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1.9: Experiment 7 - Hydration of Salt

  • Page ID
    291229
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    Learning Objectives

    By the end of this lab, students should be able to:

    • Design an experiment to accurately determine the empirical formula of a given hydrate.
    • Predict how experimental factors will impact the accuracy and precision of results.
    • Calculate the molar ratio of water to anhydrous solid to determine the hydrate's formula.
    • Explain why the experimentally determined empirical formula may not match the actual formula of Epsom salt (propose at least 2 ideas).

    Prior Knowledge:

    Introduction

    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}).

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

     

    Pre-Lab Assignment

    This pre-lab assignment is an individual assignment to be completed on your own with the help of the "Prior Knowledge" links at the top of this page. All work must be in your own words. Do not copy and paste information from the internet. The assignment will be due 10 minutes before your lab begins. Late work will not be accepted.

    The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.

    Interactive Element

     

    In-Lab Assignment

    Group Assignment

    Using Zoom Breakout rooms, you will work collaboratively with your group on a Google Doc worksheet called "Hydrated Salt Procedure/Analysis". Each person can type in this document at the same time. Remember, part of your grade comes from your participation during lab, so there will be a Peer Evaluation this week. Make sure you are contributing to discussion and to the completion of the worksheet. The worksheet will be due by the end of your lab session, and late work is not accepted. Be sure to turn your assignment in on Google Classroom.

    The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.

    Interactive Element

     

    After you have had a chance to work on the data analysis with your group during lab, you will be given the Hydrated Salt Post-Lab Problem Set. This is an individual assignment that must be completed on your own, and it is based on your Pre-Lab Primer and your In-Lab Assignment. This assignment will be due the day after your lab meets by 5 p.m. For example, if your lab is on Monday, the Post-Lab Problem Set will be due on Tuesday at 5 p.m. No late work is accepted. 

    The document below is a preview only. Please do not try to screenshot or print it off. You will be able to find your assignment to work on in your Google Classroom.

    Interactive Element

    Contributors and Attributions 

    • Robert E. Belford (University of Arkansas Little Rock; Department of Chemistry) led the creation of this page for a 5 week summer course. 

    • Elena Lisitsyna contributed to the creation and implementation of this page.

    • Mark Baillie coordinated the modifications of this activity for implementation in a 15 week fall course, with the help of Elena Lisitsyna and Karie Sanford.

    1.9: Experiment 7 - Hydration of Salt is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.