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.

   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
2. 2.

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

   • The water got lighter as it warmed
   • The gas has no mass
   • Gas escaped into the air
   • The fizzing destroyed some mass
3. 3.

   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
   • More, as the bubbles push down
   • The same mass as before
   • Zero, once the tablet is gone
4. 4.

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

   • A sealed container: nothing gets in or out
   • An open cup, so the gas has room to spread out
   • An open cup, since gas adds no mass
   • A container with a hole in the lid
5. 5.

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

   • It stays at 200 g
   • It rises, as new products form
   • It drops to 0 g
   • It drops, as the reactants are used up
6. 6.

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

   • Mass was destroyed until the fizzing stopped
   • Gas left the cup until the fizzing stopped
   • Water was added at 4 min
   • The cup was sealed the whole time
7. 7.

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

   • It doubles
   • It drops, as the iron is used up
   • It stays at 300 g
   • It rises, as rust is new matter
8. 8.

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

   • Total mass before a reaction = total mass after
   • Solids keep their mass, but a gas weighs nothing
   • Mass is destroyed when things react
   • New substances bring new mass
9. 9.

   Tala reads about atoms in a reaction. What happens to them?

   • New ones are made as products form
   • Some are destroyed and replaced
   • They turn into light
   • They are rearranged into new substances
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