Launch Day Fizz: Which Rocket Made a New Substance?

Compare properties before and after three launches to decide whether a chemical reaction happened.

Answer Key

The gases

Read the passage and Tables 1 and 2, then answer the questions.

Three Rockets for Launch Day

1Every spring, the Hilltop Middle School Rocket Club hosts a launch day for younger students. The club leader, Ms. Greta Ndiaye, launches the model rockets that have real motors. The club also builds three small demonstration rockets that use no fire. Club members Pilar Haugen and Rashid Coelho wanted to find out which of the three demonstration rockets works because of a chemical reaction.

2The bottle rocket is a plastic bottle partly filled with tap water. An adult pumps air into it to a safe pressure and then releases it, and the air pushes the water out of the bottom as the bottle shoots up. At the moment of launch, a white fog fills the bottle and is gone within a few seconds. When a gas expands quickly, it cools, and some of the water vapor in cooled air can condense into tiny droplets.

3The canister rocket is a small plastic canister with a snap-on lid. Rashid drops in half of a fizzing tablet, adds a spoonful of water, snaps on the lid and stands the canister upside down. The tablet is citric acid and baking soda pressed together. Within about 10 seconds, the lid pops off and the canister jumps a few meters into the air. Everyone nearby wears safety goggles.

4The balloon rocket rides along a string. Wearing insulated gloves, Ms. Ndiaye drops pellets of dry ice into an open flask and stretches a balloon over its mouth. When the balloon fills, she pinches it shut, slips it off and tapes it to a straw on the string. Dry ice is very cold, with a density of 1.56 g/cm³, and it turns straight into a gas without melting.

5After launch day, Ms. Ndiaye and the high school chemistry teacher collected the gas from each rocket in bags and measured two properties of each gas. They also let the liquid left in the canisters dry in a dish and tested the white powder left behind, along with the tablet's two ingredients.

Table 1. Gases Collected After Launch (20 °C)
Gas sample	Density (g/L)	Dissolves in 1 L (g)
Bottle rocket gas	1.2	0.02
Canister rocket gas	?	1.7
Balloon rocket gas	1.8	1.7

Table 2. Reference Properties of Some Gases (20 °C)
Substance	Density (g/L)	Dissolves in 1 L (g)	Other facts
Helium	0.17	0.002	Not a solid at normal pressure
Nitrogen	1.16	0.02	Freezes at −210 °C
Air (mostly nitrogen and oxygen)	1.2	0.02	A mixture, not one substance
Oxygen	1.33	0.04	Freezes at −218 °C
Carbon dioxide	1.84	1.7	Dry ice, 1.56 g/cm³; gas at −78 °C

Density = mass ÷ volume. The chemistry teacher found that 2.0 L of the canister rocket gas had a mass of 3.6 g.

The density of the canister rocket gas is 1.8 g/L.

Which substance in Table 2 best matches the canister rocket gas?

A. Carbon dioxide, because both its density and how much dissolves match
B. Air, because the canister held some air before the lid snapped on
C. Oxygen, because its density is the closest to the canister gas's density
D. Nitrogen, because it is the main gas in the air around the canister

Why did the teachers measure how much of each gas dissolves in water, and not only its density?

A. Gases dissolve too fast to weigh, so the density readings came out too low.
B. Some gases have similar densities, so a second property helps tell them apart.
C. A gas that dissolves well in water forms in a reaction, so this test proves one.
D. The density of a gas depends on its color, so they needed a test that ignores color.

The balloon rocket gas also matches carbon dioxide. Did a chemical reaction happen in the flask?

A. No, because dry ice matches solid carbon dioxide, and its gas matches carbon dioxide gas.
B. No, because the balloon gas has about the same density as the bottle rocket's air.
C. Yes, because a gas formed from a solid, which shows the atoms joined in new ways.
D. Yes, because the density went from 1.56 g/cm³ to 1.8 g/L, a big change in a property.

The canister rocket

Use Table 3 and paragraphs 3 and 5.

Table 3. Solids From the Canister Rocket
Sample	Density (g/cm³)	When heated	Fizzes in vinegar?
Citric acid (in tablet)	1.66	Melts at 153 °C	No
Baking soda (in tablet)	2.2	Breaks down, no melting	Yes
Powder left after drying	1.76	No melting up to 300 °C	No

Pilar claims that a new substance formed in the canister rocket. Underline each piece of evidence that supports her claim by itself.

The lid popped off with a loud snap.A gas that matches carbon dioxide came out, but neither tablet ingredient is carbon dioxide.The powder dissolves in water, just like both tablet ingredients.The powder does not melt at 153 °C like citric acid, and it does not fizz in vinegar like baking soda.The canister jumped a few meters into the air.

The club wants to check whether the dried powder is just leftover citric acid. Which single test, done by the chemistry teacher, would best tell the two apart?

A. Drop each one into vinegar and see whether it fizzes
B. Heat each one to about 200 °C and see whether it melts
C. Stir each one into water and see whether it dissolves
D. Look at each one with a hand lens and check its color

Suppose the canister rocket gas had a density of 1.2 g/L, and only 0.02 g of it dissolved in 1 L of water. What would that result suggest?

A. The gas was helium, since it is less dense than carbon dioxide.
B. The gas was carbon dioxide, since a fizzing tablet makes carbon dioxide gas.
C. The gas was most likely air, so these data would not show a new substance.
D. The gas was oxygen, so the tablet broke apart into separate atoms.

Reaction or not?

Use everything on the page to decide about each launch.

Use paragraph 2. What best explains the white fog in the bottle rocket at launch?

A. The pump pushed dust from outside into the bottle, which made it look cloudy.
B. The plastic bottle gave off a fine white powder as it bent under the pressure.
C. The air and the water reacted and formed a new white gas that drifted away.
D. The air cooled as it expanded, and some water vapor condensed into droplets.

Sort each change from launch day.

The tablet fizzing in water inside the canisterDry ice turning into gas inside the flaskFog forming inside the bottle rocket at launchTap water spraying out of the bottle rocket

A new substance formed	No new substance formed
The tablet fizzing in water inside the canister	Dry ice turning into gas inside the flask Fog forming inside the bottle rocket at launch Tap water spraying out of the bottle rocket

10.

Rashid says, "The canister rocket and the balloon rocket both made carbon dioxide gas, so either both were chemical reactions or neither one was." Do you agree? Write a claim, give property evidence from at least two tables, and explain your reasoning.

I disagree. Claim: A chemical reaction happened in the canister rocket but not in the balloon rocket. Evidence: Both gases had a density of about 1.8 g/L, and 1.7 g of each dissolved in 1 L of water, which matches carbon dioxide in Table 2. In the canister, the starting substances were citric acid, baking soda and water, and none of them is carbon dioxide. The powder left behind had a density of 1.76 g/cm³, did not melt up to 300 °C and did not fizz in vinegar, so it does not match citric acid (1.66 g/cm³, melts at 153 °C) or baking soda (2.2 g/cm³, fizzes in vinegar). In the flask, the starting substance was dry ice, which has the properties of solid carbon dioxide in Table 2. Reasoning: A reaction happened only if the substances after a change have different properties from the substances before it. The canister made a gas and a powder that match none of the starting substances, so new substances formed. The dry ice was carbon dioxide before and after; only its state changed, from solid to gas.