Lab Experiment #4: The Gravimetric Analysis of Barium Chloride Hydrate

Summary

In this lab experiment, students are tasked with determining the amount of water in a barium chloride hydrate (BaCl₂·xH₂O). The process involves weighing the crucible before and after heating the hydrate, allowing the water to evaporate. By measuring the mass difference, students can calculate the mass of water and subsequently determine the number of moles of water in the hydrate. The lab emphasizes the importance of precision in weighing and handling, as well as understanding the relationship between the anhydrous salt and the water of hydration to calculate the value of x in the formula BaCl₂·xH₂O.

Takeaways

• 😀 The experiment aims to determine the amount of water in a hydrated salt, specifically barium chloride (BaCl₂·XH₂O).
• 😀 The number of water molecules (X) in the salt is determined by heating the sample and measuring the mass before and after heating.
• 😀 To start, weigh the empty crucible and then place it in a desiccator to remove any moisture from the air that may affect the result.
• 😀 Add approximately 2 grams of hydrated barium chloride (BaCl₂·XH₂O) to the crucible and weigh the crucible with the hydrate.
• 😀 Heat the crucible with the hydrate for 20-25 minutes to evaporate the water, leaving only the anhydrous barium chloride (BaCl₂).
• 😀 The color of the crucible will change as it heats, indicating that moisture is being removed from the material.
• 😀 After heating, cool the crucible in a desiccator to prevent the sample from absorbing moisture from the surrounding air.
• 😀 Weigh the crucible with the anhydrous salt after cooling, and subtract the mass of the empty crucible to determine the mass of the anhydrous BaCl₂.
• 😀 The mass of water lost is calculated by subtracting the mass of the anhydrous salt from the mass of the hydrated salt.
• 😀 The moles of anhydrous BaCl₂ and water can be calculated using their respective molar masses, and the value of X is determined as the ratio of moles of water to moles of BaCl₂.
• 😀 The final step is to fill in the provided table with the calculated values, including the mass of the crucible, hydrate, anhydrous salt, and the number of moles of each component.

Q & A

What is the main objective of the experiment described in the script?

The main objective is to determine the number of water molecules (X) in the hydrated salt barium chloride (BaCl₂·XH₂O) by heating the salt and measuring the mass change.

How is the number of moles of water in the hydrate determined?

The number of moles of water is determined by measuring the mass of the hydrate before and after heating. The difference in mass corresponds to the mass of water lost, which is then used to calculate the moles of water.

What is the significance of the 'X' in the formula BaCl₂·XH₂O?

The 'X' represents the number of water molecules that are associated with each formula unit of barium chloride in the hydrated compound.

What equipment is needed for the experiment?

The experiment requires a crucible, analytical balance, burner, triangle stand, O-ring, desiccator, tongs, and a heating setup.

Why is the crucible heated before measuring the hydrated salt?

The crucible is heated to remove any moisture that might be trapped in its pores, which could affect the accuracy of the mass measurements during the experiment.

What is the purpose of using a desiccator in the experiment?

The desiccator is used to cool the crucible and prevent the absorption of moisture from the air, ensuring that the mass measurements remain accurate after heating.

How is the mass of the anhydrous barium chloride determined?

The mass of the anhydrous barium chloride is determined by subtracting the mass of the empty crucible from the mass of the crucible and the anhydrous salt after heating.

What is the role of the molar mass in the calculations?

The molar mass is used to convert the mass of BaCl₂ and water into moles. This is essential for calculating the ratio of moles of water to moles of anhydrous salt to determine the value of X.

What are the steps involved in heating the hydrate and determining its mass?

First, the hydrate is weighed along with the crucible. The crucible is then heated, and after cooling in a desiccator, the new mass of the anhydrous salt is recorded. The difference in mass is used to calculate the mass of water lost during heating.

What is the formula for calculating the moles of water in the hydrate?

The moles of water are calculated using the formula: Moles of Water = (Mass of Water) / (Molar Mass of Water). The mass of water is the difference between the mass of the hydrate before heating and the anhydrous salt after heating.