lab report
tatema87
Name: _____________________________
9
Exp 3. Report Form: Properties of Hydrates
A. Identification of Hydrates
Raw Data:
Solid Color of
Solid (Initial)
Does H2O (clear,
colorless droplets)
Appear?
Color of Residue
Did a noticeable amount of solid disappear
(dissolve) when water was
added (after swirling)?
C (cloudy
only)? Or
R (ripples)?
(Conclusion) Is residue
water soluble?
(Y or N)
Color of
solution (N/A if not
soluble!)
1 Nickel(II) chloride
2 Potassium chloride
3 Cobalt(II) chloride
4 Sucrose
5 Calcium carbonate
6 Barium chloride
Conclusions:
List each solid that you conclude is NOT a (true) hydrate, and provide your reasoning (use the # of solid to save space):
List each solid that you conclude IS a (true) hydrate, and provide your reasoning (use the # of solid to save space):
B. Percent Water in a Hydrate
Assumed Information: Vial #:_____ Chemical Formula of Anhydrous Compound (in your hydrate): _____________
Raw Data:
Mass of crucible and cover _______________
Mass of crucible, cover, and sample of solid hydrate _______________
Mass of cooled crucible, cover, and residue after heating, Reading 1
(after _____ min of cooling; still warm) _______________
Mass of cooled crucible, cover, and residue after heating, Reading 2
(after _____ min of cooling; fully cooled to room temperature) _______________
These two columns involve the observations that help you determine if the residue is water
soluble. Make sure to carefully (re)read the paragraphs in the middle of p. 2 of the
Introduction in order to make the proper conclusion in the column to the right of these two.
Report Form, Properties of Hydrates
10
Analysis Questions:
Did the mass reading of the crucible, cover, and residue increase or decrease while it cooled? _________________
Is the mass of the sample actually changing during this cooling? Be careful here! Remember the definition of
“mass” (vs. “weight”). See https://www.youtube.com/watch?v=UWq-zQ8nZKQ before you answer!
What is the lesson about “patience” to be learned here?
Calculated Quantities and Results (SHOW ALL SETUPS):
Mass of sample of solid hydrate used _______________
Mass of residue (assume this is pure anhydrous compound) _______________
Mass of H2O lost (assume the mass lost on heating is entirely due to H2O leaving) _______________
Mass Percent of H2O in the unknown hydrate _______________
(continued →)
Report Form, Properties of Hydrates
11
(Assumed) Chemical Formula of Anhydrous Compound (copy from box on earlier page, with Vial #): ________________
Mass of anhydrous compound (in your sample of hydrate), in units of amu _______________ amu
Use the following conversion: 1 amu = 1.6606 x 10-24 g
Mass of H2O (in your sample of hydrate), in units of amu _______________ amu
IMPORTANT CONCEPTUAL INTERLUDE REGARDING "FORMULA UNITS" AND "FORMULA":
A formula unit (FU) is the smallest amount of a substance one could possibly have (it’s nanoscopic!). For atomic or molecular
substances, a FU is a single atom or molecule, respectively. For ionic compounds, a FU isn't a single "entity", but rather is the smallest
grouping of ions that is net neutral. For hydrates, the water molecules are part of the FU. Analyze the table below!
Chemical
Formula Type of Substance (based on the formula!)
Basic Units making
up the substance
(Composition of)
1 Formula Unit Formula Mass
(Average mass of one Formula Unit)
Fe Monatomic
Element Atoms 1 atom of Fe 55.85 amu/FU
O2 Molecular Element Molecules 2 O atoms
(together as one molecule)
2(16.00) =
32.00 amu/FU
CO2 Molecular
Compound Molecules
2 O atoms and one C atom (together as one molecule)
2(16.00) + 12.01 =
44.01 amu/FU
CoCl2 Ionic Compound
(anhydrous) Ions 1 Co2+ ion and 2 Cl- ions
58.93 + 2(35.45) =
129.83 amu/FU
CoCl2 6 H2O Ionic Compound
(hydrate) Ions and Water
Molecules
1 Co2+ ion, 2 Cl- ions, and
6 H2O molecules
58.93 + 2(35.45) + 12(1.008) +
6(16.00) = 237.93 amu/FU
Determining the number of water molecules per formula unit of ionic compound in a hydrate is really determining part of the chemical
formula of the hydrate (the x in MAnxH2O). Stated slightly differently, x represents the ratio of water molecules to "anhydrous formula
units". For example, in a formula unit of CoCl2 6 H2O, there are six H2O molecules and one formula unit of CoCl2. That means that in
a sample of CoCl2 6 H2O containing 1000 formula units, there would be 6000 H2O molecules and 1000 formula units of CoCl2—the
ratio of H2O molecules to "anhydrous compound" (CoCl2) is 6000:1000 which equals 6000/1000 which equals 6 (or 6:1). That “6” in
front of water really means “6 H2O molecules per FU of CoCl2!
**READ THE ABOVE CAREFULLY & REPEATEDLY BEFORE (AND WHILE) YOU DO THE WORK BELOW**
Formula mass of anhydrous compound (in your hydrate) [see top of page for your formula!]: _______________ amu/FU
# of formula units (FU) of anhydrous compound in your sample of hydrate _______________ FU (Hint: Think of this as “the number of bicycles in a sample (load)” when you know the mass of the load and the mass of one bicycle!)
# of H2O molecules in your sample of hydrate _______________ FU (Note: the formula mass of anhydrous compound will not help you here! Think of what you need!)
Ratio of # of H2O molecules : # FU’s of anhydrous compound in your hydrate _________: 1 ____: 1
Complete chemical formula of your hydrate* _____________________
(to proper # of SF) (nearest integer)
* Use “nearest integer” value of the ratio as the coefficient of water in the formula (see table)!