CHEMISTRY 1
NAME: _______________________________________
BOYLE’S LAW AND ALKA-SELTZER ROCKET LAB
Part A – Boyle’s Law
1. Record today’s atmospheric pressure using barometer in front of room: _________ mmHg.
2. Obtain a 1-liter bottle from Mr. Page and a pressure gauge. Air in bottle has been pressurized
using a bicycle pump. Notice the syringe (which has been sealed) inside the bottle (see Figure 3).
Volume of syringe should be about 2 mL. If not, see Mr. Page so he can pressurize the bottle.
3. HOW TO USE PRESSURE GAUAGE. READ ENTIRE STEP BEFORE DOING ANYTHING.
Bottle should be sitting upright on table. There is a valve stem at top of bottle. Hold this with
one hand so it does not get pushed into bottle. Using other hand, QUICKLY press and release
pressure gauge onto valve stem. DO NOT press to long or you will release too much air. When
you press, make sure you are holding pressure gauge completely vertical. Try it one time. There
are two scales on gauge, so make sure you read the “psi” scale. You should get a pressure of
about 40 psi or higher. If not, see Mr. Page. To reset the pressure gauge to zero, you push the
button on the gauge.
IMPORTANT: RIGHT BEFORE YOU MEASURE THE PRESSURE EACH TIME, LOOK
TO SEE THAT THE GUAGE HAS BEEN RESET TO ZERO.
4. Read the volume of air inside the syringe and record in table below (See Figure 4). The volume
scale on syringe goes in increments of 0.2 mL so record to the nearest 0.1 mL. Using the gauge,
measure the pressure at his volume and record. DO NOT WORRY ABOUT TOTAL
PRESSURE IN TABLE AT THIS TIME. Release some pressure in bottle a little at a time until
volume of syringe increases about 0.3 to 0.4 mL. Read this new volume and measure the
pressure in the bottle at this new volume. Record volume and pressure in table. Repeat this
process until pressure inside bottle is about 5 psi. When you are done, release all the pressure in
the bottle and return bottle and pressure gauge.
VOLUME (mL)
GUAGE PRESSURE (psi)
TOTAL PRESSURE (psi)
Part B – Alka-Seltzer Rocket
1. Obtain two film canister, one Alka-Seltzer tablet and a stop watch.
2. Break the tablet into 4 equal size pieces.
3. Measure the mass of 1 piece and record in table below. Place the piece in one of the film
canisters. Place this canister to your left.
4. Measure the mass of two pieces and record in table below. Place both pieces in the second film
canister. Place this canister to your right.
# of Alka-Seltzer Pieces
1
2
Mass (g)
Moles (n)
Time to launch (s)
The active ingredient in Alka-Seltzer tablets is sodium bicarbonate, NaHCO3 (84.007g/mol),
which turns into carbon dioxide gas when mixed with water. We will be using Alka-Seltzer
pieces to examine the relationship between pressure, P, and number of moles of gas, n. The
film canister has a constant volume, and we will assume the temperature is also constant.
5. Fill a pipet with water. Add this water to film canister on left (one with 1 piece) and QUICKLY
put lid on the canister and start timing using stop watch. Stop timing when lid blows off. Record
this time in table.
6. Repeat step 5 for canister on right (one with 2 pieces).
7. Clean and dry the film canisters.
Questions:
PartA
1. Convert today’s atmospheric pressure in #1to psi:
2. Determine total pressure at each volume measurement using the following equation and record
answers in table: Total pressure(psi) = gauge pressure(psi) + atmospheric pressure(psi)
3. Make a “total pressure” versus “volume” graph on graph paper using your data.
4. This law shows as pressure ______________________, volume _______________________ or
vice versa. Pressure and volume are ______________________ proportional.
Part B
5. In the table, convert mass (g) to moles (n) using the molar mass for sodium bicarbonate. Show
example here:
6. Write a balanced equation for the reaction between sodium bicarbonate (active ingredient in
Alka-Seltzer) and water.
7. Use your equation. How many moles of gas are produced for each mole of sodium bicarbonate in
Alka-Seltzer?
8. The time is related to pressure. Longer time means less pressure build up and vice versa.
As amount of gas ______________________, pressure __________________________.
This is a _______________________________ relationship.