammonia
Very soluble
Describe the pH of ammonia
Alkaline
What is the formulae for ammonia
NH_3
Describe the manufacturing of ammonia
Ammonia is made in industry by reacting nitrogen and hydrogen.
What does ⇌ mean?
This symbol indicates the reaction is reversible.
Describe the reaction conditions for making ammonia
As the temperature increases, the yield of ammonia decreases.
As the pressure increases, the yield of ammonia increases.
A high yield of ammonia can be obtained with a high pressure and a low temperature.
Describe the Haber process
Nitrogen from the air is reacted with hydrogen from natural gas are reacted at 400-450oC. If the temperature is any higher, the backward reaction is more dominant.
An iron catalyst is used to speed up the rate of reaction.
The product is ammonia (NH_3).
Describe the Ostwald process
The Ostwald Process produced nitric acid (HNO_3).
Nitric acid is used to make nitrate salts which can be used as fertilisers.
Give the steps to the Ostwald process
Step 1:
Ammonia (from the Haber Process) is reacted with oxygen (from the air) to produce nitrogen monoxide. A platinum catalyst is used. The reaction is carried out between 600-800oC.
Step 2:
Nitrogen monoxide is reacted with oxygen to produce nitrogen dioxide.
Step 3:
Nitrogen dioxide is dissolved in water to produce nitric acid (HNO_3).
Give the equation for the Ostwald process
Ammonia + Oxygen → Nitrogen monoxide
Describe making fertilisers
The main compounds found in fertilisers are ammonium salts, potassium salts, nitrates and phosphates. Making a fertiliser requires the appropriate reactants.
We can make fertiliser salts by neutralisation.
What is the general equation for neutralisation?
Acid + Alkali (base) –> Salt + Water
Describe ammonium salts
To make ammonium salts, the alkalis used are ammonia (NH_3) or ammonium hydroxide (NH_4^+OH^-). When ammonia is used, water is not produced but when ammonium hydroxide is used, water is produced.
Describe potassium salts
To make potassium salts, the alkali potassium hydroxide or the base potassium oxide are used.
Describe Making Fertilisers with Phosphorous Present
If phosphorous is required in your fertiliser, you would use the acid phosphoric acid (HNO_3)
Describe preparing fertilisers
Fertilisers can be prepared in the laboratory by carrying out a titration.
The water from the salt solution can be evaporated.
How do we know the reaction is complete?
Because the phenolphthalein indicator turned from pink to colourless.
If there is unreacted hydrogen gas or nitrogen gas, what could we do to make the process more economical (cheaper)?
Recycle any unreacted gases.
