Witzgall Chemistry: Hydrate Lab

Summary

In this lab, students explore how to determine the formula of a hydrate, specifically copper sulfate hydrate. Hydrates are ionic compounds with water molecules loosely bonded to their crystal structure. By heating the hydrate, the water evaporates, leaving behind anhydrous copper sulfate. The mass of the hydrate and the anhydrous salt are measured, and the difference in mass reveals the amount of water that was removed. By converting the mass to moles, the ratio of copper sulfate to water can be determined, thus allowing the formula of the hydrate to be calculated.

Takeaways

• 😀 Hydrates are ionic compounds with water molecules loosely bonded to their crystal structure.
• 😀 The lab focuses on determining the formula of copper sulfate hydrate (CuSO₄ · xH₂O).
• 😀 The copper sulfate hydrate looks and feels dry, but it contains water within its crystal structure.
• 😀 To determine the formula, the hydrate is heated to drive off the water, leaving behind anhydrous copper sulfate.
• 😀 The mass of the empty crucible is first measured to get an accurate starting point.
• 😀 The hydrate is then weighed with the crucible to get its total mass, including the water it contains.
• 😀 The hydrate is heated using a Bunsen burner to remove the water, which evaporates as vapor.
• 😀 After heating, the crucible with the anhydrous copper sulfate is weighed to determine the mass of the remaining solid.
• 😀 The difference in mass between the hydrate and the anhydrous salt is used to calculate the mass of water lost during heating.
• 😀 The mass of the water and the mass of the anhydrous salt are converted to moles to find the mole ratio and determine the formula of the hydrate.
• 😀 The final result is the formula CuSO₄ · 5H₂O, indicating five water molecules are bonded to each copper sulfate unit.

Q & A

What is the main purpose of this experiment?

The main purpose of the experiment is to determine the formula of copper sulfate hydrate by heating the compound to remove water and measuring the mass changes.

What are hydrates, and why is the water in them important to this experiment?

Hydrates are ionic compounds that contain water molecules loosely bonded within their crystal structure. The water is important because its removal allows us to calculate the ratio of water to copper sulfate, which gives the formula of the hydrate.

What happens to the copper sulfate hydrate when it is heated?

When heated, the water molecules within the copper sulfate hydrate turn into vapor and evaporate, leaving behind the anhydrous copper sulfate salt.

What tool is used to heat the copper sulfate hydrate in this experiment?

A Bunsen burner is used to heat the copper sulfate hydrate in the experiment.

How do you measure the mass of the copper sulfate hydrate and the anhydrous copper sulfate?

The mass of the copper sulfate hydrate is measured first, then after heating, the mass of the anhydrous copper sulfate is measured using a balance. The difference in mass indicates the amount of water that has evaporated.

What is the mass of the empty crucible used in this experiment?

The mass of the empty crucible is 24.364 g.

What is the mass of the copper sulfate hydrate sample before heating?

The mass of the copper sulfate hydrate sample before heating is 3.52 g.

What is the significance of the color change observed in the experiment?

The color change from blue to a lighter shade indicates that the water has been removed from the copper sulfate hydrate, leaving behind the anhydrous copper sulfate, which has a different appearance.

How is the amount of water lost calculated in this experiment?

The amount of water lost is calculated by subtracting the mass of the anhydrous copper sulfate (after heating) from the initial mass of the copper sulfate hydrate.

Why is it necessary to convert the mass of copper sulfate and water into moles?

Converting the mass of copper sulfate and water into moles allows us to determine the mole ratio between the two, which helps in calculating the formula of the hydrate.