Digital Labs

Digital labs reduce printing and distribution costs, save paper, allow real-time updates, and support full-color images of your actual lab setup.

For example, an introductory organic lab converting sodium benzoate to benzoic acid includes these interactive features:

Mouse over the highlighted words to view structures and definitions. For structures, click the Enlarge button to open a new browser TAB that only contains the structure.
Mouse over the highlighted Reactant and Products (in the Chemical column of the Materials Table) and click the SDS link to open the chemical's SDS.
Mouse over the apparatus to view an image of it.
Click the pH Slide Show to launch the presentation in another TAB. This is an HTML Slideshow that can be view on any device (phone, tablet, computer, etc.).
Click the check box to the left of a procedure step to "gray it out" after it has been completed.

Digital lab guides can be "stand alone" documents or they can be integrated with the Chem21 interactive lab report webpage. In either application, students have access to their lab book and reporting webpage anywhere there is internet service. In addition, embedding images, videos and animations adds even more interactivity to the digital lab guide.

The Fate of Sodium Benzoate After Ingestion

Background

is abundantly present in many plants acting as a natural preservative, inhibiting the growth of bacteria, mold, yeast and fungus. It is then no surprise that benzoic acid and its more water-soluble salts (benzoates) have been utilized as a food preservative, especially in acidic foods and beverages.

Questions have been raised regarding the safety of the consumption of its salts - specifically, and its fate in the acidic environment of the stomach. In theory, sodium benzoate will undergo an acid/base reaction in an acidic environment, producing benzoic acid. In humans, and other animals that eat plants, benzoic acid binds to , an . . . a molecule that has an amine (NH₂), carboxyl (COOH), and R group with the following pH-dependent formulas:
low pH: H₃ ⁺
_N-CHR-CO₂H
neutral pH: H₃ ⁺
_N-CHR-C ^-
_O₂
high pH: H₂N-CHR-C ^-
_O₂ to form which is excreted from the body in the urine.

Chemistry

Sodium benzoate, when dissolved in water, . . . an ionic compound breaks apart into positive ions (cations) and negative ions (anions). into weakly basic benzoate ions and sodium ions.

C₆H₅COO^- + Na⁺

The acidic environment of the stomach can be simulated by the addition of Hydrochloric acid until the pH is lowered to approximately 2. Note that HCl is a strong acid . . . . it is 100% ionized in water.

HCl + H₂O → Cl^- + H₃O⁺

The higher the concentration of hydronium ions, the lower the pH of the solution. Theoretically, if the concentration of the hydronium ion is high enough, the benzoate ions should react with the hydronium ions in an acid/base reaction to produce benzoic acid and water.

C₆H₅COO^- + H₃O⁺ → C₆H₅COOH + H₂O

The overall reaction between sodium benzoate and aqueous hydrochloric acid is . . . .

C₆H₅COONa + HCl → C₆H₅COOH + NaCl

When sodium benzoate has been converted to benzoic acid, . . . color change, gas formation, precipitate, evolution of heat / light, or formation of a weak- / non-electrolyte. will be observed.

Materials

Glassware

Apparatus

Chemicals

50-mL Beaker
Glass Stirring Rod
Buchner Funnel
Filter Flask
Vac Adapter
pH paper or probe

Ice/water Bath

pH Probe Calibration Slideshow
(click below)

Reactants

Products

Experiment

1. Obtain approximately 2 grams of Sodium Benzoate - record the exact mass (to 3 decimal places) to the right.

1.897 g

2. Quantitatively transfer the sample to a 50-mL beaker.

3. Add 10 mL water to the beaker and stir with a glass rod to dissolve.

4. Measure out 5 mL of 3M HCl and slowly add 4 mL to beaker while stirring.

5. Continue stirring. Drop-by-drop add more 3M HCl to the beaker until the solution reaches a pH of 2.
◊ Check pH of solution with pH probe or pH paper frequently to monitor pH.
◊ Make note of any evidence of a chemical reaction.

6. Cool solution to 10°C or lower.
◊ If a precipitate has not formed, contact your lab instructor.
◊ Otherwise, collect the solid benzoic acid via vacuum filtration using 5 mL ice-cold water to wash / transfer the precipitate to an evaporating dish.
◊ Then, dry the precipitate to constant mass and record the mass.

1.426 g