Topics: Titration, Sulfate, Hydrochloric acid Pages: 10 (2112 words) Published: March 23, 2014

Unit 3 assessment O1
Analysis of fertiliser-an extended experimental investigation

In this investigation you will analyse the composition of a lawn fertiliser, or ‘lawn food’.

You may use external sources to help you complete the this section.

Q1. Why is each of the elements Nitrogen, Phosphorus, sulfur and iron included in lawn food?


Q2. What distinguishes gravimetric analysis from other forms of analysis? ____________________________________________________________________________________________________________________________________________________________________________

Q3. Briefly describe the process of volumetric analysis.
____________________________________________________________________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________________________________________________________________

Q4. Explain the chemical principle involved in spectroscopic techniques in general and specifically in colorimetry. ____________________________________________________________________________________________________________________________________________________________________________

Q5. In this assessment you will analyse the iron content of the fertiliser using a redox titration. Describe another way an analysis for iron could be performed. ____________________________________________________________________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________________________________________________________________

Q6. Phosphorus from fertilisers has been implicated in a type of pollution called eutrophication. Explain how this process arises. ____________________________________________________________________________________________________________________________________________________________________________ Unit 3 extended investigation

Part 1: Gravimetric determination of sulfate in fertiliser

Purpose: to find the proportion of sulfate present in a brand of commercial fertiliser.

Equipment: 1.0g fertiliser, 3ml 2M Hydrochloric acid solution, 5ml 0.1M silver nitrate solution, 20ml 0.5M barium chloride solution, 200ml distilled ( de-ionised) water, 20ml warm distilled water, 2x 100ml beakers, 600ml beaker, 10ml measuring cylinder, burette and stand, filter funnel, filter paper, vacuum flask and pump, glass filter crucible and rubber adaptor, filter paper, stirring rod, wash bottle with distilled water, mortar and pestle, Bunsen burner, tripod stand and gauze, bench mat, electronic balance, oven, safety goggles.


This practical activity determines the amount of sulfur present in a fertiliser in the form of sulphate ions. The sulphate is precipitated as barium sulphate from a solution containing a known mass of fertiliser by adding excess barium chloride solution:

Ba2+(aq) + SO4 2-(aq) BaSO4 (s)

The proportion of sulfate ions and therefore sulfur in the fertiliser is determined by collecting and weighing the precipitate that is formed during the reaction. This is gravimetric analysis.

1. Grind a small amount of fertiliser using a mortar and pestle. Weigh out accurately about 1.0g (record mass) of fertiliser into a 100ml beaker. 2. Add 50ml of distilled water and stir to dissolve as much of the sample as possible....
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