Gravimetria - Determinação do teor de Ferro no solo

Summary

This video demonstrates the gravimetric analysis of iron content in soil. The process involves weighing a soil sample, dissolving and digesting it with hydrochloric acid, and precipitating the iron as iron hydroxide. After filtration and calcination at high temperatures, the mass of iron oxide is determined. This mass is then used to calculate the iron content in the original sample. The video also highlights the importance of precision and safety in conducting the experiment, including handling chemicals, heating elements, and accurate measurements throughout the process.

Takeaways

• 😀 The experiment aims to determine the iron content in soil samples using gravimetric analysis.
• 😀 0.250 g of soil is weighed in duplicate for the analysis.
• 😀 Distilled water is added to the soil to dissolve it before starting the digestion process.
• 😀 Concentrated hydrochloric acid is added to the soil solution to begin the digestion process.
• 😀 The samples are heated to boiling, and after 5 minutes, the heating plate is turned off to cool the samples.
• 😀 The samples are filtered to remove insoluble impurities like sand and pebbles.
• 😀 After filtration, 100 mL of distilled water and 2 mL each of hydrochloric acid and hydrogen peroxide are added to the samples.
• 😀 The samples are heated to 70°C, and 3 g of ammonium nitrate is added to further react with the soil.
• 😀 Ammonium hydroxide is added drop by drop to raise the pH until the paper turns blue, indicating precipitation of iron hydroxide.
• 😀 The samples are filtered again, and the filter papers are dried and calcined at 1000°C to determine the iron content from the residue left after incineration.
• 😀 After calcination, the mass of the crucibles is measured to determine the iron content based on the difference in mass before and after the process.

Q & A

What is the primary goal of the laboratory procedure described in the transcript?

The primary goal is to determine the iron content in a soil sample using the gravimetric analysis method.

Why is the soil sample weighed in duplicate?

The soil sample is weighed in duplicate to ensure accuracy and reliability of the results by reducing measurement errors.

What is the purpose of adding distilled water to the soil sample?

Distilled water is added to help solubilize the soil, allowing for the separation and analysis of the iron content in the subsequent steps.

What does the digestion step involve and why is it necessary?

The digestion step involves adding concentrated hydrochloric acid (HCl) to the soil and heating it to break down the soil matrix. It is necessary to release the iron and other elements for further analysis.

What is the purpose of filtering the mixture after digestion?

The mixture is filtered to remove insoluble impurities, such as sand and pebbles, that could interfere with the chemical analysis of the iron content.

Why is hydrogen peroxide added to the mixture during the experiment?

Hydrogen peroxide is added to oxidize the iron and assist in the formation of iron hydroxide, which can then be precipitated for gravimetric analysis.

What is the significance of heating the sample to 70°C before adding ammonium nitrate?

Heating the sample to 70°C ensures that the chemicals react properly, preparing the solution for the addition of ammonium nitrate, which helps to further stabilize the iron ions.

What does the change in pH, indicated by the litmus paper turning from red to blue, signify?

The change in pH signifies the formation of a slight excess of ammonium hydroxide, causing the iron to precipitate as iron hydroxide. This is a critical step in isolating the iron content.

Why is the precipitate filtered and washed with ammonium nitrate solution?

The precipitate is filtered and washed to remove any soluble impurities, ensuring that only the iron hydroxide remains for further analysis.

What happens during the incineration step and why is it necessary?

The incineration step involves heating the filter paper and iron hydroxide in a muffle furnace at high temperatures to convert the iron hydroxide into iron oxide. This step is necessary for accurately measuring the iron content.