Learning Intentions: State that the increasing world population has led to a need for more efficient food production. State that growing plants require nutrients, including compounds of phosphorus, potassium and nitrogen. State that fertilisers are substances, which restore the essential elements for plant growth to the soil. Explain the importance of the decomposition of plant and animal protein in the recycling of nitrogen. Explain why fertilisers are a mixture of different chemicals to provide a balance of nutrients. Perform percentage composition calculations to determine the % mass of an element within a fertiliser.

Fertilisers

Chemistry is extremely important to the future of food production Chemistry is extremely important to the future of food production. As the population of the world increases, more and more efficient ways of producing food are required. Fertilisers contain compounds that are essential for plant growth. These are known as plant nutrients. The three essential elements for plant growth are (N) ____________ (P) _____________ (K)______________ Fertilisers can be natural, like manure or compost, or synthetic (made by chemists). nitrogen phosphorus potassium

Replacing nutrients in the soil for healthy plant growth As plants grow, their roots take nutrients from the soil and this means that as time goes on the level of nutrients present in the soil decreases. The next year, plants growing in the same place would not have enough nutrients for healthy growth. Different plants require different proportions of N, P and K.

There are three ways farmers can replace nutrients into over-used soils: Grow beans or clover for one year (this bacterial method of replacing nitrogen is cheaper than chemical methods) Add synthetic fertilisers (man-made) or natural fertilisers (manure) fertilisers Crop rotation means using the same field to grow different crops from year-to-year. This allows the field to recover levels of over-used nutrients.

Why are fertilisers used? Fertilisers have two main uses. They: increase the rate and amount of growth replace nutrients removed by harvesting. The nutrients are taken in through the roots of a plant along with water. This means the nutrients must be ______ in water. soluble

Complete the table below Compound Formula Solubility Could be used as a fertiliser? Ammonium phosphate   Calcium phosphate Potassium phosphate Sodium chloride

Testing Fertilisers.   It is possible to identify the presence of some common ions in a fertiliser. The ions are the ammonium ion, potassium ion and phosphate ion. The fertilisers that you are going to try and identify using these tests are: Potassium chloride, ammonium chloride potassium phosphate. Test A B C 1   2 3 Name potassium phosphate ammonium chloride Potassium chloride

Testing Fertilisers. Test 1 – ammonium ion Put 2 or 3 spatulas of your fertiliser into a test tube, added 2 or 3 spatulas of calcium hydroxide and heat gently. Test the vapour given off with damp pH paper, does it go blue? Waft and carefully smell the gas. Test 2 - potassium ion Pour water into a test tube to a depth of 2 to 3 cm. Add a spatula of your fertiliser. Use a wooden splint (spill) to stir it until it all dissolves. Place the wet end of the splint in a roaring blue flame, does the colour of the flame go lilac? Stop when the wood catches fire. Test 3 – phosphate ion To the solution in test 2 add a few drops of lithium nitrate solution. Does any precipitate form?

The ammonia molecule has a ________ shape. Ammonia (NH3) Ammonia is the key substance in the production of fertilisers. Ammonia is a colourless, pungent (sharp) gas with a strong smell. The ammonia molecule has a ________ shape. pyrimidal

Activity 1 Dry flask containing ammonia. Results: What colour does the universal indicator turn? ______________________ What does this tell us? ______________________ ______________________ What ion is therefore present in the solution? ___________________ Water in syringe to start dissolving. Water with universal indicator.

The alkali produced is called ammonium hydroxide. Ammonia gas is therefore described as being an alkaline gas. Word equation: Formula equation: ammonia + water  ammonium hydroxide NH3(g) + H2O(l)  NH4OH(aq)

Ammonium salt + soda lime Making Ammonia Ammonia can be made in the lab by heating any ammonium salt with an alkali such as soda lime or calcium hydroxide.   Ammonium salt + soda lime Heat Damp pH paper What colour did the pH paper turn? __________________ __________________ What does this tell you about ammonia gas? __________________ __________________ The Haber Process

Percentage Mass Composition of Fertilisers Remember - a good fertiliser must contain at least one of the essential elements (N, P and K), and must be soluble in water so that it can be absorbed through the roots of plants. Ammonium nitrate is a commonly used compound in fertilisers. How to calculate percentage mass: Step 1 – Calculate the mass of 1 mole of the compound. Step 2 – Calculate how much of the element is contained in 1 mole of the compound. Step 3 – Calculate the percentage.

Example Calculate the percentage mass of nitrogen in ammonium nitrate. Step 1 Find the total mass of 1 mole of NH4NO3 1 mole = 14 + (1x4) + 14 + (16x3) = 80g   Step 2 Find the mass of nitrogen in one mole (i.e. 14 x2 =28g) Step 3 Calculate the percentage mass = 28 80 x 100 = 35%

Exercise 2 Calculate the percentage mass of nitrogen in urea, (NH2)2CO. Calculate the percentage mass of nitrogen, and potassium, in potassium nitrate. Calculate the percentage mass of nitrogen in ammonium sulfate. Calculate the percentage mass of nitrogen, and phosphorus, in ammonium phosphate.

Exercise 2 Answers Calculate the percentage mass of nitrogen in urea, (NH2)2CO. GFM of (NH2)2CO= 60g ∴ % of N2 = 46.7% Calculate the percentage mass of nitrogen, and potassium, in potassium nitrate. GFM of KNO3= 101g ∴ % of N2 = 13.9%, K= 38.6% Calculate the percentage mass of nitrogen in ammonium sulfate. GFM of (NH4)2SO4= 132g ∴ % of N2 = 21.2% Calculate the percentage mass of nitrogen, and phosphorus, in ammonium phosphate. GFM of (NH4)3PO4= 149g ∴ % of N2 = 28.2%, P= 20.8%