Suppose ten atoms of carbon (C) react with 20 atoms of oxygen (O) to form 10 molecules of carbon dioxide (CO 2). According to the law of conservation of matter, how many atoms are present in this reaction? (1 point)
O 15
O 20
O 30
O 10
The correct answer is O 30.
According to the law of conservation of matter, the total number of atoms before and after a chemical reaction must remain the same. In this reaction, there are 10 carbon atoms and 20 oxygen atoms before the reaction. After the reaction, there are 10 molecules of carbon dioxide, which means there are 10 carbon atoms and 20 oxygen atoms. Adding these up, we get a total of 30 atoms.
Which procedure could be used to demonstrate that matter is conserved during a chemical change or reaction? (1 point)
• Find the mass of a piece of paper. Tear the paper into smaller pieces. Find the mass of the pieces.
• 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.
• Find the mass of a stick of butter. Heat the butter until it melts. Find the mass of the melted butter.
• Find the mass of a log. Burn the log until it turns to ash and smoke. Find the mass of the ash.
The correct answer is:
• 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 procedure demonstrates the conservation of matter during a chemical change or reaction. By measuring the mass of the reactants (acid and base) and the products (water and salt), if the reaction obeys the law of conservation of matter, the total mass of the reactants should be equal to the total mass of the products.
What is always true according to the Law of Conservation of Matter? (1 point)
• The total number of molecules before and after a chemical reaction stays the same.
• New molecules cannot be formed from the reactants during a chemical reaction.
• Atoms created during a chemical reaction must have the same mass as the atoms in the reactants.
• Atoms can be rearranged during a chemical reaction but cannot be added or removed.
The correct answer is:
• Atoms can be rearranged during a chemical reaction but cannot be added or removed.
According to the Law of Conservation of Matter, atoms cannot be created or destroyed during a chemical reaction. They can only be rearranged into different molecules or compounds. The total number of atoms before and after the reaction remains the same.
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 this observation shows that matter is not conserved in chemical reactions. Which statement explains why the student's claim is incorrect? (1 point)
• The product contained fewer atoms than the reactants.
• The reaction did not change the physical properties of the liquids.
• The combined liquid was warmer than the two separate liquids.
• The reaction produced a gas that escaped the beaker.
The correct answer is:
• The reaction produced a gas that escaped the beaker.
The student's claim is incorrect because the observation of a decrease in mass is most likely due to the escape of a gas during the reaction. Mass can only be conserved if all the products of the reaction, including any gas produced, are accounted for. In this case, the loss of mass is likely attributed to the escape of a gas, which is not accounted for in the measurement. The mass of the products, including any gas, should be compared to the mass of the reactants to determine if matter is conserved.