TITRASI ARGENTOMETRI (PART 2) : METODE MOHR || KIMIA ANALITIK

Summary

The script explains the argentometric titration method developed by chemists More, Polar, and Fajans, focusing on the distinctive indicators used in each method. The More method involves using potassium chromate as an indicator to determine the end point of titration, with precise concentration requirements to avoid errors. The process is discussed in detail, highlighting challenges like interference from other ions, the need for neutral conditions, and practical limitations. An example demonstrates the titration of table salt, calculating NaCl content using silver nitrate, and provides insight into the method's practical application and challenges.

Takeaways

• 😀 The More method in argentometric titration uses potassium chromate as an indicator to determine the endpoint.
• 😀 The concentration of the chromate indicator must be precise to avoid errors during titration.
• 😀 If the chromate ion concentration exceeds the analyte concentration, chromate will precipitate with silver nitrate, causing significant errors.
• 😀 The concentration of silver nitrate should be at least 1.33 × 10⁻⁵ M for accurate titration results.
• 😀 A smaller chromate concentration of 2.5 × 10⁻³ M is often used in practice for better endpoint visibility.
• 😀 The More method is simple and fast, but it has limitations, especially in low-concentration solutions.
• 😀 The method is less sensitive for low-concentration analytes due to early precipitation of chromate.
• 😀 Strong shaking is required to avoid interference from precipitates and prevent analyte adsorption.
• 😀 The More method works best for determining chloride and bromide ions in neutral atmospheres.
• 😀 Acidic or basic conditions interfere with the chromate indicator, affecting the titration results by changing its form.
• 😀 In the practical example, titration of NaCl in table salt shows how to calculate the NaCl content using volume and molarity data.

Q & A

What is the more method in argentometric titration?

The more method in argentometric titration is a technique where potassium chromate is used as an indicator to determine the endpoint of the titration. Silver nitrate (AgNO3) is used as the titrant to measure chloride (Cl-) or bromide (Br-) ions in a sample.

Why is the concentration of potassium chromate critical in this method?

The concentration of potassium chromate must be precise to avoid errors. If the chromate concentration is too high compared to the analyte, chromate ions will precipitate with silver ions before reaching the endpoint, leading to inaccurate results.

How is the concentration of silver nitrate determined in this titration?

The minimum concentration of silver nitrate required for accurate titration is calculated to be 1.33 × 10^-5 M. This concentration ensures that the silver nitrate can react fully with chloride or bromide ions without excess interference.

What is the significance of using a smaller concentration of potassium chromate, such as 2.5 × 10^-3 M?

A smaller concentration of potassium chromate, like 2.5 × 10^-3 M, is used to reduce the intensity of the yellow color, making the endpoint of the titration easier to observe. A higher concentration would make the solution too yellow, obscuring the endpoint.

What happens if the titration occurs in an acidic or basic environment?

In an acidic environment, the chromate ion is protonated to form chromic acid, which interferes with the titration. In a basic environment, silver hydroxide (AgOH) precipitates and may change to Ag2O, both of which complicate the titration and lead to errors.

Why is it necessary to shake the solution strongly during titration?

Strong shaking is necessary to avoid the adsorption of the analyte by the precipitate formed during the titration. This ensures that the titration proceeds without any interference from precipitated substances.

What ions can the more method be used to determine?

The more method is primarily used to determine chloride (Cl-) and bromide (Br-) ions in a solution.

What is the role of the potassium chromate indicator in this titration?

Potassium chromate acts as an indicator by forming a precipitate with silver ions at the endpoint of the titration. The color change, from yellow to red, signals the end of the reaction.

How is the NaCl content in table salt determined using the more method?

To determine the NaCl content, a known mass of table salt is dissolved in water, and a portion is titrated with silver nitrate solution. By calculating the moles of NaCl reacted and using stoichiometry, the weight of NaCl in the sample is determined.

What are some limitations of the more method?

Some limitations of the more method include its reduced sensitivity for low-concentration solutions, interference from other anions like sulfide or phosphate, and the requirement for the titration to occur in a neutral atmosphere to prevent reaction with chromate or silver hydroxide.