A chemical reaction is shown. SnO2 + H2 → Sn + H2O

What is true about this chemical reaction?

A.
It is balanced because the mass of the reactants (number of atoms) is equal to the mass of the products (number of atoms).

B.
It is unbalanced because the mass of the reactants (number of atoms) is greater than the mass of the products (number of atoms).

C.
It is unbalanced because the mass of the reactants (number of atoms) is less than the mass of the products (number of atoms).

D.
It is balanced because the number of reactants (number of atoms) is equal to the number of products (number of atoms).

Read the information about an experiment.

Jadon plans on carrying out an experiment involving the burning of steel wool to illustrate the conservation of mass. Steel wool is made of iron. When it is burned it combines with oxygen to form iron(III) oxide.

Which step in his experiment is the most important if he wants his experiment to correctly demonstrate the conservation of mass?

A.
The steel wool should be burned inside of a sealed jar or other closed system.

B.
The steel wool should be burned over a long period of time (at least two hours).

C.
The steel wool should be burned in a room that is at room temperature (20–25°C).

D.
The steel wool should be burned in its entirety sExpected Outcomes – Metals in Hydrochloric Acid

Metal Observations
Copper No reaction even when gently heated
Iron Little initial reaction.
More vigorous reaction when heated.
Positive test for hydrogen gas.
Solution turned from colorless to yellow.
Magnesium Vigorous initial reaction; rapid evolution of gas.
Positive test for hydrogen gas.
All of the magnesium seemed to disappear.
Solution remained colorless.
Zinc Initial reaction produced rapid evolution of gas; less vigorous than magnesium.
All of the zinc seemed to disappear.
Solution remained colorless.

Students in Ms. Brown's Science Lab demonstrated several chemical reactions, by placing the each above chemicals in HCl (hydrochloric acid). Unfortunately, the data did not appear to support the Law of Conservation of Matter in any of the experiments. The recorded Mass of the Reactants did not match the Mass of the Products. Based on the expected outcomes listed in the table above, what might be a reason that their demonstrations were not successful?
A.
They only used metals

B.
They perfomed the experiment in a closed system

C.
The experiment was not performed in a closed system

D.
They didn't use enough HCl that no iron is left in its original state.