Illustrated Guide to Home Chemistry Experiments

262 DIY Science: Illustrated Guide to Home Chemistry Experiments

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dISpoSAL:

The gas-generating bottle contains

only a dilute solution of sodium

acetate and sodium hydrogen

carbonate, and may be flushed down

the drain with plenty of water.

With the stopper in one hand, drop the package of sodium

hydrogen carbonate into the gas-generating bottle and

immediately insert the stopper securely.

It takes a moment for the vinegar to penetrate the paper

towel package. As soon as the vinegar penetrates the

package, the reaction commences and vigorous fizzing

begins as carbon dioxide is generated. The increased

pressure in the flask forces carbon dioxide through the

plastic tubing and into the gas-collection bottle, where it

begins to displace the water in the bottle.

Hold the gas-collection bottle to make sure that it doesn’t

tip over as it fills with gas. When the reaction ceases and

bubbles are no longer being produced, remove the free

end of the plastic tubing from the gas-collection bottle

and recap the bottle while keeping its mouth under water.

Remove the gas-collection bottle from the tub and dry

its exterior.

Determine the volume of water remaining in the bottle by

repeatedly filling the 100 mL graduated cylinder. Record

the total volume of the water remaining in the gas-

collection bottle in liters on line C of Table 14-4.

Determine the volume of gas produced by subtracting the

volume of water remaining (line C) from the total volume

of the gas-collection bottle (line A). Record the volume of

gas produced on line D of Table 14-4.

Determine the local atmospheric pressure (not

barometric pressure) in kilopascals (kPa) and enter that

value on line E of Table 14-4.

Use the thermometer to determine room temperature in

kelvins, and enter that value on line F of Table 14-4.

Use the ideal gas law, P · V = n · R · T to calculate n, the

number of moles of gas produced by the reaction (which

equals the number of moles of acetic acid consumed). We

have already determined pressure (in kPa), volume (in L),

and temperature (in K). The ideal gas constant, R, for these

units is 8.314472 L · kPa · mol–1 · K–1. Solve for n, the number

of moles, and enter that value on line G of Table 14-4.

The gram-molecular mass of acetic acid is 60.05 g/mol.

Determine the reactant mass of acetic acid by multiplying

the number of moles (line G) by 60.05 g/mol, and enter

that value on line H of Table 14-4.

Calculate the mass-percentage of acetic acid in the

vinegar by dividing the mass of acetic acid (line H) by

the mass of the vinegar sample (line B) and multiplying

that result by 100 to convert it to a percentage. Enter that

value on line I of Table 14-4.

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TABLE 14-4: Use the Ideal Gas Law to determine the percentage of acetic
acid in vinegar—observed and calculated data

Item value

A. Volume of gas-collection bottle ____.________ L

B. Mass of vinegar _______._____ g

C. Volume of water remaining ____.________ L

D. Volume of gas produced (A – C) ____.________ L

E. Atmospheric pressure ______._____ kPa

F. Room temperature _______.___ K

G. Moles of gas (and acetic acid) ___.________ mol

H. Mass of acetic acid (G · 60.05 g/mol) _______._____ g

I. Mass percentage of acetic acid (H · 100/B) ______._____ %