10th grade Why a material's molecules decide what it can do worksheet

Why a material's molecules decide what it can do

Grade 10 Science Worksheet - Challenge Me

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

1. 1.

   Ari has 74 g of silver. How many grams of copper must be added to make sterling silver, which is 92.5% silver by mass?
2. 2.

   Bo has 66 g of copper. How many grams of tin must be added to make bronze, which is 88% copper by mass?
3. 3.

   Esme has 56 g of copper. How many grams of zinc must be added to make brass, which is 70% copper by mass?

4. Read this first

   Wire coating flex test (example data)

   coating	bends to crack at 25 °C	bends to crack at −20 °C
   PVC	5000	200
   natural rubber	4000	3500
   polyethylene	6000	1500

5. 4.

   A wire will hang outdoors where winter nights reach −20 °C. Which coating does the data favor, Luz?

   • PVC: its 5,000 bends at 25 °C show it is tough enough for a winter job too
   • Polyethylene: its 6,000 bends at 25 °C is the top result of the three
   • Natural rubber: it survives 3,500 bends at −20 °C, the most of the three
6. 5.

   A student says PTFE is slippery, so it must be a weak material. Which reply is best, Milo?

   • Supported: polymers are weak materials, and a slippery coating like PTFE shows it clearly
   • Supported: low friction means the material is soft and weak throughout, so PTFE is weak
   • Not supported: slipperiness is weak attraction to other surfaces, not weak bonds in PTFE

7. Brass hardness and zinc (example data)

   zinc (%)	hardness
   0	50
   10	70
   20	85
   30	95
   40	110
   50	80

8. 6.

   A student says more zinc always makes brass harder. Which reply fits the table, Noah?

   • Supported: hardness rose at each step from 0% to 40% zinc, so the pattern holds
   • Overstated: hardness does not change with zinc, so the claim is baseless and wrong
   • Overstated: hardness rises to 40% zinc, then falls at 50%, so more can be softer

9. Four conductors (rounded values; costs are examples)

   metal	conductivity (10^6 S/m)	cost compared with copper
   silver	63.0	80 times
   copper	59.6	1 time
   gold	41.0	6000 times
   aluminum	37.7	0.3 times

10. 7.

    A student says the best conductor is always the best choice for house wiring. Which reply fits the table, Pia?

    • Overstated: silver conducts about 6% better than copper at about 80 times the cost
    • Supported: the highest conductivity, 63.0, makes silver the right wire for house wiring
    • Supported: gold resists corrosion well, so gold should be chosen for house wires
11. 8.

    Brass is harder than copper but conducts electricity worse. Which single structural idea explains both, Ren?

    • Zinc atoms of a different size disturb the rows, blocking sliding layers and scattering electrons
    • Zinc adds extra free electrons, which strengthens the bonds but slows the current somewhat overall
    • Zinc atoms form covalent bonds with copper atoms, which removes the free electrons it had before
12. 9.

    Rubber stiffens at −20 °C. Which structural idea explains it, Tala?

    • The cross-links break in the cold, so the chains lock together
    • The chains shrink to a shorter length, which makes the rubber stiff
    • The chains have too little motion to uncoil, so the rubber stiffens
13. 10.

    Spandex stretches to about five times its length and springs back. Which structure explains both, Zee?

    • Cross-links melt when the fiber is stretched and re-form when it is released again
    • Hard segments stretch while soft segments hold the chains in place, so the fiber returns afterward
    • Soft coiled segments straighten when pulled; hard segments anchor the chains and pull them back