Part 3 – Agrochemicals

1.
(a) Name the three elements that are present in most fertilisers.
(b) Apart from containing nitrogen, suggest why nitrate salts are used as fertilisers (you may wish to use page 5 of the data booklet).

2. A pupil wanted to prove that a fertiliser contained an ammonium salt.

(a) Write the chemical formula for (i) ammonium phosphate (ii) ammonium sulphite.
(b) Describe how the pupil could use sodium hydroxide and pH paper to show the presence of the ammonium ion in the salt.

3. From the list of words below, select 4 descriptions which describe the properties of ammonia.

Brown soluble solid acidic odourless fishy smell alkaline insoluble less dense than air more dense than air

4. The following flow diagram represents an industrial preparation of ammonia gas.

(a) What is happening at process X?
(b) Name the main gas that is present in the by-products.
(c) What name is given to process Z?
(d) Name the catalyst used in process Z
(e) In process Z, what are the conditions of pressure and temperature?
(f) Explain why the temperature of process Z cannot be left to reach very high temperatures.

5. A common use for ammonia is the manufacture of fertilisers. Two such fertilisers are ammonium sulphate and ammonium nitrate.

(a) Write the chemical formula for each fertiliser.
(b) Calculate the % of nitrogen in each fertiliser.

6.
(a) When some air was sparked, a brown gas formed.
(i) Name the brown gas.
(ii) Write a balanced equation to show its formation.
(iii) When does this reaction occur in nature?
(b) The brown gas was then dissolved in water.
(i) Give the name of the solution formed.
(c) Why is step (a) not used in industry to prepare this acid?

7. The industrial preparation of nitric acid uses ammonia as its starting material.
(a) Name the industrial process used to make nitric acid.
(b) Name the catalyst used in this process.
(c) Why does the catalyst not have to be heated once the reaction has started?

8. Nitrogen dioxide and bromine are both brown gases. Describe an experiment you could carry out to show which gas is which.

9.
(a) Identify the 2 compounds which can be used as fertilisers.
(b) Identify the 2 compounds which react together to produce ammonia.

10. Ammonia is made by the Haber process.

(a) The rate at which the hydrogen and nitrogen react increases as the temperature of the gases increases. Why is the Haber process carried out at only a moderate temperature?
(b) How is the ammonia removed from the unreacted gases?
(c) Name 2 chemicals that could be used to prepare ammonia in the lab.

11. Some plants can convert atmospheric nitrogen into nitrogen compounds. This is called fixing nitrogen.
(a) How are some plants able to fix nitrogen?
(b) Why would the development of cereal crops which fix nitrogen save on energy costs?

12. The graph shows how the level of
nitrates in the soil of a farmer’s field
varied throughout the year.

(a) Suggest why the levels of nitrates increased in April.

(b) During periods of heavy rain,
Nitrates from the soil are washed into rivers.
What effect does this have on the rivers?

 

 

14. The Ostwald process is used to make nitric acid. The first step involves making nitrogen monoxide and then nitrogen dioxide from ammonia.

(a) Why is nitrogen dioxide made from ammonia and not from nitrogen?
(b) The reaction is exothermic. Why is this an advantage?
(c) Name the catalyst used.

15. Different elements are needed for healthy plant growth. Carbon, hydrogen and oxygen can be obtained from carbon dioxide and water. Phosphorus and potassium can be obtained from fertilisers.

(a) Name one other essential element needed by plants.
(b) Some fertilisers contain potassium sulphate, K2SO4.
(i) Calculate the formula mass of potassium sulphate
(ii) Calculate the % K in potassium sulphate.
(c) Calcium phosphate is readily available but cannot be used directly in fertilisers. Suggest why it is unsuitable. Use page 5 of the data booklet.