Lab Exercise #4 – Chemical Composition (Hydr
FLC Chem 305
your instructor. Use gloves to handle the cobalt (II) chloride paper since it is a carcinogen.
Safety: Wear goggles at all times and keep long hair tied back. Dispose of all wastes as described by
Pre-lab Calculations: Show your calculation for theoretical %-water for each of the following
compounds, one of which is your unknown. For each calculation divide the mass of the amount of
in the hydrate (in amu) by the total mass of the hydrate (mass of the salt and water in amu):
mass of the water in the hydrate
mass of the hydrate (salt + water)
theoretical % water =
MAKE DARK MARKS
• 163 points maximum
• Only one mark per line on key
• Mark total possible
Part I Procedure
To test for water of hydration, you will heat known samples of copper (II) sulfate pentahydrate
(CuSO4.5H2O), calcium chloride dihydrate (CaCl2.2H2O), and magnesium sulfate heptahydrate
(MgSO4 7H20 – Epsom salts) and test for the presence of water with cobalt (II
) chloride paper. Use
gloves to handle the cobalt (II) chloride paper since it is a carcinogen.
1. Take a small strip of cobalt paper and place a drop of water on the paper to verify the color changes.
Record the result on page
2. Take approximately 0.5 g of each of the above hydrates and heat them separately in test tubes. As
you heat each sample, small droplets of liquid should condense near the top of the test tube. Touch
Lab Exercise #4 – Chemical Composition (th. CLC Chem 30
FLC Chem 305
Data Analysis (S
1. Determine the act
FLC Chem 305
Part I Observations:
Cobalt paper color change: went from blue
to pink & white
Hydrates tested with cobalt paper
Blue powder turned white forange. A lot
of condensation. Paper turned pink/white medium
The paper turned white. The Callo
2 H₂O bubbled with heat
Not a lot of
Change in paper. Powder become solid low
Part II and III Data/Observations
Part 3 3
Unknown Hydrate ID:
Mass of empty crucible
Mass of crucible lid
Total beginning mass of
crucible, lid, and hydrate
Mass of hydrate
Observations before heating
Total mass after 1st heating
Total mass after 2nd heating
Total mass after 3rd heating (if
Mass of anhydrous
Mass of H2O in sample (this
corresponds to the weight lost)
وما ) ۵۰
Observations after adding
water to anhydrous sample
Observations during and after the powder changed to it became a
white ,then black
When we added H₂O
Lab Exercise #4 – Chemical Composition (Hydrates)
Data Analysis (Show work and put answer on the line.)
1. Determine the actual (experimental) %-water in your sample of CuSO4.5H20. Compare this to the
%-water calculated on p. 4.2 for CuSO4.5H20 (the theoretical %-water). Show all calculations.
actual % water =
mass of H20 in hydrate sample
mass of the hydrate sample
2. Calculate the %-yield of your sample. Show all calculations.
actual % H20 in the hydrate
theoretical % H20 in the hydrate
3. Determine the actual %-water in your unknown sample. Show all calculations.
Lab Exercise #4 – Chemical Composition (Hydrates
FLC Chem 305
4. Based on your actual (experimental) %-water and your pre-lab theoretical calculated %-water values,
identify your unknown (write the chemical formula on the line). State both actual and theoretical
values and compare them. .
5. Calculate the %-error for your unknown hydrate where %-error. Note that your %-error may be
positive or negative. If your experimental value is too low, then you will have a negative %-error,
while it will be positive if your experimental value is too high.
actual % H20 – theroretical % H20
theoretical % H20
% error =
What did you learn from this experiment?
Every compound has its own chemical formula and its own name. There are numerous nomenclature
systems in chemistry, each for a unique set of substances and each with its own set of rules. You will
acids, hydrates, binary covalent compounds and simple organic compounds. Each of these systems is
learn nomenclature rules for binary ionic compounds, polyatomic compounds, acids, oxoacids, aqueous
slightly different and you have to learn the rules specific to each class of compounds.
Ionic compounds, including binary and polyatomic ionic compounds:
These consist of any positive ion (except H’) combined with any negative ion.
The positive ion, cation, may be a metal ion (such as Na*) or a polyatomic ion (such as NH4+);
The negative ion, anion, may be a non-metal (such as Cl’) or a polyatomic ion (such as SO42- or
Case 1. Ionic Compounds: Special Metal (fixed charge) + Non-Metal (monatomic anion,
Examples: KBr, potassium bromide;
AlCl3, aluminum chloride; Li3N, lithium nitride.
Note 1: Metal is always first (name unchanged), non-metal second (the ending of the non-metal is
dropped and the – ide ending is added).
Note 2: The name does not indicate how many of each atom is present or the charge on the metal atom-
you must know the charge from the location of the element in the periodic table relative to the
noble gas column. For metals, alkali metals all have 1+ charge, and alkaline-earth metals all
have 2+ charge. Other common fixed charge cations which you must know and memorize are
A13+, Zn2+, Cd2+, and Agt
Exercise Write formulas for the following cations, including the charge:
Exercise Write formulas for the following anions:
Exercise Name the following binary ionic compounds:
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