Unit 3 - Topic 4 - Plant Nutrients and Fertilisers

Question 1

Describe the importance of plants

Answer 1

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

Question 2

Describe solubility

Answer 2

The nutrients are taken in through the roots of a plant along with water. This means the nutrients must be soluble in water.

Question 3

What does soluble mean?

Answer 3

The substance dissolves in water.

Question 4

What is a Fertiliser?

Answer 4

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.

Question 5

Describe man-made fertilisers

Answer 5

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.

Question 6

Name the compounds found in fertilisers

Answer 6

Ammonium Sulphate
Ammonium Phosphate 
Ammonium Nitrate
Potassium Nitrate
Potassium Phosphate

Question 7

Why do Fertilisers Need to be Soluble in Water?

Answer 7

Fertilisers need to be soluble in water so they can be taken into the plant
through the roots.

Question 8

Describe making ammonia

Answer 8

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).

Question 9

Describe triple covalent bonds

Answer 9

Triple covalent bonds require a large amount of energy to break to allow nitrogen atoms to bond to other atoms.

Question 10

Describe nitrogen + oxygen

Answer 10

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.

Question 11

Describe preparing ammonia in the lab

Answer 11

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.

Question 12

What happens when ammonia is heated?

Answer 12

When ammonia chloride is heated with sodium hydroxide the products are sodium chloride, water, and ammonia gas.

Question 13

Describe the appearance of ammonia

Answer 13

Colourless Liquid

Question 14

Describe the smell of ammonia

Answer 14

Pungent (really strong)

Question 15

Describe the solubility in water of ammonia

Answer 15

Very soluble

Question 16

Describe the pH of ammonia

Answer 16

Alkaline

Question 17

What is the formulae for ammonia

Answer 17

NH_3

Question 18

Describe the manufacturing of ammonia

Answer 18

Ammonia is made in industry by reacting nitrogen and hydrogen.

Question 19

What does ⇌ mean?

Answer 19

This symbol indicates the reaction is reversible.

Question 20

Describe the reaction conditions for making ammonia

Answer 20

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.

Question 21

Describe the Haber process

Answer 21

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).

Question 22

Describe the Ostwald process

Answer 22

The Ostwald Process produced nitric acid (HNO_3).

Nitric acid is used to make nitrate salts which can be used as fertilisers.

Question 23

Give the steps to the Ostwald process

Answer 23

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).

Question 24

Give the equation for the Ostwald process

Answer 24

Ammonia + Oxygen → Nitrogen monoxide

Question 25

Describe making fertilisers

Answer 25

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.

Question 26

What is the general equation for neutralisation?

Answer 26

Acid + Alkali (base) –> Salt + Water

Question 27

Describe ammonium salts

Answer 27

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.

Question 28

Describe potassium salts

Answer 28

To make potassium salts, the alkali potassium hydroxide or the base potassium oxide are used.

Question 29

Describe Making Fertilisers with Phosphorous Present

Answer 29

If phosphorous is required in your fertiliser, you would use the acid phosphoric acid (HNO_3)

Question 30

Describe preparing fertilisers

Answer 30

Fertilisers can be prepared in the laboratory by carrying out a titration.

The water from the salt solution can be evaporated.

Question 31

How do we know the reaction is complete?

Answer 31

Because the phenolphthalein indicator turned from pink to colourless.

Question 32

If there is unreacted hydrogen gas or nitrogen gas, what could we do to make the process more economical (cheaper)?

Answer 32

Recycle any unreacted gases.