I am not certain what part of the Conductivity Laboratory you
wanted me to review. Although I read over everything you included
in your web site on conductivity, I will only comment on the
following:
Misc. Planning Notes re: Bonding Lab:
A water molecule is formed by *covalent* bonds.
Q. Why 0.1 mol concentration for solutions?
A. It was chosen [somewhat arbitrarily (it's easy to calculate). Also,
the] so the
solutions will have concentrations that fall w/in the range of the
Vernier(R) conductivity probe (0-20K MuS/cm).
Hardware/software:
Set the conductivity probe to the 0-20,000 (MuS/cm) range.
Using Logger Pro, open the following file:
Physical Science with Computers/16 Conducting Solutions.xmbl (or
.cmbl)
Conducting Solutions
Activity Enrichment/Extension:
Using Logger Pro, open the following file(s):
1. Physical Science with Computers/17 Saltwater.xmbl (or .cmbl)
Conductivity of Saltwater: The Effect of Concentration
2. Physical Science with Computers/18 Acid Strengths.xmbl (or .cmbl)
Acid Strengths
Addenda to Procedure:
1. In order to determine a baseline reading for conductivity, test the
conductivity of: distilled water (used to prepare solutions); and tap
water.
2. Double the concentration of at least one of the covalent solutions
(e.g., sugar); greater concentration shouldn't change conductivity.
3. Add substance(s) that have more ions, such as two of the three
substances from Vernier sample data file (in order of least to most
conductive): NaCl (two ions); *CaCl2* (three ions); *AlCl3* (four
ions)[can be ordered as AlCl3.6H2O];
or sodium sulfate (Na2SO4) (three ions), as per Dr.V's suggestion.
Inference: More ions in solution = more conductivity!
Qualification: Given equal numbers of ions, the mobility of the ions
comes
into play (based upon, in part, the size of the molecules).
Substance | Conductivity (μS/cm) [TRG] | 1 mol (g/L) | 0.1 mol(g/100mL)
NaCl (2 ions)
| 2,875 | 58.5g/L | 0.6g/100mL 1.2g(0.2M)
Starch (covalent)
|
360 | (use arbitrary amt., e.g., 0.5
g)formula weight of insoluble starch used is unknown
CuSO4 (2 ions)
Sugar (covalent)
Acetone (covalent)
Magnesium Citrate
(2 ions)
Aspartame (covalent)
Sodium Bicarbonate (2 ions)
| 3,000 | 249.7* | 2.5g*
|
387 | 342 3.42g(0.1M);6.84g(0.2M)
|
420 | 58.08 11.6g (2M)or 15mL
| 2,500 |35mL of solution: 1.745gMg/30mL
|
387 | 224 2.24g (0.1M
| 2,875 | 84.0 | 0.8
*(with 5 "waters" of hydration) [Anhydrous = NO water]
Note: FCPS "recipe" calls for either 0.5g or 2mL per 125mL distilled
water.
==
Notes re: moles:
1 mole = the number of molecules in one (1) formula weight, e.g., 1 mol
of
NaCl = 58.5g
Problem: You can't mass one molecule, so...use 6.02X1023 atoms or 1 mole
of atoms!
Solution: ...the mole is a practical work-around to the problem.
PS: Milk of magnesia {Mg(0H)2 suspended in water} and magnesium
citrate are two different formulations containing two different
compounds!