Errata

4. Buy the chemical from a vendor that does not charge hazardous shipping surcharges on small amounts of chemicals. With the exception of concentrated nitric acid and a few other chemicals, small amounts (typically 25 g or mL to 100 g or mL) of most hazardous chemicals can be shipped without surcharges under Small Quantity Exemption or ORM-D regulations.

BUYING CHEMICALS THE EASY WAY

In addition to individual chemicals, Maker Shed (http://www.makershed.com) offers various chemical kits that include, with the exception of nitric acid, most or all of the specialty chemicals needed to complete the lab sessions in this book.

"graduated cylinder, 100 ml" is not used in Laboratory 8.1, but it is listed as required equipment.

Note from the Author or Editor:
This erratum is correct. Please delete the item mentioned.

Part II ? Prepare molal solutions of sodium chloride and sucrose

To test the effect of molality and dissociation on boiling point, we need to prepare solutions of ionic and molecular (covalent) compounds of known molality. I chose to use sodium chloride and sucrose because both of these chemicals are inexpensive, readily available, and extremely soluble in water. Sodium chloride is ionic. In solution, sodium chloride dissociates into sodium ions (Na+) and chloride ions (Cl-), and should therefore have a van't Hoff factor of 2. Sucrose is molecular, and should therefore have a van't Hoff factor of 1.

Coincidentally, the solubility of both sodium chloride and sucrose in water at room temperature is just over 6 mol/L. We'll therefore prepare 6 molal, 3 molal, and 1.5 molal solutions of both of these compounds.

1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
2. Label a foam cup "6 molal sodium chloride", place it on the balance, and tare the balance to read 0.00 g.
3. Add hot tap water to the foam cup until the balance reads as closely as possible to 100.00 g. As you approach 100.00 g, use a pipette or dropper to add water dropwise.
4. Remove the cup from the balance, substitute a weighing paper, and transfer 35.07 g of sodium chloride to the weighing paper. This amount (0.6 moles) of sodium chloride added to 100.00 g of water is sufficient to make up a 6.0 molal solution of sodium chloride.
5. Transfer the 35.07 g of sodium chloride to the foam cup. Stir it periodically as you are making up the other solutions until all of the sodium chloride dissolves.
6. Repeat steps 2 through 5 in two additional labeled foam cups to make up sodium chloride solutions of 3.0 molal (100.00 g of water plus 17.53 g of sodium chloride) and 1.5 molal (100.00 g of water plus 8.77 g of sodium chloride).
7. Repeat steps 2 through 6 in three additional labeled foam cups to make up sucrose solutions of 6.0 molal (100.00 g of water plus 205.38 g of sucrose), 3.0 molal (100.00 g of water plus 102.69 g of sucrose) and 1.5 molal (100.00 g of water plus 51.34 g of sucrose).

Part III ? Determine the boiling points of sodium chloride, sucrose, and sodium carbonate solutions

In this part of the lab, we determine the boiling points of the sodium chloride and sucrose solutions.

1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
2. Transfer the 6 molal sodium chloride solution to the 250 mL beaker. Place the beaker on the heat source and apply gentle heat with constant stirring until the contents of the beaker come to a full boil.
3. Immerse the thermometer in the beaker, making sure it does not contact the beaker itself, allow the thermometer to stabilize, and record the temperature reading in Table 8-1.
4. Remove the beaker from the heat and place it aside to cool. Transfer the solution from the beaker back into its labeled foam cup. Rinse the beaker thoroughly and dry it.
5. Repeat steps 2 through 4 for the 3.0 molal and 1.5 molal sodium chloride solutions and the 6.0 molal, 3.0 molal, and 1.5 molal sucrose solutions.
6. Using the observed boiling point elevations for each of the solutions and the van't Hoff factors for each solute, calculate the formula weights of sodium chloride and sucrose, and enter those values in Table 8-1.

Repeat the experiment, but dissolve sufficient sodium chloride and sucrose in the initial 100 g of water to make the solution 1.5 molal with respect to both solutes. (Warm the water if necessary to dissolve all of the solids.) Calculate the expected boiling point elevation and then determine the actual boiling point elevation for the solution.

Retain all of the solutions for use in the following laboratory session. Allow all of the solutions to cool to room temperature, and then place them in the refrigerator to chill them. A typical refrigerator maintains a temperature of about 5 ?C. Having the solutions at this temperature reduces the time required for the freezing point determinations in the following laboratory session. (I violate my general rule of avoiding mixing laboratory materials with kitchen materials because these solutions contain only food compounds.)

Please change tritrant to titrant.

Delete everything after "in the lemon juice provide internal electric connectivity between the half-cells." Somehow we ended up with a cut-and-paste repeat of the last sentence in the 1st paragraph on the top right of the page.

Kastle-Meyer Solution

To prepare the Kastle-Meyer phenolphthalein solution, dissolve 0.1 g of phenolphthalein powder in 10.0 mL of 25% w/v aqueous sodium hydroxide in a test tube and add 0.1 g of mossy zinc and a boiling chip. Boil the solution very gently, adding water as necessary to maintain the volume, until the bright pink solution turns colorless or slightly yellowish. Allow it to cool, decant off the liquid, and dilute it to 100 mL with 70% ethanol. Store in a tightly-capped brown bottle.

Step 5 is missing a closing parenthesis.