Mass stays the same in a reaction

Answer Key - Grade 8 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Bo watches a sealed jar: 120 g of solution and a 30 g tablet react and fizz inside. Total after = total before. What is the total mass after?

   150 g
2. 2.

   Steel wool (85 g) rusts inside a sealed jar holding 40 g of air. Total after = total before. What is the total mass after, Esme?

   125 g
3. 3.

   In a teacher's demo, a tablet fizzes in water in an open cup on a scale, and the reading drops. Why, Jun?

   • Gas escaped into the air
   • The fizzing destroyed some mass
   • The water got lighter as it warmed
   • The gas has no mass
4. 4.

   Next, the teacher fizzes the same tablet in a sealed bottle on the scale. What does the scale show, Kira?

   • Less, as the fizz uses up mass
   • The same mass as before
   • More, as the bubbles push down
   • Zero, once the tablet is gone
5. 5.

   Luz wants a setup that shows mass is conserved. Which one works best?

   • An open cup, since gas adds no mass
   • A container with a hole in the lid
   • A sealed container: nothing gets in or out
   • An open cup, so the gas has room to spread out
6. 6.

   Milo graphs a sealed flask's mass while two solutions react inside. What happens to the mass?

   • It drops to 0 g
   • It rises, as new products form
   • It drops, as the reactants are used up
   • It stays at 200 g
7. 7.

   Noah graphs an open cup while a tablet fizzes in it. Which story fits the graph?

   • Water was added at 4 min
   • The cup was sealed the whole time
   • Gas left the cup until the fizzing stopped
   • Mass was destroyed until the fizzing stopped
8. 8.

   Pia graphs a sealed jar of steel wool as it rusts over 5 days. What happens to the mass?

   • It drops, as the iron is used up
   • It rises, as rust is new matter
   • It stays at 300 g
   • It doubles
9. 9.

   Ren's glossary has a blank by conservation of mass. Which meaning fits there?

   • Mass is destroyed when things react
   • New substances bring new mass
   • Solids keep their mass, but a gas weighs nothing
   • Total mass before a reaction = total mass after
10. 10.

    A reaction runs in a sealed jar. Why does its total mass stay the same, Zee?

    • Any gases made weigh nothing
    • The jar stops the reaction
    • Products are lighter but bigger
    • The same atoms are there, joined differently