Questions and Answers
What is the purpose of the lab?
To find the percent of water in a hydrate.
What is the first step in the procedure?
Which of the following describes a desiccant?
What is the formula for the hydrate used in the lab?
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How do you calculate the mass of the hydrate?
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What is the theoretical percent by mass of water in the hydrate?
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What is the formula for calculating percent error?
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Which of the following is an example of a hydrate?
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How do you calculate the experimental percent by mass of water in the hydrate?
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What is the mass of water lost in the lab?
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What is a desiccator?
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Study Notes
Purpose of the Lab
- Determine the percent of water in a hydrate, specifically copper (II) sulfate pentahydrate.
Procedure Overview
- Wear safety goggles and apron for protection.
- Clean, heat, and dry a test tube before use.
- Weigh the empty test tube and record the mass.
- Measure 2-3g of copper (II) sulfate pentahydrate, placing it in the test tube.
- Weigh the test tube with the hydrate and note the mass.
- Heat the test tube in a Bunsen Burner flame for 4-5 minutes to remove water.
- Allow the test tube to cool before weighing it again with the anhydrate.
- Dispose of the anhydrate waste responsibly and clean the test equipment.
Key Vocabulary
- Hydrate: A compound containing a specific number of water molecules.
- Anhydrate: A substance that lacks water or has had water removed.
- Desiccant: A drying agent that absorbs moisture.
- Desiccator: A sealed chamber with desiccant for drying samples.
- Constant Heating: Ensures no residual water remains in the hydrate during the experiment.
Data Table Samples
- Mass of empty test tube: 19.56g
- Mass of test tube with hydrate: 21.97g
- Mass of test tube and anhydrate after heating: 21.07g
Hydrate Formula
- The hydrate utilized in the experiment is copper (II) sulfate pentahydrate: CuSO4•5H2O.
Experimental Calculations
- Mass of Hydrate: Total mass with hydrate - mass of empty test tube = 2.41g.
- Mass of Anhydrate: Mass after heating - mass of empty test tube = 1.51g.
- Mass of Water Lost: Mass of hydrate - mass of anhydrate = 0.90g.
Theoretical Percent by Mass of Water
- Use the formula: (Molar Mass of 5H2O / Molar Mass of Hydrate) × 100.
- Molar mass of CuSO4•5H2O = 249.70g/mol; mass of water = 90.08g/mol.
- Theoretical percent by mass of water = 36.08%.
Experimental Percent by Mass of Water
- Calculated as: (Mass of water lost / Mass of hydrate) × 100.
- Resulting in an experimental value of 37.34%.
Percent Error Calculation
- Percent error is calculated using: (|Experimental - Theoretical| / Theoretical) × 100.
- This results in a 3% error.
Formula Calculation for the Hydrate
- Using ratio calculations:
- For CuSO4: 1.51g converts to 0.00946 moles.
- For H2O: 0.90g converts to 0.04994 moles.
- Final calculation shows CuSO4•5H2O.
Examples of Hydrate Formulas
- Copper (II) sulfate heptahydrate: CuSO4•7H2O.
- Cobalt (II) chloride decahydrate: CoCl2•10H2O.
- Magnesium sulfate tetrahydrate: MgSO4•4H2O.
Review Key Points
- Understand the lab's purpose, procedure, essential vocabulary, and calculations related to hydrates.
- Be able to compute the mass of hydrate, anhydrate, and water lost, along with theoretical and experimental percentages.
- Know how to derive the formula of a hydrate from experimental data and write formulas for given hydrate names.
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Description
This quiz focuses on the purpose and procedure for determining the percent of water in a hydrate, specifically dealing with copper (II) sulfate pentahydrate. It provides essential steps and safety measures for conducting the experiment effectively.
