Hydrated Crystals Lab
February 13-18, 2014
Objective: Student should be able to quantify the relationship between mass and
moles and experimentally determine the amount of water in a hydrated crystal.
Title:
The effect of heat on dehydrating crystals.
Problem statement:
How can adding heat remove water from a hydrate crystal?
Hypothesis:
If heat is added to a hydrate then water will be removed because heating the
crystal will provide the energy necessary to liberate the water molecules.
Variable:
Independent variable – adding heat
Dependent variable – removal of water (anhydrous)
Constant – heat source
Materials:
Hot plate
Balance scale
Hydrated crystal, MgSO4.nH2O (Epsom salt)
Crucible
Crucible tongs
400 ml beaker
Write the procedures from the handout in your own words.
Observations/Data table
Table 1
Observations
Solid Hydrated MgSO4
Large Beaker during initial heating
Solid Anhydrous MgSO4
Table 2
Mass Data
Mass of crucible
20.48 g
Mass of crucible + MgSO4 hydrate
28.48 g
Mass of MgSO4 hydrate
8.00 g
Mass of crucible + anhydrous MgSO4
24.69 g
Mass of anhydrous MgSO4
3.79 g
Mass of water in MgSO4 hydrate
4.21 g
Data Analysis/Results (Leave space in between each question for the answer.)
1. Calculate the percentage of water in the hydrated crystals of MgSO4 using
your experimental data.
2. Assuming that the correct formula for the hydrate is MgSO4·7H2O, calculate
the theoretical percentage of water in the hydrated crystals.
3. Calculate your percentage error by comparing your experimental and
theoretical percentages of water in the hydrate.
Hydrate Formula
4. Calculate the moles of anhydrous MgSO4.
5. Calculate the moles of water removed from the hydrate by heating.
6. Determine the ratio of moles of water to moles of anhydrous MgSO4.
7. Using this ratio, give the experimentally determined, predicted formula for
hydrated MgSO4.
Conclusion: (Paraphrase each paragraph in your own words.)
The lab entitled the effect of heating on hydrated crystals was about how
heating a hydrate liberates the water molecules from the hydrate. The hypothesis
is, if heat is added to a hydrate then water can be removed, because the heat
helps to break down the bonds that helps to remove the water molecules. A
hydrate is a compound containing a certain amount of water. The water is
trapped inside the crystal lattice and adding heat helps to remove the water from
the compound by adding the energy necessary for the removal of the water.
The procedure involved measuring 8 g of the hydrate which is Epsom salt
(MgSO4). The amount of Epsom salt was then placed in a crucible and then on the
hot plate. While the substance was being heating, I observed what took place on
the 400 ml beaker as well as the hydrate while heating. Once heated and the
water was removed an anhydrous was formed. An anhydrous is a compound in
which the water is removed. The variable that was held constant in the
experiment was the heat supplied from the hot plate.
The major findings in this experiment were that the mass of the hydrate
decreased after heating, because the water molecules were removed. The
method used in this experiment is not suitable for determining the percentage of
water in all hydrates because not all hydrates have the same ions. If an
anhydrous is left uncovered overnight it might become a hydrate again, because
of the moisture in the air. If a hydrate is added to water this would be a physical
change because the water can be removed physically by heating.
The hypothesis was therefore proven correct in this experiment. The
application of this lab in society is that sometimes packets of anhydrous form a
hydrate and used to keep cellars from being damp. However, after a period of
time, the anhydrous takes water in from the moisture that may accumulate in the
air to form a hydrate. Also, gypsum is a mineral used for making wallboard for
construction. It goes through a process call calcinning to remove water from the
substance to produce a hardened white substance called plaster of Paris. Once
the water is removed, an anhydrous is formed. The energetic process involved in
this process of removing water from a hydrate is a heat exchange process where
heat is being supplied and water is being removed to form an anhydrous.