# Determine nitrogen content in lawn fertiliser using volumetric analysis

• Malinn
In summary, a back titration was used to determine the amount of nitrogen in fertiliser. My titres are 3.9, 3.7 and 4.2, so I know this reaction occurred: NH4+ + OH- ---> NH3 +H2O. Then I boiled the solution to expel the Ammonia and the excess OH- ions were titrated against 0.1 M HCl. Is this equation correct? If so are the following calculations correct too? n (HCl)= 0.1 x 0.0039n(HVl)=0.0039
Malinn

## Homework Statement

I undertook a practical experiment where a back titration was used to determine the amount of nitrogen in fertiliser.My titres are 3.9, 3.7 and 4.2 So I know this reaction occurred:
NH4+ + OH- ---> NH3 +H2O
I then boiled the solution to expel the Ammonia and the excess OH- ions were titrated against 0.1 M HCl.

OH- +HCl ---> Cl- +H2O
Is this equation correct? If so are the following calculations correct too?
n (HCl)= 0.1 x 0.0039
n(HVl)=0.0039

If this calculation is correct, what do I have to do next?

Malinn said:
OH- +HCl ---> Cl- +H2O
Is this equation correct?

Yes and no. Yes, it will give the correct result, no there is no HCl in solution. It is completely dissociated to H+ and Cl-.

If so are the following calculations correct too?
n (HCl)= 0.1 x 0.0039
n(HVl)=0.0039

Sorry, but neither makes sense to me. I can only guess in the first you are trying to calculate number of moles of HCl, I can only guess 0.1 is molarity of the acid used, but I don't understand what is 0.0039. You should use average volume, but 0.0039 is not the average of volumes you listed. And I can't even guess what you mean by n(HVl)=0.0039, unless you made a typo and math error in one line.

If this calculation is correct, what do I have to do next?

http://www.titrations.info/back-titration

I was attempting to calculate the amount of mol of HCl was used and then using the mol ratio from the equation, calculate how many mole of nitrogen was present. The molarity of the HCl used was 0.1M and I was supposed to multiply it by 0.003933 (as this is the average of the titres) to find the mol (as the formula states n= concentration x volume (in litres)).

By doing this I hoped to find the mol of HCl used which is what was meant by n(HVl)=0.0039
the (HVl) was a typo for (HCl)

So what is the proper equation? Would this work in its place?
NaOH +HCl ---> NaCl +H2O

## 1. How does volumetric analysis determine the nitrogen content in lawn fertiliser?

Volumetric analysis is a laboratory technique used to measure the quantity of a substance in a sample. In the case of determining nitrogen content in lawn fertiliser, a known volume of the fertiliser solution is titrated with a solution of a known concentration of a chemical compound that reacts specifically with nitrogen. By measuring the volume of the titrant needed to reach the endpoint, the nitrogen content can be calculated.

## 2. What equipment is needed for volumetric analysis of lawn fertiliser?

The equipment needed for volumetric analysis of lawn fertiliser includes a burette, a pipette, a conical flask, a beaker, a magnetic stirrer, a pH meter, and a titration indicator. Other commonly used materials include a balance, a graduated cylinder, and a funnel.

## 3. How accurate is volumetric analysis for determining nitrogen content in lawn fertiliser?

Volumetric analysis is a highly accurate and precise method for determining nitrogen content in lawn fertiliser. The accuracy of the results depends on the accuracy of the equipment used, the skill of the technician performing the analysis, and the purity of the chemicals and samples used.

## 4. Can volumetric analysis be used for all types of lawn fertiliser?

Yes, volumetric analysis can be used for all types of lawn fertiliser. However, the specific titrant used may vary depending on the type of fertiliser being tested. For example, ammonium nitrate fertiliser would require a different titrant compared to urea fertiliser.

## 5. Are there any potential sources of error in using volumetric analysis for lawn fertiliser?

There are a few potential sources of error in using volumetric analysis for lawn fertiliser. These include inaccurate measurements of the sample or titrant, improper technique during titration, and contamination of the sample. To minimize error, it is important to carefully follow the procedure and use high-quality equipment and chemicals.

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