Properties & Definitions
What is the best definition of matter?
Anything that has mass and takes up space.
When salt disappears after stirring into water, what happened to the salt?
The salt dissolved and is still part of the mixture.
Is melting an ice cube a physical or chemical change?
Physical change
Name the three common states of water.
Solid, liquid, gas
Liam mixes 20 g salt with 100 g water and measures mass before and after. If nothing is added or removed, what should the total mass be after dissolving?
120 grams.
Give one example of a substance and one example of a mixture.
Substance: water (or salt, oxygen). Mixture: salt water (or sand + water).
Name one way to separate a mixture of sand and water.
Let sand settle and pour off water, or use filtration.
Which of these is evidence that a chemical change might have occurred: bubbles forming, temperature change, lasting color change — name one and why
Bubbles forming can indicate gas production, which can be evidence of a chemical change.
What happens to water molecules when ice melts?
Molecules move faster and spread out more so the solid becomes a liquid.
Which investigation would BEST help Liam find evidence that the salt is still part of the water after dissolving: observing with a magnifying glass, comparing masses before and after, measuring temperature, or counting stirs? Choose and explain briefly.
Comparing masses before and after — mass is conserved so the dissolved salt is still part of the mixture.
What property would you measure to show how much matter is in an object or mixture?
Mass
You mix two clear liquids and the final solution becomes cloudy but nothing else changes. Is this evidence of a chemical change? Explain briefly.
Not necessarily; cloudiness could be suspended particles (physical change). Need other evidence (gas, lasting color change, temperature change) to support a chemical change.
Classify burning wood as physical or chemical and give one piece of evidence supporting your answer.
Chemical change — produces new substances (ash, smoke) and odor; energy (heat/light) released.
Explain why droplets form on the outside of a cold cup on a humid day
Water vapor in the air cooled and condensed on the cold cup, forming liquid droplets.
Three mixtures: sand+water (sand settles), vinegar+baking soda (bubbles, container cooler), salt+water (salt dissolves). Which shows the clearest evidence of a chemical change and why?
Vinegar + baking soda — bubbles (gas) and temperature change suggest a chemical reaction.
A teacher says "Air is not matter." Explain why this is incorrect using the definition of matter.
Air has mass and takes up space, so it meets the definition of matter.
Explain why dissolving salt in water is considered a physical change, not a chemical change.
Salt particles separate into ions within the water but no new substance is formed; the salt can be recovered by evaporating the water.
A sample changes temperature and produces bubbles when two materials are combined. Explain why this suggests a chemical change and what additional evidence you could collect.
Gas formation and temperature change both suggest new substances formed (chemical change). Additional evidence: lasting color change, measure pH change, identify gases produced.
A puddle disappears on a sunny day. Which observation best supports that the puddle turned to a gas rather than disappeared for another reason?
Nearby surfaces are dry, no signs of runoff, and the amount of water decreased without residue — supports evaporation (liquid to gas).
A student mixes two substances and observes a gas forms. Which conclusion is best supported and what caution should they include when interpreting results?
Best supported conclusion: a chemical change may have occurred (new substance/gas formed). Caution: gas alone is suggestive but not definitive — additional evidence (color/temperature change, inability to reverse) strengthens the claim.
Describe how you would decide whether an unknown sample is a substance or a mixture using two observations or tests.
Possible answer: Try to separate components (e.g., dissolve and filter) and observe whether parts can be separated physically; measure properties like melting/boiling points—if consistent and single-valued it’s likely a substance; if variable or separable, it’s likely a mixture.
Design a short investigation (steps and measurement) to show that dissolved substance remains present in a solution even when you cannot see it.
Example: Measure mass of container + water, add known mass of salt, dissolve, then reweigh container + solution to show total mass unchanged; or evaporate water and weigh recovered solid.
A student cuts a sheet of metal into smaller pieces and then heats them until they glow red but stays the same metal. Identify which are physical and which might indicate chemical change, and justify.
Cutting is a physical change (size/shape change only). Heating until red could be physical (increase in temperature) but if oxidation occurs (surface color change, new powder forms), that would be chemical.
Describe an experiment to show that changes of state do not change the identity of a substance, including expected observations.
Example: Melt ice to water, boil to steam, collect steam and condense back to liquid, then freeze — throughout, mass and composition remain the same; water returns to original liquid/solid form.
Read Aaliyah’s investigations: ice melts then refreezes; bread grows fuzzy spots and odor changes. Fill in: Identify which is physical/chemical, and write two sentences of scientific reasoning for each explaining WHY (use evidence language).
Investigation 1 — physical change because the ice changed state from solid to liquid and back to solid; no new substance formed and the change was reversible. Investigation 2 — chemical change because mold growth and smell indicate new substances (fungus and chemical byproducts) formed and the bread’s appearance and odor changed permanently.