Elements, compounds and mixtures
Grade 10 Science Worksheet
Circle the best answer, or write your answer on the line.
Atomic masses: H = 1.008, O = 16.00. What percent of water, H₂O, is hydrogen by mass, to 0.1%, Ari?
Atomic masses: C = 12.01, O = 16.00. What percent of carbon dioxide, CO₂, is oxygen by mass, to 0.1%, Bo?
Atomic masses: Mg = 24.31, Cl = 35.45. What percent of magnesium chloride, MgCl₂, is chlorine by mass, to 0.1%, Esme?
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Boiling points at 1 atm (real data, CRC)
substance boiling point (°C) acetone 56.05 ethanol 78.4 water 100.0 table salt 1413 A flask holds 90 mL water and 10 mL acetone. It is heated slowly and the vapor is cooled and collected. What is in the first drops, Jun?
- Mostly acetone, which boils at 56 °C, the lowest of the liquids
- Mostly water, because there is far more of it than acetone in the flask
- Water and acetone in the same 9 to 1 ratio
Ethanol and water are distilled. The thermometer at the top holds near 78 °C, then jumps toward 100 °C. What happened, Kira?
- The ethanol turned into water as the temperature rose
- Water boiled first near 78 °C, then ethanol joined it at 100 °C
- Most of the ethanol boiled off near 78 °C, then water's vapor took over
Cooling two melted samples (example data)
minute sample X (°C) sample Y (°C) 0 88 88 1 83 82 2 80 77 3 80 73 4 80 70 5 80 68 6 74 65 Two melted samples cool in the same room. Which is more likely a pure substance, Milo?
- Both are pure, since both cooled from 88 °C to below 80 °C
- Sample Y: it cools smoothly and steadily each minute, without any pause
- Sample X: it holds steady at 80 °C for minutes 2 to 5 as it freezes
Noah says Y is pure too, just with a lower freezing point. What does the data show?
- Y has no flat stretch, so it is not freezing at one fixed temperature
- Y is pure, because its temperature keeps on falling each minute of the whole test
- Y must be a compound, since compounds freeze gradually
Pure benzoic acid melts at 122.4 °C. Sample 1 melts sharply at 122 °C. Sample 2 melts from 112 to 118 °C. What does sample 2 show, Pia?
- Sample 1 is the mixture, because it melts at one temperature
- It is a different pure compound that happens to melt lower
- It is impure: impurities lower and widen the melting range
Four solids (real data, CRC)
solid density (g/cm³) dissolves in water magnetic iron 7.87 no yes sand (quartz) 2.65 no no aluminum 2.70 no no table salt 2.17 yes no Tala stirs a sand-and-aluminum mix into water to float one off. Will density separate them?
- Yes: aluminum is denser, so it sinks to the bottom and the sand floats on top
- Yes: sand is less dense than water, so it floats away
- No: both sink, and their densities differ by only 0.05 g/cm³
Aluminum is a metal, yet a magnet leaves it behind in a sand mix. Why, Zee?
- Aluminum is too dense for a magnet to lift
- Magnets attract only some metals, such as iron, and aluminum is not one
- The sand's mass blocks the magnet from reaching the aluminum