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Science Quick Check. 1 Correct Answer Per Question.

1. Suppose 10 atoms of carbon (C) react with 20 atoms of oxygen (O) to form 10 molecules of carbon dioxide ( CO2
). According to the law of conservation of matter, how many atoms are present in this reaction?
a. 20
b. 30
c. 15
d. 10

2. Which procedure could be used to demonstrate that matter is conserved during a chemical change or reaction?
a. Find the mass of a log. Burn the log until it turns to ash and smoke. Find the mass of the ash.'
b. Find the mass of a piece of paper. Tear the paper into smaller pieces. Find the mass of the pieces.
c. Find the mass of an acid and a base. Combine them to produce water and a salt. Find the mass of the water and salt.
d. Find the mass of a stick of butter. Heat the butter until it melts. Find the mass of the melted butter.

3. What is always true according to the Law of Conservation of Matter?
a. New molecules cannot be formed from the reactants during a chemical reaction.
b. Atoms can be rearranged during a chemical reaction but cannot be added or taken away.
c. The total number of molecules before and after a chemical reaction stays the same.
d. Atoms created during a chemical reaction must have the same mass as the atoms in the reactants.

4. A student combines two liquids in a beaker. She observes that the mass of the combined liquid is less than the mass of the two separate liquids. The student claims that this observation shows that matter is not conserved in chemical reactions. Which statement explains why the student’s claim is incorrect?
a. The reaction produced a gas that escaped the beaker.
b. The product contained fewer atoms than the reactants.
c. The combined liquid was warmer than the two separate liquids.
d. The reaction did not change the physical properties of the liquids.

1 answer

Here are the correct answers to each question:

  1. According to the law of conservation of matter, how many atoms are present in this reaction?

    • b. 30 (10 carbon atoms + 20 oxygen atoms = 30 atoms total)

  2. Which procedure could be used to demonstrate that matter is conserved during a chemical change or reaction?

    • c. Find the mass of an acid and a base. Combine them to produce water and a salt. Find the mass of the water and salt. (This demonstrates a chemical change where mass should be conserved.)

  3. What is always true according to the Law of Conservation of Matter?

    • b. Atoms can be rearranged during a chemical reaction but cannot be added or taken away. (This is the essence of the Law of Conservation of Matter.)

  4. Which statement explains why the student’s claim is incorrect?

    • a. The reaction produced a gas that escaped the beaker. (This explains the loss of mass if gas was produced and escaped into the air.)