Why a material's molecules decide what it can do

Answer Key - Grade 10 Science Worksheet - Building Confidence

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

1. 1.

   A polyethylene chain has 1000 repeat units, each C₂H₄ with a mass of 28 g/mol. What is the chain's molar mass, Ari?

   28,000 g/mol
2. 2.

   A PTFE chain has 500 repeat units, each C₂F₄ with a mass of 100 g/mol. What is the chain's molar mass, Bo?

   50,000 g/mol
3. 3.

   A PVC chain has 600 repeat units, each C₂H₃Cl with a mass of 62.5 g/mol. What is the chain's molar mass, Esme?

   37,500 g/mol
4. 4.

   Hammered copper flattens, but a hammered salt crystal shatters. Which structural idea explains the difference, Jun?

   • Copper has no bonds between its atoms, so its layers can flow like a liquid under a hammer
   • Metal layers slide while shared electrons hold them; sliding salt ions meet like charges
   • Salt particles are lighter than copper atoms, so a hammer breaks them apart more easily
5. 5.

   Brass is harder to bend than pure copper. What best explains it, Kira?

   • Zinc atoms are lighter than copper atoms, so the metal packs more tightly together
   • Brass has more free electrons than copper, so its bonds are stronger
   • Zinc atoms are a different size, so the layers of atoms cannot slide as easily
6. 6.

   Graphite and diamond are both pure carbon, but only graphite conducts. Why, Luz?

   • Graphite has layers with free electrons; diamond's electrons are locked in bonds
   • Diamond atoms have no electrons of their own, so no electrons are available to carry current
   • Graphite has a little metal mixed in, while diamond has no metal inside it
7. 7.

   A rubber band stretches and snaps back. Which structure explains it, Noah?

   • Its free electrons slide along the band and pull the ends together
   • Long, coiled chains straighten when pulled and coil up again when released
   • Its atoms stretch apart when pulled and spring back when released like tiny springs
8. 8.

   A copper wire is coated with plastic. Why does the plastic stop the current, Pia?

   • The plastic is thick enough that electrons cannot squeeze through
   • Its electrons stay in bonds, so none are free to carry current
   • The plastic repels electrons because it is charged negatively

9. Read this first

   Wire coating scores (example scores, 1 to 5)

   material	flexibility	insulation	low cost
   PVC plastic	4	5	4
   natural rubber	5	5	2
   copper	3	1	3

10. 9.

    A coating needs an insulation score of at least 4 and a low-cost score of at least 3. Which material passes, Ren?

    • PVC plastic and natural rubber, which both insulate well
    • PVC plastic only, since rubber's cost score is 2
    • Natural rubber only, since it is the most flexible
11. 10.

    A coating needs an insulation score of at least 4 and a total of at least 12. Which materials pass, Tala?

    • PVC plastic and natural rubber, with totals of 13 and 12
    • PVC plastic alone, since rubber's total of 12 cannot beat PVC's 13
    • Neither material, since a total of 12 is not above the limit of 12