1.7: Experiment 6 - Hydration of Salt

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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:

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 one 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.

Experiment Design

Interactive Element

Lab Report

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) 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.