Why a material's molecules decide what it can do
Grade 10 Science Worksheet
Circle the best answer, or write your answer on the line.
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A material's scores and weights (example data)
criterion weight score strength 50% 8 light weight 30% 5 low cost 20% 4 Using the table, what is the material's weighted score, to 0.01 points, Ari?
Using the table, what is the material's weighted score, to 0.01 points, Esme?
A milk jug (HDPE) is stiffer than a grocery bag (LDPE). Both are polyethylene with the same C–C bonds. Which difference explains it, Jun?
- HDPE has stronger bonds inside each chain than LDPE does, so it resists bending more
- HDPE's straight chains pack closely and hold on along their length; LDPE's branched chains cannot
- LDPE has longer chains, which tangle and tear apart more easily than HDPE chains do
Rubber with added sulfur (typical behavior)
sulfur added (% by mass) behavior 0 soft and sticky, flows when warm 2 stretches and snaps back 30 hard and brittle Sulfur links rubber chains together. Which statement does the table support, Kira?
- More sulfur makes the rubber stretchier and stretchier, from 0% up to 30% sulfur
- A few cross-links let chains snap back, while too many lock them into a hard solid
- Sulfur breaks the long chains into short pieces, so the rubber hardens at 30%
Polyethylene softens when heated and can be remelted; a cured epoxy glue cannot. Which structure explains it, Luz?
- Polyethylene's bonds are stronger than epoxy's, so it flows like a liquid when it is heated
- Epoxy's chains are bonded into one network; polyethylene's are held by weak attractions that heat loosens
- Epoxy's chains are shorter than polyethylene's, so heat cannot move them past one another
Steel is iron with about 1% carbon and is harder than pure iron. Which structural idea explains it, Milo?
- Small carbon atoms sit in gaps between iron atoms and block the layers from sliding
- Carbon atoms replace iron atoms of the same size, so the rows stay perfect and strong
- Carbon adds free electrons, which hold the iron atoms together more tightly than before
Two steel samples (example data)
sample chromium (%) after a month in salt water A 8 rust spots B 18 no rust Stainless steel needs at least 10.5% chromium to form a protective oxide film. Which sample resists rust, and why, Noah?
- Both: each contains some chromium, which is what stops rust in any kind of steel
- Sample B: its 18% chromium is above 10.5%, enough for a continuous oxide film
- Sample A: its 8% chromium leaves more iron, which is the stronger metal
Alloying copper with zinc lowers its electrical conductivity. Which structural idea explains it, Pia?
- Zinc atoms are heavier, which slows each electron by the same amount as it passes
- Zinc atoms of another size disturb the regular rows and scatter the moving electrons
- Zinc atoms hold on to their electrons, so no electrons are left free to move through the metal
Bike frame metals (example scores, 1 to 10)
material strength light weight low cost steel 7 3 9 aluminum alloy 6 8 6 titanium alloy 9 8 2 Weights: strength 40%, light weight 35%, low cost 25%. The cost score must be at least 3. Which material is the best choice, Ren?
- Titanium alloy: 6.9, the highest total of the three materials, so it should be picked
- Aluminum alloy: 6.7, the highest total among those with a cost score of at least 3
- Steel: 6.1, the material with the top cost score, so it is the safest pick
Weights now: strength 20%, light weight 30%, low cost 50%. Which material has the highest total, Tala?
- Titanium alloy, since it is both strong and light
- Aluminum alloy, still the strongest choice overall
- Steel: 6.8, ahead of aluminum alloy's 6.6
