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Digital Labs

Digital labs avoid the cost of publication / transportation, saves trees, allows real-time changes, and welcomes full color photos of YOUR lab equipment and setup. Below is an introductory organic chemistry lab that converts sodium benzoate into benzoic acid. This particular digital lab embeds the following interactivity:

  1. 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.
  2. 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.
  3. Mouse over the apparatus to view an image of it.
  4. 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.).
  5. 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 with a separate interactive lab report webpage OR data entry, calculations, essay answers, image uploads, balanced equations, etc. can be integrated into a single digital lab guide webpage. In addition, embedding images, videos and animations add 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 -
O
2
high pH: H2N-CHR-C -
O
2
to form which is excreted from the body in the urine.



The 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





The Experiment


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

Mass (g) used is reported here in the actual lab report.

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.