Conservation of mass in reactions

Question 1

Why is mass conserved in a chemical reaction?

• A. Products are always the same substances as reactants
• B. Energy is conserved
• C. Atoms are only rearranged; none are made or destroyed
• D. Reactions happen too fast to change mass

Question 2

In a sealed flask, 12 g of substance A reacts completely with 5 g of substance B. 2 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 3

20 g of calcium carbonate is heated in an open tube until it all breaks down. 11.2 g of calcium oxide is left. What mass of carbon dioxide escaped, in g?

Answer g

Question 4

Why is mass conserved in a chemical reaction?

• A. Energy is conserved
• B. Reactions happen too fast to change mass
• C. Products are always the same substances as reactants
• D. Atoms are only rearranged; none are made or destroyed

Question 5

In a sealed flask, 17 g of substance A reacts completely with 17 g of substance B. 4 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 6

20 g of calcium carbonate is heated in an open tube until it all breaks down. 11.2 g of calcium oxide is left. What mass of carbon dioxide escaped, in g?

Answer g

Question 7

Magnesium ribbon is burned in a crucible. The ash weighs more than the ribbon did. Why?

• A. The crucible got heavier
• B. Heat has mass
• C. Oxygen atoms from the air have combined with the magnesium
• D. Burning creates new atoms

Question 8

In a sealed flask, 21 g of substance A reacts completely with 39 g of substance B. 2 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 9

50 g of calcium carbonate is heated in an open tube until it all breaks down. 28 g of calcium oxide is left. What mass of carbon dioxide escaped, in g?

Answer g

Question 10

Who is often credited with showing that mass is conserved by careful weighing in sealed vessels?

• A. Marie Curie
• B. Isaac Newton
• C. Dmitri Mendeleev
• D. Antoine Lavoisier

Question 11

In a sealed flask, 20 g of substance A reacts completely with 29 g of substance B. 8 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 12

5 g of calcium carbonate is heated in an open tube until it all breaks down. 2.8 g of calcium oxide is left. What mass of carbon dioxide escaped, in g?

Answer g

Question 13

Vinegar and baking soda react in an open beaker on a balance. The reading goes down. Is mass destroyed?

• A. Yes: chemical reactions always lose mass
• B. Yes: some atoms disappear
• C. No: carbon dioxide gas escapes into the air
• D. No: the balance is broken

Question 14

In a sealed flask, 12 g of substance A reacts completely with 27 g of substance B. 8 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 15

10 g of calcium carbonate is heated in an open tube until it all breaks down. 5.6 g of calcium oxide is left. What mass of carbon dioxide escaped, in g?

Answer g

Question 16

Why is mass conserved in a chemical reaction?

• A. Energy is conserved
• B. Atoms are only rearranged; none are made or destroyed
• C. Reactions happen too fast to change mass
• D. Products are always the same substances as reactants