Graviemertic analysis of Shulphate content on Fertiliser

[JackOddy]

Hey guys, the following prac is being carried out for a major Year 12 Assignment:

Prac - Gravimetric determination of sulfate in fertiliser

1. Finely grind a small quantity of fertiliser using a motar and pestle. Accurately weight around 1.0g of the ground fertiliser in a 100ml beaker. Record the mass and the brand of fertiliser.

2. Add 50ml of distilled water and stir to dissolve as much of the fertiliser sample as possible. Filter the mixture into a 600ml beaker, washing the residue several times using distilled water

3. Add about 3ml of 2M hydrochloric acid to the filtrate and add more water so that the total volume is about 200ml. Boil the solution

4. Slowly add 15ml of 0.5M barium chloride solution from a burette to the hot solution. A white precipitate will form. Stir continuously.

5. Boil the mixture for a further minute. Remove it form the heat and allow the precipitate to settle. Ensure that no sulfate ions remain in the solution by adding several drops of barium chloride solution. If more precipitate forms, add a further 3ml of barium chloride solution and test again for unreacted sulfate ions.

6. Weigh in a clean, dry filter paper.

7. Place the filter paper in the funnel and collect the precipitate in the filter paper. use about 10ml of distilled water to wash any precipitate remaining in the beaker into the filter paper.

8. Collect the last drops of filtrate in a 100ml beaker and test for chloride ions by adding a few drops of silver nitrate solution to filtrate. If the solution becomes cloudy, wash the precipitate with a further 10ml of warm water and repeat the test

9. Allow filter paper and filtrated to dry

10. Weigh filter paper and filtrated and determine the mass of the residue.
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I have a couple of questions:
1. Why do you have to add the Hydrochloric acid to the filtrate in the first place? What's the point of adding it?
2. It doesn't state any concentration of AgNO3, would anyone suggest how i could find an appropriate concentration for this?

 

[Borek]

Are these your questions, or questions being part of the prelab quizz/report?

You have to show your attempts at solving the question to receive help. This is a forum policy.

 

[JackOddy]

No, no, these are just my questions, there's no questions on the sheet about. In-fact i told my teacher about it and she said to use sites like these.

 

[Borek]

1 M AgNO₃ will do.

As for low pH - think what substances can coprecipitate with barium sulfate.

 

[LudusRex]

I would like to provide some insights on the content provided. Firstly, the purpose of this practical is to determine the amount of sulfate present in the given fertilizer sample. This is important as sulfate is an essential nutrient for plant growth and an excess or deficiency can impact crop yield. Gravimetric analysis is a commonly used method for determining the amount of a certain substance in a sample.

To answer your first question, the addition of hydrochloric acid serves to remove any other ions that may interfere with the precipitation of sulfate ions. This is necessary to ensure accurate results. Hydrochloric acid also helps to increase the solubility of the barium chloride, making it easier to form the precipitate.

In regards to the concentration of silver nitrate, it is not specified in the procedure as it may vary depending on the laboratory and the equipment available. However, a commonly used concentration for silver nitrate in this type of analysis is 0.1M. This can be adjusted if needed, but it is important to maintain the same concentration throughout the experiment for consistency.

Additionally, it is important to mention the importance of proper lab techniques and precautions when carrying out this experiment. This includes wearing appropriate personal protective equipment, proper handling and disposal of chemicals, and accurate measurement of reagents. Any errors or inconsistencies can greatly affect the results and should be avoided.

Overall, this practical is a good way to determine the sulfate content in fertilizers and can provide valuable information for agricultural purposes. It is important to follow the procedure carefully and accurately to obtain reliable results.