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3: Experiment 3 - Hydrated Salt

  • Page ID
    212568
  • Ancillary Documents

    Learning Objectives

    Content:

    • Empirical Formula
    • Mole Ratio
    • Ionic Hydrates
    • Dehydration

    Process:

    • Work in groups to design the experiment. Propose the experiment protocol to rest of the students in the class.
    • Perform the experiment according to the experiment protocol.
    • Name the hydrate according to the results of the experiment.

    Prior Knowledge:

    Epsom salt (MgSO4·7H2O) is a heptahydrate of magnesium sulfate: within one mole of magnesium sulfate heptahydrate are seven moles of water.  This water can be driven off by heat to form the anhydrous (dehydrated) ionic compound, magnesium sulfate. The mass of water evaporated is obtained by subtracting the mass of the anhydrous solid from the mass of the original hydrate (\ref{3}):

    \[m_{\ce{H2O}} = m_{\text{Hydrate}} - m_{\text{Anhydrous Solid}} \label{3}\]

    From the masses of the water and anhydrous solid and the molar mass of the anhydrous solid, the number of moles of water and moles of the anhydrous solid are calculated as shown below (\ref{4}, \ref{5}):

    \[n_{\ce{H2O}} = \frac{m_{\ce{H2O}}}{MM_{\ce{H2O}}} \label{4}\]

    \[n_{\text{Anhydrous Solid}} = \frac{m_{\text{Anhydrous Solid}}}{MM_{\text{Anhydrous Solid}}} \label{5}\]

    In order to determine the formula of the hydrate, [\(\text{Anhydrous Solid}\ce{*}x\ce{H2O}\)], the number of moles of water per mole of anhydrous solid (\(x\)) will be calculated by dividing the number of moles of water by the number of moles of the anhydrous solid (Equation \ref{6}).

    \[x = \frac{n_{\ce{H2O}}}{n_{\text{Anhydrous Solid}}} \label{6}\]

     

    Supplies

    • Epsom salt (Magnesium Sulfate)
    • Scale 
    • Aluminum foil
    • Measuring spoon
    • Tongs
    • Oven
    • Scissors 
    • Calculator
    • Cell phone with camera
    • Laptop or computer with camera, speakers and microphone hooked up to internet

     

    Safety

    Wear safety goggles and gloves

    DO NOT perform any lab work outside of the stated lab hours

    All students MUST be in constant contact with their teams vie Zoom Breakout Rooms. Your Teammates have to be able to see and hear you. 

    Procedure

    This is a two period lab where you will be working in your Kitchen Chemistry Lab while connected with your group via Zoom Breakout Rooms. Your Lab Reports are individual assignments, but you're welcome to communicate with your group and discuss the results. Keep in mind, that you have to use your own data and no two reports can be exactly the same.

    June 2, 2020

    For your experiment design use the supplies mentioned above. You can substitute aluminum pie pans for aluminum foil.

     Parameters you need to account for in your proposal:

    • Humidity, water adsorbed to surface materials
    • Spattering of sample upon heating as water escapes from hydrated salt
    • Insufficient heating to cause all water to escape (how do you determine the process is complete?)
    • Safety considerations

    Each member of your team will have a role for the experimental design assignment. Roles will rotate from lab to lab in alphabetical order. 

    1. Manager

    • Responsible for ensuring that all team members are present and actively participating according to their roles.
    • Responsible for the Safety component in all aspects of the experiment
    • Validates group members have the supplies
    • Keeps Team on track
    1. Theoretician  

    • Responsible for formulating the purpose and the goal of the experiment
    • Leads the team in developing the theoretical foundations of the science behind the experiment.
    1. Engineer 

    • Responsible for Experimental Design
    • Leads the team in developing experimental procedures
    1. Analyst  

    • Responsible for the quality of data
    • Leads the team in analyzing the data and the experimental error
    1. Spokesperson (Optional, for groups with 5 students)

    • Responsible for writing the presentation of the proposal
    • Delivers the presentation to te instructor/TA and the rest of the class

    Don't forget to submit your proposal. Your instructor/TA will use them to come up with a final experimental protocol that you will be using during the next lab period.

    Interactive Element

    The final version of the experiment procedure will be posted in Google Classroom. This is the only set of instruction you are to follow during this lab.

    Since your instructor/TA won't be there in person to supervise your experiment, you will need to upload a few photos taken during the lab:

    • Picture of you wearing your safety glasses!
    • First five items from your supplies list for this lab before you start. 
    • Your scale every time you weigh anything. The weighted items must be seen and the display of your scale must be readable.
    • Your hydrous salt sample.
    • Your anhydrous salt sample.

    Complete your Lab Report and submit it via Google Classroom.

    Interactive Element

    Contributors and Attributions

    Robert E. Belford (University of Arkansas Little Rock; Department of Chemistry). The breadth, depth and veracity of this work is the responsibility of Robert E. Belford, rebelford@ualr.edu. You should contact him if you have any concerns. This material has both original contributions, and content built upon prior contributions of the LibreTexts Community and other resources, including but not limited to:

    • Elena Lisitsyna
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