Fertiliser is a natural chemical substance that is used to enrich soil in order to promote plant growth

Fertiliser is a natural chemical substance that is used to enrich soil in order to promote plant growth. In influences plant growth, colour of the plant and help prevent weed diseases and infections. Plants require many different chemical substances to help plant growth, but the most important ones are phosphorus, nitrogen and potassium, these three are the main nutrients that are needed for plant growth and are found in most lawn fertilizers. Nitrogen is the nutrient that’s the most important since it promotes plant growth, however, too much nitrogen can have a harmful effect on plants and soil.

Nitrogen is very important for plant growth because it is a major component of chlorophyll. It is also a major component of amino acids, the main source of protein. Without proteins, plants would die. Some proteins are used for structural units in plant cells while others as enzymes, making possible many of the biochemical reactions. Nitrogen is a component of ATP, ATP allows cells to conserve and use the energy released in metabolism. Finally, nitrogen is a significant component of nucleic acids such as DNA, the genetic material that allows cells to grow. Without nitrogen, all plants would not be able to survive.

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Since the ammonium that is present in lawn fertilizer is a weak acid, therefore, it will be very difficult to see the endpoint therefore back titration takes place. “Back titration is a titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent. The remaining excess reagent is then titrated with another, second reagent. The second titration result shows how much of the excess reagent was used in the first titration, thus allowing the original analyte concentration to be calculated” (Helmenstine, 2018).

Before titration, sodium hydroxide was reacted with ammonium in the fertiliser to produce ammonia and water:
NH4+ (aq) + OH- (aq) ? NH3 (g) + H2O (l)

The basic solution that’s needed for titration will be reached through heating the solution to remove the ammonium ions. By heating it, the rate of reaction between the ammonium ions and hydroxide ions increases, which produces water and ammonia. Since ammonia is an extremely volatile gas, boiling the solution will increase the vaporization rate, which is the desired outcome to vaporize all of the ammonium ions in the solution. Once the red litmus paper, which tests for a base, no longer turns blue which means that the ammonia which will completely evaporated and no longer present in the solution.

In fertilisers the NH4+ ions present are a weak acid to produce a noticeable endpoint in direct titration. Back titration can be used the percentage by mass composition of nitrogen in the fertiliser. Therefore the NH4+ ions are reacted with an excess of sodium hydroxide solution and the amount of unreacted sodium hydroxide can be found through titration with a hydrochloric solution, this is used to deduce the amount of NH4+ ions present by subtracting it from the initial amount of NaOH to find the amount that reacted with it. The amounts of ions present can then be calculated from the amount of sodium hydroxide that reacted with HCl, this is a back titration.

Variable analysis:
Controlled Variables:
Variable to Control/monitor

Why does it need to be controlled?
What value will it be kept at?

How will the variable be controlled/measured?

Temperature of the room and the solution
As temperature increases particles collide with more energy and this increases the speed of the reaction
Room temperature
The experiment will occur in the same room and will be monitored
Volume of solution in the flask
Using different volumes lawn fertilizer and water solution can have an impact on the titration because the more solution is used, the longer it will take to reach its end point
20 cm3
Using a 20 cm3 pipette and a pipette filler, into a clean 250 cm3 conical flask.

Amount of NaOH solution
The amount of unreacted sodium hydroxide will determine the endpoint, and help find the percentage by mass of nitrogen in lawn fertilizer
0.1 mol dm-3
0.1 mol dm-3 of solution will be measure for each titration with the use of a pipette

Independent Variable: The lawn fertilizer used
Different brands of lawn fertilizer are used to compare the percentage by mass of nitrogen in various lawn fertilizers. The lawn fertilizer is weighed in grams.
Dependent Variable: the percentage by mass of nitrogen in different lawn fertilizer determined with the use of titration calculations. This result is determined as a percentage (%)

Materials:
300 cm3 0.1 mol dm-3 NaOH
300 cm3 0.1 mol dm-3 HCl
12 grams of fertiliser
3 x 250 cm3 volumetric flask
2 x 250 cm3 conical flasks
Burette clamp
50 cm3 measuring cylinder
Hot plate
Balance
Red litmus paper
Methyl red indicator

Safety Considerations:
Both hydrochloric acid and sodium hydroxide is a hazardous and corrosive solution that has the ability to corrode metallic surfaces. When the acid or mist comes in contact with skin, eyes or internal organs the consequences can be burning sensation, abdominal pain, shock or even severe burns. Proper eye protection and gloves must be used. The acid should be stored in a cool, dry and well-ventilated area away from sources of moisture. It must be kept away from incompatible materials like oxidizing agents, organic materials, metals and alkalis.
Since I am evaporating ammonium, I need to make sure that when heating the solution it is done in (FIND WORD ) to make sure no one inhales the gas. Since ammonium is very toxic when heated it must be kept in a safe place, therefore, it would be kept away from people.

Method:
Weigh 1.2 grams of fertilizer. Look at the brand of the fertilizer and the nitrogen content specified by the manufacturer on the package.
Dissolve the fertiliser in 250 cm3 of distilled water in a volumetric flask.
Swirl the content of fertilizer and water to dissolve the ammonium compounds in the fertilizer
Place 20 cm3 of the fertilizer solution into three conical flasks
Place 20 cm3 of NaOH into the three conical flasks
To the first flask add 50 cm3 of distilled water. Boil the mixture for 10 minutes (if necessary add more water to maintain a constant volume of solution)
Test the vapour at the top of the flask with a moist strop of red litmus paper (if ammonia is present the paper will turn blue).
Continue heating until the point where the litmus paper does not detect the presence of ammonia.
Cool the flask under running water
Repeat steps 5-8 with the two other conical flasks
Fill a burette with the stock HCl (aq) solution and adjust the level to 0.00 cm3.
Add three drops of methyl red indicator to each conical flask containing the fertilizer mixture that was boiled.
Complete a titration by adding the acid (use a steady flow from the burette) until endpoint is observed (endpoint is observed when the initially yellow solution becomes orange).
For each flask, record the burette reading once the endpoint has been reached