Conservation of mass in reactions

Question 1

In a sealed flask, 29 g of substance A reacts completely with 38 g of substance B. 3 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 2

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. No: carbon dioxide gas escapes into the air
• C. Yes: some atoms disappear
• D. No: the balance is broken

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

In a sealed flask, 12 g of substance A reacts completely with 26 g of substance B. 12 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 5

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

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

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

In a sealed flask, 6 g of substance A reacts completely with 20 g of substance B. 3 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 8

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

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

Question 9

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 10

In a sealed flask, 37 g of substance A reacts completely with 25 g of substance B. 6 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 11

Why is mass conserved in a chemical reaction?

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

Question 12

25 g of calcium carbonate is heated in an open tube until it all breaks down. 14 g of calcium oxide is left. What mass of carbon dioxide escaped, in g?

Answer g

Question 13

In a sealed flask, 9 g of substance A reacts completely with 32 g of substance B. 5 g of product D forms along with product C. What mass of C forms, in g?

Answer g

Question 14

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

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

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

In a sealed flask, 10 g of substance A reacts completely with 21 g of substance B. 6 g of product D forms along with product C. What mass of C forms, in g?

Answer g