Conservation of Mass (Difficult)

A student mixes two liquids in a sealed flask. A gas forms and inflates a balloon. The total mass of the flask and balloon remains the same. What does this demonstrate?

• The gas has no mass

• Mass was lost in the reaction

• The balloon added mass

• Mass was conserved in a closed system

Answer explanation

The experiment shows that even though a gas was produced, the total mass of the system (flask and balloon) remained unchanged. This demonstrates that mass was conserved in a closed system during the reaction.

Tags

NGSS.MS-PS1-5

Why is it important to use a closed container to test conservation of mass?

• To trap any escaping matter

• To measure changes in color

• To cool the reaction faster

• To prevent a chemical change

Answer explanation

Using a closed container is crucial to trap any escaping matter during a reaction, ensuring that all mass is accounted for. This supports the principle of conservation of mass, which states that mass cannot be created or destroyed.

Tags

NGSS.MS-PS1-5

A student burns a substance in an open dish. After the reaction, the mass is lower. What best explains this?

• Matter was destroyed

• Energy was created

• Gas escaped into the air

• Atoms changed into heat

Answer explanation

The decrease in mass after burning indicates that gas escaped into the air. During combustion, gases like carbon dioxide and water vapor are produced and released, leading to a lower mass of the remaining substance.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

A chemical reaction takes place and forms a gas, which escapes from the system. What effect does this have on the observed mass?

• It stays the same

• It appears to increase

• It appears to decrease

• It becomes unpredictable

Answer explanation

When a gas escapes from the system during a chemical reaction, the total mass of the remaining substances decreases. Therefore, the observed mass appears to decrease.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

What evidence best supports that mass is conserved in a chemical change?

• New substance forms

• Heat is released

• Total mass before and after is equal in a closed system

• A gas is produced

Answer explanation

The best evidence for mass conservation in a chemical change is that the total mass before and after is equal in a closed system. This shows that no mass is lost or gained during the reaction, confirming conservation.

Tags

NGSS.MS-PS1-5

A chemical equation shows the same number of atoms on both sides. What does this mean?

• The atoms changed into energy

• Mass is conserved

• The reaction failed

• New atoms were created

Answer explanation

The equality of atoms on both sides of a chemical equation indicates that mass is conserved during the reaction. This means that the total mass of reactants equals the total mass of products, adhering to the law of conservation of mass.

Tags

NGSS.MS-PS1-5

A sealed flask contains two reactants. After the reaction, a new substance and bubbles form. What would the total mass of the flask be?

• Greater than before

• Less than before

• Equal to before

• Zero

Answer explanation

According to the law of conservation of mass, the total mass of a closed system remains constant. Therefore, even after the reaction and formation of a new substance and bubbles, the total mass of the flask will be equal to before.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

A student records the following: the mass of reactants is 50 grams, and the mass of products in an open system is 42 grams. What should the student conclude?

• Mass was destroyed

• 8 g of product disappeared

• Some products escaped the system

• The scale is broken

Answer explanation

In an open system, some products can escape into the environment. The mass of reactants (50 g) is greater than the mass of products (42 g), indicating that 8 g of products likely escaped, not that mass was destroyed.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

A teacher models a chemical reaction with colored blocks to represent atoms. After rearranging the blocks into new groups, what does the model represent?

• Atoms are lost in reactions

• Mass becomes heat

• Atoms rearranged but conserved

• New atoms are made

Answer explanation

The model shows that during a chemical reaction, atoms are not lost or created; they are simply rearranged into new groups. This illustrates the law of conservation of mass, confirming that atoms are conserved.

Tags

NGSS.MS-PS1-5

Which observation best supports the idea that atoms are conserved?

• New substances form with different properties

• Mass of products equals mass of reactants

• Gas forms and escapes

• Heat is produced during the reaction

Answer explanation

The observation that the mass of products equals the mass of reactants supports the conservation of atoms, as it indicates that no atoms are lost or created during a chemical reaction.

Tags

NGSS.MS-PS1-5