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.
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?
Bo has 66 g of copper. How many grams of tin must be added to make bronze, which is 88% copper by mass?
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Three frame metals (typical values, rounded)
material strength (MPa) density (g/cm³) structural steel 400 7.85 aluminum alloy 310 2.70 titanium alloy 950 4.43 A frame must be as strong as possible for its mass. Which comparison is best supported, Jun?
- Aluminum is the clear choice, since it has the lowest density of the three metals listed
- Titanium and steel tie, since both are stronger than aluminum in the strength column
- Titanium gives the most strength per density: about 214, against 115 and 51
Card
Cookware metals (rounded). Thermal conductivity in W/(m·K): copper 401, aluminum 237, stainless steel 16. Copper reacts with acidic foods; stainless steel does not.
A pan must spread heat evenly and be safe with acidic foods. Which design uses the card best, Kira?
- A copper core for even heat, lined with stainless steel that resists acid
- Solid copper, since it conducts heat better than the other two metals do
- Solid stainless steel, since it does not react with the acid in tomato sauce
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
- Not supported: slipperiness is weak attraction to other surfaces, not weak bonds in PTFE
- Supported: low friction means the material is soft and weak throughout, so PTFE is weak
Brass hardness and zinc (example data)
zinc (%) hardness 0 50 10 70 20 85 30 95 40 110 50 80 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 rises to 40% zinc, then falls at 50%, so more can be softer
- Overstated: hardness does not change with zinc, so the claim is baseless and wrong
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 A student says the best conductor is always the best choice for house wiring. Which reply fits the table, Pia?
- Supported: gold resists corrosion well, so gold should be chosen for house wires
- 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
Brass is harder than copper but conducts electricity worse. Which single structural idea explains both, Ren?
- 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
- Zinc atoms of a different size disturb the rows, blocking sliding layers and scattering electrons
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
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